WO2012034115A1

WO2012034115A1 - Airborne contaminant sensor device and method for using the same

Info

Publication number: WO2012034115A1
Application number: PCT/US2011/051169
Authority: WO
Inventors: Joseph J. Belbruno; Susanne E. Tanski
Original assignee: Trustees Of Dartmouth College
Priority date: 2010-09-10
Filing date: 2011-09-12
Publication date: 2012-03-15

Abstract

The present invention is a nanotechnology-based personal sensor device composed of molecularly imprinted polymers that are interrogated using radio frequency identification (RFID) technology for use in simultaneously monitoring airborne contaminants, e.g., of second-hand cigarette smoke.

Description

AIRBORNE CONTAMINANT SENSOR DEVICE AND

METHOD FOR USING THE SAME

Background of the Invention

[0001] This patent application claims the benefit of priority from U.S. Provisional Application Serial Number 61/466,101 filed March 22, 2011 and from U.S. Provisional Application Serial Number 61/381,512 filed September 10, 2010, the content of each of which is herein incorporated by reference in its entirety.

[0002] Molecular imprinting is a technique that allows for the production of molecule specific receptors that are analogous to biological receptor binding sites without the cost or environmental sensitivity of the natural systems (Shea (1994) Trends Polym. Sci . 2:166; ulff (1995) Angew. Chem. Int. Ed. 34:1812; Mosbach & Ramstrom (1996) Biotechnology 14:163; BelBruno (2009) Micro and Nanosystems 1:163) . Molecularly imprinted polymers (MIPs) may be based on either covalent or non-covalent binding between the host polymer and the target or template molecule. Various MIP- based devices have been suggested for use in the detection of surface-binding molecules, inorganic compounds, organic compounds, polymers, biological molecules, nanoparticles , viruses, and biological arrays (WO 2008/063204 and US 2009/0115605) .

[0003] Nicotine is a characteristic component of tobacco smoke and cotinine is a major metabolite of nicotine that is detected in the urine of smokers. Other reports of nicotine MIPs have appeared in the literature. For example, nicotine- targeted MIPs based on the synthesis of the polymer from methacrylic acid monomers have been reported

(Sambe, et al . (2006) J. Chroma tog . A 1134:88; Thoelen et al . (2008) Biosensors and Bioelectronics 23:913-918) . However, poly (methylacrylic acid) exhibits solvent incompatibility with nicotine, thereby making the production of thin films challenging

Summary of the Invention

[0004] The present invention is a device for monitoring exposure to airborne contaminants. The device is composed of at least two poly (4 -vinylphenol ) or nylon films, each molecular imprinted with an airborne contaminant; a sensor for detecting binding between the airborne contaminant and the film, and a radio frequency interrogator unit to read the sensor and transmit an interrogation signal . In certain embodiments, the airborne contaminant is selected from the group of CO, nicotine, 4- (methylnitrosamino) -1- (3-pyridyl) - 1-butanone and formaldehyde. In other embodiments, the sensor is a capacitive or conductive sensor, e.g. composed of polyaniline or polycarbozole . In particular embodiments, the poly (4 -vinylphenol) or nylon film is produced by phase inversion-spin coating. A method for monitoring exposure to airborne contaminants using the device of the invention is also provided.

Brief Description of the Drawings

[0005] Figure 1 is a schematic drawing of an RFID circuit of the instant device .

[0006] Figure 2 is a schematic drawing showing sensor placement over the circuit .

Detailed Description of the Invention

[0007] The present invention is a MIP-based personal sensor that can be readily interrogated using radio frequency identification (RFID) technology for use in simultaneously monitoring airborne contaminants, such as those from second-hand tobacco smoke. The instant personal monitoring device is similar to the small badges used to monitor radiation doses and can be monitored locally such that immediate feedback on exposure is provided. The specific airborne molecules detectable with the instant device include, but are not limited to, CO, nicotine, 4- (methylnitrosamino) -1- (3-pyridyl) -1-butanone (NNK) and formaldehyde. Quantification of one or a combination of these components of second-hand smoke can indicate that second-hand smoke is present .

[ 0008 ] The instant device is composed of at least two poly (4-vinylphenol) (PVP) and/or nylon films, each molecular imprinted with an airborne contaminant; a sensor; and a radio frequency identification component. As is conventional in the art, molecular imprinting is a process by which guest or host molecules (functional monomers or polymers) are allowed to self -assemble around a molecular template, thereby forming a recognition element, which has binding sites corresponding to functional groups in the template molecule. The recognition elements form a binding cavity which is cross- linked into a matrix. The template molecule is removed, leaving behind a molecularly-imprinted polymer (MIP) complementary in shape and functionality to the template molecule, which will rebind chemical targets identical to the original molecular template. In the instant case, the host molecule is PVP or nylon composite, which non-covalently binds the template molecules, has solvent compatibility with the template molecules and is capable of forming a binding cavity around airborne contaminants. For use in the instant invention, the nylon can be any nylon conventionally used in preparing molecular imprinted films and includes, but is not limited to, nylon 6 and nylon 6/6. [0009] Thin films of the invention can be produced by any conventional method. However, the ability to control the thickness and formulate the films in an environment typical of printed circuit production is an important feature of film production for the instant sensors. Thus, in particular embodiments, the instant films are produced by phase inversion-spin coating onto a suitable substrate. The wet phase inversion procedure (Wang, et al . (1997) Langmuir 13:5396; Shibata, et al . (1999) J. Appl . Poly. Sci. 75:1546; Trotta, et al . (2002) J^". Membr. Sci. 201:77) for preparation of MIPs involves a polymerized starting material that is dissolved with the template in a theta solvent. A template-host network is allowed to form in solution and precipitated by immersion in a non-solvent. Originally developed to produce MIP membranes, this procedure has been adapted to the production of thin, 300 nm to 5 μπι, films via spin coating (Crabb, et al . (2002) J. Appl. Polym. Sci. 86:3611; Richter, et al . (2006) J. Appl. Polym. Sci. 101:2919; Campbell, et al . (2009) Surface and Interface Analysis 41:347) and hydrogen bond interactions between the template and host polymer.

[00010] By way of illustration, thin films containing PVP can be produced by mixing PVP (e.g., 10%-15% by weight) in conventional casting solution with the template molecule {e.g., about 5%-10% by weight) in a suitable solvent. For example, nicotine is readily dissolved in methanol, whereas dimethylformamide (DMF) is a suitable solvent for formaldehyde and NK. The solution is allowed to mix at room temperature, e.g., from six to 24 hours, to form the hydrogen-bonded network in solution. Subsequently, thin films are cast onto a substrate using a spin coater at 5000-7000 rpms for about 30 seconds. The thin film is allowed to dry and the template molecule is removed by washing with water. In accordance with the present invention, a separate molecular imprinted film is produced for each template molecule so that detection in the assembled device occurs independently for each airborne contaminant. In this respect, certain embodiments of the instant device feature at least two films each independently molecular imprinted with CO, nicotine, 4- (methylnitrosamino) -1- (3-pyridyl) -1-butanone (N K) or formaldehyde .

[00011] The substrate of the instant molecular imprinted film can be a rigid or flexible material, which may be conducting, semiconducting or dielectric. The substrate can be a monolithic structure, or a multilayer or other composite structure having constituents of different properties and compositions. Suitable substrate materials include quartz, glass, alumina, mica, silicon, III-V semiconductor compounds, and other suitable materials. Optionally, additional electronic elements may be integrated into the substrate for various purposes, such as thermistors, integrated circuit elements or other elements.

[00012] To detect an interaction (i.e., binding) between a molecular imprinted film and a template molecule (i.e., airborne contaminant) , the instant device further includes one or more sensors . Any suitable electrical property may provide the basis for sensor sensitivity, for example, electrical resistance, electrical conductance, current, voltage, capacitance, transistor on current, transistor off current, and/or transistor threshold voltage. In the alternative, or in addition, sensitivity may be based on a measurements including a combination of properties, relationships between different properties, or the variation of one or more properties over time. In some embodiments of the instant invention, the sensor is a capacitive sensor, a conductive sensor or a combination thereof. Depending on the type of sensor, the sensor can be a separate element of the device or integrated with the molecular imprinted film.

[00013] Capacitive sensors are well-known in the art and any suitable sensor can be employed. For example, the capacitive sensor can have a sandwich-type electrode configuration, wherein the molecular imprinted film is placed between two capacitor elements or electrodes. The electrode material can be chosen from any suitable conductor or semiconductor e.g., gold, platinum, silver, and the like. By way of illustration, the instant device can use a set of interdigitated electrodes with the molecular imprinted film coated onto the electrode assembly. Specifically, a sandwich- type capacitive sensor can be produced by depositing chromium on a glass, silicon or mica substrate by thermal evaporation. The chromium is patterned by photolithography and treated, subsequently, by wet etching. An insulating Si0₂ layer with a thickness between 40 nm and 200 nm is deposited onto the bottom electrode surface using an electron-gun thermal deposition technique. Subsequently, the molecular imprinted polymer layer is spun coated on the substrate surface. In the final step, a Cr film with a thickness of 70 nm is deposited on the molecular imprinted polymer film surface by thermal evaporation, followed with patterning by photolithography and wet etching.

[00014] As indicated, the instant device can alternatively incorporate one or more conductive sensors. In this embodiment, a conductive polymer is used such that the template molecule becomes the doping agent. Accordingly, in the presence and absence of the template molecule, the conductivity of the polymer will be different. Conductive polymers of use in this embodiment of the invention are so- called n -electron-conjugated conductive polymers. For example, polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, or a copolymer of two or more kinds of these materials are suitable conductive polymers. By way of illustration, a polyaniline-nylon 6 composite film was prepared for the detection of formaldehyde (see Example 3) . Accordingly, in particular embodiments, the conductive polymer is polyaniline or polycarbozole .

[00015] To remotely communicate the output of the sensors, the instant device further includes a radio frequency interrogator unit . Such interrogator units typically include an antenna, and transmit an interrogation signal or command via the antenna. The instant device can operate over a wide range of carrier frequencies. For example, the device can operate with carriers of 915-5800 MHZ, wherein the frequency selectivity is based on selection of the antenna. Moreover, in so far as the instant device employs multiple MIP films to simultaneously detect multiple airborne contaminants, the device further includes multiplexing RFID circuitry. The sensors of the instant device have a range of values and the interrogator unit must be capable of reading two or more separate sensors (Figure 1) . As such, in certain embodiments, the instant device also has a multiplexing amplifier circuit that includes on-board memory to store values . This includes assembling on-board memory and addressing hardware and certifying the operational status before calibration of the final device to assure that the assembled sensor functions within the same parameters as the individual components. An example of an RFID circuit of the instant device is shown in Figure 2. [00016] Interrogator units also generally include dedicated transmitting and optionally receiving circuitry. Active transmitters are known in the art. See, for example, US Patent No. 5,568,512, which also discloses how the transmit frequency for the transmitter is recovered from a message received via radio frequency from the interrogator. Moreover, many examples of wireless communications circuits are known in the art, and any suitable low-power circuit may be employed. The invention is intended to be practiced with any radio communications circuit with low power requirements, for example, a circuit appropriate for extended operation in a remote battery-powered device without need for recharging.

[00017] The device of the instant invention can transmit radio frequency signals to a receiver and/or host computer in communication with the interrogator. An exemplary receiver includes a conventional Schottky diode detector. When a host computer is employed, the host computer can act as a master in a master-slave relationship with the interrogator. The host computer can include an applications program for controlling the interrogator and interpreting responses, and a library of radio frequency identification device applications or functions. Most of the functions communicate with the interrogator.

[00018] Although sensor systems described herein are particularly suitable for efficient operation by conventional power sources used in portable/remote electronics (e.g., battery, solar cell, miniature fuel cell) , the instant device can also use alternative energy resources, such as a thermocouple, radio- frequency energy, electrochemical interactions, supercapacitors , energy scavenging mechanisms, or the like, or combinations thereof . [00019] In so far as the instant device can detect airborne contaminants such as CO, nicotine, 4- (methylnitrosamino) -1- (3-pyridyl) -1-butanone and/or formaldehyde, the device of this invention is of particular use in monitoring exposure to second-hand tobacco smoke. Upon exposure of the instant device to an air sample, the molecular imprinted films bind airborne contaminants in the air sample, sensors of the device sense said binding, and radio frequency signals are transmitted to alert the user of exposure to the airborne contaminants .

[00020] While conventional technologies can measure nicotine and particulate matter in indoor environments, the current technology involves large air sampling devices and hinders the process of immediate feedback, since complex procedures are required, in an analytical laboratory, to quantify the samples. Moreover, the sampling technique collects all airborne material and the analytical instruments are required to sort out the adsorbed material . The instant device is unique in that it is small (personnel badge sized) , easy to read, simple (no laboratory analysis is needed) , the MIP films are targeted to specific contaminants and a number of contaminants can be simultaneously detected. As a wall -mountable or wearable, personal badge-type, second-hand smoke detector, the instant device finds application in, e.g., medical centers to monitor the environment of pediatric (and other) patients, and to measure tobacco smoke contamination in supposedly smoke -free environments such as hotel rooms and rental cars. Since the specific sensor in the monitor may be readily changed to monitor a different air-borne contaminant, the instant device can be adapted to detect an array of different molecules or hazardous vapors. [00021] The invention is described in greater detail by the following non-limiting examples.

Example 1: Production of PVP MIP Films

[00022] The aromatic nature and hydrogen bonding potential make Poly ( -vinylphenol ) (PVP) an ideal host matrix for MIPs. The PVP films were produced by spin coating; a simple deposition technique that is sensitive to the composition and viscosity of the solution and the rotating speed of the plate (Bronside, et al. (1987) J. Imaging Technol. 13:122) .

[00023] Solutions composed of 10 mL of methanol (Acros Organics; ACS Reagent Grade 99.8%) with 10 wt % of PVP powder obtained from Polysciences , Inc. (MW=22,000; T_g 150 °C) and 5 wt% of nicotine or cotinine were nitrogen purged, covered, and stirred at room temperature for 24 hours. Control films (NIPs) were similarly produced, but without the nicotine or cotinine. Films were spin cast from these solutions onto 22 mm square glass microscope cover slips. Typically, the slides were prewashed with spectroscopic grade isopropanol and acetone prior to polymer deposition. The coating solution was dropped onto a stationary substrate and the spin coater was operated at 4000 rpm for 30 seconds with negligible ramp up time. The rotation spreads the solution evenly over the surface and also causes the solvent to evaporate leaving a thin film of material on the substrate. The concentration of PVP in the casting solution is the dominant variable for the film thickness, which increases rapidly with increasing concentration (solution viscosity) . Cast films are quite stable and may be stored or used for an indefinite time.

[00024] The template molecule was removed from the film by immersion in deionized water for five hours. Nicotine (or cotinine) removal was confirmed by FTIR measurements. Template reinsertion (or reinsertion of the complementary template molecule) was accomplished by immersion of the template extracted (or control) film in a 5 wt % solution of the molecule in deionized water for 2.5 hours. This reinsertion, as with the template removal procedure, is an equilibrium-controlled process and reinsertion occurs to approximately 50% of the initial concentration (via qualitative FTIR measurements) . Additional immersion time was not found to increase the relative amount of template molecule reinserted into the film. FTIR spectra were recorded over a narrow region of interest, -3400 cm^-1 for the OH stretch of PVP, which is missing when hydrogen bonded to nicotine or cotinine or -1700 cm^"1 in the carbonyl region of cotinine, to confirm the interaction of the template with the polymer in the film. The surface topography of the films is characterized by average roughness measurements, R_ai using scanning force microscopy (SFM) . It is defined as the average deviation of the profile from a mean line or the average distance from the profile to the mean line over the length of the assessment. The surface roughness, R_a, is given by the sum of the absolute values of all the areas above and below the mean line divided by the sampling length.

[ 00025 ] All nanoindentation experiments were performed using the electrostatic transducer of the Hysitron triboscope in the UBI 1 (Hysitron User Handbook: Feedback Control Manual. 10025 Valley View Road, Minneapolis, MN; Hysitron, Inc.) . The transducer is a three-plate capacitor, the mid-plate of which carries the indenter fixed to a thin stylus. Application of a DC voltage generates an electrostatic force driving the indenter into the sample surface, while the capacitance change as a measure of penetration depth is recorded. The data consist of a force - displacement curve. For soft samples such as polymers, the stiffness of the internal springs holding the indenter must be subtracted from the applied load in order to obtain the sample stiffness. Hardness, H, is calculated as the applied load, F, divided by the area, A_c, of the indenter tip at the contact depth, ^_c; the area is depth-dependent (Olivier & Pharr (1992) J^". Mater. Res. 7:1562) . The modulus is derived from the slope of the force-displacement curve upon unloading when the sample elastically recovers. The tip elastic properties can effectively be ignored for polymeric materials. Investigations are performed with a blunted 90° diamond cube corner tip. The calibration of the tip to determine the depth dependent area function A_c(hc) was obtained with the standard curve- fitting method using fused quartz with its known reduced modulus as the reference material. Additionally, calibration with a sharp silicon grating was performed (Richter, et al . (2006) High Pressure Res. 26:99) . A commercial grid with ultra sharp conical silicon tips was used. The small apex angle of the grid tips (below 20°) together with their large height (700 nm) offers the opportunity for exact examination of the shape of the diamond indentation tip apex. By means of the AFM software using the so-called bearing function, the shape of the diamond indenter can be reconstructed and the area function A_c can be obtained. The advantage of this technique over the curve-fitting method is the direct observation of the tip shape, which also allows the estimation of the blunt tip radius, which was 600 nm in our experiments.

[ 00026 ] Thermal drift and creep behavior of the piezoelectric scanner must be minimized. At the nanoscale, drift is measured and compensated in the resulting data. This compensation factor is part of the standard UBI software and a correction measurement is performed before each indent. Typical drift rates range up to 0.5 ntn/s. The penetration depth of the indent should not exceed 30% of the polymer film thickness to avoid substrate effects. Most experiments were performed with smaller penetration depths, however depth-dependent measurements sometimes show an increase in hardness and reduced modulus with increasing penetration indicating the influence of the glass substrate .

[ 00027 ] Depth-dependent mechanical properties are obtained through indentation tests where repeated loading and unloading are performed at the same location on the sample surface (Richter, et al . (2006) Colloids and Surfaces, A 284/285:401; Fischer-Cripps (2002) Nanoindentation, Springer, New York; Olivier & Pharr (1992) supra; Wolf & Richter (2003) New J^". Phys . 5:15.1; Maier, et al . (2002) Mater. Character. 48:329; Ward & Hadley (1993) An Introduction to the Mechanical Properties of Solid Polymers, John Wiley & Sons, Chichester; Nowicki, et al . (2003) Polymer 44:6599; Du, et al . (2000) Polymer 42:5901; Drechsler, et al . (1998) Appl . Phys. A66:825; Tsui, et al . (2000) Macromolecules 33:4198; VanLandingham, et al . (2001) in: Tsukruk & Spencer (Eds.) Macromolecular Symposia, Wiley-VCH Verlag, Weinheim, pp. 15-43) . Eight cycles of multi-indentation were performed to calculate the depth- dependent hardness and the indentation modulus. In general, multi -cycling means, after loading to a maximum load, F_max, the sample is partially unloaded to a minimum load, F_min = 0.1 F_max to 0.25 m_ax, required to prevent the tip from losing contact with the sample and sliding to a new lateral position. The sample is then reloaded to the same or an increased maximum load {F_max + AF) and the cycle is repeated. After the onset of plastic deformation, the loading curve is an overlap of both plastic and elastic deformations . Multi-cycling delivers a set of data that includes the entire material response, from the first indenter- sample contact to the maximum penetration.

[00028] Computational Details. All optimizations were performed with NWChem, a Computational Chemistry Package for Parallel Computers, v5.1 , with no symmetry or geometric constraints. The correlation and exchange effects were calculated using the Perdew-Burke-Ernzerhof (PBE) exchange- correlation functional (Adamo & Barone (1998) J^". Chew. Phys. 110:6158) with the 6-31G* basis set (Hariharan & Pople (1973) T eoret. Chimica Acta 28:213) both for all atoms. Several relative orientations of the PVP molecule (s) relative to nicotine or cotinine were optimized to ensure that the total energy of the complex was not dependent upon this factor. All calculations were run in parallel on a Linux cluster composed of 94 Quad-Core (2x) AMD Opteron nodes (752 cpus) , and 6 Quad-Core (2x) Intel nodes (48 cpus) . In aggregate, the Linux cluster had 3 terabytes of memory and more than 35 terabytes of disk space. Geometric structures were visualized using the AVOGADRO molecular editor program.

Example 2: Nanohardness Analysis of Nicotine- and Cotinine- Imprinted Poly (4 -vinylphenol) Films

[00029] Control PVP and MIP Film General Features. The structure of the MIP and NIP films was dependent on the viscosity of the solution. This was mainly controlled by the temperature and spin casting conditions such as speed and deposition time, in addition to the PVP concentration in the solution. The pure PVP films deposited from the casting solution containing 10% polymer had a characteristically smooth morphology. In the present analysis, the pure PVP film had a surface roughness, R_a, of 11.5 nm, over a 130 μπι x 130 μτ sample. No significant morphological features were found in the control PVP films; the films were flat. The as produced' MIP films containing, for example nicotine template molecules, showed a different surface morphology in comparison to the control films. Surface stripes, representing different heights, were the main surface feature. The surface roughness of this type of sample was measured to be 69.2 nm, over the same 130 μχα x 130

sampling size. Removal of the nicotine from the MIP resulted in a loss of the stripe morphology and the observation of a number of pores in the surface. The pores were apparently formed during the solidification process of the polymer films and were caused by the presence of the template molecules and the porogen solvent during the film growth process (Campbell, et al . (2009) supra) . The assumption was that the pores were present in the 'as produced' samples, but lay beneath the stripe morphology. The template molecules were smaller than the size of the pores observed in the films. The additional volume of the measured pores resulted in part from: the geometrical form of the template molecule, the arrangement of that molecule within the polymer host, and the evaporation of the solvent through the polymer film. The surface roughness R_a, of the nicotine-removed MIP was 44.1 nm, over the 130

x 130 μιη sample. Reinsertion of nicotine into this MIP restored the strip morphology somewhat, but had minimal effect on the roughness of the surface (R_a = 33.1 for the 130 μπι square sample) . The different film morphology in the SFM images was characteristic for the presence of the template molecules.

[00030] Nanomechanical Properties . The contact pressure (hardness) can vary even for homogeneous matter such as the control sample, since the deformation starts with purely elastic deformation, and after yielding, the plastic contributions increase after a saturation value of H is obtained for very large indents. This means the hardness decreases with increasing indentation depth. Within the indentation size effect model (Wolf & Richter (2003) supra) the hardness will be higher in a small indentation area where fewer defects are encountered. With increasing indentation size (depth) , more defects such as dislocations, are generated by the contact pressure. For very thin polymer films, the indentation modulus is not constant due to the increased substrate influence with increasing depth. The elastic behavior of pure PVP films occurs by deformation of the polymer molecules and movement of the chains after the adhesion energy has been overcome .

[00031] The multi-cycling load-depth curves for MIP films with template molecules in the casting solution for the spin coating process showed significant differences in comparison to pure PVP films. From the load-depth curves, it was clear that the 'as produced' nicotine-loaded MIP films had indentation depths of approximately 175 nm with a maximum applied force of 300 μΝ; removal of the nictoine increased the penetration depth to nearly 200 nm. Unexpectedly, reinsertion of nicotine reduced the penetration depth to a value 35 nm less than the original imprinted film. Clearly, the presence of the template molecule in the MIP led to a stiffer film and analogous results were recorded for cotinine imprinted films. The assignment of the basis of the change in nanomechanical properties to the template was reinforced by the fact that the MIP with the template removed was less stiff than a pure PVP film for the same applied force.

[00032] The nanomechanical behavior of the polymer films indicated that hardness decreased slightly with increasing depth, whereas the indentation modulus increased slightly with increasing depth. The hardness of the control PVP film had the value of 0.38 GPa with an indentation modulus of 11.7 GPa. MIP films with cotinine were stiffer with a hardness value of 0.59 GPa and an indentation modulus of 14.7 GPa. Nicotine imprinted films were slightly stiffer than the control film with a hardness value of 0.43 GPa and a modulus of 11.6 GPa. Extraction of the template molecules meant that the molecular cavities were still in the polymer matrix, but the space was empty. Thus, the network character and therefore the mechanical properties changed. For example, the hardness for MIP films „ with nicotine extracted yielded smaller values of 0.31 GPa for the hardness. Reloading of either template resulted in an increase of the hardness to values greater than those of the original 'as produced' MIP films. The percentage increase in hardness was greater for the reinsertion of nicotine into a nicotine-targeted MIP than for cotinine into a cotinine- targeted MIP. Loading, extraction and reloading of nicotine or cotinine in the MIP films were clearly measurable with the nanoindentation method.

[ 00033 ] These results indicate a strongly hydrogen-bonded network between the polymer chains via the template molecules. In the ideal case, the molecular cavities with nicotine template molecules were formed by two hydrogen bonds that cross-linked between two PVP molecules; cotinine had three such potential hydrogen bonding sites. However, the imprinting process could be incomplete with fewer hydrogen bonds established. Template molecules can bond to the polymer molecule at several points along the chain with efficiencies dependent on the number and distribution of template molecules in the MIP film. From the nanomechanical investigations it was contemplated that hydrogen bonds of the template molecules between the PVP chains resulted in a cross-linking between the chains, separated the PVP molecules, (preventing an easy movement of the chains, and could reduce the adhesion energy between pure PVP molecules. This could result in either, mechanically stiffer or softer MIP networks. Two different molecular mechanisms were proposed for the polymer response during an applied external contact pressure. In pure PVP, the indentation tip could cause a deformation of the PVP molecules and a sliding motion between the chains. The molecular cavities and micro-pores change the mechanical properties in two directions compared to pure polymer films. Filled cavities (template-loaded MIP) showed an increase in hardness in comparison to pure PVP films. This meant a stiffer molecular network was established. In MIP films, the chains are fixed by hydrogen bonds and the sliding motion is inhibited in general. The filled molecular cavities prevent strong elastic deformation. Empty cavities after extraction of the template, result in a large decrease in the hardness. This could be caused by the fact that the empty MIP network can be easily squeezed together, resulting in a lower hardness in comparison to the pure polymer network. In MIP films, the PVP chains are fixed by the hydrogen bonds and the formed molecular cavities, but the deformation around the empty cavities is flexible (breathing cavities). Therefore, no gliding motion of the chains occurs. This means, the main effect for the change of the mechanical properties in different stages of MIP films originates from the formed molecular cavities. If they are filled with the template molecule the material is harder; if the cavities are empty, the compression of the cavities leads to a much softer material . The elastic compression of the empty cavities and pores acts in the same direction as the mechanism of deformation and gliding of the PVP chains .

[00034] Computational Study of Hydrogen Bonding. Reports in the literature indicate the usefulness of computational chemistry in selecting a polymer host for MIP development with a particular target molecule (Breton, et al . (2007) Biosens . Bioelectron. 22:1948). However, it was contemplated that computational studies would be of use in providing information to understand experimental MIP results. The optimized structures of nicotine and cotinine were first obtained for reference. These molecules differ only by the addition of a carboxyl group on the pyrrolidine ring of cotinine. The geometry of the planar pyridine ring, including bond lengths, in the two molecules is identical. The presence of the oxygen atom in cotinine results in bond shortening in the pyrrolidine ring, as well as a further distortion from planarity relative to the nicotine pyrrolidine ring. The pyrrolidine nitrogen becomes more sp2-like rather than the pyramidal angle observed in the nicotine molecule. As a final reference point, the 4- vinylphenol dimer structure was optimized and was found to have a hydrogen bond length of 1.876A and a hydrogen bond energy of 0.34eV. The geometric parameters of the 4- vinylphenol molecule were unchanged in the dimer.

[00035] Nicotine has two potential hydrogen binding sites and cotinine has three such sites. In both clusters, the 4- vinylphenol geometry was identical to that of the unbonded molecule and the pyridine rings bond lengths were unaffected by the hydrogen bond. The hydrogen bond from 4VP to the pyridine nitrogen in nicotine had a length of 1.822A, while that to the pyrrolidine nitrogen was 1.788A. The C-N bond lengths in this ring both increased. The total hydrogen bonding energy was 0.84eV. In cotinine, only two hydrogen bonds formed. The bond to the pyridine nitrogen had a length of 1.820A and that to the carboxyl -oxygen was 1.784A with a total hydrogen bonding energy of l.OOeV. Attempts to add a third hydrogen bond at the pyrrolidine nitrogen site failed, as the additional PVP molecule was repulsed from the ring. The C-N bond lengths in the pyrrolidine ring both decreased upon hydrogen bonding. Finally, it was noted that attempts to obtain a n-n complex between cotinine and 4VP indicated that the ring interactions were repulsive. Clearly, the DFT calculations indicated that cotinine would complex to the PVP host matrix with a greater binding energy than would the nicotine template and the experimental results reflected the results of those calculations.

Example 3: Preparation of Polyaniline-Nylon Films

[00036] Polyaniline has the general structure:

Polyaniline was selected for the instant film given conductivity (Scheme 1) .

Geometrical Relaxation

SCHEME 1

[00037] Using phase inversion, formaldehyde cavities were created in a polyaniline (PANI) -Nylon 6 composite film. Films were produced by dissolving 0.2 g of PA I, 0.2 g of Nylon 6 and 200 μΐ of formaldehyde in formic acid. The formic acid dissolved the composite and formaldehyde to form a rigid polymer- formaldehyde network. After sufficient mixing, the imprinted polymer solution was uniformly spin- coated onto a glass substrate to form a thin film. After making the formaldehyde imprinted films, the formaldehyde molecules were extracted from the film aerially, leaving behind formaldehyde-specific receptor sites that were capable of molecular recognition and binding of formaldehyde molecules with remarkable specificity.

[00038] Infrared spectra analysis conclusively indicated that formaldehyde molecules could bind to the PANI -Nylon 6 composite through strong hydrogen bonding due to the presence of an elongated carbonyl group at 1722 cm^-1. This peak was present in the imprinted polymer composite and noticeably absent in the control. This analysis indicated that PANI -Nylon 6 was successfully imprinted with formaldehyde. Moreover, the intensity of the peak indicated the efficacy of the imprinting process.

[00039] Changes in electrical resistance of imprinted polymer and control polymer following controlled exposure to formaldehyde vapor were determined using lithographically patterned interdigitated electrodes. The results of this analysis indicated that because the imprinted polymer had formaldehyde -specific cavities, it was able to selectively adsorb the formaldehyde molecules, which caused a dramatic increase in resistance of the film. In contrast, the control film with no cavities exhibited a relatively insignificant increase in electrical resistance in response to the formaldehyde vapor.

Claims

hat is claimed is:

1. A device for monitoring exposure to airborne contaminants comprising:

(a) at least two poly (4-vinylphenol) or nylon films each molecular imprinted with an airborne contaminant,

(b) a sensor, and

(c) a radio frequency interrogator unit.

2. The device of claim 1, wherein the airborne

contaminant is selected from the group of CO, nicotine, 4- (methylnitrosamino) -1- (3-pyridyl) -1-butanone and

formaldehyde .

3. The device of claim 1, wherein the sensor is a capacitive or conductive sensor.

4. The device of claim 3, wherein the conductive sensor comprises polyaniline or polycarbozole .

5. The device of claim 1, wherein the poly (4- vinylphenol) or nylon films are produced by phase

inversion-spin coating.

6. A method for monitoring exposure to airborne contaminants comprising:

(a) exposing at least two poly (4 -vinylphenol ) or nylon films, each film molecular imprinted with an airborne contaminant, to an air sample,

(b) sensing binding of airborne contaminants in the air sample to the films, and

(c) transmitting by radio frequency whether said airborne contaminants from the air sample have bound to said films, thereby monitoring exposure to airborne contaminants .