WO2016196980A1 - Thermal energy harvesting based sensors - Google Patents

Abstract

A method for detecting a constituent in a gas includes, for example, exposing a sensing material to the constituent in the gas in an environment subject to thermal energy providing thermal radiation, detecting the constituent in the gas based on absorption, reflection, and/or extinction of a portion of the thermal radiation in connection with the sensing material exposed to the constituent, and wherein the detecting does not employ a separate light source.

Description

THERMAL ENERGY HARVESTING BASED SENSORS

GOVERNMENT RIGHTS

[0001] This invention was made with Government support under U.S. Department of Energy Technology Laboratory, grant contract number DE-FE0007190. The Government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATION

[0002] This application claims the benefit of U.S. Provisional Application No.

62/171 ,408, filed June 5, 2015, entitled "Thermal Energy Harvesting Based Chemical Sensors", which is hereby incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

[0003] This disclosure relates generally to sensors, and more specifically, to detection of a constituent in a gas using intrinsic thermal energy in an environment and without employ a separate light source.

BACKGROUND

[0004] U.S. Patent No. 7,864,322, issued to Carpenter et al., discloses optical methods and systems for detecting a constituent in a gas containing oxygen in harsh environments. The method includes providing a sensing material comprising a metal embedded in a catalytically active matrix, exposing the sensing material and the constituent in the gas to a temperature above about 400 degrees Celsius, projecting light onto the sensing material, and detecting the constituent in the gas by a change in the absorption spectrum of the sensing material due to the exposure of the sensing material to the constituent in the gas at the temperature which causes a chemical reaction in the sensing material compared to the absorption spectrum of the sensing material in the absence of the constituent in the gas. The system for detecting a constituent in a gas containing oxygen includes a sensing material comprising a metal embedded in a catalytically active matrix, a light source for directing light on to said sensing material, a light detector for detecting light reflected from the sensing material, and a processor operable to detect the constituent in the gas by a change in the absorption spectrum of the sensing material due to the exposure of the sensing material to the constituent in the gas at the temperature which causes a chemical reaction in the sensing material compared to the

absorption spectrum of the sensing material in the absence of the constituent in the gas.

SUMMARY

[0005] Shortcomings of the prior art are overcome and additional advantages are provided through the provision, in one embodiment, of a method for detecting a constituent in a gas which includes, for example, exposing a sensing material to the constituent in the gas in an environment subject to thermal energy providing thermal radiation, detecting the constituent in the gas based on absorption, reflection, and/or extinction of a portion of the thermal radiation in connection with the sensing material exposed to the constituent, and wherein the detecting does not employ a separate light source.

[0006] In another embodiment, a method for detecting at least one constituent in a gas is provided. The method includes, for example, exposing a sensing material to at least one constituent in the gas at a temperature in an environment subject to thermal energy providing thermal radiation, measuring a first plurality of discrete wavelengths in connection with absorption, reflection, and/or extinction of a portion of the thermal radiation in connection with the sensing material exposed to the constituent at the temperature, measuring a second plurality of the discrete wavelengths in connection with a portion of the thermal radiation at the temperature to serve as a reference, detecting at least one constituent in the gas based on the measured first plurality of the discrete wavelengths in connection with the absorption, the reflection, and/or the extinction of the portion of the thermal radiation regarding the sensing material and the measured second plurality of discrete wavelengths in connection with the portion of the thermal radiation serving as the reference, and wherein the detecting does not employ a separate external light source.

[0007] In another embodiment, a sensor system for detecting a constituent in a gas in an environment subject to thermal radiation includes, for example, a sensing material having a metal, a metal oxide, and/or a thermal radiation absorbing material in a catalytically active matrix, a first detector for detecting thermal radiation regarding said sensing material exposed to the constituent, and a processor operable to detect the constituent in the gas based on absorption, reflection, and/or extinction of a portion of the detected thermal radiation in connection with said sensing material exposed to the constituent, and wherein said sensor system does not employ a separate light source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The subject matter which is regarded as the disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. The disclosure, however, may best be understood by reference to the following detailed description of various embodiments and the accompanying drawings in which:

[0009] FIG. 1 is a schematic illustration of a thermal energy harvesting based sensor according to an embodiment of the present disclosure.

[0010] FIG. 2 is a comparison of the experimentally collected thermal intensity spectrum emitted from the thermal imaging bench (solid heavy line), the nanorod absorbance spectrum (dashed line), and the expected theoretical spectrum calculated from Planck's law eq 1 at 700 degrees C (solid thin line). The furnace emission curve will peak at wavelengths well beyond the 1 , 100 nm detection limit of a CCD spectrograph.

[0011] FIG. 3 illustrate the sensing results for air-H2 mixture with H2

concentrations: 200, 500, 1000, 2000, 10000 ppm. Thermal imaging data (shown in the left graph), white light data (shown in the right graph), gas on and off times for both experiments are 40 minutes.

[0012] FIG. 4 illustrate the sensing results for air— CO mixture with. CO concentrations: 2, 5, 10, 50, and 100 ppm. Thermal imaging data (left), white light data (right), gas on and off times for both experiments are 40 minutes.

[0013] FIG. 5 illustrate the sensing results for air— NO2 mixture. NO2

concentrations: 5, 10, 20, and 98 ppm. Thermal imaging data (left), white light data (right), gas on and off times for both experiments are 40 min.

[0014] FIG. 6 illustrate calibration plots from thermal imaging and white light imaging data for NO2 (left), H2 (middle), and CO (right) analyte gases in an air background (white light imaging curve extending above and thermal imaging curve extending below).

[0015] FIG. 7 illustrates plots of white light full spectrum PCA (left) and thermal imaging full spectrum PCA (right).

[0016] FIG. 8 illustrates graphs of (A) Overlay of the gas on/gas on spectra (top row) and (B) corresponding difference spectra (bottom row) for the highest concentrations of each of the three analyte gases for CO (left), hte (middle), and NO2 (right). Arrows on the CO difference spectrum point to the location of the four selected wavelengths.

[0017] FIG. 9 illustrates plots of white light PCA done with wavelength reduction (left). Thermal imaging PCA done with wavelength reduction (right). Four

wavelengths (730, 745, 785, and 860 nm) were chosen for the plot.

[0018] FIG. 10 illustrates longitudinal plasmon peak wavelength vs nano-rod aspect ratio for previously deposited samples as well as predicted plasmon peak positions obtained through linear extrapolation of the experimental data points.

[0019] FIG. 1 1 is a schematic illustration of a thermal energy harvesting based sensor according to an embodiment of the present disclosure.

[0020] FIG. 12 illustrate (a) Room temperature FTIR spectra showing the longitudinal NIR plasmon peak of the 44 nm x 170 nm Au nanorod sample and inset eSEM image of the 44 nm x 170 nm AuNR-YSZ sample and (b) comparison of data point frequency for visible light-absorbing AuNR sample (spectrum collection time = 220 seconds) and NIR-absorbing AuNR sample (spectrum collection time = 20 seconds). The starts of the 10,000 ppm H2 exposures from both tests were set to t=0 hours for comparison. Each data point averages 10 spectra.

[0021] FIG. 13A illustrate plots of gas sensing for the analyte gases: H2, CO, and NO2, with the left plot being 200, 500, 1000, 5000, and 10000 ppm H2 in air carrier gas, the middle plot being 2, 5, 10, 50, 100 ppm CO in air carrier gas, and the right plot being 2, 5, 10, 50, 100 ppm NO2 in air carrier gas. A spectral smoothing procedure followed by internal referencing was performed to minimize baseline drift. The remaining baseline drift was corrected by removing linear drifts of 0.6 nanometer from the H2 curve, 0.65 nanometer from the CO curve, and 0.5 nanometer from the NO2 curve. The centroid position, or the center of mass of the absorbance curve, was used to track changes in the LSPR peak position.

[0022] FIG. 13B illustrate calibration plots for the H2, CO, and NO2 results shown in FIG. 13A. Each data point averages 25 individual centroid positions from the Acentroid vs. time graph to determine the average shift at each analyte gas concentration.

[0023] FIG. 14(a) is a full spectrum PCA performed on wavelength range of 1050 nm to 1 ,700 nm. FIG. 14(b) is a reduced wavelength PCA using wavelengths of 1350, 1410, 1470 nm with similar selectivity as with the full spectrum PCA.

[0024] FIG. 15 is a plot showing increase of peak position with sample temperature for horizontally polarized white light measurements. Thermal imaging spectra have been collected at similar temperatures down to a sample temperature of 275 degrees C which is shown as an inset graph.

[0025] FIG. 16 is a diagrammatic illustration of a thermal harvesting sensor according to an embodiment of the present disclosure.

[0026] FIG. 17 is a flowchart of a method for detecting a constituent in a gas according to an embodiment of the present disclosure.

[0027] FIG. 18 is a flowchart of a method for detecting a constituent in a gas according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0028] The present disclosure and certain features, advantages, and details thereof, are explained more fully below with reference to the non-limiting

embodiments illustrated in the accompanying drawings. Descriptions of well-known materials, fabrication tools, processing techniques, etc., are omitted so as to not unnecessarily obscure the disclosure in detail. It should be understood, however, that the detailed description and the specific examples, while indicating

embodiments of the present disclosure, are given by way of illustration only, and are not by way of limitation. Various substitutions, modifications, additions and/or arrangements within the spirit and/or scope of the underlying concepts will be apparent to those skilled in the art from this disclosure. Reference is made below to the drawings, which are not drawn to scale for ease of understanding, wherein the same reference numbers used throughout different figures designate the same or similar components.

[0029] The present disclosure, in some embodiments, is directed to detection of gas phase constituents using plasmonically active materials and thermal energy harvesting, which avoids the need or use of a separate light source. For example, the present disclosure, in some embodiments, is directed to the design of the plasmonically and catalytically active metal nanoparticles comprised of either gold or silver (or other plasmonically active materials), embedded in ceramic materials, which are optimized for the absorption of thermal energy from operating

temperatures ranging from room temperature or from about 300 degrees Celsius to about 1 ,500 degrees Celsius. It is through the absorption of the thermal energy and the use of imaging optics that either absorption or reflection or extinction

spectroscopic measurements can be made without the need or use of any external incident light source. Thus integration of plasmonically active composite structures into functional devices may be relatively simple and cost effective.

[0030] As described below, the present disclosure may be directed to and include:

- Harsh environment chemical sensors employing gold nanoparticles embedded in a metal oxide thin film nanocomposite.

- Nanocomposite thin films designed to absorb wavelengths of light that are emitted from a thermal energy source (i.e. , black body radiation source).

- Plasmonically active materials made of either gold, silver, copper, nickel or any other plasmonically or another optically active material which are designed to absorb wavelengths of light emanating from a thermal energy source. Tuning of the wavelength of absorption may be made by changing the plasmonically active material's chemistry, shape (sphere, rod, triangle), size or its placement in a periodic or aperiodic array of nanoparticles of the same composition or a mixture thereof within a metal oxide host material.

- Light emanating from thermal energy source serves as the intrinsic light source for operation of the plasmonics based chemical sensor, thus making the need and use of an external incident light source obsolete for optically active chemical sensors.

- Fiber probes used to couple the detection optics to the

nanocomposite film, and/or the nanocomposite film could be deposited on the probe itself or coupled to it with an appropriate mounting apparatus. Still other optical devices and techniques may be employed.

- The probe or other optical devices and techniques could be operated in either a reflection or a transmission (or absorption) detection mechanism.

- For reflection an appropriately coupled reflecting mirror may be mounted in concert with the nanocomposite to serve as the reference and a fiber probe would need to be aligned for detection of this reflection data. A series of wavelength division multiplexers may be used for detection of required data at specific wavelengths.

- For reflection mode, a separate fiber probe may be coupled to the nanocomposite film to monitor its reflection. A series of wavelength division multiplexers may then be used for detection of required data at specific wavelengths.

- For transmission (or absorption), an appropriately coupled fiber probe may be used to monitor the transmission through the reference part of the

nanocomposite film. A series of wavelength division multiplexers may then be used for detection of required data at specific wavelengths. For transmission (or absorption) mode a separate fiber probe may be coupled to the nanocomposite film to monitor its transmission (or absorption) properties. A series of wavelength division multiplexers may then be used for detection of required data at specific wavelengths.

- The wavelengths used for detection in either reflection or transmission may be determined from a series of calibration data that uses statistical algorithms to determine which wavelengths provide the preferred sensitivity and selectivity for the target gases of interest.

- A series of wavelength division multiplexers, bandpass filters, spectrometers or other wavelength selection devices may be used in series to select the wavelengths of interest for either the reflection or transmission measurements and may be coupled with appropriate detectors such as photodiodes, CCD, PMT or another such device used for the detection of photons. [0031] As will be appreciated, no external incident light source need be employed for operation, for example, in harsh environments compatible chemical sensing devices. Such a technique may allow for simpler and cost effective optical chemical sensors that may be integrated into a functional device that may be of interest in industrial applications.

[0032] For example, in some embodiments, an all-optical chemical sensing device that is compatible with harsh environment conditions present in a range of combustion applications does not require or need an incident external light source. The chemical sensing device absorbs thermal energy emitted from a combustion source and uses that as its light source for measurement of absorption or reflection properties of the sensor. The collected absorption, reflection, or extinction properties are then characterized at key wavelengths of interrogation and changes in this data as a function of time and combustion conditions are used to determine the

concentration and chemical speciation of the target gases of interest.

[0033] In some embodiments, near-infrared (NIR) thermal energy harvesting has been employed for gold nanorods (AuNRs) (and may be extended the IR if using an appropriately optically active material), allowing concentration dependent, ppm-level, gas detection of h , CO, and NO2 at 500 degrees Celsius without using a white light source. Part-per-million detection capabilities of the gold nanorods have been demonstrated with a factor of 1 1 reduction in collection times in the NIR as compared to measurements made in the visible light region. Decreased collection times were enabled by an increase in S:N ratio, which allowed a demonstration of selectivity through the use of both full spectral and a reduced spectral-based principal component analysis. Furthermore, low temperature thermal imaging spectra have been obtained at sample temperatures ranging from 275 degrees Celsius to 500 degrees Celsius, showing the possibility of energy harvested gas sensing at lower temperatures. These findings are promising in the area of miniaturizing plasmonic gas sensing technology and integration in areas such as gas turbines.

[0034] FIG. 1 schematically illustrates a thermal energy harvesting based sensor system 100 according to an embodiment of the present disclosure, which does not require use of a separate light source. In this embodiment, thermal energy harvesting based sensor system 100 is operable for testing the detection and measurement of a constituent in a gas, however portions of the thermal energy harvesting based sensor system may be suitably employed for detection or measurement of a constituent in a gas such as in a combustion chamber. In other embodiments, the present disclosure may be applicable to biological, medical, and other fields with operating temperatures ranging from ambient conditions up to those applicable to combustion, by tuning the plasmonic absorber to match the thermal conditions. Thermal energy harvesting based sensor system 100 may incorporate the methodology described below.

[0035] In this embodiment, thermal energy harvesting based sensor system 100 may generally include a quartz flow tube 101 , a heat source 102 such as an oven that extension around at least a portion of the quartz flow tube, a sensing material 1 10 such as a metal, a metal oxide, and/or a metal embedded in a catalytically active matrix disposed in the quartz flow tube, a detector 120 such as a spectrograph 122 and a CCD 124 for detecting thermal radiation regarding the sensing material exposed to the constituent, and a processor 130 such as a computing unit or computer operable to detect and/or measure the constituent in the gas based on absorption, reflection, and/or extinction of a portion of the detected thermal radiation in connection with the sensing material exposed to the constituent in the gas. As will be appreciated, the heat source may be a suitable body for providing thermal radiation in an environment for detection and/or measurement of a constituent in the environment. For example, the heat source may be a combustion chamber such as a combustion chamber in a turbine where detection and/or measurement of a constituent is desired in the combustion chamber, or a portion of a turbine for where detection and/or measurement of a constituent in a gas is desired in an inlet or exhaust portion of the turbine.

[0036] In this embodiment, a reflector 140 such as a mirror may be used to increase the amount of thermal energy which passes through the sensing material. For example, thermal energy from heat source 102 may be reflected by reflector 140 to pass through sensing material 1 10. Collection optics such as a lens 150, shutter 152, and an iris 154, may be used to focus radiation from the sensing material into the CCD spectrometer detector for analysis of the absorbance, extinction or reflectance spectra. [0037] In this embodiment, processor 130 controls the automated gas exposures, such as introduction of a constituent via a gas inlet 104 for the sensor tests as well as the automated data collection and analysis. Heat source 102 is used for controlling the temperature of the sample and at the same time the thermal energy that is used and harvested.

[0038] In some embodiments, the present disclosure is directed to detection of gases such as H2, CO, and NO2 at 500 degrees C or greater using materials having thermal stability and reliability. In other embodiments, other gases may be detected such as oxygen, hydrocarbons, and other chemistries. It has been found that gas sensing results using the harvested thermal energy are in good agreement with sensing experiments using an external incident light source. Principal Component Analysis (PCA) may be used to reduce the wavelength parameter space from 665 variables down to 4 variables with similar levels of demonstrated selectivity. The combination of a plasmonic-based energy harvesting sensing paradigm with PCA analysis offers a novel path toward simplification and integration of plasmonic-based sensing methods.

[0039] For example, the present technique is applicable to high temperature emission gas sensors for combustion environments such as turbine engines and coal-fired power plants. Reliable and sensitive harsh environment chemical sensors are needed in order to meet the requirements of increasing gas emission regulations within combustion related applications. Solution to satisfy the current demand of harsh environment sensors may be cost-effective and be able to withstand high temperatures (500-800 degrees C) as well as oxidizing or reducing environments. Development of a variety of metal oxide nanocomposite-based chemical sensing materials and sensing paradigms have shown promise in satisfying these

requirements. However, implementation of miniaturized gas sensing technologies in these extreme combustion environments is limited by cost, reliability, and integration barriers.

[0040] Thermal energy harvesting techniques coupled with plasmonics-based chemical sensing methods and PCA analysis, may serve as promising sensing paradigms that satisfy the challenging requirements as well as having broader applications in sensing and catalysis research initiatives. [0041] Plasmonics-based chemical sensing is effective in obtaining concentration dependent gas measurements both at room temperature and at elevated

temperatures. For example, plasmonic sensors are sensitive (ppm level), high temperature (500 degrees C or greater) sensing responses for analyte gases such as H2, CO, and NO2 in the presence of an air based carrier gas. The operating principle of these plasmonic sensors is based on the localized surface plasmon resonance (LSPR) property possessed by materials with a high density of free electrons that oscillate in resonance within an electromagnetic field. This oscillation results in absorption or scattering of the incident radiation that can be probed by absorption, reflection or extinction measurements. In addition to an electron density dependence, the LSPR oscillation frequency is also highly dependent on changes to the dielectric environment as dictated by the Drude equation for nanorods given in eq 1 :

N₀€²

Equation 1 is the Drude equation modified for nanorod geometry to determine resonant peak frequency (w): No is the free electron density, e is the elementary charge, eb is the interband contribution term, e_m is the matrix dielectric constant, V7 is the shape factor for the /th axis, m_e is the electron mass, and εθ is the permittivity of free space.

[0042] Nanorods show higher sensitivity than nanoparticles of other geometries such as bipyramids and spheres. Sensitivity dependence of nanorods for a unit change in the refractive index of the surrounding medium and the sensitivity is proportional to the aspect ratio, according to the equation:

Equation 2 is the absorption cross section (Oabs) equation for nanorod geometry: V is the particle volume, c is the speed of light in a vacuum, £_m is the matrix dielectric constant, Yi is the shape factor for the /th axis which is directly proportional to the aspect ratio, ω is the resonant peak frequency, and ε1 and z2 are the real and imaginary parts of the dielectric function of the metal, respectively.

[0043] It can be seen from eq 2 that increasing the nanorod aspect ratio increases sensitivity. Specifically, the condition for resonance in eq 2 is fulfilled when ε1 = Yiz_m. By plotting the product of Yi and £_m on a graph of ε1 vs wavelength, it is observed that a nanorod with a higher aspect ratio will exhibit a larger peak shift and more sensitivity for a unit change in the dielectric constant of the matrix compared to a nanorod with a lower aspect ratio. In addition, nanorods show large absorption cross sections at their LSPR resonance wavelengths. Gold nanorods exhibit a size-normalized absorption coefficient that is over an order of magnitude larger than other geometries such as nanospheres and nanoshells. By fabricating nanorods with electron beam lithography, the degree of tunability of the rods is enhanced, which allows creation of optimal nanorod samples for use in

environments with different temperatures and thus different distributions of thermally radiated photons. Furthermore, analyte gases can react and alter either the free electron density or the dielectric environment surrounding the plasmonically active nanoparticle such that its LSPR frequency shifts upon gas exposures. For this reason, the LSPR peak frequency (wavelength) and the corresponding absorption spectrum are observables for use in plasmonics-based gas sensing experiments.

[0044] Au nanoparticles are applicable to plasmonics-based sensing due to their high resistance to oxidation and their shape dependent catalytic and plasmonic properties. In particular, Au particles with nanorod geometries have highly tunable SPR properties based on their aspect ratio (ratio of rod length to width). Rods that have higher aspect ratios have a red-shifted longitudinal LSPR peak. This allows the nanorods to be tuned to different absorption wavelengths, convenient for a diverse set of applications. Furthermore, Au nanorods are stable at high temperatures when encapsulated within a yttria-stabilized zirconia (YSZ) overcoat layer. Specifically, Au nanorods with a yttria-stabilized zirconia (YSZ) overcoat layer give repeatable high temperature, 500 degrees C, sensing results for h , CO, and NO2 in an air carrier gas.

[0045] In accordance with the present disclosure, the use of a data analysis method such as principal component analysis (PCA), the number of monitored wavelengths required to identify analyte gases can be reduced, while retaining a significant amount of important information about the data. By selecting the optimal wavelengths to monitor, the required detector may be reduce, for example, from a full-size spectrometer down to several diode detectors combined with narrowly tuned bandpass filters so that only those selected wavelengths are monitored as a function of time and exposure. For example, wavelength division multiplexers and/or an array of embedded sensors may be desirable for obtaining accurate sensing information. Such an approach may overcome the drawbacks of existing optical sensor technology which hinder the placement of multiple sensors in optimal feedback locations. For example, this limitation is a result of optical sensing approaches typically requiring both a spectrometer to probe and track optical properties and an external incident light source. Integrating multiple spectrometers into a sensing application is not practical due to both size and cost limitations and further miniaturization of this hardware component is challenging.

[0046] With plasmonic-based emission gas sensors used in combustion

environments, there is an ample amount of thermal radiation due to operating temperatures that can range between 500 and 800 degrees C. In accordance with the present disclosure, it is possible to harvest this thermal radiation for use in optical measurements. Such a thermal energy harvesting method of the present disclosure allows eliminating the need for an external incident light source, simplify the system design, and favor integration of the sensing system into industrial scale applications. Combining this approach with a PCA-enabled wavelength reduction process offers a method toward easing the integration concerns noted above.

[0047] Thermal radiation is a property of any blackbody above absolute zero and is a consequence of molecular vibrations with the resulting intensity and energy distribution of emitted thermal radiation being dependent on the temperature of the body. As the temperature of a blackbody is increased, the magnitude of its spectral radiance is increased according to Plank's law:

Equation 3 is Planck's law to determine the spectral radiance as a function of wavelength, U{A), in units of energy per volume per unit wavelength, where h is the Planck constant, A is the wavelength of thermally radiated light, c is the speed of light in a vacuum, k is the Boltzmann constant, and T is the temperature of the heated body.

[0048] The distribution of spectral radiance at temperatures in the range of 500- 800 degrees C has a maximal radiance wavelength in the infrared region. However, there is a higher energy "tail" to these distributions that show there is a fraction of the total spectral radiance occurring in the visible and near-infrared light region. This radiation may be exploited for plasmonic gas sensing by an appropriately designed sample that can harvest or absorb this energy in accordance with the present disclosure.

[0049] The present disclosure addresses the obstacle that thermal radiation is isotropic and nondirectional as in an incandescent lightbulb. This obstacle can be overcome if the thermal radiation source mimics a weak white light source via an apparatus designed to direct the thermal radiation such that an absorbance measurement can be obtained. If this radiation is directed through a plasmonically active chemical sensor, with appropriate referencing to Planck's spectral radiance equation, it is expected that chemical sensing observations can be obtained that are similar to when an external incident light experiment is performed.

[0050] With reference again to FIG. 1 , with proper mirror alignment, a fraction of the emitted light from the furnace is reflected back through the sample, housed within a quartz flow cell, thus more closely mimicking a low intensity quasi-directional coherent white light source. At above 600 degrees C, the thermal radiation emitted by the furnace is strong enough in the visible region of the spectrum that the thermal radiation is harvested by the plasmonically active sensing material, thereby enabling an absorbance measurement experiment to be performed. The thermally harvested LSPR absorption spectrum is then monitored as a function of time and changes in analyte gas concentration (referred to below as thermal imaging experiments).

Characteristic changes in the LSPR spectrum may then be calibrated for selective detection of the analyte gas. [0051] Au nanoparticles which have a strong absorption cross section in the high energy "tail" region of the blackbody radiation from the furnace are employed, e.g., patterned Au nanorods were used because of their advantages in being easily tuned through modification of its aspect ratio.

[0052] The spectral overlap of the LSPR absorption spectrum with both the thermal energy emitted by the tube furnace operating at 600 degrees C (both scaled and offset for clarity) as well as the calculated spectral irradiance from Planck's distribution are illustrated in FIG. 2. Both thermal imaging and white light imaging spectra were then acquired individually as a function of time and h , CO, and NO2 gas exposure concentrations at an operating temperature of 510 degrees C in an air carrier gas. A comparison of the thermal imaging and the white light LSPR peak position vs time data as a function of analyte gas concentration is shown in FIGS. 3- 5.

[0053] The data shown in FIGS. 3-5 exhibit the expected trends: a blue shift in plasmon peak position for reducing gases and a red shift in peak position for oxidizing gases. The mechanism behind this has been elucidated in the literature and is based on the Drude equation given above which shows a direct dependence of the peak frequency on the free electron density and an indirect dependence on the matrix dielectric constant. A proposed reaction mechanisms for both H2 and CO are interfacial charge transfer reactions, which include adsorption followed by reaction forming H2O and CO2 through removing oxygen anions from the lattice followed by electron transfer to the gold nanoparticles. Electron transfer to the Au particles decreases the polarizability and the dielectric function of the metal oxide matrix and induces a blue shift in the LSPR wavelength. The reaction mechanism proposed for NO2 is dissociative adsorption forming NO and O, and then O radical ionization via electron transfer. The electron transfer removes electrons from the Au nanorods to form oxygen anions and, in doing so, increases the polarizability and the dielectric function of the matrix, thus inducing a red shift in the LSPR wavelength. This type of mechanism for NO2 is not unexpected as it has been previously shown to catalytically react on heated gold-metal oxide surfaces. Since the number of incident photons is higher for the white light imaging as compared to thermal imaging, a higher number of generated hot carriers are expected in the white light measurements due to the increased intensity of the generated plasmonic fields. Hot electrons, as they extend further away from the nanoparticle, can facilitate reactions such as H2 dissociation on Au. Thus, an increased magnitude of reaction is expected when using a white light source and hence an increased peak shift magnitude. Generally, each type of experiment had response and recovery times of 300 seconds or greater. It is expected that the response and recovery times can be improved for industrially relevant applications. The results shown in FIGS. 3-5 are also repeatable, as shown by the 20+ hours of experimental testing through the noted gas cycles.

[0054] FIG. 6 illustrates calibration plots for the Au nanorods, which plot the change in the centroid peak position determined from the polynomial fit to the LSPR spectra as a function of H2, CO, or NO2 concentration for both the thermal imaging and white light experiments. The plots show a sensitive response at low

concentrations.

[0055] At lower concentrations of an analyte gas, the slope for the white light imaging experiment is steeper for all gases considered. The reason for this may be due to a plasmonically activated hot electron transfer reaction mechanism via the increased electron— hole pairs generated, which is not as prevalent in the thermal imaging results due to the reduction in incident photons. At larger analyte gas concentrations, the white light and thermal imaging plots have nearly identical slopes. The dissociation of NO2 and the availability of sites for the resulting oxygen anions depend on the availability of oxygen vacancies in the YSZ layer. As the sample is purged with air before the start of NO2 exposures, it is likely that the oxygen vacancies are at least partially saturated, and this would be the reason for a reduced rate of NO2 dissociation and hence the reduced magnitude of peak shift for NO2 as compared to H2 and CO. Furthermore, as there is no appreciable difference between the white light and thermal imaging data for the NO2 experiments, we can speculate at this point that plasmonic enhancement (as described above) is not a dominant factor for this reaction.

[0056] The collected thermal imaging data has larger error bars due to two reasons: (a) the number of measurements collected per time period and (b) the lower signal-to-noise (S/N) ratio in these measurements. Fewer measurements are collected in the thermal imaging because of the large exposure times required to obtain a single measurement and the high averaging that is used to improve the S/N ratio. Comparing the thermal imaging calibration curves, the error bars for H2 are smaller than those for both NO2 and CO. This is a result of the different collection times used as discussed in the Methods section. These collection parameters resulted in a higher number of available points per cycle for H2 than for both CO and NO2, which gives a lower error when all the available points are averaged. The percent error for the white light H2 test, while comparable to that from the white light tests for both CO and NO2, appears large when compared to a particularly good thermal test that also averages a higher number of values as discussed above.

Improvement of the S/N ratio in the thermal imaging measurements can be handled by exchanging the reflection mirror with a focusing mirror, which would increase the number of photons that pass through the sample and are collected by the

spectrometer. Furthermore, when nanorods are patterned with dimensions such that they harvest thermal energy further in the near-infrared region (1000 nm— 2000 nm), their absorption cross section maxima will overlap with a higher number of emitted photons as illustrated by the Planck distribution equation, which should also lead to an improved data set.

[0057] In view of the foregoing description, a plasmonics-based chemical sensing does not necessarily require an external incident light source, and optimizing the sensor design by miniaturizing and simplifying the detector component.

[0058] One approach according to the present disclosure may employ integrating an optical sensor having a selective wavelength detection. For example, such approach may utilize narrow band-pass filters combined with diode detectors or other wavelength selection methods such that each is operable to monitor a single wavelength. The wavelengths to be monitored may be selected that have the greatest impact on the total variation in the data.

[0059] A method of data analysis in providing the necessary information for analyte gas discrimination using the above principle may include principal

component analysis (PCA). PCA performs dimensional reduction by generating PC vectors that are linear combinations of the original input variables. The PC vectors lie in directions of maximum variance in the data and are orthogonal to each other. Projection of a combination of principal components onto a subspace is known as a scores plot. The scores plot of the first several principal components usually describes most of the variance present in the data.

[0060] PCA has been completed for both the white light and the thermal imaging data using the difference spectra obtained from subtracting the LSPR gas-on spectrum from the LSPR gas off spectrum (both spectra were first fitted using the same polynomial routine noted above to reduce random variances in the data set and then smoothed using the Savitzky-Golay algorithm) followed by autoscaling preprocessing for each of the concentrations used in the H2, CO, and NO2

experiments. Subtraction of the gas spectra was done after completion of the experiment as a separate step in the data analysis. The difference spectra were limited to the wavelength region between 600 and 1000 nm in order to cut out the regimes where noise was dominant, which may negatively influence the PCA analysis. The resulting PC scores plot is displayed in FIG. 7 for both the white light and thermal imaging experiments.

[0061] The white light data shown in FIG. 7 shows a unique gas response for the three analyte gases. This unique response indicates that a single Au nanorod— YSZ nanocomposite reacts differently to these gases and may be used to distinguish between H2, NO2, and CO in a system with an unknown combination of these gases. The thermal imaging data has issues distinguishing between the two reducing gases but with an improved S/N ratio, a more absolute picture will be possible. A

determination of the down selected wavelengths to use for a reduced data set PCA analysis was completed through inspection of the overlaid LSPR spectra for gas on and off conditions and the resulting difference spectra used to produce the PC scores plots in FIG. 7.

[0062] Examples of the overlaid LSPR and their corresponding difference spectra are displayed in FIG. 8, panels A and B, respectively, for the highest concentrations used in the white light experiment. Arrows in this figure show wavelengths at 730, 745, and 860 nm that displayed significant differences, with 785 nm being the wavelength closest to the LSPR peak position during the air gas cycle. In doing the wavelength reduction, the PCA input wavelength variable set is reduced from 665 to 4. Rerunning the PCA analysis with this reduced wavelength data set generates the PC scores plot for both the white light and thermal imaging experiments, which is shown in FIG. 9.

[0063] Inspection of FIGS. 8A and 9 illustrate that with this approach an even greater separation has been achieved for the white light imaging experiment between the reducing gas clusters than with the full spectrum analysis. A conclusion from this analysis is that a full absorption spectrum obtained using an imaging CCD spectrometer is not necessary. In fact, the experiment may be as simple as monitoring the intensity changes at 730, 745, 785, and 860 nm as a function of time and emission gas exposure, which may be done with narrow bandpass filters and diode detectors that are referenced to l₀ values. Therefore, it is clear that a reduced data set can be used to demonstrate the selective detection of the target gases. While the wavelength reduction and PCA analysis approach has not been effectively extended to the thermal imaging data, due to the lower S/N ratio in these

measurements, it is expected with an improved S/N ratio that this same approach may be easily and reliably extended to the thermal imaging measurements.

[0064] At temperatures of 500 degrees C and above, a large amount of the total thermal irradiance emanates from the near and mid infrared regions. Energy harvesting has been demonstrated in the short wavelength near-infrared region where there is a minority of thermal photon counts. An advantage with using Au in a nanorod geometry is the proven dependence of the longitudinal peak position on the aspect ratio. When the length of the patterned nanorods, and therefore the aspect ratio, is increased, the longitudinal peak can be shifted further into the near-infrared region if not into the mid-infrared region, which would allow an improved S/N ratio. This characteristic is displayed in FIG. 10, which plots the Au longitudinal plasmon peak position as a function of the nanorod aspect ratio. An improved S/N ratio along with the assistance of improved accuracy due to curve fitting will result in an improved calibration curve. All nanorods had the same width, and ranged in length from 70 to 100 nm, giving aspect ratios between 1 .6 and 2.25. Aspect ratios ranging from 3.75 to 15.2 are realized by increasing the rod length to 165 and 667 nm, respectively, and performing a linear extrapolation of the experimental data points. In FIG. 10, the red points pertain to the extrapolation of experimentally obtained longitudinal plasmon peaks between 1500 nanometer (6667 cm^-1) and 4500 nanometer (2222 cm^-1), the latter of which is in an accessible region for FTIR spectrometers. Also, as noted above, it is predicted from theory that rods with a higher aspect ratio will exhibit a higher peak shift for a given change in the dielectric constant of the surrounding medium and, hence, a higher sensitivity for a given concentration of an analyte gas. Therefore, improved results may be expected with full spectrum and reduced wavelength PCA. Extending the aspect ratio so that absorbance occurs in the NIR and mid-IR regions may benefit experiments at the current operating temperature of 500 degree C as well as lower operating

temperatures as the nanorods absorb blackbody radiation closer to the peak in Planck's distribution. It is noted that: (1 ) if low temperatures are to be the target application (100 degrees C), then thermal stability of the nanorods is less of an issue as stabilization may be performed at temperatures as low as 200 or 300 degrees C; and (2) a change in metal oxide may be needed. YSZ is an excellent oxygen ion conductor at temperatures above 350 degrees C. However, at the lower

temperatures YSZ may not be well suited for these targeted applications and a change in metal oxide matrix material to ΤΊΟ2 or Ce02 or other metal oxide may be needed.

[0065] The periodicity that is present in the nanorods has large effects on the resulting optical properties and may be easily tuned and modified with e-beam lithography or other patterning methods. Optimal aperiodic array of nanorods may exhibit less reflection. Fabricating aperiodic arrays of nanorods may be beneficial for fiber optic applications since the signal needs to be preserved after contacting the plasmonic sensing element in the cable.

[0066] Additional optical properties of the Au nanorods may be explored include plasmonically induced processes like hot electron generation and transfer.

Plasmonically induced hot electron transfer catalyze the dissociation of H2. The particle size and hot electron lifetime control the rate of hot electron production and also their energy distribution. Specifically, larger particles produce more hot carriers but with lower energies. As the energy of the hot electrons has been discovered to peak very close to the plasmonic frequency, one can exploit the intense plasmonic excitation for longer nanorods that is expected with this thermal harvesting approach, so that there is an increased rate of hot carrier formation through electron— hole pair generation and possibly increased activity compared to smaller nanorods whose plasmonic excitations peak at lower wavelengths. It is expected that with proper design of the plasmonically active nanocomposite, the hot electron generation and transfer processes may be active in the thermal energy harvesting mechanism.

[0067] In the above described examples, nanorod sample preparation included the following. The Au nanorods were fabricated with a multistep process involving physical vapor deposition (PVD) and electron beam lithography. Specifically, a 99.9% pure YSZ target was used to deposit a 65 nanometer thick layer by PVD onto a quartz substrate followed by an annealing procedure. PMMA photoresist was spin- coated on top of the annealed base layer. A chromium layer was then used to serve as a charge-dissipating layer during the patterning step. Next, the sample was patterned with electron beam lithography, followed by Ti and Au depositions using electron beam evaporation. The PMMA resist was then lifted off using acetone. A final 25 nm thick YSZ layer was deposited on top of the Au nanorods to serve as a thermal stabilization layer for the Au nanorods at high temperatures.

[0068] Gas exposure details included the following. Gas exposure experiments that used either harvested thermal radiation (referred to as thermal imaging experiments) or an external incident white light source (referred to as white light imaging experiments) were completed. The thermal imaging and white light imaging exposure experiments both used the same Au nanorod— YSZ nanocomposite sample in order to demonstrate h , CO, and NO2 analyte detection in an air background carrier gas. Blank measurements with YSZ alone were not completed as YSZ has a bandgap of nearly 5 eV (250 nm, about 300 nm if in the oxidized state) and thus does not absorb light at the wavelengths of interest used for this study. Optical measurements were obtained with flatfield and background corrections which account for electronic noise and the differences in sensitivity of the CCD array detector. A blank substrate was referenced in real time throughout the experiment to correct for thermal power fluctuations and or white light fluctuations, thereby minimizing baseline drift. A full absorbance spectrum was collected for each spectral acquisition. These absorbance spectra were then fitted using a polynomial fitting approach from which the peak position was extracted.

[0069] The thermal imaging results were obtained with a furnace temperature of 600 degrees C, with the measured temperature of the sample being 510 degrees C. Sensing measurements were conducted using the setup schematically shown in FIG. 1 (left). A fraction of the thermally emitted photons reflect off of the mirror and are directed back through the nanorod sample. The photons are then dispersed and detected using a CCD imaging spectrograph to generate an absorbance spectrum, which were obtained through averaging 10 spectra (each with 22 s acquisition time) every 4 minutes for H2 and through averaging 10 spectra (each with 22 seconds acquisition time) every 7 minutes for CO and NO2.

[0070] White light imaging results were obtained using the same setup as with the thermal imaging results, except that the mirror was removed and a quartz tungsten halogen light source was used. Spectra were collected via averaging 10 spectra (each with 0.5 second acquisition time) every 30 seconds for the duration of the experiment for H2, CO, and NO2.

[0071] As described above, thermal radiation can be effectively harvested in the visible region of the electromagnetic spectrum by plasmonically active Au nanorods, and facilitate the collection of absorption spectra without the need for an external incident light source. Gas sensing results the present disclosure of thermal energy harvesting have been performed and compared to white light gas sensing

experiments which employ an external light source, and both show strong

concentration dependence for the different analyte gases. At lower concentrations, the white light results show higher sensitivity, which is indicative of a plasmonically activated process. Wavelength reduction has been performed using PCA methods, which significantly reduces the number of wavelengths that are required for acquiring effective sensing data. A combination of both thermal harvesting and wavelength reduction results in a new sensing paradigm, which leads to a highly simplified sensor design that may be low cost, reliable, and easier to integrate into emission gas application environments.

[0072] FIG. 1 1 schematically illustrates a thermal energy harvesting based sensor system 200 according to an embodiment of the present disclosure employing a near infrared imager and which does not require use of a separate light source. In this embodiment, thermal energy harvesting based sensor system 200 is operable for testing the detection and measurement of a constituent in a gas, however portions of the thermal energy harvesting based sensor system may be suitably employed for detection or measurement of a constituent in a gas such as in a combustion chamber. Thermal energy harvesting based sensor system 200 may incorporate the methodology described below.

[0073] In this embodiment, thermal energy harvesting based sensor system 200 may generally include a quartz flow tube 201 , a heat source 202 such as an oven that extension around at least a portion of the quartz flow tube, a sensing material 210 such as a metal, a metal oxide, and/or a metal embedded in a catalytically active matrix disposed in the quartz flow tube, a detector 220 such as a near infrared spectrometer 226 for detecting thermal radiation regarding the sensing material exposed to the constituent, and a processor 230 such as a computing unit or computer operable to detect and/or measure the constituent in the gas based on absorption, reflection, and/or extinction of a portion of the detected thermal radiation in connection with the sensing material exposed to the constituent in the gas. As will be appreciated, the heat source may be suitable body for providing thermal radiation in an environment for detection and/or measurement of a constituent in the environment. For example, the heat source may be a combustion chamber such as a combustion chamber in a turbine where detection and/or measurement of a constituent is desired in the combustion chamber, or a portion of a turbine for where detection and/or measurement of a constituent in a gas is desired in an inlet or exhaust portion of the turbine.

[0074] In this embodiment, a reflector 240 such as a mirror may be used to increase the amount of thermal energy which passes through the sensing material. For example, thermal energy from heat source 102 may be reflected by reflector 140 to pass through sensing material 1 10. Collection optics such as a lenses 250, an iris 254, and a filber optic cable 256 may be used to focus radiation from the sensing material into the NIR spectrometer for analysis of the absorbance, extinction or reflectance spectra.

[0075] In this embodiment, processor 230 controls the automated gas exposures, such as introduction of a constituent via a gas inlet 204 for the sensor tests as well as the automated data collection and analysis. Heat source 202 is used for controlling the temperature of the sample and at the same time the thermal energy that is used and harvested.

[0076] The present disclosure is also directed to near-infrared (NIR) thermal energy harvesting for gold nanorods (AuNRs), allowing concentration dependent, ppm-level, gas detection of H2, CO, and NO2 at 500 degrees C without using a white light source. Part-per-million detection capabilities of the gold nanorods are demonstrated with a factor of 1 1 reduction in collection times in the NIR as compared to measurements made in the visible light region. Decreased collection times are enabled by an increase in S:N ratio, which allows a demonstration of selectivity through the use of both full spectral and a reduced spectral-based principal component analysis. Furthermore, low temperature thermal imaging spectra have been obtained at sample temperatures ranging from 275-500 degrees C, e.g., enabling energy harvested gas sensing at lower temperatures. The present disclosure may be suitably employed in the miniaturizing plasmonic gas sensing technology and integration in areas such as gas turbines.

[0077] For example, the present technique is applicable to gas sensing at high temperatures may be applicable in multiple industries with applications that range from optimization of combustion in power plants to sensing gas emissions from aircraft. Building resilient, stable, and sensitive gas sensors that can withstand these high temperatures may save significantly on costs and reduce gas emissions.

Plasmonic gas sensing of analyte gases such as H2, CO, NO2 as well as organic and sulfide compounds may potentially satisfy industry demands for high temperature, low ppm-level gas detection devices.

[0078] As described below, the ability to harvest thermal energy from combustion sources reduces design complexity and may provide practical integration schemes. The present disclosure directed to thermal energy harvesting based sensor system results in collection times less than 30 seconds while simultaneously improving the S:N ratio across the spectral range in the NIR to wavelengths around 1400 nm, which has led to wavelength down-selection while maintaining both high sensitivity and selectivity towards the target gases. Wavelength down-selection reduces the number of wavelength variables for gas selectivity to three individual wavelengths. Thus, high quality plasmonics sensing data is achievable without both an external incident light source as well as complex detection optics. Additionally, optical sensing in the NIR has the benefit of comparatively low cost optics and electronics due to the mass usage of NIR equipment by the telecommunication industry.

[0079] In order to sufficiently harvest thermal radiation from the NIR regime, 44 nm x 170 nm gold nanorods (AuNRs) have been fabricated due to the strong longitudinal peak position dependence on the aspect ratio (rod length divided by rod width). AuNR samples, with their longitudinal peak in the near-infrared region, offer rapid gas sensing capabilities without an external incident white light source. Gas selectivity may include monitoring several key wavelengths within the plasmonic absorption band. These features allow miniaturization of typically large sensing components. Another benefit of thermal harvesting in the NIR is that the sensors can operate at a broader temperature range. For example, low temperature thermal imaging spectra have been collected down to a sample temperature of 275 degrees C. Further use of these methods may be widely applicable to plasmonics related work in energy, biological and other materials related fields with operating

temperatures ranging from ambient conditions up to those applicable to combustion, simply by tuning the aspect ratio of the plasmonic absorber to best match the thermal conditions. The present technique should also allow extraction of sample temperature due to the demonstrated linear increase of plasmon peak position with increasing temperature. Alternatively, by using a selected wavelength approach that tracks independent wavelengths for both temperature and gas concentration, temperature extraction as well as analyte gas selectivity may be possible within a single AuNR sample.

[0080] Plasmonic sensors utilize the properties of a surface plasmon resonance (SPR), created by incident light exciting conduction band electron oscillations, which induces the scattering and absorption of light. When the interrogated particles are smaller than the wavelength of the incident light, a localized surface plasmon resonance (LSPR) occurs, which refers to the confinement of the electron

oscillations to the particle surface. LSPR results in a localized electromagnetic field enhancement that is strongly sensitive to the dielectric constant of the local environment immediately surrounding the nanoparticle, thereby allowing sensitive gas detection since even small amounts of adsorbed/reacted analyte gas is enough to alter the matrix dielectric constant and the metal's free electron density. [0081] Lithographically patterned AuNRs offer several advantages. For example, patterned AuNRs have benefits of uniformity of the rod size and spacings as well as ease of tunability. Additionally, patterned AuNRs with a YSZ capping layer may be thermally stable at the high temperatures and reactive conditions common in combustion environments. The thermal stability of AuNRs with a YSZ capping layer has been further reinforced by multiple 20 hour gas sensing experiments with both white light and thermal imaging measurements on the same nanorod sample. The benefits of YSZ-capped, lithographically patterned AuNRs make them an ideal candidate for harvesting NIR radiation from combustion sources.

[0082] For nanorod nanoparticles, the LSPR frequency is expressed by the Drude equation (equation 1 as also described above),

which relates it to the free electron density of the metal nanoparticle and the matrix dielectric constant. Shape-dependent SPR properties such as those present in AuNRs can be modeled by modifying the Drude equation with a shape factor, Yi, which accounts for the effects of the nanorod aspect ratio.

[0083] The resonant peak frequency of AuNRs is described by eq. 1 above and is a function of the dielectric constant of the metal, dielectric constant of the matrix, and the free electron density. Different gas environments can alter these parameters and lead to different optical responses, opening the door for gas sensing. The AuNR- YSZ sample used in these high temperature sensing experiments has a baseline resonant frequency in an air atmosphere, determined by molecular oxygen dissociative adsorption and formation of different ionized species with eventual formation of monoatomic oxygen anions (O^"). The monoatomic oxygen anions can fill vacancy sites in the YSZ matrix after extracting another electron to form O^2". The different analyte gases used also adsorb to the sample surface and either donate or remove oxygen anions from the YSZ matrix, affecting the free electron density of the metal and the matrix dielectric constant. A plasmon peak shift to higher energies is caused by reducing gases, H2 or CO, where surface adsorption and subsequent reaction with an oxygen anion forms H2O and CO2, respectively. These reactions consequently increase the free electron density and decrease the matrix dielectric constant causing a blue shift in the LSPR peak position. A peak shift to lower energies occurs upon exposure to an oxidizing gas such as NO2, and is due to dissociation of the NO2 onto the sample surface and oxygen donation to the matrix causing electron transfer from the gold and an increase in the matrix dielectric function. By collecting frequent absorbance spectra during a gas exposure experiment and extracting the longitudinal peak position from each one, the peak position may be observed to change significantly and characteristically with each analyte gas type.

[0084] With reference again to FIG. 1 1 , the thermal radiation emitted by a high temperature combustion source is isotropic but, through experimental design, the NIR thermal radiation can be effectively focused through the plasmonically active AuNR sample and be used as the incident light source. As shown in FIG. 1 1 , a spherical gold-coated mirror with high reflectivity in the NIR region, was used for the purpose of redirecting light exiting the furnace back through the AuNRs for enhanced spectral acquisitions. Collection optics with computer controlled mass flow

controllers and a NIR spectrometer complete the hardware needed to acquire energy harvested NIR absorption spectra referenced to the thermal radiation emitted by the furnace.

[0085] To allow for thermal energy harvesting of near-infrared radiation, rods with dimensions of 44 nm x 170 nm were employed, which resulted in a longitudinal plasmon peak position of approximately 1420 nm (FIG. 12a) which is ideal for NIR energy harvesting.

[0086] Referencing Planck's blackbody distribution curve, there is a significant increase in spectral radiance in the near infrared region as compared to the visible region at the same temperature. For a blackbody emitter temperature of 600 degrees C, the spectral radiance at 1420 nm is 458x higher than the spectral radiance emitted at 800 nanometers. While this calculation is for an ideal blackbody, this is qualitatively apparent in the experimental data noted in FIG. 12b. Specifically, with these higher signal counts in the NIR, 1 1x more data points are able to be collected within a given gas exposure experiment, thus enabling improved spectral and time dynamic data sets. [0087] A single NIRQuest512 near-infrared spectrometer 1 10 (FIG. 1 1 ) was used to measure NIR absorbance spectra as a function of both time and gas exposures for these sensing experiments. A mathematical replacement for a real-time reference was used to achieve improved baseline stability. For example, internal referencing may be used to correct for baseline drift. Internal referencing requires selection of a single non-absorbing wavelength for a given sample and then using that wavelength to "re-normalize" the rest of the absorbance curve to the absorbance value at that wavelength. Optical sensing experiments, especially those at long time scales, benefit from having a real-time reference since light sources have varying scan-to-scan intensity across the spectral range and also drift systematically.

Internal referencing is a solution to this problem and can also work with the thermal harvesting technique since, similar to white light experiments, the intensity of thermal radiation produced by the furnace coils varies slightly around the furnace setpoint. This typically is not a significant problem in the thermal harvesting experiments, but provides extra stabilization to the technique over the 20 hour gas exposure

experiments.

[0088] With reference to FIG. 13A, gas sensing using the internal referencing procedure has been performed for different levels of h , CO, and NO2 exposures up to maximum concentrations of 10000 ppm H2, 100 ppm CO, and 100 ppm NO2 in an air background and a 500 degrees C sample temperature. The purge time for each analyte gas concentration in all of the sensing tests was 40 minutes. The absorption spectral data acquired from these experiments were used to determine the change in the LSPR centroid position as a function of time and gas exposure, FIG. 13A (top), as well as the calibration curves determined from these exposures, FIG. 13B

(bottom). As expected both the H2 and CO exposures show a characteristic blue shift in the LSPR while NO2 exposures result in a red shift in the LSPR.

[0089] The calibration curves shown in FIG. 13B were obtained by averaging 25 centroid positions from each gas concentration and then plotting this averaged centroid shift vs. gas concentration for the three analyte gases. The average error bar percentages are 5.7 percent for H2, 8.3 percent for CO, and 12.5 percent for NO2. In all of the tests, the observed baseline noise is translated to the analyte gas response since it is noise coming from the detector as well as the light source. In the NO2 test, since it has the smallest magnitude of peak shift between the three gases, the noise is more prevalent in the gas response and this is seen from the high error bar percentage. All of the calibration curves shown appear to have not reached their saturation limit, and could likely give concentration dependent measurements at higher concentrations of the analyte gases. Lower limit sensitivity values for the three analyte gases are: - 0.00034 nm/ppm H2, -0.029 nm/ppm CO and 0.022 nm/ppm NO2 and were calculated by analyzing the slopes of the calibration curves for the lowest three concentrations for each analyte gas. Lower concentrations of NO2 and CO were used to illustrate the high sensitivity at concentrations important to industrial applications. For example, stationary gas turbines have between 2-20 ppm NO2 and between 5-330 ppm CO by volume in its exhaust stream, which fall within the detection capabilities of the sample used here. Distinguishing the analyte gas responses, especially the two reducing gases may employ Principal Component Analysis (PCA). PCA is a multivariate analysis method that is used in fields such as image compression, electronic noses, and gas sensing to visualize seemingly hidden relationships between independent variables.

[0090] PCA was employed for the H2, CO, and NO2 gas sensing results shown above, by reducing the dimensionality of a vast dataset, through Singular Value Decomposition (SVD), and by projecting the data points onto the eigenvectors of the covariance matrix which correspond to the principal component axes or the directions of maximum variance within the data. This results in a PCA scores plot which can show clustering of data representing each gas. For these measurements, the inputs to the PCA algorithm are averaged difference spectra (i.e. air-H2 spectra minus the air-only spectra) for the 5 different concentrations. FIG. 14(a) shows the full spectrum PCA result that contains 413 wavelengths in the range of 1050 nm to 1 , 700 nm. Similar degrees of selectivity are achieved with the reduced wavelength approach (FIG. 14(b)) by selecting the wavelengths: 1350, 1410, 1470 nm. The wavelengths 1 ,350 and 1 ,470 nm were selected to capture variance on either side of the LSPR absorbance peak, where the intensity at a given wavelength is shifting a particularly large amount from either a red or blue curve shift. The 1 ,410 nm wavelength was chosen due to its proximity to the plasmon peak position.

Comparison of the gas-on and gas-off spectral overlays confirmed the choice of this wavelength subset. By reducing the wavelengths collected, the amount of collected information can be reduced significantly. By only requiring a small subset of wavelengths to be monitored while retaining the required detection limits and selectivity characteristics, the detection hardware can be simplified. NIR optical components such as sources and spectrometers have low cost and are highly available due to demand from the telecommunications industry. AuNR-YSZ samples may be mounted on fiber optic cables and, combined with wavelength-dispersive multiplexing and detectors, and may allow placement of a distributed network of optical plasmonic sensors in a combustion source. The NIR thermal energy harvesting approach along with multivariate analysis may allow for miniaturization and integration of low-cost optical gas sensors.

[0091] NIR thermal energy harvesting according to the present disclosure may also function at lower temperature regimes. Lower temperatures may be applicable to such applications as photothermal therapy or bio-imaging, or combustion/catalytic environment applications that harvest low temperature thermal radiation. Using catalysts at lower temperatures allow improved energy efficiency and increased long-term stability of the catalyst. For example, the Linic group, developed for Ag plasmonic nanostructures may allow low temperature catalysis which utilize a combination of sample heating and low-intensity visible light to drive catalysis. With collection of low temperature thermal imaging spectra, it is possible the AuNR sample may act in a similar fashion, but may harvest and use the thermal radiation to reduce complexity.

[0092] FIG. 15 illustrates that the longitudinal peak position of the NIR-absorbing AuNR sample increases linearly with temperature for polarized white light

measurements. Thermal imaging spectra have been taken at a series of similar sample temperatures and extend down to a sample temperature of about 275 degrees C (the lowest temperature thermal imaging spectra is shown inset in FIG. 15). There are several spectral features that are expected to change with

temperature. First, the full width at half maximum increases with increasing temperatures due to electron-phonon scattering. Also, due to thermal expansion of the particles, the free electron density will decrease due to the same number of free electrons occupying a larger volume.

[0093] The linear peak position dependence on sample temperature for the white light measurements points to the possibility of temperature extraction with both white light as well as thermal imaging measurements. The plasmon linewidth (FWHM) may allow temperature extraction due to the temperature dependence of linewidth as demonstrated with spheroidal metal particles. Another approach for simultaneous temperature sensing may be use a wavelength that is active only with changes in temperature and not affected by the presence of gases. Based on the current gas reaction mechanism as described above, it is likely that this nanorod sample be applicable for gas sensing down to a sample temperature of about 350 degrees C since YSZ continues to conduct oxygen ions down to this temperature. There is a temperature threshold (typically below about 350 degrees C) for the YSZ matrix where oxygen ion conduction becomes less appreciable and it may be beneficial to instead use T1O2, Ce02 or another active material to obtain gas sensing

measurements.

[0094] Industrial applications may desire increased signal for optical sensing measurements as this permits faster gas detection and an increased signal-to-noise ratio. As described above, thermal energy harvesting methods can be extended into the near-infrared region by demonstrating concentration dependent surface plasmon peak shifts and gas selectivity with both full spectrum PCA analysis and reduced wavelength PCA analysis. Such an approach may reduce the required white light source to a mirror and the full-size spectrometer down to a handful of wavelength- tuned diode detectors to monitor selected highly information-dense wavelengths and collect both sample and reference measurements for a given wavelength.

[0095] In some embodiments, rods may be fabricated that absorb in the mid- infrared, allowing even lower temperature thermal imaging spectra to be obtained. The thermal imaging method may allow absorption measurements down to body temperature and give in vivo sensing measurements. This may allow photothermal therapy or bio-imaging with these particles all using surface plasmon resonance.

[0096] In the above sampling, the 44 nm by 170 nm nanorod sample was fabricated using both physical vapor deposition and electron-beam lithography. A 65 nm YSZ base layer was used, on top of which the AuNRs were lithographically patterned. This was followed by the deposition of a "capping" layer of YSZ of 50 nm thickness. A step anneal process was then used on the nanorod sample at temperatures of 300, 400, 500, and 600 degrees C. [0097] Gas Sensing employed a NIRQUEST 512 element array detector that provided a spectral range of 900-1 ,700 nm allowing near infrared absorption measurements. The parameters for the collected spectra were 2 second integration time per scan and 10 scans were averaged for one spectra.

[0098] FIG. 16 is a diagrammatic illustration of a thermal harvesting sensor 300 according to an embodiment of the present disclosure. In this embodiment, the technique of the present disclosure is implemented in a optical fiber component based assembly. For example, two optical fibers are employed, a first optical fiber 360 for collecting or obtaining the absorbance, scattering, extinction, or reflected radiation, In, and a second optical fiber 370 for reference thermal energy, l₀. Thermal energy absorbing and sensing material 310 may be either deposited on the end of the collection optical fiber, or mounted on a separate substrate in line with the collection fiber. The sensing material such as plasmonically active materials as described above may be suitably employed. Thermal harvesting sensor 300 may also include a wavelength division multipliers 380 and 390, and diode detectors 385 and 395. The wavelength division multipliers may be used to select characteristic wavelengths to be detected by the diode detectors. These selected wavelengths may be determined from previous experiments which have detailed that they are the preferred ones for capturing the sensing data of interest with the sensing

characteristics needed for the implantation/application. The detectors may be photodetectors as described above such as photodetector with or without a filter. In some embodiments, the same type of sensing material may be use. A different filter may be employed with each different optical fiber so that the combination of sensors and filters may be operable for selectively detecting a different narrow range of emission frequency. Three sets of wavelength division multipliers and photodiodes are illustrated in FIG. 16 but may include more of less sets as determined through the sensing characteristics required for the specified application. Other

embodiments of detection of characteristic wavelengths for a complete description of the sensing application are envisioned (narrow bandpass filters, and other optical components) and would be applicable as well. Thermal harvesting sensor 300 may incorporate features described above in connection with the systems of FIGS. 1 and 10. [0099] FIG. 17 is a flowchart of a method 400 for detecting a constituent in a gas according to an embodiment of the present disclosure. For example, method 400 may include at 410 exposing a sensing material to the constituent in the gas in an environment subject to thermal energy providing thermal radiation, and at 420 detecting the constituent in the gas based on absorption, reflection, and/or extinction of a portion of the thermal radiation in connection with the sensing material, wherein the detecting does not employ a separate light source.

[00100] The sensing material may include a metal, a metal oxide, and/or a metal embedded in a catalytically active matrix. In some embodiments the detecting may include comparing the absorption, the reflection, and/or the extinction of the portion of the thermal radiation in connection with the sensing material with the constituent in the gas and absorption, reflection, and/or extinction of a portion of the thermal radiation in connection without the constituent in the gas. In some embodiments, the detecting may include detecting at least one wavelength in connection with the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material.

[00101] In some embodiments, the detecting may include detecting infrared radiation in connection with the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material. In some embodiments, the detecting comprises detecting a plurality of discrete different wavelengths regarding the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material. The discrete wavelengths may be 730 nm, 745 nm, 785 nm, 860 nm, and/or other subsets for selected wavelengths that are characteristic for that particular application and materials of choice. The detecting may include employing a plurality of photodiode and a plurality of bandpass filters, and/or other devices for detection of absorption, reflection, and/or extinction of the portion of the thermal radiation in connection with the sensing material.

[00102] The detecting may include employing a principal component analysis process or another statistical type algorithm used to identify patterns in the datasets.

[00103] The absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material may be in the range between about 300 nm to 5,000 nm, or about 900 nm to about 2000 nanometers, or other suitable range. [00104] The sensing material may include a metal, a metal oxide, and/or a metal embedded in a catalytically active matrix, and the exposing may include exposing the sensing material to the constituent in the gas in the environment subject to a temperature of a melting point of the plasmonically or optically active component in the sensing material.

[00105] The exposing may include exposing the sensing material to the constituent in the gas in the environment subject to a temperature in the range between about room temperature and about 1 ,500 degrees Celsius, or about 500 degrees Celsius and about 1 ,500 degrees Celsius, or other suitable range.

[00106] The method may further include determining a concentration of the constituent in the gas based on the absorption, the reflection, and/or the extinction of thermal radiation in connection with the sensing material. The method may further include redirecting (such as with a mirror) a portion of the thermal radiation onto the sensing material.

[00107] The environment may be a combustion chamber. The constituent may include hydrogen gas, carbon dioxide gas, nitrogen dioxide gas, and/or other target gases of interest. The catalytically active matrix may include a yttria stabilized zirconia matrix, a ceria matrix, a titania matrix, or other catalytically active materials. The sensing material may include a metal such as gold, silver, copper, nickel, and/or other catalytically active materials. The sensing material may include metal nanorods or other geometries. The sensing material may include gold, silver, copper, nickel, and/or other catalytically or optically active materials nanorods or other geometries. The nanorods may be tailored based on its aspect ratio. The providing the sensing material may include providing the sensing material on an optical fiber, or other light collection medium coupled to fibers or detection optics.

[00108] FIG. 18 is a flowchart of a method 500 for detecting a constituent in a gas according to an embodiment of the present disclosure. For example, method 500 may include at 510 exposing a sensing material to the constituent in the gas at a temperature in an environment subject to thermal energy providing thermal radiation, at 520 measuring a first plurality of discrete wavelengths in connection with absorption, reflection, and/or extinction of a portion of the thermal radiation in connection with the sensing material at the temperature, at 530 measuring a second plurality of the discrete wavelengths in connection with a portion of the thermal radiation at the temperature to serve as a reference, and at 540 detecting the constituent in the gas based on the measured first plurality of the discrete

wavelengths in connection with the absorption, the reflection, and/or the extinction of the portion of the thermal radiation regarding the sensing material and the measured second plurality of discrete wavelengths in connection with the portion of the thermal radiation serving as the reference wherein the detecting does not employ a separate external light source

[00109] The first measuring and the second measuring may be performed generally at the same time. The first measuring may include employing a first probe and the second measuring may include employing a second probe, and wherein the first probe and second probe are disposed generally side-by-side. The first probe may include a fiber optic cable or other light collection medium coupled to fibers or detection optics, and the second probe may include a fiber optic cable or other light collection medium coupled to fibers or detection optics. The first measuring may include employing a first plurality of photodiodes and a first wavelength division multiplexer, and wherein the second measuring comprise employing a second plurality of photodiodes and a second wavelength division multiplexer.

[00110] The sensing material may include a metal, a metal oxide, and/or a metal embedded in a catalytically active matrix.

[00111] The discrete wavelengths may be in the range from visible into the IR regions, e.g., including infrared radiation. The temperature may be in the range between about room temperature and about 1 ,500 degrees Celsius, or in the range between about 500 degrees Celsius to about 1 ,000 degrees Celsius, or other suitable range.

[00112] The detecting may include determining a concentration of the constituent in the gas based on the measured first plurality of discrete wavelengths in

connection with the absorption, the reflection, and/or the extinction of the thermal radiation in connection with sensing material, and the measured second plurality of discrete wavelengths in connection with the thermal radiation serving as the reference. [00113] The environment may include a combustion or combustion chamber. The constituents may include hydrogen gas, carbon dioxide gas, nitrogen dioxide gas, and/or other target gases of interest. The catalytically active matrix may include a yttria stabilized zirconia matrix, a ceria matrix, a titania matrix, or other catalytically active materials. The sensing material may include a metal comprising gold, silver, copper, nickel, and/or other catalytically active materials. The sensing material may include metal nanorods or other geometries. The sensing material may include gold, silver, copper, nickel, and/or other catalytically active materials nanorods or other geometries. The nanorods may be tailored based on its aspect ratio.

[00114] The sensing material may include an array of different optically active materials, and the measuring the first plurality of discrete wavelengths comprises measuring a plurality of first plurality of discrete wavelengths in connection with absorption, reflection, and/or extinction of a portion of the thermal radiation in connection with the different optically active materials of the sensing material at the temperature.

[00115] In the various embodiments, for example, a computing unit or computer may be employed having a processor, memory, and input/output devices. In some embodiments, the memory may include a database of a plurality of constituents in gases based on absorption, reflection, and/or extinction of a portion of thermal radiation in connection with the sensing material exposed to the constituent at one or more temperatures. Such as database may be operably employed for comparison to the detected absorption, reflection, and/or extinction of a portion of thermal radiation in connection with the sensing material exposed to a constituent to detect the constituent and/or determine the concentration of the constituent. In some

embodiments, the memory may include operable programming or algorithms for determining one or more constituents in a gas based on a shift in the one or more of the wavelengths associated with the absorption, reflection, and/or extinction of a portion of thermal radiation in connection with the sensing material exposed to a constituent. Such an algorithm may be operably employed to detect the constituent and/or determine the concentration of the constituent based on the detected absorption, reflection, and/or extinction of a portion of thermal radiation in connection with the sensing material exposed to the constituent. In some embodiments, a separate reference sensing material or other material may be exposed to the same thermal radiation without the constituent at the same time as the detected absorption, reflection, and/or extinction of a portion of thermal radiation in connection with a sensing material exposed to the constituent. Using operable databases or algorithms, detection of the constituent and/or determination of a concentration of the constituent may be performed.

[00116] It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments and/or aspects thereof may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the various embodiments without departing from their scope.

[00117] While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments, they are by no means limiting and are merely exemplary. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the various embodiments should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

[00118] In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein." Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means- plus-function format and are not intended to be interpreted based on 35 U.S.C. §1 12, sixth paragraph, unless and until such claim limitations expressly use the phrase "means for" followed by a statement of function void of further structure.

[00119] It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. [00120] While the disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments of the disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

[00121] This written description uses examples in the present disclosure, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

CLAIMS:

1 . A method (400) for detecting a constituent in a gas, the method comprising:

exposing (410) a sensing material to the constituent in the gas in an environment subject to thermal energy providing thermal radiation;

detecting (420) the constituent in the gas based on absorption, reflection, and/or extinction of a portion of the thermal radiation in connection with the sensing material exposed to the constituent; and

wherein the detecting does not employ a separate light source.

2. The method of claim 1 wherein the sensing material comprise a metal, a metal oxide, and/or a thermal radiation absorbing material in a catalytically active matrix.

3. The method of claim 1 wherein the detecting (420) comprises comparing the absorption, the reflection, and/or the extinction of the portion of the thermal radiation in connection with the sensing material with the constituent in the gas and

absorption, reflection, and/or extinction of a portion of the thermal radiation in connection without the constituent in the gas.

4. The method of claim 1 wherein the detecting (420) comprises detecting at least one wavelength in connection with the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material.

5. The method of claim 1 wherein the detecting (420) comprises detecting infrared radiation in connection with the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material.

6. The method of claim 1 wherein the detecting (420) comprises detecting a plurality of discrete different wavelengths regarding the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material.

7. The method of claim 6 wherein the discrete wavelengths comprises 730 nm, 745 nm, 785 nm, 860 nm, and/or other subsets for selected wavelengths.

8. The method of claim 6 wherein the detecting (420) comprises employing a principal component analysis process.

9. The method of claim 6 wherein the detecting (420) comprises employing a plurality of photodiode and a plurality of bandpass filters, and/or other devices for detection of absorption, reflection, and/or extinction of the portion of the thermal radiation in connection with the sensing material.

10. The method of claim 1 wherein the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material is in the range between about 300 nm to 5,000 nm.

1 1 . The method of claim 1 wherein the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material is about 900 nm to about 2000 nanometers.

12. The method of claim 1 wherein the sensing material comprises a metal, a metal oxide, and/or a thermal radiation absorbing material in a catalytically active matrix, and the exposing (410) comprises exposing the sensing material to the constituent in the gas in the environment subject to a temperature of a melting point of the plasmonically or optically active component in the sensing material.

13. The method of claim 1 wherein the exposing (410) comprises exposing the sensing material to the constituent in the gas in the environment subject to a temperature in the range between about room temperature and about 1 ,500 degrees Celsius.

14. The method of claim 1 wherein the exposing (410) comprises exposing the sensing material to the constituent in the gas in the environment subject to a temperature in the range between about 500 degrees Celsius and about 1 ,500 degrees Celsius.

15. The method of claim 1 wherein the exposing (410) comprises exposing the sensing material to the constituent in the gas in the environment at about room temperature.

16. The method of claim 1 wherein the detecting (420) comprising determining a concentration of the constituent in the gas based on the absorption, the reflection, and/or the extinction of thermal radiation in connection with the sensing material.

17. The method of claim 1 wherein the exposing (410) comprises redirecting the portion of the thermal radiation onto the sensing material.

18. The method of claim 1 wherein the environment comprises combustion.

19. The method of claim 1 wherein the constituent comprises hydrogen gas, carbon dioxide gas, nitrogen dioxide gas, and/or other target gases of interest.

20. The method of claim 1 wherein the catalytically active matrix comprises a yttria stabilized zirconia matrix, a ceria matrix, a titania matrix, or other catalytically active materials.

21 . The method of claim 1 wherein the sensing material comprises a metal comprising gold, silver, copper, nickel, and/or other catalytically active materials.

22. The method of claim 1 wherein the sensing material comprises metal nanorods or other geometries.

23. The method of claim 1 wherein the sensing material comprises gold, silver, copper, nickel, and/or other catalytically or optically active materials nanorods or other geometries.

24. The method of claim 22 wherein the nanorods are tailored based on its aspect ratio.

25. The method of claim 1 wherein the exposing (420) comprises exposing the sensing material on an optical fiber, or other light collection medium coupled to fibers or detection optics.

26. A method (500) for detecting at least one constituent in a gas, the method comprising:

exposing (510) a sensing material to the at least one constituent in the gas at a temperature in an environment subject to thermal energy providing thermal radiation;

measuring (520) a first plurality of discrete wavelengths in connection with absorption, reflection, and/or extinction of a portion of the thermal radiation in connection with the sensing material exposed to the constituent at the temperature;

measuring (530) a second plurality of the discrete wavelengths in connection with a portion of the thermal radiation at the temperature to serve as a reference;

detecting (540) the at least one constituent in the gas based on the measured first plurality of the discrete wavelengths in connection with the absorption, the reflection, and/or the extinction of the portion of the thermal radiation regarding the sensing material and the measured second plurality of discrete wavelengths in connection with the portion of the thermal radiation serving as the reference; and wherein the detecting does not employ a separate external light source.

27. The method of claim 26 wherein the detecting (540) comprising determining a concentration of the constituent in the gas based on the measured first plurality of discrete wavelengths in connection with the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material, and the measured second plurality of discrete wavelengths in connection with the thermal radiation serving as the reference.

28. The method of claim 26 wherein the first measuring and the second

measuring (520, 530) are performed generally at the same time.

29. The method of claim 26 wherein the first measuring (520) comprises employing a first probe and the second measuring (530) comprises employing a second probe, and wherein the first probe and second probe are disposed generally side-by-side.

30. The method of claim 29 wherein first probe comprise a fiber optic cable or other light collection medium coupled to fibers or detection optics, and the second probe comprise a fiber optic cable or other light collection medium coupled to fibers or detection optics.

31 . The method of claim 26 wherein the first measuring comprise employing a first plurality of photodiodes and a first wavelength division multiplexer, and wherein the second measuring comprise employing a second plurality of photodiodes and a second wavelength division multiplexer.

32. The method of claim 26 wherein the sensing material comprise a metal, a metal oxide, and/or a thermal radiation absorbing material in a catalytically active matrix.

33. The method of claim 26 wherein the discrete wavelengths are infrared radiation.

34. The method of claim 26 wherein the temperature is in the range between about room temperature and about 1 ,500 degrees Celsius.

35. The method of claim 26 wherein the temperature is in the range between about 500 degrees Celsius to about 1 ,000 degrees Celsius.

36. The method of claim 26 wherein the environment comprise combustion.

37. The method of claim 26 wherein the constituent comprises hydrogen gas, carbon dioxide gas, nitrogen dioxide gas, and/or other target gases of interest.

38. The method of claim 26 wherein the catalytically active matrix comprises a yttria stabilized zirconia matrix, a ceria matrix, a titania matrix, or other catalytically active materials.

39. The method of claim 26 wherein the sensing material comprises a metal comprising gold, silver, copper, nickel, and/or other catalytically active materials.

40. The method of claim 26 wherein the sensing material comprises metal nanorods or other geometries.

41 . The method of claim 26 wherein the sensing material comprises gold, silver, copper, nickel, and/or other catalytically active materials nanorods or other geometries.

42. The method of claim 41 wherein the nanorods are tailored based on its aspect ratio.

43. The method of claim 26 wherein the sensing material comprises an array of different optically active materials, and the measuring the first plurality of discrete wavelengths comprises measuring a plurality of first plurality of discrete wavelengths in connection with absorption, reflection, and/or extinction of a portion of the thermal radiation in connection with the different optically active materials of the sensing material at the temperature.

44. A sensor system (100, 200, 300) for detecting a constituent in a gas in an environment subject to thermal radiation, said sensor system comprising:

a sensing material (1 10, 210, 310) comprising a metal, a metal oxide, and/or a thermal radiation absorbing material in a catalytically active matrix.

a first detector (120, 220, 390) for detecting thermal radiation regarding said sensing material exposed to the constituent;

a processor (130, 230, 330) operable to detect the constituent in the gas based on absorption, reflection, and/or extinction of a portion of the detected thermal radiation in connection with said sensing material exposed to the constituent; and

wherein said sensor system does not employ a separate light source.

45. The sensor system of claim 44 wherein said processor (130, 230, 330) is operable to determine a concentration of the constituent in the gas based on the absorption, the reflection, and/or the extinction of thermal radiation in connection with the sensing material.

46. The sensor system of claim 44 wherein said processor (130, 230, 330) is operable to determine a concentration of the constituent in the gas based on one or more detected discrete wavelengths in connection with the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material.

47. The sensor system of claim 44 wherein said first detector (120, 220, 320) is operable to detect at least one wavelength in connection with the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material.

48. The sensor system of claim 44 wherein said first detector (120, 220, 320) is operable to detect infrared radiation in connection with the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material.

49. The sensor system of claim 44 wherein said first detector (120, 220, 320) is operable to detect a plurality of discrete different wavelengths regarding the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material.

50. The sensor system of claim 44 wherein said processor (130, 230, 330) is operable to compare the absorption, the reflection, and/or the extinction of the portion of the thermal radiation in connection with the sensing material with the constituent in the gas and absorption, reflection, and/or extinction of a portion of the thermal radiation in connection without the constituent in the gas.

51 . The sensor system of claim 50 wherein the discrete wavelengths comprises 730 nm, 745 nm, 785 nm, 860 nm, and/or other subsets for selected wavelengths.

52. The sensor system of claim 50 wherein said processor (130, 230, 330) is operable to detect the constituent in the gas using a principal component analysis process.

53. The sensor system of claim 50 wherein said first detector (120, 220, 320) a plurality of photodiodes (364) for detection of the absorption, the reflection, and/or the extinction of the portion of the thermal radiation in connection with the sensing material.

54. The sensor system of claim 44 wherein the absorption, the reflection, and/or the extinction of the thermal radiation in connection with the sensing material is in the range between about 300 nm to 5,000 nm.

55. The sensor system of claim 44 wherein said sensor system is operable to detect the constituent in the gas in the environment subject to a temperature in the range between about room temperature and about 1 ,500 degrees Celsius.

56. The sensor system of claim 44 wherein said sensor system is operable to detect the constituent in the gas in the environment subject to a temperature in the range between about 500 degrees Celsius and about 1 ,500 degrees Celsius.

57. The sensor system of claim 44 further comprising a reflector (140, 240) redirecting a portion of the thermal radiation onto the sensing material.

58. The sensor system of claim 44 wherein said sensor system is operable to detect hydrogen gas, carbon dioxide gas, and/or nitrogen dioxide gas.

59. The sensor system of claim 44 wherein said catalytically active matrix comprises a yttria stabilized zirconia matrix, a ceria matrix, and/or a titania matrix.

60. The sensor system of claim 44 wherein said sensing material comprises a metal comprising gold, silver, copper, and/or nickel.

61 . The sensor system of claim 44 wherein said sensing material comprises metal nanorods.

62. The sensor system of claim 44 wherein said sensing material comprises gold nanorods, silver nanorods, copper nanorods, and/or nickel nanorods.

63. The sensor system of claim 62 wherein the nanorods are tailored based on its aspect ratio.

64. The sensor system of claim 44 wherein said sensing material is disposed on an optical fiber.

65. The sensor system of claim 44 further comprising a second detector (325) for detecting a portion of the thermal radiation to serve as a reference, and said processor operable to detect the constituent in the gas based on the portion of the detected thermal radiation in connection with said sensing material and the portion of the thermal radiation serving as a reference.

66. The sensor system of claim 65 wherein the first measuring and the second measuring (520, 530) are performed generally at the same time.

67. The sensor system of claim 65 wherein the sensing material comprises an array of different optically active materials, and the measuring the first plurality of discrete wavelengths comprises measuring a plurality of first plurality of discrete wavelengths in connection with absorption, reflection, and/or extinction of a portion of the thermal radiation in connection with the different optically active materials of the sensing material at the temperature.