Abstract:
An integrated mesopump-sensor suitable for disposition in two- and three-dimensional arrays having small dimensions is disclosed. One mesopump is formed of an electrostatically attractable flexible diaphragm disposed through cavities or pumping chambers formed between two opposing electrostatically chargeable material layers. Fluid is pumped through the chambers by sequentially moving the diaphragm toward the first chargeable layer, then towards the second chargeable layer, which can pull and push the fluid through a series of chambers, and past the sensor. One group of sensors utilizes multiple and varied chemoresistive sensors which can vary in resistance differently in response to the presence of various analytes. Another group of sensors utilizes chemo-fluorescent sensors that fluoresce in the presence of particular analytes. Some mesopump-sensor systems can be manufactured using MEMS technology and can be coupled to controllers for sequencing the pumps and analyzing sensor outputs using methods including Principle Component Analysis.

Description:
This application is a divisional of U.S. patent application Ser. No. 09/586,093, filed Jun. 2, 2000, now U.S. Pat. No. 6,568,286 entitled. “3D ARRAY OF INTEGRATED CELLS FOR THE SAMPLING AND DETECTION OF AIR BOUND CHEMICAL AND BIOLOGICAL SPECIES. This application is also related to U.S. Divisional Patent application Ser. No. 10/340,231, filed Jan. 10, 2003. 

   FIELD OF THE INVENTION 
   The present invention is related generally to electronic sensors for detecting airborne chemical and biological agents. More specifically, the present invention is related to microelectromechanical systems (MEMS) which can detect harmful chemical and biological agents. 
   BACKGROUND OF THE INVENTION 
   Air or gas phase sensing and measurement systems are currently used in many applications, such as industrial process controls, environmental compliance measuring, and explosive detection. In one example, on-line gas chromatography and on-line optical spectroscopy are used to measure process conditions using the gas phase components. In another example, the concentration of combustion gases and stack particulates are measured to insure environmental regulatory compliance. Such systems often transport the gas to be measured to the sensor or sensors for property measurements using a pump. The pumps used to drive the gas are often bulky and consume large amounts of power. This often limits the application of such systems. In addition, many such sensor systems have a single pump for driving the gas to the sensors. As such, the failure of the pump may cause the entire system to fail. 
   SUMMARY OF THE INVENTION 
   The present invention provides an integrated pump and sensor for improved detection and reliability. Preferable, many micro-pumps are provided wherein each micro-pump is in fluid communication with one or more miniature sensors. More preferably, the micro-pumps are mesopumps formed using MEMS technology, wherein each sensor has a dedicated and often individually controllable pump. Such pump/sensor systems can be easily mass produced into a 3D array of integrated lightweight pump-sensors systems. Such system can be used in many applications, including medical gas phase diagnosis, industrial control sensing, agriculture measurements, landmine detection, harmful chemical and biological agent detection, etc. 
   An illustrative embodiment of the present invention provides an integrated mesopump-sensor assembly suitable for disposition within two- and three-dimensional arrays having small dimensions. One mesopump is formed of an electrostatically attractable flexible diaphragm disposed through cavities or pumping chambers formed between two opposing electrostatically chargeable layers. 
   The mesopump may be formed of a first, upper layer of a dielectric material having a concave cavity formed in the material lower surface, the cavity having a conductive layer covered by an insulating dielectric layer. A second, lower layer of similar construction may be disposed beneath the first layer in an opposing orientation such that the two concave cavities form a pumping chamber. An interposing layer of a flexible electrically conductive diaphragm material is provided between the upper and lower layers. The diaphragm could be made of insulating material covered on both sides with conductive layers. The flexible diaphragm is attracted toward either the upper or lower layer by applying an electrical potential to either the upper or lower layer conductive portion relative to the interposing diaphragm layer. 
   Another (second) layer of pumping chambers may be formed by forming concave cavities in the lower surface of the second layer, followed by a second diaphragm layer, followed by an opposing third layer having opposing concave cavities to form a second level of pumping chambers, as further described below. During operation, fluid to be sensed is passed from a first pumping chamber downward to a second chamber, laterally to a third chamber, upward to a fourth chamber, and out through an outlet conduit. 
   One group of sensors includes chemo-resistive sensors that vary in electrical resistance and/or impedance in response to the presence of an analyte. Various chemo-resistive sensors may vary in composition such that the sensor outputs vary in response to the presence of an analyte from sensor to sensor. The outputs of such single sensors may be unable to identify a particular analyte, but can be collectively analyzed according to Principle Component Analysis (PCA) techniques to identify particular compounds. The multiplicity of sensors that can be provided by two- and three-dimensional arrays of mesopump sensors are well suited to the multiple inputs used by PCA. 
   Another type of suitable sensor utilizes chemo-fluorescent compounds which fluoresce in response to the presence of general or particular compounds. Many other sensor types are suitable for use with the present invention, including spectroscopic sensors over either broad or narrow wavelengths. 
   The mesopump-sensors can be arrayed into stacks and coupled to controllers, including micro-controllers or general purpose computers. Computer programs or logic within the controllers can be used to sequence the operation of the pumping chambers and to analyze the sensor outputs. One embodiment includes controller programs that perform PCA. Controller programs can be utilized to operate pump sequencing in either bi-directional or uni-directional modes, depending on the limitations of the mesopumps and on the intended application. Bi-directional modes of operation can be used to push and pull fluid to be sampled past the sensor and can also be used to economize on the number of chambers needed to form a pump channel. 
   In one mode of operation, a bi-directional “shallow breathing” mode is utilized to draw a fluid such as air into the mesopump-sensor just past the sensor, then expel the fluid so as to minimize any fouling of the mesopump interior past the sensor. Bi-directional modes of operation can also be used to attempt to clean filters of particles and to push clean, purged air past a sensor, where the sensor may have become saturated. Filters may be provided on one or all external fluid orifices, and may include an impactor type filter to trap particles that have entered the mesopump. 
   The integrated mesopump sensors can provide a large number of small, lightweight, and closely spaced sensors that can be used advantageously to detect airborne agents, including harmful chemical and biological agents or trace amounts of TNT or other explosives from buried land mines. The large numbers of individually controllable sensors also may provide a system that can sequentially operate sensors that are likely to become saturated or poisoned, and to activate pumping and detailed sensing only in response to general sensor outputs or triggers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a three-dimensional stack of mesopumps having ten pumping levels with three pump channels per level and pneumatic connectors at either end; 
       FIG. 2  is a longitudinal, cross-sectional view of a single mesopump pumping chamber formed of a top concave layer, a bottom concave layer, and a flexible diaphragm disposed therebetween; 
       FIG. 3  is longitudinal, cross-sectional view of a mesopump pumping level having a top chamber level and a lower chamber level, each having three pumping chambers; 
       FIG. 4  is a fragmentary, highly diagrammatic longitudinal cross-sectional view of a mesopump pumping level having four electrostatic pumping chambers, illustrating a sequence of events used to pump fluid through the mesopump; 
       FIG. 5  is a longitudinal cross-sectional view of an integrated mesopump-sensor, wherein the sensor is disposed near a fluid intake channel to the mesopump; 
       FIG. 6  is a longitudinal cross-sectional view of a stack of six of the integrated mesopump-sensors of  FIG. 5 ; 
       FIG. 7  is a top view of a integrated mesopump-sensor chamber level having a fluid intake, sensor, impactor filter, mesopump, and fluid outlet, with fluid conduits and two chambers shown in phantom; 
       FIG. 8  is a top view of a bi-directional integrated mesopump-sensor chamber level having a fluid intake/outlet, sensor, impactor filter, and mesopump, with fluid conduits and single chamber shown in phantom; 
       FIG. 9  is a top view of an integrated mesopump-sensor chamber level having three pump channels, each with a fluid intake, heater, sensor, mesopump, and fluid outlet, with fluid conduits and three chambers shown in phantom; 
       FIG. 10  is a longitudinal cross-sectional view of an integrated mesopump sensor having a top mounted light source and photo detector and an oblique reflecting surface in the fluid pathway; and 
       FIG. 11  is a highly diagrammatic view of an integrated mesopump sensor having a controller which can be used for controlling pump sequencing and interpreting sensor outputs. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a mesopump block device  30  having an inlet header  32  and an outlet header  34  including an inlet pneumatic connection  36  and an outlet pneumatic connection  38 . Each pump preferably is a mesopump, such as described in U.S. Pat. No. 5,836,750, which is incorporated herein by reference. 
   Mesopump device  30  includes a first pump channel  40 , a second pump channel  42 , and a third pump channel  44 . In the embodiment illustrated, each pump channel includes a series of four pumping chambers for pumping fluid from the inlet to the outlet. First pump channel  40  includes a first pump chamber  46 , a second pump chamber disposed beneath chamber  46  (not shown in FIG.  1 ), a fourth pump chamber  48 , and a third pump chamber disposed beneath fourth pump chamber  48  (not shown in FIG.  1 ). Arrows  50  show generally the fluid flow through first pump channel  40 , illustrating flow through first pump chamber  46 , the second pump chamber, the third pump chamber, and fourth pump chamber  48 . Fluid can also flow through second pump channel  42 , and third pump channel  44  in a similar manner from inlet to outlet. 
   In the embodiment illustrated, there are ten pump channel levels stacked on top of each other. Each pump channel level includes two chamber levels. In this embodiment, there are three pump channels disposed side by side. Each pump channel is two pumping chambers deep. Mesopump  30  is formed of a three by ten (3×10) stack, meaning that the device is three pump channels in width and ten pump channels in depth. The 3×10 stack of mesopumps may be less than about one inch in any dimension. 
   As viewed in  FIG. 1 , the back side of a concave pumping chamber such as chamber  46  is disposed toward the top or outside of the device. In other words, where the planes are formed of a transparent material, the back or convex side of the pumping chamber is displayed toward the outer surface, with the concave surfaces of two opposing faces facing each other to form a pumping cavity. 
     FIG. 2  illustrates a longitudinal cross-sectional view of a single pumping chamber  60 . Chamber  60  includes generally an inlet  62 , a cavity  64 , an inter-chamber conduit  66 , and a back pressure vent  68 . Disposed within cavity  64  is a flexible diaphragm  70 . 
   Pumping chamber  60  includes generally a first or top layer  72  and a second or bottom layer  74  and can be about 10 millimeters in diameter in one embodiment. First layer  72  includes a conducting layer  80  and dielectric layer  82 . Pumping chamber  60  can be formed by sandwiching together or layering first layer  72  over diaphragm  70  over second layer  74 , thereby trapping diaphragm  70  between the upper and lower layers. First layer  72  and second layer  74  can be formed of materials such as polycarbonate or polyetherimide and can be about 0.5 millimeters thick in one embodiment. 
   Diaphragm  70  can include a first dielectric layer  86 , an inner flexible layer  88  having one or more conducting surfaces, and a lower insulating or dielectric layer  90 . Diaphragm  70  can be formed of a flexible material such as polyimide or polyester. In one embodiment, diaphragm  70  is formed of commercially available material such as KAPTON™, available from E. I. du Pont de Nemours &amp; Co., Wilmington, Del. or some other metalized polymer film, and is about 25 micrometers thick. 
   Second layer  74  can also include a conducting layer  94  and an insulating or dielectric layer  96  disposed over conducting layer  94 . Conducting layers  80  and  94  can, for example, be a metallic film such as aluminum formed by printing, plating, sputtering, evaporation, or EB deposition of metal, followed by patterning using dry film resist if needed, as is well known in the art. In one embodiment; shadow masks are used to pattern the deposition of evaporated metal to form layers  80  and  94 . In one embodiment, aluminum is deposited at a thickness of about 100-500 Angstroms. A similar conducting material can be deposited upon the flexible diaphragm  70 . 
   Dielectric material can be deposited through a thin film deposition process such as sputtering, ion beam sputtering, evaporation, and spin coating. The insulating material can be formed of material similar to the diaphragm material, such as polyimide or polyester. In one embodiment, the flexible diaphragm layer  88  can be about 25 microns and have an aluminum layer on each side of about 100 Angstroms thick. 
   In the embodiment illustrated, a first layer electrode  100  is coupled to the first layer conductive surface  80 . A diaphragm electrode  102  is connected to the diaphragm conductive material  88 , and a second layer electrode  106  is electrically coupled to second layer conductive layer  94 . These electrodes may be used to create an electrical potential between the first layer conductive surface  80  and diaphragm conductive material  88 , or between the second layer conductive surface  94  and the diaphragm conductive material  88 . When a potential is created between diaphragm electrode  102  and first layer electrode  100 , diaphragm  70  will be electrostatically attracted to first layer  72 . The dielectric or insulating layers or coatings upon first layer  72  and diaphragm  70  serve to prevent a short between the diaphragm and the first or second layers when the diaphragm is pulled against first layer  72  or second layer  74 . 
   In  FIG. 2 , the diaphragm  70  is in closer proximity to first layer  72  at a location nearer the end of the pumping cavity such as at  108 , than at a location more centered in the pumping cavity such as at location  110 . Thus, when the electrical potential is established between diaphragm  70  and first layer  72 , the location of diaphragm  70  nearest the ends of cavity  64  is pulled more strongly than the more central portions of the diaphragm. This causes the flexible diaphragm to be pulled in a wave resembling a peristaltic wave closing contact sequentially from the outer most to the inner most locations of cavity  64 . 
   Cavity  64  is divided into a top cavity portion  112  and a bottom cavity portion  114  by diaphragm  70 . When diaphragm  70  is moving upward, fluid is forced outward through back pressure vent  68 , wherein the fluid is normally ambient air. When diaphragm  70  is forced downward toward second layer  74 , fluid will normally flow downward through back pressure vent  68  and into top cavity portion  112 . At about the same time, the fluid of interest, such as air to be sampled, will be forced downward through inter-chamber conduit  66 . Thus, the ambient air that flows through the back pressure vent  68  is makeup air that alleviates any vacuum formed in top chamber portion  112 . 
   In the embodiment illustrated, diaphragm  70 , when pulled downward toward second layer  74 , may immediately force some fluid into inlet aperture  63  extending into cavity  64 . Thus, some of the fluid of interest may initially be urged back through inlet  62 . However, diaphragm  70  will soon seal fluid inlet aperture  63 , preventing any further back flow of fluid other than through inter-chamber conduit  66 . 
     FIG. 3  further illustrates chamber  60  disposed within a pump channel  130 , having two chamber levels with three chambers in each chamber level. The fluid flow may be seen to flow from inlet  62 , into first cavity  64 , into a second cavity  132 , into a third cavity  134 , into a fourth cavity  136 , into a fifth cavity  138 , into a sixth cavity  140 , and exiting through an outlet  142 . Conduit  137  is a chamber interconnect between cavities  136  and  138 . Thus, six cavities are used in series to form one mesopump. 
   Pump channel  130  is formed of first layer  72 , first diaphragm layer  70 , second layer  74 , second diaphragm layer  71 , and third layer  144 . Thus, three material layers and two diaphragm layers serve to form the pump channel. A fourth layer  146  may be disposed on the outside of first layer  72  forming a first back pressure channel  148 . Likewise, a fifth layer  150  may be disposed on the outside of third layer  144  to form a second back pressure channel  152 . Back pressure channels  148  and  152  can serve to provide the makeup air and air to be expelled from the back side of the diaphragm used in the pump. It is contemplated that a separate layer may not be required, as the back pressure channels may be formed directly into or within the first and/or third layers. 
     FIG. 4  illustrates a single, double chamber level pump channel  200 . Pump channel  200  is illustrated in a highly diagrammatic form to illustrate the operation of the pumping chambers. Pump channel  200  includes a first pumping chamber  202 , a second pumping chamber  204 , a third pumping chamber  206 , and a fourth pumping chamber  208 . The fluid flow to be sampled or moved may be seen to flow from an inlet  222 , through first chamber  202 , through a chamber interconnect conduit  210 , into second chamber  204 , exiting second chamber  204  through conduit  212 , entering third chamber  206 , exiting third chamber through inter-chamber conduit  214 , entering fourth chamber  208 , and exiting through exit conduit  216 . In one embodiment, mesopump  200  includes a first diaphragm  240  extending through first chamber  202  and fourth chamber  208 . Mesopump  200  also includes a second diaphragm  242  extending through second chamber  204  and third chamber  206 . In one embodiment, each diaphragm is formed of a single continuous piece of material extending through two chambers. 
   First chamber  202  includes an upper conductive surface  220  and a lower conductive surface  224 . Second chamber  204  includes an upper conductive surface.  226  and a lower conductive surface  230 . Third chamber  206  includes an upper conductive surface  232  and a lower conductive surface  234 . Fourth chamber  208  includes an upper conductive surface  236  and a lower conductive surface  238 . The conductive surfaces are preferably coated with a dielectric layer. In one embodiment, the diaphragm is moved by maintaining the diaphragm conductive potential at ground or neutral and applying an electrical potential to the upper or lower surface of the pumping chamber. For example, the portion of diaphragm  240  within pumping chamber  202  can be moved upward by applying an electrical potential to upper conductive surface  220 . Diaphragm  240  can be pulled downward within pumping chamber  202  by applying an electrical potential to bottom conductive surface  224 . 
     FIG. 4  illustrates mesopump  200  in five different phases, three of which are distinct. Beginning with phase 0, an initial phase, diaphragm  240  may be seen to be in a lower position within both first chamber  202  and fourth chamber  208 . Lower diaphragm  242  may be seen to be in an upper position within second chamber  204  and a lower position within third chamber  206 . 
   In transitioning to phase 1, an electrical potential may be applied to first chamber upper surface  220 , third chamber upper surface  232 , and fourth chamber upper surface  236 . As indicated by arrows in phase 1, diaphragms within first chamber  202 , third chamber  206 , and fourth chamber  208  move upward. This movement within first chamber  202  pulls the fluid to be sampled into first chamber  202 , indicated by cross-hatched area  235  within first chamber  202 . 
   In transitioning to phase 2, electrical potential can be applied to the lower surfaces of the first, second, and fourth chambers. This can act to move the diaphragm downward to the lower surfaces of the first, second, and fourth chambers. The fluid sample of interest  235  is pushed and pulled downward from first chamber  202  into second chamber  204 . This occurs because of the downward force of upper diaphragm  240  and the vacuum or pulling effects of lower diaphragm  242 . While some fluid may be initially expelled through inlet  222 , as previously explained, the peristaltic action of upper diaphragm  240  acts so as to close off any fluid exit through inlet  222 . 
   In transitioning to phase 3, an electrical potential can be applied to upper surface  226  of second chamber  204  and lower surface  234  of third chamber  206 . While first chamber  202  remains sealed by the lower position of upper diaphragm  240 , the upward movement of lower diaphragm  242  acts to force the fluid of interest through conduit  212 , into a third chamber  206 . In one embodiment, lower diaphragm  242  is affixed to a lower surface of conduit  212 , thereby forming a flow passage above the diaphragm. 
   In transitioning to phase 4, an electrical potential may be applied to upper surface  220  of first chamber  202 , upper surface  232  of third chamber  206 , and upper surface  236  of fourth chamber  208 . The fluid of interest is thus pushed up by lower diaphragm  242  and pulled by upper diaphragm  240  into fourth chamber  208 . At the same time, a new fluid sample  237  of interest may be pulled into first chamber  202  by the upward movement of upper diaphragm  240  within first chamber  202 . As may be seen from inspection of  FIG. 4 , phase 3 is similar in diaphragm positions to phase 0, and phase 4 is similar in diaphragm positions to phase 1. 
   In a subsequent phase, such as the immediate next phase, the fluid sample of interest  235  can be expelled from fourth chamber  208  through exit outlet  216 . In embodiments having more than four chambers, the fluid expelled from fourth chamber  208  can be expelled into another chamber. In this way, a long pipeline of chambers can be formed for various purposes. 
   In some embodiments, after pulling in a fluid sample of interest, the logic operating mesopump  200  can be used to expel the fluid from fourth chamber  208  back into third chamber  206 , thence into second chamber  204 , into first chamber  202 , and out inlet conduit  222 . This is but one way in which mesopump  200  can be operated in a bi-directional manner. If desired, samples may be held for long time periods within the samples of the mesopump by simply trapping a sample in one of the chambers. This may be desirable where further analysis is desired for one of the fluid samples. 
   Referring now to  FIG. 5 , an integrated mesopump-sensor  300  is illustrated, including some elements previously described in  FIG. 4  with respect to mesopump  200  and utilizing the same reference numerals to aid in understanding the integrated mesopump-sensor. Material layers adjacent to the layers forming the top and bottom of the pumping chambers which can form the makeup and vent air channels are not shown in FIG.  5 . 
   Mesopump-sensor  300  includes first chamber  202 , second chamber  204 , third chamber  206 , and fourth chamber  208 . Air or another fluid to be sampled can flow through an intake  308 , past a sensor  303 , through a first filter  306 , through inlet  222 , through the four pumping chambers, through outlet  216 , and through a second filter  302 . 
   Sensor  303  is represented diagrammatically as an object enclosing the fluid intake channel to the mesopump portion in FIG.  5  and having a first part  304  and a second part  305 . In one embodiment, sensors are placed on the walls of narrow individual flowing channels so as to maximize the surface-to-volume ratio and maximize the interaction between analyte and sensor material. The type of sensor used as sensor  303  can be varied according to the application. 
   In one embodiment, sensor  303  is a chemoresistive sensor that varies in resistivity or impedance depending on the amount of analyte present in the fluid sample and adsorbed onto the sensor. In some embodiments, the sensor is formed of a polymer and a plastisizer, with the plastisizer varied in composition across multiple integrated mesopump sensors to give multiple readings for a fluid sample that is believed to be similar across multiple sensors. In one example of a chemoresistive sensor, electrically conductive polymer elements include a polymer film which swells upon exposure to an analyte which can induce changes in resistivity and/or impedance in the polymer film, enabling direct low power electrical signal readout to be used as the sensing signal. 
   Processable thin films of electrically conducting organic polymers can be prepared on the individual sensor elements. The processable films can be plasticized during deposition, providing diversity and systematic control over the chemical bonding properties of each of the chemoresistor elements. For example, various non-conductive polymers such as polystyrenes can be dissolved in tetrahydrofuran (THF) and carbon black suspended in the mixture, which can then be applied to interdigitated electrodes and the THF allowed to evaporate, leaving a polymer film. Each polymer can have a different resistivity response to an adsorbed analyte. In another example, the same polymer can be mixed with various plasticizers to create the sensors, with the resistivity response varying according to the plasticizer used. In one such example, poly(pyrrole) can have various plasticizers added to create different sensors. See, for example, U.S. Pat. Nos. 5,571,401 and 5,911,872, and Proc. Natl. Acad. Sci., USA, Vol. 92, No. 7, pp. 2652-2656, March 1995, which are all incorporated herein by reference. 
   In some embodiments, the sensors do not individually identify chemical species, but may create a multiple-dimensioned output that can be used to identify the analyte. In particular, Chemometric or Principle Component Analysis (PCA) methods and software may be used to identify a chemical or biological species or at least a genus. PCA methods are well known, see for example Chemometrics and Intelligent Laboratory Systems 1 &amp; 2, pub. Elsevier Science Publishers (1986 &amp; 1987), or Chemometrics, A Practical Guide, Beebe et al., pub. Wiley &amp; Sons. Both of the aforementioned books are incorporated herein by reference. The present invention can support the presence of arrays of different sensors all within a small volume. The large number of differing lightweight and small volume sensors supported by the present invention can provide for PCA identification within handheld field units not previously practicable. 
   In some embodiments, sensor  303  may include a heater or have a heater upstream to warm the fluid to be measured and/or the sensor itself to an appropriate temperature. One use of the heaters is to warm a polymeric sensor to desorb any adsorbed or absorbed analyte. For example, after a time period and/or a cumulative amount of analyte exposure, the mesopump logic can be set to purge the sensor with a relatively clean fluid and/or heat the sensor directly or indirectly to desorb the analyte from the possibly saturated sensor. After a time period and/or sensor output indicates that the sensor is likely desaturated, a normal sensing mode may be entered. In one embodiment, the heater is deposited directly on a capillary tube used as a substrate for the sensing polymer. In another embodiment, the heater is embedded in a substrate that surrounds the sensing polymer. In yet another embodiment, the heater is placed upstream to heat the air or fluid that subsequently flows over the polymer. 
   Other examples of sensors suitable for sensor  303  include analyte specific sensors which primarily or exclusively identify a single species or a narrow genus of chemical or biological agents. In one embodiment, a fluorescent sensor be used which varies in fluoresce and quenching in response to the presence of trace amounts of an agent which, in some embodiments, include TNT and DNT. For example, certain pentiptcene derived conjugated polymers can provide an excellent and highly sensitive fluorescence chemosensor for the detection of electron-deficient unsaturated species including TNT, DNT and BQ. Detection of TNT, in particular, can be utilized in landmine detection. See J. Am. Chem. Soc., Vol. 120, No. 21, pp. 5321-5322 (1998), and J. Am. Chem. Soc., Vol. 120, No. 46, pp. 11864-11873 (1998), both of which are incorporated herein by reference. 
   Light may be provided by sensor first part  304 , and absorbed by and fluoresced from sensor part  305  having a fluorescing agent, and detected by a detector in either first part  304  or second part  305 . In one general embodiment, the sensor may be a chemo-optical sensor. The absorbance of the carrying fluid and sample may be measured, with sensor first part  304  having an emitter and sensor second part  305  having a detector. Infrared or near infrared absorbance may be used, with each sensor  303  detecting absorbance at a different wavelength. 
   Mesopump sensor  300  can be operated either uni-directionally or bi-directionally, and can utilize the filter illustrated or utilize different filters. In one method, mesopump sensor  300  is operated in a uni-directional manner, with the fluid to be sampled, such as air, taken in through port  308 , past sensor  303 , through filter  306 , through the pumping chambers, and out through filter  302 . In this mode of operation, the first filter  306  may serve to keep particles out of the pumping chambers. In a second uni-directional mode of operation, fluid to be sampled may be taken in through second filter  302 , through the pumping chambers, past first filter  306 , and past sensor  303 . In this mode of operation, second filter  302  may act to screen contaminate particles such as dust from entering the pumping chambers, and first filter  306  can act to screen finer contaminate particles from nearing the sensor. In this mode of operation, if the filters become sufficiently clogged so as to impair the operation of the mesopump sensor, various modes of handling the clogging are available, depending on the contaminant, the filter, and the sensor. 
   In one mode of operation, the clogged pump channel is shut down, and a fresh pump channel is put on line to take over the function. This mode of operation illustrates one advantage of the present invention, where tens, hundreds, or even thousands of the sensors may be available to take over ad seriatim, each for a period of time or cumulative loading. In another mode of operation, the clogged pump channel can be operated in reverse to backwash the filters in an attempt to force the contaminants from the filters. This mode of operation may be more successful where the air to be used to backwash the filters is either purified or filtered, or the contaminants are such as can be removed from the sensor during normal air flow and do not irreversibly adhere to or otherwise poison the sensor. In yet another mode of operation, filters may be provided on either end of the mesopump pump channels, such that pumping in a first direction traps dust in a first filter and backwashes the second filter, and the reverse occurs in the reverse pumping direction. Filters can be made of many materials including Porex® Porous Plastics such a polyethylene or polypropylene sheets, available from Porex Technologies Corp, Fairborn Ga. 
   As indicated above, the mesopump may be operated in a bi-directional manner so as to prevent the sensor from becoming saturated with the analyte or other material. In one example, mesopump  300  is operated in a measuring mode in a first direction, bringing in air through port  308  and expelling air through port  216 . At a point where sensor saturation is believed possible, the pumping direction can be reversed, operating in a purifying mode, bringing in air through port  216  and expelling air through port  308 . In this purifying mode of operation, the air entering through port  216  can either be purified by a filter, such as a charcoal or HEPA filter, or provided with a purified gas source. The purifying mode of operation can be continued until the analyte or other absorbant is believed to have been sufficiently desorbed from sensor  303 . The purifying mode of operation can be particularly useful where chemoresistive or fluorescent polymers are used to detect the analytes. In one bi-directional “shallow breathing” mode of operation, the mesopump is operated with the goal of drawing a fluid sample past the sensor, then expelling the fluid sample through the same intake port. In this mode, a goal is to draw the sample past the sensor but not into the mesopump, so as to reduce fouling of the mesopump. 
   Referring now to  FIG. 6 , an array of integrated mesopump-sensors  320  may be seen to be formed of six layers of integrated mesopump sensors  300 , as discussed with respect to FIG.  5 . In a preferred embodiment, the mesopump-sensors are grouped as a three-dimensional array. The integrated mesopump sensors may be separated by vent channels  322 , as discussed with respect to channels  148  and  152  of FIG.  3 . The channels may be formed by standoffs, channels formed in the layers, or with separate layers, as discussed with respect to FIG.  3 . It may be seen that an array of integrated mesopump-sensors can be formed by layering the pump body layers and the diaphragm layers. It may also be seen that the air intakes or ports are disposed relatively close together, and can be fed by a common header, such as illustrated by intake  36  of FIG.  1 . In this way, the air sample reaching each of the sensors may be reasonably expected to be similar in composition at any point in time. 
   Referring now to  FIG. 7 , a single pumping layer or chamber level of an integrated mesopump-sensor  350  is illustrated. The layer of material representing the top layer is represented by reference numeral  351 . The elements illustrated in  FIG. 7  would lie within a material layer in one embodiment and be visible only if the material forming the top layer were transparent or translucent, which layers formed of polycarbonate may be. Mesopump-sensor layer  350  includes an intake port  352 , a sensor  354 , and electrodes or optical connection lines  356  and  359 . Electrodes  356  and  359  can include connections for supplying power to sensor  354  and for obtaining a signal from sensor  354 . In those embodiments having heaters, electrodes  356  and  359  may include an electrical line for powering a heater for the sensor and/or the fluid to be sampled. A fluid conduit  358  continues from sensor  354  in an arc, terminating at an impactor filter  360 . 
   The geometry of arced conduit  358  operates to accelerate any particles within the conduit, causing them to strike the impactor filter, while the carrying fluid, such as air, continues on to a second fluid conduit  362 . The momentum of the particles causes them to strike the impactor filter. The impactor filter can be formed of any material suitable for trapping the particles that strike it. One group of suitable materials for forming impactor filter  360  includes adhesives. 
   Fluid conduit  362  continues on to a first pumping chamber  364 , having a vent hole  366  extending up through the top of layer  351 . In the view illustrated in  FIG. 7 , the back side of a concave surface would be visible when the top layer is transparent or translucent. A fourth pumping chamber  370  is also illustrated. In one embodiment, a second pumping chamber is disposed beneath first pumping chamber  364 , and a third pumping chamber is coupled laterally to the second chamber with a conduit. In this embodiment, the third chamber can be coupled to fourth chamber  370  via a fluid conduit, as previously described. An electrode  368  may be seen extending from first chamber  364  as well as an electrode  372  extending from fourth chamber  370 . Electrodes  368  and  372  can be used to apply an electrical potential to the conductive layers of the chambers and initiate electrostatic movement of the diaphragms, as previously described. Fluid may exit from fourth chamber  370  through another fluid conduit  374 . Integrated mesopump-sensor layer  350  can be operated in either a uni-directional mode or a bi-directional mode, depending on the controlling logic. 
   Referring now to  FIG. 8 , a bi-directional integrated mesopump-sensor level  380  is illustrated, including a pump body layer  382 . As described with respect to the embodiment illustrated in  FIG. 7 , a fluid sample can flow from conduit  352  to impactor filter  360 , and to first chamber  364 . In this bi-directional embodiment, there is no second conduit to expel the sample fluid apart from conduit  352 , requiring this embodiment to operate in a bi-directional mode, rather than having the option of operating in a uni-directional mode. The chamber can be operated so as to bring fluid in past sensor  354  in a first direction, then expel the fluid past sensor  354  in the opposite direction, before bringing in a second sample of fluid. 
     FIG. 9  illustrates a top view of a single integrated mesopump-sensor pumping level  400  having a two-dimensional array of three pump channels each formed of four pumping chambers, two of which are illustrated as visible through a translucent top pumping layer material  402 . Pumping level  400  includes a first pump channel  404 , a second pump channel  406 , and a third pump channel  408 . Previously described reference numerals refer to previously discussed elements. In the embodiment illustrated, each pump channel includes a first conduit  410  leading to an excitation source  412 , continuing on through a second conduit  420  to a sensor (detector)  422 , and further onward to first pumping chamber  364 . As previously discussed, the fluid to be sampled can continue on to fourth pumping chamber  370 , exiting through conduit  374 . In the embodiment shown, the excitation source  412  are heaters powered through heater electrodes  414 , and sensors  422  are powered through sensor power electrodes  416 , with signals returning through sensor signal electrodes  418 . 
   It is contemplated that flow sensors  425   a-c  may be provided in the pump channels fro increasing the flow of gas therein. The flow sensors may be microbridge structures of the type as described in, for example, U.S. Pat. Nos. 4,478,076; 4,478,077; 4,501,144; 4,651,564; 4,683,159; and 4,576,050. 
     FIG. 10  illustrates an integrated mesopump-sensor pumping level  500  similar in many respects to mesopump-sensor pumping level  300  illustrated in FIG.  5 . Mesopump sensor  500  includes an optical sensing chamber  502  which has light both supplied from and detected by devices disposed on the same side of the level, in this embodiment, on the top side of the pumping level. Optical sensing chamber  502  can be used in conjunction with fluorescing materials sensitive to analytes of interest, as previously discussed. A light emitter  504  emits light downward toward a sensor material  506 , such as a fluorescing polymer. Any fluorescence from material  506  is visible to, and reflected by, for example a diagonal reflecting mirrored surface  508  which directs the fluorescence upward to a detector  510 . In one embodiment, the diagonal surface is integrally formed into the body of the mesopump-sensor. Light paths are denoted by arrows  512 . Positioning the emitter and detector on the same side allows for ease of manufacturing. Sample fluid flow is similar to that previously discussed and can be pulled into and pushed out of an intake  516 . 
   Referring now to  FIG. 11 , an integrated mesopump-sensor system  600  is schematically illustrated having a controller  602  electronically coupled to a single mesopump-sensor pump channel  604 . Controller  602  can have various integrated or separate display components, not requiring illustration, for displaying the operating status and analyte values. In one embodiment, a plurality of control and sensing lines are coupled to each pumping layer. In the embodiment illustrated, the electronic control and sensing lines include a heater supply electrode  606  and a pair of sensor signal lines  608 . Also included in the embodiment illustrated is a pair of control lines for each pumping chamber. Mesopump-sensor layer  604  has four pumping chambers, with pumping control line pairs  610 ,  612 ,  614 , and  616  being coupled to the first, second, third, and fourth pumping chambers, respectively. In one embodiment, as discussed with respect to  FIGS. 2-4 , the upper and lower conductive layer in each pumping chamber are connected to a separate electrical potential source. In some embodiments, the diaphragm is electrically at ground, while in other embodiments, the diaphragm is electrically coupled to a separate control line. 
   Controller  602  can be any suitable device for controlling and sensing the outputs of the mesopump-sensor device. In some embodiments, controller  602  includes a programmable microcontroller, for example a controller in the PIC family of microprocessors. In other embodiments, controller  602  includes microprocessors having a control program stored in firmware which may or may not be re-writable. In still other embodiments, controller  602  includes a general purpose computer with suitable input/output hardware. 
   Controller  602  is preferably capable of being programmed with a variety of programs, which can be implemented as high-level computer languages, low-level computer languages, and as more direct machine control representations such as Boolean or ladder logic control languages. The control portion of the programs can include timing control portions for controlling the timing of the pumping chamber operation. The timing control may include, for example, a repetitive cycle for controlling the upper and lower potentials of the conductive layers of the pump channels relative to the diaphragms. 
   It is contemplated that the control program may include logic for reversing the direction of the pumping. This may be used to pull in a clean purging fluid to desaturate the sensor, to move the fluid to be sampled back and forth past the sensor for increased sensitivity, or to backwash the filter in an attempt to clean them. 
   Some control programs may include activation logic to activate dormant pump channels when other pump channels detect a particular substance, or become saturated or otherwise damaged during operation. For example, the control program may operate pump channels in sequence, putting new pump channels on line after a time period when it is feared that a sensor may be saturated or even poisoned. The control program may also, for example activate or deactivate pumping depending on the applications. One example of such a sensor is the detection of a general class of material by a broad detecting sensor, followed by activation of several sensors and/or more specific sensors to detect a species of interest, such as TNT. 
   Controller  602  preferably includes analysis programs to analyze the sensor outputs. In one embodiment, neural networks software or hardware is included in controller  602 . In another embodiment, chemometric or principal component analysis (PCA) programs are included within controller  602 . In still other embodiments, spectroscopic analysis programs are included within controller  602 . In embodiments having multiple sensors, each for detecting a small portion of the information needed to identify the analytes of interest, applicants believe that PCA software may be of particular use. In embodiments where controller  602  includes a general purpose computer, a variety of programs may be executed on the controller, many of the programs being user supplied and developed for specific applications. 
   Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.