Abstract:
The present invention relates to a new fluorescence detection platform based on the integration of grating-assisted surface plasmon coupled emission (GASPCE). This innovation builds upon the traditional SPCE technique by adding a grating to the metal surface which thereby provides additional emission confinement. The original conical emission pattern associated with the traditional SPCE technique is “squeezed” into a “two-beam” emission pattern that is more readily interrogated and collected by a waveguiding structure. With the GASPCE method and system of the present invention, a fluorescence emission can be coupled into optical waveguide with greater efficiency. As such, the integration of the GASPCE and existing optical fiber networking offers distributed real-time sensing capabilities. Also, the integration with an integrated optical chip may enable multi-channel array sensing or high-throughput florescence sensing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application claims priority under 35 U.S.C. §119(e) to the U.S. provisional patent application identified by U.S. Ser. No. 60/625,663, filed Nov. 5, 2004 entitled “OPTICAL FIBER SENSORS USING GRATING-ASSISTED SURFACE PLASMON-COUPLED EMISSION (GASPCE)”, the entire content of which is hereby expressly incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fluorescence detection platform, and more particularly, but not by way of limitation, to a fluorescence detection platform based on the integration of grating-assisted surface plasmon coupled emission. 
     2. Description of the Prior Art 
     The phenomenon known as surface plasmon-coupled emission (SPCE) involves the coupling of surface plasmon resonance (SPR) and nearby spontaneous emission. Since the observance of SPCE in 1975, an abundance of literature containing both experimental and theoretical works has been recorded. It has been shown that, for example, the fluorescence of molecules nearby a metal film can be coupled into the surface plasmon (SP) mode, re-radiated out penetrating through the metal film into a higher refractive index substrate, and then focused at a well-defined angle. This angle generally corresponds to the “minimum total reflection angle”, which is often used to generate SPR in the Kretschmann configuration (i.e., the SPCE emission angle is the same as the SPR excitation angle with the same wavelength). Since there is a one-dimensional confinement applied to the emission, the SPCE radiation pattern is a cone  10 , as shown for example in  FIG. 1 . 
     Various experiments demonstrating SPCE have been conducted. An example of an experiment setup conducted by Weber is shown above in  FIGS. 1 and 2 . The experiment setup includes a rhodamine-methanol solution  12  excited by a p-polarized Ar laser (514.5 nm) through a high refractive index prism  14  and a 75-nm thick Ag film  16 . Since the transmission spectral bandwidth of the emission through a filter  17  is broad, the range of the corresponding SP angle is also large, and the emission cone  10  has a thick width. When this emission cone  10  is projected onto a linear photograph plate  18 , a wide band is shown. If a color film is used for the same experiment, it will show rainbow-like color bands. This is essentially an “SPR grating”, which emits light of different colors into different angles. 
     The SPR grating effect and the preferential emission of SPCE through metal thin film into the high refractive index (prism) side can be understood by the wavenumber (also known as the propagation constant or momentum) matching criteria:
 
k 0 n p  sin θ f =Re[k sp ],  (1)
 
where k 0 , k sp , n p , and θ f  are the free-space wavenumber, SP wavenumber, refractive index of the prism, and SPCE emission angle, respectively. As the SP wavenumber,
 
               k   sp     =       k   0     ⁢           ɛ   m     ⁢     ɛ   s           ɛ   m     +     ɛ   s                   
(where ε m , ε s  are the permittivities of the metal and sample solution), changes at different emission wavelength due to the material dispersion, the emission angle shifts correspondently.
 
     SPCE can be modeled as a dipole emitter located in the proximity of a metal structure. In particular,  FIG. 3  shows a SPCE emission pattern numerically simulated by using the two-dimensional (2D) finite difference time domain (FDTD) method. Black vertical lines  20  indicate the boundaries of the metal layer. To the left side of the black vertical lines  20  is free space  22 , and the right side is filled with high refractive index material  24  (e.g., glass). A dipole normal to the metal surface emits preferentially to the high refractive index side at the SPR excitation angle. 
     The potential applications of SPCE are significant since any spontaneous emission process, such as fluorescence, fluorescence resonance energy transfer (FRET), Raman scattering, second harmonic generation (SHG), etc., may take advantage of the SPCE phenomenon. More particularly for fluorescence-related sensing applications, the use of SPCE offers several interesting and highly desirable features. Such features include:
         Highly efficient fluorescence collection   Background noise reduction   Fluorescence intensity enhancement   Photostability improvement       

     Generally, due to the isotropic emission pattern of fluorescence, the common spontaneous emission collection efficiency is about 1%. However, the SPCE has an emission pattern that essentially focuses itself into a narrower spatial distribution. Although, only the vertically oriented dipole has a high probability of SPCE coupling. As such, the averaging effect (among vertical and horizontal orientation) dilutes the maximum harvest efficiency of the traditional SPCE technique to about 50-60%. This emission confinement not only improves the signal collection efficiency, but also reduces background noise due to reduced data collection volume, near-field coupling, and possible polarization discrimination. 
     SPCE is categorized as the so-called “forbidden light”  30  detection scheme. When ambient light  32  enters a higher-refractive-index material  34 , the transmitted light is only allowed to go into a transmission angle  36  smaller than the critical angle  38 . As shown in  FIG. 4 , no other light besides the emission originated at the proximity of the material interface can be coupled into the forbidden region  30  (i.e., the transmission angle is greater than the critical angle). Therefore, forbidden light  31  has ultra-high signal to noise ratio (SNR) due to the very dark background and only the presence of the dipole radiation close to the interface (which is the intended signal). Since a major portion of the SPCE is focused into an emission angle  40  greater than the critical angle  38 , SPCE is an excellent candidate for the forbidden light detection scheme. In addition, SPCE light is p-polarized with great polarization purity, which enables further boosting of SNR via polarization filtering. 
     The effect on the emission of presenting a metal surface to fluorescencing molecules can be quite different depending on the newly created photonic mode density (PMD). The presence of metal can introduce a new pathway or alter the existing mechanism of the decay processes, which may either boost the radiative rate and hence fluorescence enhancement, or promote non-radiative decay and hence fluorescence quenching. Many theoretical works have been conducted to understand this behavior. 
     Fluorescence is a radiative decay process, which competes with several other nonradiative decay mechanisms. It is well known that the radiative decay can be engineered by the surrounding PMD. The spontaneous emission usually interacts with the PMD via the evanescent field (near field). Enderlein has conducted some theoretical studies about such effect by modeling it as the dipole-interface interaction using the semi-classical electromagnetic theory. The modification of FRET due to the changing PMD can also be modeled as the resonance dipole-dipole interaction (RDDI) using a similar approach. However, the evanescent field generated near the noble metal surface via SPR is stronger and extends farther than the one near the dielectric interface via total internal refection (TIR). Therefore, the modification of the emission due to SPR is more dramatic than its counterpart produced by refractive index contrast. This fact grants SPCE, which utilizes SPR, a stronger improvement over other techniques of coupling spontaneous emissions. 
     The fluorescence intensity enhancement of SPCE comes from several factors. First, the excitation may be locally amplified via the SPR enhancement. Secondly, the radiative lifetime may be reduced due to the change of the PMD around the emitter, and hence the quantum yield efficiency is increased. Finally, the non-radiative decay is reduced in the competitive process, which results in less damage onto fluorescencing molecules and improves photostability. 
     The probability of the SP-coupled radiative decay rate has been calculated by Weber in 1979.  FIG. 5  shows that the probability SPCE can be as high as 93% when the fluorescing molecule is vertically oriented and 120-nm away from the metal surface. However, the horizontally oriented molecule has much lower SPCE coupling probability under the same condition. In an orientation-randomized scenario, the averaged SPCE is presented as a dashed line in  FIG. 5 . 
     Ford et al. also published similar calculations in 1984.  FIG. 6  presents the relative decay probability of both non-radiative and radiative mechanisms. It can be seen that the non-radiative decay (dotted lines) dominates when the molecule-metal separation is under 10-nm for both vertically (⊥) and horizontally (∥) oriented molecules. As the separation increases, the SPCE-related decay (solid lines) rises up quickly for the vertically oriented molecule, but not for the horizontal one. 
     The SPCE coupling range can be rather long such that it actually peaks at around 120 nm, which agrees well with Weber&#39;s results. The free-space non-SPCE related radiative decay also has been presented as dashed lines in  FIG. 6 . At about 120-nm away from metal surface, the free-space radiative decay actually dominates for the horizontally oriented molecules. Therefore, the preferential emission characteristic is “diluted” in the orientation-randomized case. Both works discussed above have been cited by Lakowicz, who estimates the emission harvest efficiency can still be up to 60% under the averaged results. 
     Ultimately, these previous studies indicate that the presence of metal should be able to enhance the fluorescence as long as the separation of the fluorophores and metal surface is well controlled. Several other experimental works have successfully demonstrated this capability. 
     As can be seen from the above discussions, the SPCE phenomenon has significant potential for harvesting and sensing spontaneous emission processes, particularly fluorescence emissions, with extraordinary SNR. While SPCE techniques offer some advantages, there is still a need for a compact optical collection system to collect the wide-angle emission produce by SPCE. It is to such a system and method that the present invention is directed. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows a prior art experimental setup of surface plasmon-coupled emission (SPCE). 
         FIG. 2  shows experimental results of the SPCE of  FIG. 1 . 
         FIG. 3  shows a dipole field coupled into SPCE. 
         FIG. 4  shows a forbidden light region and radiation pattern of SPCE in a numerical simulation. 
         FIG. 5  shows the calculated probability of surface plasmon (SP) emission of an Ag film. The conditions are ε s =1.766, ε m =−15.5+i0.5, 2=600 nM , and Q.E.=1. 
         FIG. 6  shows the relative decay probability of both non-radiative and radiative mechanisms. 
         FIG. 7  shows an emission pattern of a grating-assisted surface plasmon-coupled emission (GASPCE). 
         FIG. 7   a  is a diagram showing the SPCE structure constructed in accordance with the present invention. 
         FIG. 8  shows a coupling of the GASPCE and a waveguiding structure. 
         FIG. 9  is an SPCE structure constructed in accordance with the present invention. 
         FIG. 10  shows an embodiment of an orientation of gratings. 
         FIG. 10   a  shows an embodiment of an orientation of gratings with reference to the Cartesian coordinate system and definition of polar (θ) and azimuthal (φ) angles. 
         FIG. 10   b  shows an embodiment of an orientation of gratings and two emission beams with reference to the Cartesian coordinate system from a second perspective. 
         FIG. 10   c  shoes an embodiment of an orientation of gratings and two emission beams with reference to the Cartesian coordinate system from a third perspective. 
         FIG. 11  shows a GASPCE phase matching map. 
         FIG. 12  shows GASPCE collection using an evanescent-wave coupling block. 
         FIG. 13  shows an array GASPCE sensing platform using an evanescent-wave block. 
         FIG. 14  shows a GASPCE sensing platform using an integrated optical chip. 
         FIG. 15  is an example of a microarray GASPCE substrate constructed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Broadly, the present invention relates to improvements in surface plasmon-coupled emission (SPCE) sensing. More particularly, referring to  FIG. 7 , the present invention allows more efficient collection of a wide-angle emission, such as a spontaneously emitted fluorescent signal via the SPCE, by incorporating a grating structure  50  with an SPCE structure  52  to provide a grating-assisted surface plasmon-coupled emission (GASPCE) system  54 . The GASPCE system  54  is further illustrated with reference to  FIG. 7   a . which shows the grating structure  50  along with the SPCE structure  52 , as illustrated by its structural elements of an emitting material  52   a , an electrically conductive, light penetrable layer  52   b  and a substrate layer  52   c . Further, an emitter  52   aa  of the emitting material  52   a  is illustrated in  FIG.7  (see also  FIG. 8 ). The grating structure  50  of the present invention enhances the emission pattern of the SPCE structure  52  so as to provide additional confinement (in both the polar and azimuthal directions) of the emission. As such, the GASPCE system  54  can have a “two beam” distribution  56   a  and  56   b , as shown in  FIG. 7 , and facilitate coupling of emitted light signals into waveguiding structures, such as optical fibers. Such features of the present invention allows for higher signal collection efficiency, achieving ultra-high SNR, reduced cost in the collection optics and/or detector dimension requirements, compact and robust packaging, and fiber optic sensing applications. 
     For such an unusual wide-angle emission generally associated with SPCE, common approaches include using mirrors, large numerical aperture optics, or total-internal-reflection-based optics. The optical alignment, excessive optical loss, scattering-induced stray light, and optical surface quality maintenance of those methods are troublesome and problematic for the practical implementation of SPCE. Instead of trying to capture the SPCE with complex optical designs, the present invention utilizes the grating-assisted SPCE (GASPCE) configuration to further enlarge the already wide SPCE emission angle to almost a grazing angle  58  (i.e., where the transmission angle is close to 90°), as shown for example in  FIG. 7 . The resulting grazing-angle emission beams can be coupled into waveguiding structures conveniently and efficiently. The coupling of the GASPCE and the waveguiding structures has several significant advantages. First, optical waveguides can be designed to allow only certain guiding modes to propagate inside the waveguide channels with minimum loss. The non-propagating mode, which can be imagined as the light bouncing inside the waveguide with wrong angles, will experience significant loss and quickly die out in the channel. 
     Shown in  FIG. 8  is the coupling of the GASPCE and a waveguide  59 , illustrated via ray tracing. The solid lines  60  indicate the GASPCE in the forbidden light region, which is trapped and propagating along the waveguide  59  with low loss. The dashed lines  62  indicate the non-GASPCE light, which enters into the waveguide  59  with an angle smaller than the critical angle and hence experience significant loss in the waveguide. 
     Optical waveguide technologies, such as optical fibers, have been mature in the industry. The optical quality of the core/cladding interface is so high that the background noise due to the scattering can be minimized and the purity of the forbidden light (i.e., the GASPCE) can be well maintained. 
     Further, because gratings are an established and accepted technology, the present invention can be readily implemented and easily commercialized. For example, traditional grating SPR platforms have been widely accepted due to their flexibility. Prior art, such as Kitson et al., have presented work to assist grating design for surface plasmon wave (SPW) excitation. Commercial products, such as the FLEX CHIP from HTS Biosystems, are readily available in the market. Also, disposable grating SPR sensing plates have also been proposed and there is significant interest in grating-assisted SPW. 
     Referring to  FIG. 9 , in one embodiment of the present invention, an SPCE structure  64  of the GASPCE system includes a metal layer  65  (shown as  65   a  and  65   b ) and a substrate layer  66 . 
     The metal layer  65   a  of the SPCE structure  64  can be for example silver, gold, aluminum film, or any metallic film that is capable of supporting surface plasmon resonance. The substrate layer  66  of the SPCE structure  64  is a transparent dielectric medium, such as glass material, polymer material, or silica. The metal layer  65   a  may be directly deposited on a permanent substrate  66 , or the metal layer  65   b  may be deposited on a removable substrate  67  and then optically attached to a subsequent optical surface  68  so that the SPCE surface may be easily renewed. 
     The grating structure of the GASPCE system of the present invention can be implemented in various ways. For example, the grating structure may be formed 1) on the metal layer of the SPCE structure, 2) on a substrate layer and then transferred to the metal layer of the SPCE structure, or 3) via a refractive index perturbation in the substrate layer of the SPCE structure. Although the present invention is described as including a grating structure, it should be understood that any periodic photonic structure at the proximity of the emitter and the metallic layer that alters the light propagation mode may be used for the GASPCE system in accordance with the present invention. 
     Traditionally, gratings have been used in SPR sensing to facilitate the excitation of the surface plasmon wave (SPW) from the free-space side. Since the wavevector of the SPW is always greater than the incident wavevector, it is impossible to excite the SPW at a planar metal surface from the free-space side. The presence of a grating modifies the phase matching criteria so that excitation of SPW from free-space side is possible. 
     In the present invention, referring to  FIG. 10 , the presence of gratings has two effects. First, the grating structure  70  breaks the symmetry in the azimuthal direction so that by super-imposing the gratings upon the SPCE structure, additional emission confinement in the azimuthal direction can be achieved. This means that the GASPCE will emit toward the specific azimuthal  74  (φ) angle in addition to the original polar  72  angle confinement. Secondly, the grating further enlarges the polar emission angle. With these two modifications, the coupling of GASPCE to waveguiding structure is feasible. 
     The three-dimensional coordinate system related to the GASPCE system  54  is further defined with reference to  FIGS. 10-10   c . In the Cartesian coordinate system, the X, Y and Z coordinates are used to describe a location. In the present application, the Z axis is perpendicular to the SPCE structure  52  of  FIG. 7 . The X axis is perpendicular to the grooves of the grating structure  50 . For GASPCE emission, it is more convenient to use the spherical coordinate system to specify the spatial distribution with radial distance, polar angle  72  and azimuthal angle  74 . Thus, the polar angle θ  72  is defined with respect to the Z axis and the azimuthal angle φ  74  is defined with respect to the X axis. 
     The GASPCE system  52  constructed in accordance with the present invention not only specifies the polar angle  72  but also the azimuthal angle  74  of the emission due to the presence of the additional requirement of the grating period which is discussed below. Due to the additional design of the grating structure  50 , the GASPCE emission light will be directed into a specific polar angle  72  and a pair of azimuthal angles  74  (see also  FIG. 7 ). Therefore, it is termed two-dimensional confinement. 
     The theoretical background of GASPCE is discussed below with reference to the grating orientation and notations noted in  FIG. 10 . The grating-modified phase matching criterion among the wavevectors of incident field, SPW, and grating are as follows: 
                         k   gaspce     ⁢   sin   ⁢           ⁢   θ     =       ±     k   spw       ±     n   ⁢           ⁢   G         ,       k   gaspce     =       2   ⁢   π       N   ⁢           ⁢     γ   gaspce           ,     G   =       2   ⁢   π     Λ       ,           (   1   )               
and n is an arbitrary integer; where k gaspce , k spw , and G are wavevectors for the SPCE field, SPW field, and grating respectively; λ gaspce  and Λ are the SPCE wavelength and the grating period  76  respectively; and N is the refractive index of the substrate.
 
     Equation (1) can be visualized in the phase matching map as it is shown in  FIG. 11 . In previous studies, the interest was on exciting SPW from the free-space side. In the present invention, a similar analysis is extended to address the GASPCE phenomena. In  FIG. 11 , the doted circular region  80  indicates the possible distribution of the wavevector of k gaspce  sin θ, wherein two specific wavevectors have been shown as block arrows  82  and  84 . Similarly, the circular region  86  and block arrows  88  and  90  stand for the possible distribution and two specific wavevectors of k spw . The circular region  92  with smallest radius is the distributing zone of the free space wavevector, k o  sinθ. The intersection point(s) of the doted circles  80  and the solid circles  86  specify the satisfied phase matching condition(s) to allow GASPCE.  FIG. 11  demonstrates one satisfied GASPCE condition located at the intersection of doted circles  80  and the solid circles  86  where the emission polar angle is 90° (i.e., sinθ=1) and the azimuthal angle (φ) is 0° and 180° with a grating period requirement of 
             Λ   =         2   ⁢   π         k     gaspce   +       ⁢     k   spw         ⁢       (       i   .   e   .     ,         k     gaspce   +       ⁢     k   spw       =   G       )     .             
By choosing the grating wavevector (G) large enough (i.e., the grating period small enough), there is no intersection of circles  92  and circles  86  possible so that emission to the free-space is prohibited and all the GASPCE is toward the high refractive index substrate (with the GASPCE wavevectors represented by the block arrows  82  and  84 ).
 
     As such, the GASPCE of the present invention creates a two-dimensional emission confinement in both polar and azimuthal direction over the original SPCE. Such capabilities provide the following advantages:
         Facilitating the coupling of SPCE-related spontaneous emission into waveguiding structures (e.g., fiber optics) for signal collection.   Enabling array sensing for multi-target or high throughput detection and remote/distributed detection schemes.   Further improving the signal-to-noise ratio via propagation mode limitation of the waveguide coupling.   Allowing the sensor to be packaged in a rug and miniaturized form by reducing the moving parts and eliminating optical alignments.       

     To demonstrate various embodiments and uses of the present invention, the following examples of are set forth hereinafter. It is to be understood that the examples are for illustrative purposes only and are not to be construed as limiting the scope of the invention as described herein. The invention is capable of other embodiments, or of being practiced or carried out in various ways. 
     EXAMPLE 1 
     In one embodiment, as shown in  FIG. 12 , a GASPCE system  100  of the present invention includes an evanescent wave block  102  which has a glass block  104  with a standard optical fiber  106  running though and immobilized inside the glass block  104 . The fiber  106  is bent with a radius of curvature so that some controlled erosion and polishing of the top surface of the fiber  106  exposes the fiber core or cladding for light coupling. The evanescent wave block  102  provides a flat surface to allow (1) the guided light to interact with an ambient material disposed on the evanescent wave block and (2) the GASPCE to be coupled into the optical fiber. The evanescent block  102  includes a combination of a metal grating  108  and a coupling facet  110  to achieve GASPCE collection. The coupling facet  110  includes a light emitter layer (e.g., a fluorescing polymer), a metal layer, and a substrate block or layer. The light emitter layer and metal layer may be directly deposited on the substrate block  102 . In an alternative embodiment, the light emitter layer and the metal layer can be deposited on a transparent glass or plastic slide and then the slide can be attached to the substrate block via index matching fluid. For example, the glass or plastic slide with the grating structure engraved on top of it can have a metal coating and a fluorescence reporter. In one embodiment, the glass or plastic slide is disposable, which provides a cost-effective way to renew the sensor. 
     An excitation light (pump)  112  may be provided either from outside of the block  102  or from inside of block  102  through the optical fiber  106 .  FIG. 12  shows the configuration with the excitation from the topside  114  of the block  102 . The GASPCE is coupled into the optical fiber  106  propagating both directions, which may be merged and sent to the detector. In this first configuration, the excitation light is blocked with a high isolation ratio due to the forbidden light principle. The expected result is an extraordinary fluorescence signal-to-noise ratio. 
     As discussed above, the excitation light may also be delivered to the sensing facet  110  via the optical fiber  106 . In this configuration, the excitation of surface plasmon resonance (SPR) at the incident wavelength is possible since the light is incident from the higher refractive index side. When SPR is generated, the incident field can be amplified and the fluorescence signal strength is further enhanced. The incident light will also be absorbed almost completely at the SPR condition and the contamination to the signal can be minimized. Further, a remote distributed sensing network or parallelized array sensing can be facilitated when both excitation and the generated signal is transported inside the same waveguide. When multiple sensors are used, as discussed further below, various multiplexing schemes can be readily adopted from the telecommunication industry to address each individual sensor in the sensing network. 
     EXAMPLE 2 
     For array sensing applications, a plurality of the evanescent-wave blocks  102   a - 102   e  described above in Example 1 can be grouped together, as shown for example in  FIG. 13 . In this configuration, different reporters (e.g., fluorescence reporters) may be used to form the light signal emitter layers for different channels. The various reporters and the GASPCE grating  108   a  and metal layers  109  may be directly deposit on the substrate blocks  102   a - 102   e . They may also be deposited on a glass slide  120  with partitions  122  aligned to the different substrate blocks  102   a - 102   e  so that various light signals  124  (e.g., fluorescent signals) may go to dedicated waveguide structures  106  via GASPCE. 
     EXAMPLE 3 
     The integration of the GASPCE system of the present invention with an integrated optical chip enables multi-channel array sensing or high-throughput fluorescence sensing. For example, as shown in  FIG. 14 , an integrated optics chip  130 , such as an optical chip sold under the trademark HYDEX from Little Optics of Annapolis Junction, Md., can be used to form at least one waveguide  126  of the waveguide structure for the collection of GASPCE. Examples for constructing and using the optical chip are described in more detail in U.S. Pat. No. 6,614,977, the entire content of which is hereby incorporated herein by reference. 
     EXAMPLE 4 
     As an example of one application of the present invention, the GASPCE-based optical fiber sensor can be incorporated with a vapor sensing instrument taught in U.S. Pat. No. 6,558,626, issued to Aker et. al, the entire contents of which are hereby expressly incorporated herein. In such an example, a detector for detecting vapors emitted from energetic compounds present in a sample can include a housing, a pump, and a sensing assembly. The housing defines an enclosed sensing volume. The housing has an inlet and an outlet communicating with the enclosed sensing volume such that a carrier, such as a gas or fluid, can be moved sequentially through the inlet, the enclosed sensing volume and the outlet. The pump communicates with the housing to move the carrier sequentially through the enclosed sensing volume at a predetermined flow rate. The sensing assembly senses the vapors of the energetic compound delivered by the carrier as the carrier passes through the housing. The sensing assembly includes a sensing unit, a source of excitation, at least one light detector, and a converter assembly. 
     The sensing unit includes a GASPCE structure disposed in the housing. The GASPCE structure includes a substrate layer, a metal layer disposed on the substrate layer, and a grating structure disposed on the metal layer. The sensing unit also includes a light signal emitter layer comprising an amplifying fluorescent polymer, which is disposed on the GASPCE structure nearby the metal layer of the GASPCE structure. The light signal emitter layer is also positioned on the GASPCE structure so as to be openly communicating with the enclosed sensing volume of the housing. The intensity of light emitted by the amplifying fluorescent polymer will vary in response to interaction of the amplifying fluorescent polymer with molecules of the energetic compound delivered by the carrier. 
     The source of excitation of the sensing assembly produces a medium that interacts with the light signal emitter layer of the sensing unit to cause the amplifying fluorescent polymer of the light signal emitter layer to generate light. When a light signal is emitted by the amplyifing fluorescent polymer, the light signal travels through the GASPCE-enabling structure, is coupled into the grating-assisted surface plasmon mode, and is reradiated into the previously described GASPCE pattern. The fluorescence light signal is then coupled into a waveguiding structure (e.g., optical fiber) and delivered to a light detector. 
     The light detector outputs a signal indicative of the intensity of the received portion of the light generated by the amplifying fluorescent polymer. The converter assembly receives the signal from the light detector and converts such signal into a format perceivable by an individual. 
     EXAMPLE 5 
     Traditional microarray fluorescence detection system excites and detects the fluorescence signal from the sample material deposited on a glass substrate. The signal collection efficiency and signal to noise level can be low due to the nature of fluorescence emission distribution. GASPCE scheme can be used as the improved microarray system. The substrate may be an integrated optical chip with waveguiding structure embedded underneath the GASPCE structure. Shown in  FIG. 15  is a simple 3×3 microarray GASPCE system  140  where multiple excitation waveguides  142   a - 142   c  run horizontally and detection or output waveguides  144   a - 144   c  go vertically. Multiple sensing patches  146   a - 146   i  are deposited on the intercepting areas of the excitation waveguides  142   a - 142   c  and detection waveguides  144   a - 144   c . Each patch  146   a - 146   i  has an emitting material  148  deposited on the GASPCE layered. The grating structure  150  for GASPCE has grooves  152  run along with the excitation waveguide  142  so that the emission is coupled into the output waveguide  144  running vertically. 
     Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be apparent to those skilled in the art that certain changes and modifications may be practiced without departing from the spirit and scope thereof, as described herein. Also, it is to be understood that the phraseology and terminology employed herein is for purpose of description and should not be regarded as limiting. 
     The entire contents of each of the following references are hereby expressly incorporated herein. 
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