CA2153389A1

CA2153389A1 - Fiber optic sensor and methods and apparatus relating thereto

Info

Publication number: CA2153389A1
Application number: CA002153389A
Authority: CA
Inventors: Ralph C. Jorgenson; Sinclair S. Yee
Original assignee: Ralph C. Jorgenson; Sinclair S. Yee; The University Of Washington
Current assignee: University of Washington
Priority date: 1993-01-11
Filing date: 1994-01-05
Publication date: 1994-07-21
Also published as: US5647030A; JPH08505475A; EP0678194B1; US5835645A; DE69407161D1; ATE160871T1; ES2114175T3; JP2938973B2; EP0678194A1; DK0678194T3; DE69407161T2; WO1994016312A1; US5359681A

Abstract

There is disclosed fiber optic sensor which detects a sample in contact with the sensor by surface plasmon resonance (SPR) measurements, as well as methods and apparatus relating thereto. The fiber optic SPR sensor of this invention employs a limited range of incident angles and uses incident light having multiple wavelengths.
In preferred embodiments, both an in-line transmission-based fiber optic SPR sensor and a terminated reflection-based fiber optic SPR sensor are disclosed. The fiber optic SPR sensor includes a surface plasmon supporting metal layer in contact with an exposed portion of the optical fiber core, and may optionally contain one or more additional layers deposited on the surface plasmon supporting metal layer. In further embodiments, methods are disclosed for detecting a sample by contacting the sample with the fiber optic SPR sensor of this invention, as well as sensing apparatus which contain the fiber optic SPR sensor in combination with a source of electromagnetic radiation of multiple wavelengths and a detection device.

Description

~,VO 94/16312 21~ 3 3 8 9 PCT/US94/00158 Description FIBER OPTIC SENSOR AND
METHODS AND APPARATUS RELATING THERETO

Technical Field The present invention is generally directed to a optical fiber sensor and, more specifically, to a optical fiber sensor which utilizes surface plasmon resonance to detect a sample, to a sensing apparatus which employs the optical 10 fiber sensor, and to methods of detecting a sample using the same.

Background of the Invention Surface plasmon waves are electromagnetic waves which may exist at the boundary between a metal and a dielectric (hereinafter referred to as the l5 "sample"). Such waves can be exited by light which has its electric field polarized parallel to the incident plane (i.e., transverse magnetic (TM) polarized). When the parallel component of the propagation constant of the incident light equals the real part of the surface plasmon wave propagation constant, the incident light resonantly excites the surface plasmon waves, and a20 fraction of the incident li~ht energy is transferred or dispersed to surface plasmon resonance (SPR). This dispersion of energy depends on both the dielectric constant of the metal and that of the sample in contact with the metal. By monilolil.g the resonance wavevector of the metaVsample interf~ce, the dielectric constant of the sample (gas or solution) may be obtained. ~lt~rn~tively, if the 25 sample is co~ ted by a chemical species, dielectric constant measurements may provide the concc~ alion of the chemical species in the sample.
Traditionally, SPR has been me~cllred using the Kretschm~nn ronfiguration (Kretschm~nn and Raether, Z. Naturforsch. Teil A 23:2135-2136, 1968). In this configuration7 a thin layer of highly reflective metal (such as gold 30 or silver) is deposited on the base of a prism. The metal surface is then contacted with the sample, and the SPR reflection spectra of the sample is me~cllred by coupling TM polarized, monochromatic light into the prism and me~cllrin~ the reflected light intensity as a function of the angle of incidence.
The angle of lllillilllulll reflectivel intensity is the resonance angle at which 3s m~ . coupling occurs between the incident light and the surface plasmon waves. This angle, as well as the half-width of the resonance spectrum and the -

2 PCT/US94/00158 33~ ~ 2 intensity at the angle of ...il.;...l.,,, reflective intensity, may be used to characterize or sense the sample which is in contact with the metal surface (Fontana et al., Applied Optics 27:3334-3339, 1988).
Optical sensing systems have now been constructed based on the 5 Kretschrnann configuration described above. Such systems utilize the sensitivity of SPR to changes in the refractive indices of both bulk and thin film samples, as well as to changes in the thickness of thin films. These systems, in conjunctionwith ~l,ropliate chemical ssncinp layers, have led to the development of a variety of SPR-based chemical sensors, including immnnoassay sensors (e.g, 10 Liedberg et al., Sensors and Actuators 4:299-304, 1983; Daniels et al., Sensors and Actuators 15:11 17, 1988; Jorgenson et al., IEEE/En,~ineerin~ Medicine and Biolo~ Society Proceedin~s 12:440-442, 1990), gas sensors (e.g., Liedberg et al., supra; Gent et al., Applied OPtics 29:2843-2849, 1990), and liquid sensors (e.g., Matsubaru et al., Applied Optics 27:1160-1163, 1988).
While the Kretschm~lm configuration for SPR-based chemical sensors offers sigIuficant sensitivity, their relatively large size has severely restricted their application. For example, these bulk optic s~n~in~ systems are limited by their use of a coupling prism c~llsing such systems to be relatively large, expensive, and inapplicable for remote sensing applications. Moreover, such sensors generally require a monochromatic light source, are expensive to r~cture due to configuration constraints (such as the presence of a prism), and require that the incident light sweep over a broad range of incidence angles.
Accordingly, there is a need in the art for an improved SPR sensor, as well as for a~p~lus and methods relating thereto. Specifically, there is the need for an SPR sensor which readily ~ lils remote s~n~ing is inexpensive, and is free from the limitin~ con~ now present with exi~ting SPR-based chemical sensors.

Summary of the Invention It is an object of the present invention to provide a optical fiber sensor which utilizes SPR to detect a sample in contact with the sensor. It is a further object to provide a sensor which utilizes an optical fiber as the sensor itself, and avoids the use of a coupling prism. An additional object is to provide a fiber optic SPR sensor which lltili~es incident light having multiple wavelengths as the excitation energy. Yet a filrther object is to provide methods and ~pa~lus for detecting a sample using the fiber optic SPR sensor of this invention. The WO 94/16312 21;~ ~ 3 & ~ PCT/US94/00158 present invention fulfills these objectives, and provides further related advantages.
In one embodiment of this invention, a fiber optic SPR sensing apparatus is disclosed. The al~p~lus contains a fiber optic SPR sensor in combination with a source of electromagnetic radiation of multiple wavelengths and a detection device. The fiber optic SPR sensor is an optical fiber having a core waveguide and a cl~d~ling or cl~d~1ine/buffer layer surrounding the core waveguide, and wherein the optical fiber has a first end and a second end and atleast one sensing area located between the first end and the second end or located 0 at the second end of the optical fiber. The s.oncin~ area of the optical fiber is defined by an SPR supporting metal layer which is contact with at least a portion of an exposed surface of the optical fiber core waveguide which is free from thesurrounding cl~d-lin~ or cl~d~linglbuffer layer. The output from the electromagnetic radiation source is applied to the first end of the optical fiber core waveguide such that the radiation propae~tes from the first end towards thesecond end by total int~rn~l reflections (TIR), and exits the optical fiber at either the first end or the second end. A detection device monitors the radiation exiting an end of the optical fiber.
In a ~lcre~lcd embo-iimçnt, the fiber optic SPR sensor is an in-line tr~ncmicsion-based optical fiber sensor. Such a sensor cont~inc an optical fiberhaving a core waveguide and a c~ ing or cl~ line/buffer layer su,l~u.,ding the core waveguide, and having an input end and an output end. The sensor has a sensing area located between the input end and output end defined by an SPR
supporting metal layer in contact with at least a portion of the optical fiber core waveguide free from the sullou,lding cl~dtlin~ or cl~d-ling/buffer layer. A source of electrnm~netic radiation of multiple wavelengths is applied to the input end of the optical fiber core waveguide such that the radiation propagates from the input end towards the output end by TIR. A detection device then monitors the radiation exiting the output end of the optical fiber waveguide.
In a fur~er preferred embo-iim~nt the sensing ap~ us of the present includes a t~rmin~ted reflection-based fiber optic SPR sensor. This sensor contains an optical fiber having a core waveguide and a cl~d~ling or cl~d~ling/buffer layer su~ou~lding the core waveguide, and having an input/output end and a terminal reflection end. The tçrrnin~l reflection end is defined by an end face of the core waveguide in contact with a ~ loled layer.
The sensing area of the sensor is located between the input/output end and ~3~ 4 tçrmin~l reflection end, and is defined by an SPR supporting metal layer in contact with at least a portion of the optical fiber core waveguide free from the surrounding cl~ lin~ or cl~ling/buffer layer. A source of electromagnetic radiation of multiple wavelengths is applied to the input/output end of the optical s fiber waveguide, and the radiation propagates from the input/output end towards the termin~l reflection end by total intern~l reflections, intçrn~lly reflects off the ll.i.lul~d layer in contact with the end face of the core waveguide, and prop~g~tes back down the optical fiber waveguide by total intern~l reflections towards the input/output end. A detection device monitors the radiation exiting lo the input/output end of the optical fiber waveguide.
In another embodiment of this invention, a method for detecting a sample is disclosed. In this method, a sample was contacted with a fiber optic SPR
sensor of the present invention. A source of electromagnetic radiation of multiple wavelengths is applied to one end of the fiber optic SPR sensor and theradiation exiting the sensor is detected.
In yet a further embollimçnt the present invention discloses a fiber optic SPR sensor. The sensor has an optical fiber core waveguide and a c~ ling or cl~-ling/buffer layer ~ulluullding the core waveguide. A s~n~ing area is locatedbetween a first and second end of the optical fiber and is (i~fined by an SPR
supporting metal layer in contact with at least a portion of the surface of the optical fiber core waveguide free from the ~ull~ullding c~ Aing or cl~ ling/buffer layer. In ~"e~lled embo~iim~nt~ the fiber optic SPR sensor is anin-line tr~n~mi~cion-based fiber optic SPR sensor or a t~rmin~ted reflection-based fiber optic SPR sensor.
These and other aspects of this invention will become evident upon reference to the following detailed description and ~tt~ e~ drawings.

Brief Description of the Drawin~s Figure l(a) represents the prior art Kretsçhm~nn configuration for a buL~c op~ic SPR-based chemical sensor, and Figure l(b) illu~ es an SPR reflection spectra obtained from the prior art sensor of Figure l(a) for a bulk dielectric of water, a wavel~n~th of 620 nm, a 550 Angstrom-thick silver film, and a fused slllca pnsm.
Figure 2 illustrates an in-line tr~n~mi~sion-based fiber optic SPR sensor of this invention.
Figure 3 illustrates a t~rmin~te~l reflection-based fiber optic SPR sensor.

WO 94/16312 ~ 3 3 ~ ~ PCT/US94/00158 -s Figure 4 illustrates a further embodiment of a terminated reflection-based fiber optic SPR sensor.
Figure 5 is a calculated three-dimensional SPR reflection spectra for a buLk dielectric of water.
5 Figure 6 is a contour plot of two theoretical three-(lim~neional SPR
reflection spectra for water and a 37.1% sucrose solution.
Figure 7 is the calculated SPR spectra of reflected light intensity versus wavelength for a number of angles prop~g~ting inside a optical fiber sensor.
Figure 8 is a calcnl~te~l SPR spectra taking into account the number of reflections each angle encounters.
Figure 9 is the non-linear distribution function of prop~g~ting angles within the optical fiber, and assumed to be Ga~lssi~n.
Figure 10 is the calculated SPR spectra for a bulk refractive index of water and a 37.1% sucrose solution.
Figure 11 illustrates a sensing a~y~lus of the present invention employing an in-line tr~nemieeion-based fiber optic SPR sensor.
Figure 12(a) illustrates represent~tive air and sample SPR spectra, Figure 12(b) depicts a norm~li7P~l sample SPR spectra, and Figure 12(c) are n~ rm~li7e~1 SPR spectra collected using the in-line tr~n~mi~sion-baeed fiber optic SPR sensor of Example 2.
Figure 13 is a plot of the norm~li7e~1 SPR optical fiber sensor spectra measured by the 6, 10, and 18 mm in-line fiber optic SPR sensors of Example 2.
Figure 14 depicts the calcnl~te~l and e~ nt~lly ~elf ~ ed SPR
coupling wavelçngth versus the refractive index for the sucrose solutions of Example 2.
Figure 15 illustrates a sensing appalalus of the present invention l~tili7ing a t~ e~l reflection-based fiber optic SPR sensor.
Figure 16 illustrates the theoretical and expt~ lly observed SPR
coupling wavelength versus the refractive index of the solutions detected in Example 3 lltili7in~ an SPR suppor~ing metal layer of either silver or gold.
Figure 17 illustrates the nonn~li7ç~1 SPR reflection spectra (referenced to air) for Buffer A, de-ionized water, BSA and rhFXIII.
Figure 18 illustrates the shift in the norm~li7ed SPR spectra due to binding of rb-antiFXIII over time (0-55 mimltes).
Figure 19 illustrates the shift in the SPR spectra of Figure 18 over time.

WO 94116312 PCTtUS94tO0158 ? ~3~ 6 Detailed Description of the Invention This invention is directed to a optical fiber sensor which detects a sample in contact with the sensor by surface plasmon resonance (SPR) measurements.
5 The present invention is also directed to methods and ~palalus relating to theuse of the fiber optic SPR sensor to detect a sample. ln preferred embodiments, the fiber optic SPR sensor of this invention includes an in-line tr~ncmiccion-based sensor and a tPrmin~te~ reflection-based sensor. The fiber optic SPR
sensor of this invention advantageously elimin~tes the traditional bulk optic 10 prism in favor of an optical fiber design which permits remote sPncin~ and multiplexing between multiple fiber optic SPR sensors.
As mentioned above, prior art SPR-based chemical sensors are generally based on the Kretsçl....~.... configuration (see, Kretcc~lm~nn and Raether, Z.Naturforsch. Teil A 23:2135-2136, 1968). Such a prior art SPR-based 15 chemical sensor is illu~LIal~d in Figure l(a). Specifically, a highly reflective metal layer (10), such as gold or silver, is deposited on base (12) of prism (14).
TM polarized, monochromatic incidPnt light (16) is directed into the prism and reflects off the prism base/metal layer interface. The intensity of reflected light (18) is me~ red by a detection device (not shown). A sample (11) is brought in 20 contact with exposed s~lrf~ce (15) of metal layer (10), and the monochromaticincjdPnt light is directed into the prism at angle ~ with respect to the normal of the metal layer/sample interface. At a~ o~,iate angles of incidence, the monochromatic incident light excites surface plasmon waves (13). The SPR
reflection spectra obtained from the prior art SPR-based chemical sensor of 25 Figure l(a) is represPnte~ in Figure l(b) by a two-llimpn~ion~l plot of reflected light intPn~ity versus the angle of incidence. The angle of .~.;..;....~... reflective intPn~ity is the surface plasmon resonance angle (~sp) at which mzlx;-.-,--..
coupling of energy occurs between the incident light and the surface plasmon waves. This angle is depPn~lPnt upon the sample in contact with the exposed 30 surface of ~e metal layer.
In contrast to prior art SPR-based chemical sensors which utilize a single monochromatic incident light source and modulate the incident angle, the fiber optic SPR sensor of this invention employs a limittoll range of incident angles and uses incident light having multiple wavelengths. As used herein, the phrase 35 "incident light having multiple wavelengths" means, at a mi~ ...., two waveleng~s, and is preferable a range of wavelengths sufficiently broad to wo 94/16312 21~ 3 3 ~ ~ PCTIUS94/00158 encompass the resonance spectrum of the sample. For example, black body radia*on or a white light source may serve as the incident light. ~lt~ hvely, two or more discrete wavelength.c may be employed in the practice of the presentinven*on. Furthermore, as used herein, the phrase "limited range of incident 5angles" means the range of prop~g~*ng angles supported by a given optical fiber.
Suitable optical fibers of the present invention include commercially available fibers which support int~rn~l propagation of light by TIR. Such fibersmay generally be characterized by three parameters: the optical fiber core m~tçri~l the numerical aperture of the fiber, and the optical fiber core diameter.
10The choice of the optical fiber core material will effect the position of the resonance (i.e., where it occurs in the wavelength region). For example, a silica optical fiber with a refrac*ve index of 1.46 permits measurements of effective refrac*ve indices from about 1.32 to about 1.45, and may be e~ c~ Pnt~lly observed as the resonance shifts from 400 nm up to 1000 nm. Other optical fiber 15core materials will similarly effect the position of the resonance. Thus, use of optical fiber core materials of a higher refractive index than silica will shift the dynamic range of the effective refractive indices to higher values. For example,sapphire, with a refractive index of 1.76, will result in a sensor with a dynamic range of effective refractive indices of from about 1.45 to about 1.75. Similarly, 20use of a plastic optical fiber core, such as a polymethylmethacrylite (PMMA) with a refractive index of 1.50, would permit m~ lrements of effective refractive indices from about 1.33 to about 1.49. If an optical fiber core material with a lower refractive index than silica was employed, the dynamic range of themeasurable sample refractive index would be shifted towards smaller values.
25The dynamic range of the fiber optic SPR sensors may also be modified by addition of al)p,o~liate dynamic range-controlling layers, as discussed in greater detail below.
The mlm~rical aperture of the optical fiber de~ es the acceptance angle of light that is allowed to propagate in the fiber. In the practice of this 30invention, suitable numerical apc.lulcs may range from about 0.05 to about 0.6, and are preferably from about 0.2 to 0.4, and most preferably from about 0.25 toabout 0.35. The numerical aperture also detr...li~es the intern~l propagation angles of the light prop~g~ting in the fiber. For example, a silica optical fiber with a mlmerical aperture of 0.3 supports int~orn~l prop~g~tin~ angles of light 35 ranging from 90 to 78.5 (relative to the normal of the core/cl~ lin~ interface), and thus the limited range of incident angles for this fiber would range from 90 -?,~ S~3Q~ ~

to 78.5. The core diameter of the fiber may vary depending upon the specific application. Preferably, the optical fiber core diameter ranges from about 1 micron to about 2000 microns, and more preferably from 100 microns to 600 microns, and most preferably from 200 microns to 400 microns.
As an optional component, one end of the optical fiber may have an element which reflects the light prop~g~ting within the fiber such that the light reverses its direction of propagation. A suitable element which may accomplish this function is a ~ ored layer located on the end surface of the optical fiber core. For example, if light is directed into the optical fiber at a first end, and the ll~i,loled layer is located at a second end of the fiber, light propag~ting toward the second end will be reflected (upon contact with the n~illored layer) back toward the first end of the optical fiber. Such l~lhlult;d layers may be adhered to the end surface of the optical fiber core by known techniques, such as by electron beam evaporation, therrn~l evaporation, spullt;lillg, electrodeless plating, or adhering or gluing a suitable n~illored layer to the end of the fiber. Suitable m~teri~l~ for the m~lloled layer including highly reflective metals, such as silver, gold and chrome. The ,l~hloled layer should be of sufficient thickness to provide adequate reflectivity, and should not support SPR at the end of the fiber. A
metal thickness of about 2000 Angstroms (or greater) generally provides sufficient reflectivity, and a metal thickness in excess of about 1000 Angstromsgenerally will not support SPR at the end of the fiber. The a~propliate thickness for any given millored layer having the above characteristics may be readily ~ele~ ed by one skilled in this art.
Detection of a sample with the fiber optic SPR sensor of this invention is made, in part, by conhcting the sample with the slon~ing area of the optical fiber.
The s~on.~ing area is made by exposing a portion of the optical fiber core by removal of the surrounding c~ lin~ or cl~3tling/buffer layers, and ~ ering an SPR supporting metal layer to the exposed optical fiber core. The SPR
supporting metal layer of the optical fiber is then exposed to the sample of i~ e~l, and the refirachve index of the sample is (3cl.. i~.ed by the methods disclosed below.
The cl~l(ling or cl~-ling/buffer layers of the optical fiber may be removed to expose a portion of the core by know techniques. For exampie, the cl~ ing or cl~ ling/buffer layers may be removed by a torch, or by chemical 35 agents which etch away the cl~-ling or cl~ ing/buffer layers while preservingthe fiber core material. Alternatively, the cl~ ling or cl~ ling/buffer layers may WO 94116312 2 1 ~ 3 3 ~ 3 PCT/US94/00158 .._ be removed by commercially available, mechanical strippers (e.g., Clausse, No-Nik Optical fiber Stripper, Edmond Scientific Catalog, Bamngton, NJ).
Once a portion of the optical fiber core is exposed, the SPR supporting metal layer is adhered to the exposed core. As used herein, the term "SPR
5 supporting metal layer" means a highly reflective metal that supports SPR at the metaVsample interface, and has a pe~ ivity constant wherein the real part of the pc;llli~ rity is negative and its m~gnit~1de is greater than the m~gnitll-le of the im~gin~ry part. Within the visible and near-IR region (400 nm - 1000 nm), both silver and gold satisfy this criteria. However, if the above wavelength range is10 extended into the infrared, other metals, such as alul~ " copper and tantalum, may also be employed.
The SPR supporting metal layer is preferably adhered to the exposed portion of the optical fiber core to a thickness which will optimize the resonance curve - that is, to a thickness which makes the SPR resonance spectrum sharp.
15 When the SPR supporting metal layer is silver, this layer is l,-e~ldbly adhered to the exposed core at a thickness of about 550 Angstroms. If a thinner thickness is used, the resonance spectra will substantially broaden, and if a thickness in excess of 600 Angstroms is employed, the resonance will severely ~limini.~h or disappear. One skilled in this art.may readily ~lel~ e the al,pro~,iate 20 thickness of the SPR supporting metal layer for any given optical fiber/SPR
supporting metal layer combination by varying the thickness to optimize the resonance curve.
A single optical fiber may contain one or more sensing areas, of the same or diL~elel.L geometry, and with the same or different SPR supporting metal 25 layers. Such sensing areas may be located along the length of the optical fiber, at one end of e optical fiber, or both. In addition, while any portion of the optical fiber may serve as the sensing area, in a p-~fe,led embodiment the c~ ling or cl~ ling/buffer layers are removed from the entire ci~ ~,ence of the optical fiber core, and the SPR supporting metal layer is symmetrically deposited on the30 exposed core to a u~uform thickness.
An energy source which emits light having multiple wavelengths serves as the source of incident radiation. Generation of the incident radiation may be byany of a number of commercially available devices. For example, a tungsten halogen lamp provides radiation with a wavelength range that is sufficiently 35 broad to encompass the resonance spectrum between 400 nm and 1000 nm.
However, other white light sources can be employed. Moreover, best results WO 94116312 2~ S33~ PCT/US94/00158 may be obtained when the current and temperature of a white light source are controlled in order to minimi7~ any background spectral variation. The energy source may be coupled into the optical fiber by use of commercially available optical fiber illnmin~tion instruments, such as an Oriel, Optical fiber Source for s Radiometry (this specific instrument focuses white light emitted from a bulb into one end of the optical fiber).
Suitable detection devices of the present invention are capable of detecting the int~ncity of all or a portion of the wavelengths of light exiting the optical fiber. For example, when the fiber is connected to a optical fiber 10 spectrograph, the light exiting the fiber is reflected off a grating towards a linear array detector. Upon reflectance offthe grating, the light is linearly dispersed as a function of wavelength. Individual photodiodes in the array detector then mç~cllre the int~ncity along the length of the array detector, and detects the light intensity versus linear llispl~cement (which is proporhonal to wavelength). A
15 spectrophotometer may also be employed to measure light intensity versus wavelength, or a circular variable inle.~~ ce filter wheel may be used in front of a photodetector. Such a filter wheel allows for a certain narrow b~n~lp~cs oflight which changes as a function of wheel rotation, and ~cl~ m~cnrement of the spectral intensity of the light. Similar detection devices could employ a 20 dispersing prism, linear variable int~rf~ce filter, or individual in~ ence filters when only a limite~l number of wavelengths are of interest.
By measuring the resonance spectrum, the complex refractive index of the sample in contact with the s~n.cing area of the optical fiber sensor can be ed. A sample's complex refrachve index incll~des both the real and 25 im~gin~ry refractive index components. The real component of a sample's complex refrachve index is inversely proporhonal to the speed at which light prop~g~tes through the sample, and is generally considered the "true" refrachve index of the sample. The im~gin~ry component of a sample's complex refractive index is related to the sample's absorbance or ~ nll~tion of light. For example,30 by measuring the resonance spectrum of a solution col~ ;"g sugar, the concen~ ion of the sugar can be del~lmilled (~Csllming the sugar is the only varying analyte in the solution that caused the real refractive index of the sample to change). Such measurements have utility in the m~nllf~cture of sugar-col~li3;,.i..g beverages, as well as the alcohol content of a solution, or the 35 hydrogenation of vegetable oil. Similarly, the fiber optic SPR sensor of thisinvention may be used to measure the absorbance of a sample. For example, use 21 ~ .~3 i~

_ Il of a dye indicator for one or more specific analytes within a sample (such as acid/base dye indicators for pH and CO2) may be employed.
In addition, the sensing area may optionally contain one or more additional layers adhered to the SPR supporhng metal layer to yield effective refractive indices detectable by the sensor. Such additional layers may include a dynamic range-controlling layer and/or a reactive layer. A "dynamic range-controlling layer" is a layer adhered to the SPR supporting metal layer to alterthe dynamic range of the fiber optic SPR sensor. For example, the dynarnic range for a silica fiber, having a refractive index of 1.46, is about 1.32 to about 1.45. Adherence of a dynamic range-controlling layer of low refractive index (e.g., 1.2) to the SPR supporting metal layer will shift the dynamic range of the sensor to higher values (e.g., 1.42 to 1.55).
As used herein, the term "reactive layer" means a layer which interacts with the sample such that the effective refractive index detected by the sensor is altered. The addition of a reactive layer permits the m~nnf~cture of afiber optic SPR sensor which is more sensitive to, or more selective for, a satnple (or analyte within a sample). For example, suitable reactive layers inclll~e an ~ntig~n or antibody bound to the SPR supporhng mehl layer. This type of reactive layer will selectively bind the compl~m~nt~ry antibody or ~nti~Pn in the sample, increase the thickness of the reactive layer, and causes a shift in the effective refractive index measured by the sensor. In general, suitable reactivelayers are altered in some m~nn-or upon contact with the sample, thus ch~ngin~
the effective refractive index m~cllred by the sensor. Other reactive layers inclll(le sol-gel films and polymer co~ting~7 and may be a&ered to the SPR
supporting metal layer by known techniques.
Figures 2-4 illustrate plefe.led embo~liment~ of the fiber optic SPR sensor of this invention. In Figure 2, an in-line tr~ncmicsion-based fiber optic SPR
sensor is depicted. This sensor is made by removing a section of optical fiber çl~tlin~ (21) and buffer (23) from core (26) of optical fiber (20), and depositing an SPR supporhng metal layer (26) on exposed surface (28) of core (22).
In Figure 3, a termin~ted reflection-based fiber optic SPR sensor is illustrated. In this embodiment, a mirrored layer (34) is a&ered to the end of optical fiber (30). Specifically, the ~ oled layer is in contact with end face (32) of optical fiber core (36), and covers cl~d~ling layer (37) and buffer layer (38) of the optical fiber. An SPR supporting metal layer (39) is a&ered to an exposed surface (33) of core (36).

2~ ~33~ 12 Figure 4 illustrates a further embodiment of a tçrmin~ted reflection-based fiber optic SPR sensor wherein the sensing area is located at the end of the optical fiber. Cl~d-lin~ layer (42) and buffer layer (44) are removed from optical fiber (40) to expose surface (45) of core (46). An SPR supporting metal layer 5 (48) is adhered to exposed surface (45) of core (46). Mirrored layer (49) is in contact with end face (43) of core (46).
The following examples are offered by way of illustration, not limit~tion.

EXAMPLES
Example I
Calculated SPR Shift Between Water and Sucrose Solution A calculated three--limen~ional SPR reflection spectra for a range of wavelengths (400-1000 nm) is illustrated in Figure 5. This spectra was calculated using a matrix method to dete~ e the fresnel reflection coefficients 15 of a mllltil~yered structure and ~csllmes a silica optical fiber, a 550 Angstrom silver layer, a bulk sample of water, and TM polarized light. The refractive index values for silver silica and water was obtained from ~e lil~ralule (e.g., see Hass and Hadley, Optical Properties of Metals, ~meriG~n Institute of Physics Handbook, D. Gray ed., McGraw-Hill, New York, pp. 149-151, 1972; Querry et 20 al., Water (H20), Handbook of Optical Constants of Solids II, E. Palik ed., American Press, Boston, pp. 1059-1077, 1991; Malitson, J.O.S.A. 55:1205-1216, 1965). The change in the SPR coupling angle as a function of wavelength (as illustrated in Figure 5) is ~,lhl,~ily due to the increased m~ e of the silver complex refractive index over the wavelength range of 400-1000 nm. This large 25 change in silver refractive index (about one order of m~ibl-le) is colllpa~ed to the relatively small change in both the silica and water refractive indices (i.e., 0.019 and 0.128 index of refractionunits, re~pecLi~ely). Figure 6 depicts a contour plot of two calc~ ted three-~1imen~ional SPR reflection spectra for water and a sucrose solution (37.1% by weight) as the buLk sample media. This figure 30 illustrates the resonance coupling angle dependency upon waveleng~ and the three--limen~ional SPR spectra dependence upon the buLk dielectric refractive index between the water and sucrose spectra.
In order to model the spectrum of the SPR fiber optic sensors several factors must be considered, including: (1) the three ll;...c.~ional SPR reflection 35 spectra, (2) the number of reflections each prop~g~ting mode of undergoes, and

(3) the density of prop~g~~in~ modes in the optical fiber sensor. Figure 7 WO 94/16312 21 S 3 ~ & ~ PCT/US94/00158 -illustrates the theoretical SPR spectra (assuming a core diameter of 400 microns, a sensing area of 10 mm in length, and a constant light intensity over all wavelengths) of reflected intensity for one reflection versus wavelength for a number discrete angles prop~g~ting inside the fiber optical sensor (i.e., 90, 87, 5 84, 81 and 78). The number of reflections in the fiber sensor area, N, is a function of the mode propagation angle, ~, the diameter of the fiber core, d, and the length of the sensing area, L, and is governed by the following equation:
N= Lldtan~
Thus, to ~le~ e the effective SPR spectra, taking into account the lo multiple reflections, the spectra for a single reflection is raised to the power of the number of reflections the specific prop~g~ting angle undergoes with the sensor int~ ce. Figure 8 illustrates the effective SPR spectra of intensity versus the wavelength for the propag~ting angles of Figure 7. The spectra for the lowest order mode, 90, travels parallel to the meridonial axis of the fiber and does not reflect off the interf~ce. Therefore, the spectrum is that of the 90 spectrum of Figure 6 raised to the power of zero, which yields a constant spectrum corresponding to no sl~rf~ce plasmon waves excited by the 90 prop~g~ting angle. Similarly, the smallest prop~g~ting angle in the fiber (i.e., 78) has aneffective spectra which is greatly broadened since it undergoes 5.31 reflectionswithin the length of the sensing area.
The SPR fiber optic signal detected at the output end of the fiber represents an accnm~ te~ spectra for the entire range of prop~g~ting angles, andnot the spectra for any specific mode. Moreover, this signal is not an equally weig_ted average of all the angles prop~g~ting in the fiber. Thus, the theoretical signal must be weighte~ with the energy distribution function of all prop~g~tingangles in the fiber. For this purpose, the propagation angle density distribution function may be ~csllmed to be G~nsci~n~ sp~nning the range of the allowed prop~g~tin~ angles in the fiber is illustrated in Figure 9. Figure 10 l~"esellls the theoretical SPR fiber optic signal obtained by weight averaging ~e ~nF~ r spectra of Figure 8 with the density distribution of function of Figure 9 for a bulk water sample and a 37.1% sucrose solution. Thus, an a~p,o~ ate 200 nm shift in SPR coupling wavelength is predicted, and corresponds to a change of 0.06 index of refraction units between the water and sucrose samples.

~,~333~ 14 Example 2 In-Line Tr~n~mi~ion-Based Fiber optic SPR Sensor A silica/polymer fiber Type FP-400 UHT (3M, Minneapolis, Minnesota), having a diameter of 400/600/760 microns (i.e., core, cl~ ling and buffer 5 diameters, respectively) and a numerical aperture of 0.3 was used in this example. The buffer and cl~ lin~ layers were removed by a torch (Weber and Schultz, Biosensors and Bioeletronics 7:1930197, 1992), and the exposed core surface wiped with Dynasolve 100 (Dynaloy Inc., Hanover, NJ). Specifically, three fiber optic sensors were fabricated by removing 6, 10 and 18 mm of the 0 cl~(ling/buffer layers along the length of three fibers. Each fiber was then mounted in an electron-beam evaporator such that the flux of the evaporated metal (silver) was perpendicular to the axis of the fiber. The fibers were rotated during silver deposition, resulting in a 550 Angstrom silver film deposited symmetrically about the fiber. The deposition process was monitored using a 15 quartz crystal detector.
Figure 11 illusllales the experim~.nt~l set-up of this example. The three in-line tr~n~mi~sion-based fiber optic SPR sensors were fabricated as disclosed above. The output of a tungsten halogen lamp was indepen-l~ntly focused into each of the optical fibers. A mode scrambler was used to populate all modes of 20 the optical fibers. The sçn~ing area of the sensor was then enclosed by a three milliliter flow cell constructed using a syringe with two syringe stoppers and inlet and outlet ports. The output of the fiber optic SPR sensor was connected to a fiber optic spectrograph (American Holographic, Littleton, MA) via a SMA
connector. The flat field grating is an ~meric~n Hologla~hic Model #446.33, 25 which dispersed a range of wavelengths from 400 nm to 900 nm with a linear dispersion value of 20 nm/mm. The detector inside the spectrograph was a 1024-element CCD linear array detector. The theoretical wavelengtll resolution was d~ ed by the linear dispersion value of the grating and the 25.4 micron width of the CCD element is 0.5 nm. A data acquisition board was used with an 30 IBM co,lll)atible colll~ulel for automated acquisition.
Six sample solutions of high fructose corn syrup diluted with deionized water were ~I~,paled. The refractive indexes of these samples solutions were ~el~ ...,;.~ed to be 1.333, 1,351, 1.364, 1.381, 1.393 and 1.404, respectively, using an Abbe Refractometer (Milton Roy Tabletop Refractometer 3L) at a 589 nm 35 wavelength. The tr~n.cmi1ted spectral intensity distribution was m~ lred for each sensor while air was in the flow cell, and then measured again for each of WO 94116312 212~ 3 3 8 ~ PCT/US94/00158 the six pre~ ed sucrose solutions by introducing 15 ml of each solution into theinput port of the flow cell.
Since the intensity of the incident light was not constant for all wavelengths (400-900 nm), an air spectra was collected when the sensing area of 5 the sensor was in contact with air (i.e., there is no surface plasmon resonance excitation in this wavelength range for air having a bulk refractive index of 1.00).
The SPR spectra collected for each sa nple was norrn~li7e~1 against the air spectra using the following equation:
N(~) = 1 - [Iair (~ sample(~ air(~)]

where Iair(~) is the intensity of the air spectra at wavelength ~ and ISaTnple(~) is the intensity of the sample spectra at wavelength ~. A plot of N(~) versus yields the nonn~li7e~ spectra. Figure 12(a) illustrates a representative air andsaTnple SPR spectra, and Figure 12(b) depicts the nonm~li7.~d sample spectra according to the above equation. This calibration technique effectively norm~li7.es the system transfer function, attributed by the light spectral output, the photo diode array spectral sensitivity, and the fiber spectral absorbance.
Figure 12(c) depicts the norm~li7ed tr~ncmilte~ light intensity as a function ofwavelength measured by the 10 mm sensor for the fructose solutions with refractive indexes of 1.351, 1,393 and 1,404.
The resonance wavelength shift for the increasing bulk refractive indices of the sample is con.cictçnt with the calc~ te~l results illustrated in Figure 10.
However, it should be noted that the resonance spectra appears slightly broader than predicted. This observation is believed to be attributable, in least in part, to the large input fiber connected to the spectrograph (i.e., 400 microns), and thus the full spectrograph resolution is not optimi7e~1 It is believed that narrower resonance spectra may be achieved by reducing the diameter of the input optical fiber core to the spectrograph or by employing the use of a narrower slit.
Figure 13 is a plot of the SPR optical fiber sensor spectra measured by the 6, 10 and 18 mm sensors for a single fr~ctose solution (i.e., refractive index of 1.351). The tr~n~mitte~ spectral intensity distribution depends upon the length of the SPR sçn~ing area as illustrated in Figure 13, a longer sçncing area resulted in a deeper observed resonance spectra. Thus, the size of the sensing area can be optimi7e~1, and prim~rily depends on ~e sllnf~ce area of the sensing area, ~e diameter of the optical fiber core, and the numerical aperture. Due to the 2~3 PCT/US94/00158 cylindrical geometry of the fiber, both TE and TM polarized light (with respect to the core/metal interface) are allowed to propagate in this multi-mode fiber.
Thus, the expected optimal trAn~mitte~ light intensity at resonance is 0.5 rather than 0.0, since SPR can only be excited with TM polarized light.
Theoretical and ~c~ PntAl SPR coupling wavelength versus the refractive index of the fructose solutions are plotted in Figure 14 for the three SPR optical fiber sensors of Figure 13. The response of all three sensors are ingood agreement with the calculated shifts of Example 1. To plot the Abbe Refractometer measured refractive indices of the sample solutions in Figure 14 the values were corrected for wavelength using the refractive dispersion measurement (Abbe Refractometer Operator's Manual and Dispersion Table, Milton Roy Con,pan~, Analytical Products Division, Rochester, New York, 1986). The theoretical sensitivity of the fiber optic SPR sensor to refractive index was calculated from the SPR wavelength response curve of Figure 13.
Because the response is non-linear, the sensitivity is a function of wavelength,with increased sensitivity at longer wavelengths. The theoretical sensitivity torefractive indices is 2.5 x 10~ at a wavelength of 500 nm, and 7.5 x 10-5 at a wavelength of 900 nm, Assnming an optimal wavelength resolution of the spectrograph of 0.5 nm, and the observed sensitivity at these wavelPn~h~ is in good agreement.

Example 3 Terminated Reflection-Based Fiber optic SPR Sensor Figure 15 illustrates a tPrminAted reflection-based fiber optic SPR sensor of the present invention. This sensor is similar to the in-line tr~nemieeion sensor described above, but uses a micro-fabricated mirror at the end of the optical fiber to intPrn~lly reflect the light prop~ tin~ through the fiber. In this embo-liment the light travels through the sensing area twice, thus the s~n.eing length can be one half the length of the s~nein~ area of the in-line tr~nemieeion sensor.
The t~nnin~ted reflection-based fiber optic SPR sensors were constructed by ~LIippi~g off 1 cm of the cl~d-lin~ and buffer layers at the end of two separate silica optical fibers (0.3 mlmerical aperture, 400 micron core diameter). The fibers were then individually mounted vertically in an electron beam evaporator chamber such that the stripped end of each fiber was face down. An evaporated metal (silver) was then deposited on the stripped end face of each fiber, to a thichless of 3000 Angstroms by using a mask to prevent deposition on the WO 94/16312 2 1 5 3 3 8~ PCT/US94/00158 -]7 exposed surface of the core. The fibers were then mounted in an electron beam chamber in the same fashion as the in-line fiber-optic sensors of Example 2, andeither a silver or gold metal layer symmetrically deposited on the exposed core surface of the fibers to a thickness of 550 Angstroms.
In this example, light was coupled into a single branch of a 50:50 two way fiber optic splitter from a tungsten-halogen lamp. Fifty percent of the coupled light was then transferred to the sensor branch of the splitter. A SMA connectorwas used to connect the splitter to the SPR fiber optic sensor. The light was tr~ncmitted down the probe to the sensor area and reflected back up the optical 0 fiber by the micro-fabricated mirror. The mirror thickness was such that SPRdoes not occur at the end of the optical fiber (in this example, the mirror thickness is 3000 angstroms). The returned light is then split again and connected to an optical fiber spectrograph to m.o~cllre the spectral intensity of the signal light. The rem~ining arm of the splitter was index matched to a solution of glycerol so as to minimi7e back reflection. However, a reference signal couldalso be measured by using a spectrograph with two inputs, one for the signal andthe other of a real time reference. The liquid samples of this experiment was six solutions Co~ g glycerol at various concentrations to yield samples having dirr.,.~nl refractive indices.
The results obtained from the two termin~ted probes are illu~ ted in Figure 16, and are coI si~t.ont with the data and calculated results of an in-line tr~n~mi~sion SPR fiber optic sensors. The wavelength offset observed between the ~ te~ gold and silver probes is believed to be due to the dirr~e..ce in the pcl~ ity constants between the two metals (see Figure 16) of the SPR
supporting metal layer.

Example 4 Tmmmloassay Utilizin~ Termin~te~l Reflection-Based Fiber Optic SPR Sensor This example illustrates the use of the fiber optic SPR sensor of Example 3 in combination with a reactive layer deposited on the surface of a SPR supporting gold layer. The observed shifts in the SPR spectra of Example 3 above (i.e., Figure 16) towards larger coupling wavelengths, ~spr~ is due to increasing refractive indices of the bulk chemical sample. A similar shift can be caused by the presence of a thin film reactive layer between the metal and the sample. The adsorption of such a thin film layer (provided the thin film layer WO 94/16312 S 3 3 8 9 1 g PCT/US94/00158 has a diLrelellt refractive index than the bulk sample) will cause a shift in ~spr This is because the surface plasmon waves "sense" an effective refractive index,neff, that is representative of the combination of the refractive indices of thesurface plasmon support layer, the thin film, and the thickness of the thin film.
5 Changes in the film parameters (such as film thickness and/or complex refractive index) will cause a shift in ASpr. These changes can be solved for by analyzing the properties of the measured SPR spectrum.
To illu~ te this aspect of the present invention, ploleil- solutions were ple~Jared co~ the following components: recombinant human Factor XIII
10 (rhFXIII) expressed and purified from yeast (ZymoGenetics, Inc., Seattle, W~chin~ton), bovine serum albumin (BSA, Fraction V, Sigma, St. Louis, MO), and a rabbit anti-rhFXIII biotinylated polyclonal IgG plel)alalion (rb-antiFXIII, Protein-A purified, est. 98% IgG). Both the rhFXIII and BSA samples were at a concentration of 10 mg/ml in Buffer A solution (pH 7,2, 2% sucrose, 0.1 mM
EDTA-Na2, 10 mM glycine) while the rb-antiFXlII was at 0.5 mg/ml in phosphate buffered saline (pH 7.4). All c~mic~ were purchased from Sigma Ch~mical.
Figure 17 illustrates the SPR reflection spectra"efelenced to air, for Buffer A, deionized water, BSA and rhFXIII which was obtained by dipping the 20 tPrmin~te~l reflection-based fiber optic SPR sensor in the respective solution.
- The spectra was not effected by mechanical agitation or stirring of the test solution and the spectra for both the BSA and rhF~II solutions shifted to the same extent. This indicates that the sensor is incçn~itive to the molecular weight of the protein (rhFXIII is 168 kD and BSA is 69 kD), but responsive to the mass 25 of protein adsorbed to the surface of the sensing area.
The sensor was l~rere-lced to air, and tested in Buffer A and deionized water. The sensor was then coated with rhFXIII by placing the sensor in the rhFXIII solution until no spectral shift occurred. The sensor was then dipped into the BSA solution, and the interaction of the rb-antiFXIII was studied over a 30 course of 55 ,..i~ (es by placing the sensor in the antibody solution. The interaction of the polyclonal rb-antiFXIII with rhFXIII absorbed to the surface of the SPR supporting metal layer was found to be sufficient slow (hours) to permitmeasurement. The temporal shift in SPR spectra due to binding of rb-antiFXIII
is illustrated in Figure 18, and de~ tion of the minim~ for each SPR spectra 35 is depicted in Figure 19.

WO 94/16312 21 3 3 3 ~ 9 PCT/US94100158 As illustrated by Figure 19, over 50% of the observed response occurred within the first 10 minlltes of exposure. The multi-phasic response behavior of the sensor is consi~tçnt with the nature of the polyclonal antibody use in this study, and represents the average response from a multitude of anti-ideotype S IgGs with differing kinetic characteristics for rhFXIII. The sensor response was found to be reversible, as demonstrated by cleaning the probe with a 0.1 N
NaOH solution, and by subsequent spectral comparisons (for air and Buffer A) between the sensor prior to exposure to the test solutions versus subsequent to exposure.
From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deparhng from the spiritand scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

Claims

1. A fiber optic surface plasmon resonance sensing apparatus, comprising:
a fiber optic surface plasmon resonance sensor, comprising an optical fiber having a core waveguide and a cladding or cladding/buffer layer surrounding the core waveguide, wherein the optical fiber has a first end and a second end and has at least one sensing area located between the first end and the second end or at the second end, wherein the sensing area is defined by a surface plasmon resonance supporting metal layer in contact with at least a portion of a surface of the optical fiber core waveguide free from the surrounding cladding or cladding/buffer layer;
a source of electromagnetic radiation of multiple wavelengths whose output is applied to the first end of the optical fiber core waveguide such that the radiation propagates from the first end towards the second end by total internal reflections and exists the optical fiber; and a detection device for monitoring the radiation exiting the optical fiber.

2. A fiber optic surface plasmon resonance sensing apparatus, comprising:
an in-line transmission-based fiber optic surface plasmon resonance sensor wherein the sensor comprises an optical fiber having a core waveguide and a cladding or cladding/buffer layer surrounding the core waveguide and having an input end and an output end, wherein the optical fiber has a sensing area located between the input end and output end, and wherein the sensing area is defined by a surface plasmonresonance supporting metal layer in contact with at least a portion of the optical fiber core waveguide free from the surrounding cladding or cladding/buffer layer;
a source of electromagnetic radiation of multiple wavelengths whose output is applied to the input end of the optical fiber waveguide such that the radiation propagates from the input end towards the output end by total internal reflections;
a detection device for monitoring the radiation exiting the output end of the optical fiber.

3. A optical fiber surface plasmon resonance sensing apparatus, comprising:
a terminated reflection-based optical fiber surface plasmon resonance sensor, wherein the sensor comprises an optical fiber having a core waveguide and a cladding or cladding/buffer layer surrounding the core waveguide and having an input/output end and a terminal reflection end, wherein the terminal reflection end is defined by an end face of the core waveguide in contact with a mirrored layer, wherein the optical fiber has a sensing area located between the input/output end and terminal reflection end or at the terminal reflection end, and wherein the sensing area is defined by a surface plasmon resonance supporting metal layer in contact with at least a portion of the optical fiber core waveguide free from the surrounding cladding or cladding/buffer layer;
a source of electromagnetic radiation of multiple wavelengths whose output is applied to the input/output end of the optical fiber waveguide, and wherein the radiation propagates from the input/output end towards the terminal reflection end by total internal reflections, internally reflects off the mirrored layer in contact with the end face of the core waveguide, and propagates back down the optical fiber waveguide by total internal reflections towards the input/output end;
a detection device for monitoring the radiation exiting the input/output end of the optical fiber waveguide.

4. The sensing apparatus of claim 3 wherein the sensing area of the sensor is located at the terminal reflection end of the optical fiber.

5. The sensing apparatus of any one of claims 1-4 wherein the sensing area further contains at least one additional layer adhered to the surface plasmon resonance supporting metal layer.

6. A method for detecting a sample, comprising:
contacting the sample with a optical fiber surface plasmon resonance sensor, wherein the sensor comprises an optical fiber core waveguide and a cladding or cladding/buffer layer surrounding the core waveguide, wherein the optical fiber has a first end and a second end and has at least one sensing area located between the first end and the second end or at the second end, wherein the sensing area is defined by a surface plasmon resonance supporting metal layer in contact with at least a portion of a surface of the optical fiber core waveguide free from the surrounding cladding or cladding/buffer layer, and wherein the sensing area of the sensor is in contact with the sample;
directing a source of electromagnetic radiation of multiple wavelengths into thefirst end of the optical fiber core waveguide such that the radiation propagates from the first end towards the second end by total internal reflections and exists the optical fiber, and wherein the propagating radiation interacts with the sensing area of the sensor which is in contact with the sample; and detecting the radiation exiting the optical fiber core waveguide.

7. A method for detecting a sample, comprising:
contacting the sample with an in-line transmission based optical fiber sensor, wherein the sensor comprising an optical fiber having a core waveguide and a cladding or cladding/buffer layer surrounding the core waveguide and having an input end and an output end, wherein the optical fiber has a sensing area located between the input end and output end, wherein the sensing area is defined by a surface plasmon resonance supporting metal layer in contact with at least a portion of the optical fiber core waveguide free from the surrounding cladding or cladding/buffer layer. and wherein the sensing area of the sensor is in contact with the sample;
directing a source of electromagnetic radiation of multiple wavelengths into theinput end of the optical fiber waveguide such that the radiation propagates from the input end towards the output end of the optical fiber core waveguide by total internal reflections, and interacts with the sensing area of the sensor which is in contact with the sample; and detecting the radiation exiting the output end of the optical fiber waveguide.

8. A method for detecting a sample, comprising:
contacting the sample with a terminated reflection-based optical fiber surface plasmon resonance sensor, wherein the sensor comprising an optical fiber having a core waveguide and a cladding or cladding/buffer layer surrounding the core waveguide and having an input/output end and a terminal reflection end, wherein the terminal reflection end is defined by an end face of the core waveguide in contact with a mirrored layer, wherein the optical fiber has a sensing area located between the input/output end and terminal reflection end or at the terminal reflection end, wherein the sensing area is defined by a surface plasmon resonance supporting metal layer in contact with at least a portion of the optical fiber core waveguide free from the surrounding cladding or cladding/buffer layer, and wherein the sensing area is in contact with the sample;
directing a source of electromagnetic radiation of multiple wavelengths into theinput/output end of the optical fiber core waveguide such that the radiation propagates from the input/output end towards the terminal reflection end by total internal reflections, internally reflects off the mirrored layer in contact with the end face of the core waveguide, and propagates back down the optical fiber core waveguide by total internal reflections towards the input/output end and wherein the propagating radiation interacts with the sensing area of the sensor which is in contact with the sample: and detecting the radiation exiting the input/output end of the optical fiber waveguide.

9. The method of claim 8 wherein the sensing area of the sensor is located at the terminal reflection end of the optical fiber.

10 The method of any one of claims 6-9 wherein the sensing area further contains at least one additional layer adhered to the surface plasmon resonance supporting metal layer.

11. A optical fiber surface plasmon resonance sensor, comprising an optical fiber having core waveguide and a cladding or cladding/buffer layer surrounding the core waveguide, wherein the optical fiber has a first end and a second end and has at least one sensing area located between the first end and the second end or at the second end, wherein the sensing area is defined by a surface plasmon resonance supporting metal layer in contact with at least a portion of a surface of the optical fiber core waveguide free from the surrounding cladding or cladding/buffer layer.

12. An in-line transmission-based optical fiber surface plasmon resonance sensor. comprising an optical fiber having a core waveguide and a cladding or cladding/buffer layer surrounding the core waveguide. and having an input end and an output end, wherein the optical fiber has a sensing area located between the input end and output end, and wherein the sensing area is defined by a surface plasmon resonance supporting metal layer in contact with at least a portion of the surface of the optical fiber core waveguide free from the surrounding cladding or cladding/buffer layer.

13. A terminated reflection-based optical fiber surface plasmon resonance sensor, comprising an optical fiber having a core waveguide and a cladding or cladding/buffer layer surrounding the core waveguides and having an input/output end and a terminal reflection end, wherein the terminal reflection end is defined by an end face of the core waveguide in contact with a mirrored layer, wherein the optical fiber has a sensing area located between the input/output end and terminal reflection end or at the terminal reflection end, and wherein the sensing area is defined by a surface plasmon resonance supporting metal in contact with at least a portion of the surface of the optical fiber core waveguide free from the surrounding cladding or cladding/buffer layer.

14. The sensor of claim 13 wherein the sensing area of the sensor is located at the terminal reflection end of the optical fiber.

15. The sensor of any one of claims 11-14 wherein the sensing area further contains at least one additional layer adhered to the surface plasmon resonance supporting metal layer.