Abstract:
A method of detecting at least one analyte in extra-cellular spaces includes the step of inserting a microprobe through the stratum corneum toward the stratum basale of the skin of a subject into extra-cellular spaces containing interstitial fluid having at least one analyte to be detected, said microprobe having a diameter at its tip no larger than approximately 10-50 microns. The method further includes optically testing for a predetermined analyte in the extra-cellular space adjacent the distal end of the microprobe without drawing a sample of the interstitial fluid. Preferably the microprobe body includes a sensor layer covering the distal optical tip of the microprobe body, the sensor layer being adapted to interact with a predetermined analyte to be detected in the interstitial fluid, and an optical detector responsive to interaction of the sensor layer with the predetermined analyte to signal detection of said predetermined analyte.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. application Ser. No. 09/143,258 now U.S. Pat. No. 6,197,257 (filed Aug. 20, 1998) on Micro Sensor Device. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a method and apparatus for detection of analytes, and more particularly to such method and apparatus for the painless detection of such analytes in extracellular space. 
     2. Description of the Prior Art 
     The past decade has seen an increased effort for new and less invasive means of detecting relevant compounds in biological systems. In the past such detection has involved clinical assays using in vitro diagnostics requiring invasive sampling methods. Newer philosophies in medicine and related disciplines have tended to use less invasive means that are more comfortable to the subject and which tend to reduce the possibility of transmission of infection. 
     It is known in the art to use non-invasive spectral techniques to quantitatively determine the presence and concentration of analytes. For example, U.S. Pat. No. 4,882,492 to Schlager teaches a non-invasive near-infrared measurement of blood analyte concentrations, in particular the measurement of blood glucose levels. Schlager recognizes that certain wavelengths of light in the near-infrared spectrum are absorbed by glucose. In that patent, modulated light is directed against a tissue (such as an earlobe). Some portion of the light is passed through the tissue and its spectrum is modified in response to the amount of glucose in the blood and tissue. Similar approaches are shown in U.S. Pat, No. 4,014,321 to March, U.S. Pat. No. 4,655,225 to Dahne et al., U.S. Pat, No. 4,805,623 to Jobsis, and U.S. Pat. No. 5,179,951 to Knudson. However methods using various parts of the infrared spectrum for detecting some analytes are relatively unproven to date due to their inability to differentiate multiple occurrences of the analytes at different concentration levels in different body compartments using the available spectral data. 
     Cygnus, Inc. has demonstrated a technique for collection of glucose in interstitial fluid found in extra cellular space. This technique uses reverse ionopherisis to attract heavier salt molecules to the outside surface of the skin and uses electrochemical means for detecting glucose. This method is currently the subject of an FDA PMA review. One drawback of this method is the initial time delay for retrieval of sufficient fluid for sampling. This method also requires the subject to constantly have a device in place for collection of the fluid. 
     SpectRx has developed an alternative method for accessing the interstitial fluid by using a laser to ablate small apertures in the surface of the skin sufficient to release interstitial fluid from extra cellular space. Although this method has also produced data which correlates well with constituents found in blood, it suffers from a progressive closure of the aperture and a correlation between sufficient aperture size and the amount of discomfort caused by the initial ablation of the skin. 
     TCPI has developed a method similar to that of Cygnus which draws interstitial fluid outside the skin. This method however uses a replaceable patch that changes colormetrically according to the presence of the analyte. This method also requires several minutes more than present blood testing methods. 
     Integ has disclosed a method to access interstitial fluid in an intradermal layer, sampling the interstitial fluid by drawing interstitial fluid through a capillary and then testing the fluid in situ or extracting the fluid to an external apparatus. The Integ method may be prone to rupture of small capillaries that are found in the upper layers of the dermis and to contact with nerve endings that abut the dermal/epidermal junction. There has also been controversial data produced as to whether glucose levels in particular track well between levels produced in the intradermal interstitial fluid and that found in capillaries or veins. Apparently the Integ method draws a one microliter sample from the interstitial fluid, which sample is analyzed for glucose. 
     In summary, the prior art methods could be improved in that they suffer from insufficient sampling quantities, delayed periods of testing required for sample collection, destruction of skin cells at the stratum corneum level, discomfort to the subject, and the production of quantities of blood. 
     SUMMARY OF THE INVENTION 
     Among the various objects and features of the present invention may be noted the provision of a method and apparatus for detecting analytes in extra cellular space which overcomes the problems associated with sampling. 
     Another object is the provision of such a method and apparatus which substantially reduces or eliminates delay time before detection can be accomplished which in the prior art results from the necessary delay for sample collection. 
     A third object is the provision of such a method and apparatus which prevents the destruction of skin cells at the stratum corneum level. 
     A fourth object is the provision of such a method and apparatus which reduces or eliminates discomfort of the subject. 
     A fifth object is the provision of such a method and apparatus which reduces or eliminates the production of quantities of blood during the testing. 
     Other objects and features will be in part apparent and in part pointed out hereinafter. 
     Briefly, the new method is a micro invasive detection of analytes in extra-cellular spaces that are on the epidermal side of the epidermal/dermal junction. Although the initial (outermost) layer of the epidermis at the surface of mammalian skin is considered to be a non-nucleated (dead) strata of cells known as the stratum corneum, there are several layers of the epidermis with those closer to the stratum basale, the layer that precedes the epidermal/dermal junction, all found to be living cells requiring nutrients from extra-cellular space. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a micro sensor device constructed according to the present invention; 
     FIG. 2 is a block diagram of the micro sensor device constructed according to the present invention; 
     FIG. 3 is a perspective view of a tip portion of the micro sensor device shown in FIG. 1; 
     FIG. 4 is a schematic view of the micro sensor device of the present invention being employed to sense a concentration in a sample; 
     FIG. 5 is perspective view of the micro sensor device of FIG. 1 illustrated monitoring a concentration of glucose in a hand of a patient; 
     FIG. 6 is a block diagram of another embodiment of the integrated sensor head constructed according to the present invention; 
     FIG. 7 is a block diagram of a second embodiment of the micro sensor device constructed according to the present invention; and 
     FIG. 8 is an exploded view of an optical member for use in the present invention suitably designed for connection to a standard SMA connector. 
    
    
     Similar reference characters indicate similar parts throughout the several views of the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like numbers refer to like items, number  10  identifies a preferred embodiment of a micro sensor device constructed according to the present invention- As illustrated in FIG. 1, the device  10  comprises a pencil or pen shaped body  12  which includes an integrated sensor head  14 , a central body portion  16 , and an end cap  18 . The central body portion  16  further includes a display device  20 , such as an LED (light emitting diode) type display or an LCD (liquid crystal display) type display, for displaying information. The end cap  18 , which may be removable from the central body portion  16 , is used to allow access into the interior of the central body portion  16 . Batteries (not shown) can be inserted into the central body portion  16  to supply power to the device  10 , as will be explained. The central body portion  16  may also include an ON/OFF switch  22  which may be used to operate the device  10 , a speaker  24  which may be used to audibly indicate certain information, and an LED  26  which may be used to indicate that a reading has been completed. Other switches (not shown) may be incorporated into the central body portion  16  to further control the device  10 . Additionally, the central body portion  16  houses electronic circuitry and other components which will be illustrated and explained in further detail herein. The device  10  is sized and shaped to be a hand held type device that is portable and preferably is the size and shape of a pencil or a pen. 
     With reference now to FIG. 2, a block diagram of the circuitry and components of the device  10  is shown. The device  10  includes a computer  30  which is connected to the display  20  by a wire  32 , to the switch  22  by a wire  34 , to the speaker  24  by a wire  36 , and to the LED  26  by a wire  38 . The computer  30  may consists of, by way of examples, a microprocessor, a microcontroller, an ASIC chip, or any other known equivalent device which is capable of processing electrical signals. The computer  30  may also be connected to a power supply, such as a battery, although the power supply and such connection are not illustrated in FIG.  2 . 
     Additionally, the computer  30  may also be connected to other switches (not shown) which may be provided with the device  10  to further control or operate the device  10 . The computer  30  and the other components  20 ,  22 ,  24 , and  26  are all housed within the central body portion  16 . 
     The integrated sensor head  14  comprises a light source  40 , a detector  42 , and a tip portion  44  all incorporated or integrated within the integrated sensor head  14 . For example, the integrated sensor head  14  may be formed by any suitable injection molding method or technique. Additionally, the integrated sensor head  14  is of an extremely small size on the order of about under 30 microns in size. The light source  40  is operatively connected to the computer  30  by an electrical connection  46  and the detector  42  is likewise electrically connected to the computer  30  by an electrical connection  48 . The tip portion  44  consists of an extremely small needle shaped analyte. The light source  40  may be an LED, a laser, a laser diode, or other light excitation source. The light source  40  is adapted to project a beam of light  50  into the tip portion  44 . The beam of light  50  passes through the tip portion  44  and a reflected pattern of light  52  may be reflected back from a sample (not shown) through the tip portion  44  to the detector  42 . The detector  42  provides the reflected pattern of light  52  to the computer  30  for processing to determine the concentration of material within a sample. The detector  42  may be, for example, a photodiode, a miniature spectrometer, or any other device which may detect light. 
     The integrated sensor head  14  is shown in greater detail in FIG.  3  and again is preferably a small device on the order of under 30 microns in size or diameter. In particular, the sensor head  14  is of unitary construction having the light source  40 , detector  42 , and tip portion  44  incorporated therein. The electrical connections  46  and  48  extend from the light source  40  and the detector  42 , respectively, and terminate at a first end  54  of the sensor head  14 . In this manner, the connections  46  and  48  mate with corresponding connections or terminals (not shown) in the central body portion  16 . The use of the electrical connections  46  and  48  eliminates any alignment problems which would been associated with other types of connectors, such as an optical connection. Additionally, the sensor head  14  is mated or connected to the central body portion  16  in any suitable manner, as for example by screw type attachment or even frictional engagement. 
     The tip portion  44  may be chemically treated or use an enzymatic process or treatment which enables the tip portion  44  to interact with the sample to be detected or monitored. Properties of the tip portion  44  may vary dependent upon the sample and the chemical or substance to be detected by the device  10 . As constructed and with particular reference to FIG. 2, the tip portion  44  allows for the beam of light  50  to pass through and the reflected pattern of light  52  to be reflected through the tip portion  44 . As indicated above, the tip portion  44  is extremely small and because of its size it can be inserted through gaps in between most cells or through the membrane of a cell without, damaging the cell. Additionally, the tip portion is small enough that when it is inserted into a human, for example a human hand, there will be little or no sensation felt. 
     The tip portion  44  may have specific chemical sensitivities based upon the properties of a dye matrix. A dye may be chemically activated by a different chemical compound which enables sensing of a specific chemical property within a sample or a substance. The tip portion  44  provides for enhanced sensitivity, selectivity, and stability when detecting a concentration within a sample or substance. In this manner, the sensor device  10  interacts with the substance or sample to detect a specific chemical or concentration within the substance. Some examples of how the tip portion  44  may be chemically treated to have specific chemical sensitivities or to interact with the sample to be detected or monitored may be found in U.S. Pat. Nos. 5,361,314 and 5,627,922. 
     With reference now to FIGS. 1,  2 , and  4 , the operation of the device  10  will be explained in detail. In order to operate the device  10 , the on/off switch  22  is pressed to initialize the device  10 . Once powered, the device  10  may be inserted into a sample  60  to test for a particular concentration of material within the sample  60 . As shown in FIG. 4, the sample to be tested is a liquid  62  in a beaker  64 . The tip portion  44  is inserted into the liquid  62  and at this point in time a beam of light, such as the beam of light  50 , is transmitted into the liquid  62 . With the tip portion  44  being in contact with the liquid  62 , the liquid  62  reacts chemically with the tip portion  44  and the color of the chemical composing the sensor device  10  changes. As a result of this change, the pattern of the light reflected back into the tip portion  44  changes, such as that shown by the pattern of reflected light  52 . This pattern is sensed by the detector  42  and signals are provided to the computer  30  which performs a calculation to determine the concentration of the particular chemical being sensed and the result may be displayed in the display  20 . 
     Additionally, the chemical properties of the tip portion  44  of the sensor portion  14  may be changed to react with another chemical to detect some other chemical within a sample. Further, instead of changing the chemical properties of the tip portion  44 , it may only be necessary to change the light source  40  to detect some other chemical within a sample. It is also possible to have a cap (not shown) which covers the tip portion  44  when the device  10  is not in use. The cap may also have incorporated therein a mechanism for keeping the tip portion  44  sterilized. 
     The tip portion  44  may be constructed by using any suitable injection molding method or technique and precision injection molding methods for molding extremely small parts may be employed. Another method or technique for constructing the tip portion  44  may include a micro fabrication process known as micro-electro-mechanical systems (MEMS) fabrication process wherein an extremely small sized part may be carved out of a substance. Even a micro-electro-mechanical system (MOEMS) may be used to produce the tip portion  44 . Additionally, the tip portion  44  may be manufactured from silicas, plastics, polymers, or even pyrex. Other known methods for construction of the tip portion may be a heat drawn process or even swaging. 
     Referring now to FIG. 5, the sensor device  10  is again shown having a pencil like body  12  which includes the central body portion  16 , the end cap  18 . and the sensor head  14  which has been inserted into a hand  80  in order to detect the presence of a concentration of material, such as example glucose. The central body portion  16  includes the display  20  for displaying information such as glucose concentration, the ON/OFF switch  22  for operating the device  10 , the speaker  24 , and the LED  26 . The tip portion  14  is shown being inserted into the hand  80  and because of its extremely small size little or no sensation will be felt. The other components of the sensor device  10 , which were discussed with reference to FIG. 2, are all housed within the central body portion  16  and the tip portion  14 . 
     Once inserted into the hand  80 , actuation of the sensor device  10  will cause the computer  30  to operate the light source  40 . The light beam  50  is produced and sent through the tip portion  44 . With the tip portion  44  being in contact with the hand  80 , the tip portion  44  reacts chemically and the pattern of light  52  is generated and reflected back through the tip portion  44  to the detector  42 . The detector  42  transmits the pattern of light  52  to the computer  30  which then calculates the concentration of glucose within the hand  80 . The result may be displayed in the display  20  or audibly indicated by the speaker  24 . Once the result is indicated the device  10  may be removed from the hand  80  and turned off. 
     FIG. 6 illustrates another embodiment of an integrated sensor head  100  which may be used with the device  10 . The sensor head  100  comprises a first integrated portion  102  which includes a tip portion  104  and a second integrated portion  106  which includes a light source  108 , a detector  110 , and connectors  112  and  114  which are connected to the light source  108  and the detector  110 , respectively. The first integrated portion  102  may be connected to the second integrated portion  106  by any suitable method or constructions, such as by a screw type construction. In this embodiment the first integrated portion  102  is easily removable from the second integrated portion  106  and the first integrated portion  102  may be interchanged with new first integrated portions  102  as need be. For example, the tip portion  104  of the first integrated portion  102  may lose its effectiveness over time, degrade, or become contaminated and removal of the first integrated portion  102  is all that will be required to change to a new tip portion  104 . In this manner, the sensor head  100  has the feature of a replaceable tip portion  104 . Additionally, the first integrated portion  102  including the tip portion  104  is disposable and easily discarded from second integrated portion  106 . The second tip portion  106  incorporates the light source  108 , the detector  110 , and the connectors  112  and  114  and there is no need to replace these elements  106 - 114  in this embodiment. 
     FIG. 7 depicts a block diagram of another embodiment of a micro sensor device  200 . The sensor device  200  comprises a computer  202  which is connected to a display device  204  by a wire  206 , to a power switch  208  by a wire  210 , to a speaker  212  by a wire  214 , and to an LED  216  by a wire  218 . The computer  202  may consists of, by way of examples, a microprocessor, a microcontroller, an ASIC chip, or any other known equivalent device which is capable of processing electrical signals and controlling various output devices or components. The computer  202  may also be connected to a power supply, such as a battery or a rechargeable battery, although the power supply and such connection are not illustrated in FIG.  7 . Additionally, the computer  202  may also be connected to other switches (not shown) which may be provided with the device  200  to further control or operate the device  200 . The computer  202  and the other components  204 ,  208 ,  212 , and  216  are all housed within a central body portion  220  of the device  200 . 
     An integrated sensor head  222  is connected to the central body portion  220  by any suitable means. The integrated sensor head  222  comprises a light source  224 , a first detector  226 , a second detector  228 , and a tip portion  230  all incorporated or integrated within the integrated sensor head  222 . For example, the integrated sensor head  14  may be formed by any suitable injection molding method or technique. Additionally, the integrated sensor head  222  is of an extremely small size on the order of about under 30 microns in size. The light source  224  is operatively connected to the computer  202  by an electrical connection  232  and the first detector  226  is likewise electrically connected to the computer  202  by an electrical connection  234 . The second detector  228  is also connected or interfaced to the computer  202  by a connection  236 . The tip portion  230  consists of an extremely small needle shaped analyte. The light source  224  may be an LED, a laser, a laser diode, or other light excitation source. The light source  224  is adapted to project a beam of light  238  into the tip portion  230 . The beam of light  228  passes through the tip portion  230  and a first reflected pattern of light  240  may be reflected back from a sample (not shown) through the tip portion  230  to the first detector  226 . The first detector  226  provides the first reflected pattern of light  240  to the computer  202  via the connection  234  for processing to determine the concentration of material within a sample. 
     Additionally, a second reflected pattern of light  242  may be produced and reflected back from a sample (not shown) through the tip portion  230  to the second detector  228 . The second detector  228  provides the second reflected pattern of light  242  to the computer  202  via the connection  236  for processing to determine the concentration of material within a sample. 
     Examples of the first detector  226  and the second detector  228  were previously noted above with respect to the detector  42 . In this manner, two different substances may be monitored or detected by the device  200 . Although the device  200  is depicted to show the monitoring of at least two different chemical compounds or substances it is also contemplated that more than two chemical compounds or substances may be sensed, detected, or monitored by the device  200  by adding additional components, as has been taught and illustrated. 
     Although not illustrated, it is also possible and contemplated to have an integrated head sensor which has the light source  224  and the two detectors  226  and  228  incorporated within a first integrated head portion and the tip portion  230  incorporated within a second integrated head portion which is separable from the first integrated head portion. In this manner, the second integrated head portion in essence becomes a disposable component of the micro sensor device. 
     It is preferred that the method of the present invention uses an optical member, such as the previously shown optical members or more preferably such as microprobe  301  shown in FIG. 8, that has been fabricated to have a tip size less than 20 microns to enter at the stratum corneum and rest in or proximal of extracellular space of the stratum basale of the epidermis. Microprobe  301  includes a distal tip portion  303  extending proximally 9.8914 mm to a base portion  305 . Both base portion  305  and tip portion  303  are tapered, with a substantial step where the tip portion meets the base portion. Base portion  305  has a width of 5.1068 mm at its proximal end and a length of 9.5791 mm, and tapers at approximately four degrees to the step where it meets the tip portion  303 . 
     It is preferred that the optical member be molded to the final shape, preferably using a two-part RTV rubber silicone mold using known molding techniques. That mold is prepared using a hard durometer type silicone such as that sold under the trade designation G-380 by Silicones, Inc. Such a silicone is suitable for small parts. The first part of the mold is prepared by creating a pattern from a modified micropipette tip and a pulled silica optical fiber tip  307 . Specifically the micropipette tip is an Eppendorf-style tip that has been trimmed at the bottom to expand the diameter to approximately 600 microns. The pulled silica optical fiber tip  307  is made from silica fiber having a diameter of 600 microns (such fibers are available from 3M). The fiber is placed into an optical fiber puller such as that sold under the trade designation P2000 by Sutter Instruments. The tip is pulled so that the fiber tapers from 600 microns down to 10-50 microns at its extreme tip. The silica pulled tip is then placed into the Eppendorf-style pipette tip and held in place by friction. This pattern (pipette tip plus pulled fiber tip) is then placed into a glass vial that has been filled with the RTV silicone to form the first part of the mold. 
     The second part of the mold is prepared by taking a standard optical fiber SMA connector  308  and removing the lock nut from the assembly. The remaining portion of the assembly (minus the lock nut) is placed as a cover on the poured mold containing the optical member pattern. After curing and removal of the SMA connector, the mold is then refilled in the female impression that has remained from the SMA connector. The final part is a male SMA silicone molded piece  309  (FIG. 8) that custom fits the first part of the mold. 
     Alternatively, the mold can be made using machining or stereolithography or other conventional techniques. 
     The optical pattern is then removed from the first part of the mold and replaced by another silica optical fiber piece  307  that has been tapered in an identical manner and has been measured to be the length from the tip of the mold to abut against the face of the second part of the mold. This tapered fiber is then placed inside the mold and remains there as a permanent portion of the final part. The body of the final part is then poured using a hard durometer polyurethane such as that sold under the trade designation IE-71 DC by Innovative Polymers. The second part of the mold is then placed into the first part of the mold, during the cure process. After curing, the final part is manually released from the mold and is ready for application of the sensor chemistry. 
     Unlike methods used to penetrate through the epidermal/dermal junction, which can access capillary structures, the present method has no possibility of accessing capillaries since the capillaries do not extend beyond the epidernal/dermal junction. In addition the present method has no possibility of exciting nerve endings since the nerve endings are all found beneath the epidermal/dermal junction. The molded part is covered with a sensor layer that is designed to target a specific analyte(s) in the extra-cellular space of the epidermis. By way of illustration, the following analytes are among the many which may be targeted: 
     
       
         
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 ACETALDEHYDE 
               
               
                   
                 Acetate 
               
               
                   
                 Acetic Acid 
               
               
                   
                 ADENOSINE 5′-MONOPHOSPHATE 
               
               
                   
                 ALANINE 
               
               
                   
                 ALCOHOL ESTER 
               
               
                   
                 ALIPHATIC NITRO 
               
               
                   
                 COMPOUNDS 
               
               
                   
                 ALKALINE PHOSPHATASE 
               
               
                   
                 ALLYL ALCOHOL 
               
               
                   
                 ALTRONOLACTONE 
               
               
                   
                 AMINO ACIDS 
               
               
                   
                 Aminophenol 
               
               
                   
                 AMMONIA 
               
               
                   
                 AMP 
               
               
                   
                 AMYLAMINE 
               
               
                   
                 AMYLASE 
               
               
                   
                 ARGININE 
               
               
                   
                 Aromatic Amine 
               
               
                   
                 Aromatic Diamine 
               
               
                   
                 ARSENATE 
               
               
                   
                 ASCORBIC ACID 
               
               
                   
                 ASPARTATE 
               
               
                   
                 BENZALDEHYDE 
               
               
                   
                 Benzidine 
               
               
                   
                 BENZYLAMINE 
               
               
                   
                 BORATE 
               
               
                   
                 BUTANOL 
               
               
                   
                 BUTYLAMINE 
               
               
                   
                 CADAVERIN 
               
               
                   
                 Carbohydrate 
               
               
                   
                 Catechol 
               
               
                   
                 Chlorogenic Acid 
               
               
                   
                 CHOLESTEROL 
               
               
                   
                 CHOLINE 
               
               
                   
                 CHOLINESTERASE 
               
               
                   
                 CHYMOTRYPSIN 
               
               
                   
                 Cresol 
               
               
                   
                 DEXTRAN 
               
               
                   
                 dextrose 
               
               
                   
                 DIAMINE 
               
               
                   
                 Dianisidine 
               
               
                   
                 DIHYDRO-OROTATE 
               
               
                   
                 DIHYDROXYACETONE 
               
               
                   
                 Dihydroxyphenylalanine 
               
               
                   
                 DIOXY-D-GLUCOSE 
               
               
                   
                 DIOXY-FLUORO-D-GLUCOSE 
               
               
                   
                 Dopamine 
               
               
                   
                 EMULSIN 
               
               
                   
                 ERYTHROSE 
               
               
                   
                 ETHANOL 
               
               
                   
                 ETHYL MERCAPTAN 
               
               
                   
                 FORMALDEHYDE 
               
               
                   
                 FORMIC ACID 
               
               
                   
                 FRUCTOSE 
               
               
                   
                 FURFURAL 
               
               
                   
                 FURFURYL ALCOHOL 
               
               
                   
                 GALACTONOLACTONE 
               
               
                   
                 GALACTOSE 
               
               
                   
                 GLUTAMIC ACID 
               
               
                   
                 GLUCONO-LACTONE 
               
               
                   
                 GLUCOPYRANOSE 
               
               
                   
                 GLUCORONIDASE 
               
               
                   
                 GLUCOSE 
               
               
                   
                 GLUCOSE-6-PHOSPHATE 
               
               
                   
                 GLUCOSIDASE 
               
               
                   
                 GLUTAMATE 
               
               
                   
                 GLUTAMATE PYRUVATE 
               
               
                   
                 TRANSAMINASE 
               
               
                   
                 GLYCERALDEHYDE 
               
               
                   
                 GLYCERIN 
               
               
                   
                 GLYCEROL 
               
               
                   
                 GLYCOLATE 
               
               
                   
                 GLYOXYLATE 
               
               
                   
                 HEXYLAMINE 
               
               
                   
                 HISTAMINE 
               
               
                   
                 HISTIDINE 
               
               
                   
                 HYDROGEN PEROXIDE 
               
               
                   
                 Hydroquinone 
               
               
                   
                 HYDROXYMETHYL 
               
               
                   
                 FURFURAL 
               
               
                   
                 HYDROXYPHENYLACETIC ACID 
               
               
                   
                 HYDROXYPHENYLLACTIC ACID 
               
               
                   
                 HYPOXANTHINE 
               
               
                   
                 HYDROXY ACIDS 
               
               
                   
                 INORGANIC PHOSPHORUS 
               
               
                   
                 ISOBUTYLAMINE 
               
               
                   
                 ISOPROPANOL 
               
               
                   
                 LACTASE 
               
               
                   
                 Lactate 
               
               
                   
                 LACTATE DEHYDROGENASE 
               
               
                   
                 Lactic Acid 
               
               
                   
                 LACTOSE 
               
               
                   
                 LEUCINE 
               
               
                   
                 LIPASE 
               
               
                   
                 LYSINE 
               
               
                   
                 LYSINE DECARBOXYLASE 
               
               
                   
                 MALTOSE 
               
               
                   
                 MANDALATE 
               
               
                   
                 MANNOSE 
               
               
                   
                 MANNONOLACTONE 
               
               
                   
                 MELIBIOSE 
               
               
                   
                 METHANOL 
               
               
                   
                 METHIONINE 
               
               
                   
                 METHYL SULFATE 
               
               
                   
                 METHYL-D-GLUCOSE 
               
               
                   
                 METHYL-L-AMINO ACIDS 
               
               
                   
                 METHYLCATECHOL 
               
               
                   
                 MOLYBDATE 
               
               
                   
                 MONOAMINE 
               
               
                   
                 MONOMETHYL SULFATE 
               
               
                   
                 N,N-diethyl-p-phenylenediamine 
               
               
                   
                 N,N-dimethyl-p-phenylenediamine 
               
               
                   
                 NAD 
               
               
                   
                 NADH 
               
               
                   
                 NADPH 
               
               
                   
                 NITROETHANE 
               
               
                   
                 OCTYLAMINE 
               
               
                   
                 OXALATE 
               
               
                   
                 OXALIC ACID 
               
               
                   
                 PECTIN 
               
               
                   
                 PECTIN ESTERASE 
               
               
                   
                 Phenol 
               
               
                   
                 Phenylalanine 
               
               
                   
                 Phenylenediamine 
               
               
                   
                 PHOSPHATE 
               
               
                   
                 PHOSPHATIDYL CHOLINE 
               
               
                   
                 POLYAMINE 
               
               
                   
                 PROLINE 
               
               
                   
                 PROPANOL 
               
               
                   
                 PROPYLAMINE 
               
               
                   
                 PURINE 
               
               
                   
                 PUTRESCIN 
               
               
                   
                 PYRIDOXAMINE PHOSPHATE 
               
               
                   
                 Pyrocatechol 
               
               
                   
                 Pyrogallol 
               
               
                   
                 PYRUVATE 
               
               
                   
                 PYRUVIC ACID 
               
               
                   
                 RAFFINOSE 
               
               
                   
                 SALICIN 
               
               
                   
                 SARCOSINE 
               
               
                   
                 SORBOSE 
               
               
                   
                 SPERMIDINE 
               
               
                   
                 SPERMINE 
               
               
                   
                 STARCH 
               
               
                   
                 SUCROSE 
               
               
                   
                 SULFITE 
               
               
                   
                 THIAMINE 
               
               
                   
                 TREHALOSE 
               
               
                   
                 TRYPTOPHAN 
               
               
                   
                 TUNGSTATE 
               
               
                   
                 TYRAMINE 
               
               
                   
                 Tyrosine 
               
               
                   
                 URIC ACID 
               
               
                   
                 VALINE 
               
               
                   
                 VERBASCOSE 
               
               
                   
                 VITAMIN B1 
               
               
                   
                 VITAMIN C 
               
               
                   
                 XANTHINE 
               
               
                   
                 XYLOPYRANOSE 
               
               
                   
                   
               
             
          
         
       
     
     Of course, any number of other analytes could be tested for as well. 
     The sensor layer is preferably applied to the molded part as follows: A ruthenium dye complex such as that sold under the trade designation #206229 by Sigma is dissolved in ethanol as a solvent. A poly-methyl-methyl-acrylate (PMMA) such as that sold under the trade designation #182230 by Aldrich Chemical is dissolved in acetone as a solvent to create a 10-15% solution of polymer by weight. The ruthenium dye solution is then mixed into the PMMA polymer solution to create a solution that can be dip coated using an automated dip coater onto the tip of the optical member to create a stable oxygen sensitive coating. 
     An enzyme in a near neutral pH buffer such as glucose oxidase (among the sources of glucose oxidase is Fluka) is mixed with cellulose in bead form such as those cellulose beads sold under the trade designation #C-7204 by Sigma that have been crushed to approximately one micron in diameter to create a thick slurry of enzyme, cellulose and buffer. This slurry is then dip coated onto the optical member tip in the same manner as the oxygen sensitive coating. 
     The optical member is then further dip-coated into a gluteraldehyde solution such as that sold under the trade designation #01201-5 by Polysciences to chemically crosslink the enzyme and cellulose with the gluteraldehyde. The sensor is then allowed to dry in air or a desiccator overnight for the gluteraldehyde to polymerize sufficiently. 
     A final coating is then applied to the outside of the sensor tip using a poly-methyl-methyl-acrylate, chemically modified to include an acrylic acid group, that creates a stable and hard surface which protects the other coatings and allows diffusion of glucose and oxygen into the sensor. It is perferred that the modified poly-methyl-methyl-acrylate be that sold under the trade designation #37691-4 by Aldrich Chemical. 
     The signal produced by the interaction with the optical member and the analyte(s) is then passed to an optical detector such as a spectrometer such as that sold under the trade designation 52000 by Ocean Optics and then after interpretation of the signal by a suitable algorithm the data can then be displayed. 
     Note that the micro-invasive method is of particular advantage for immediate access to a sufficient quantity of fluid for measurement, unlike absorbing systems that require delays until sufficient quantity can be collected. Moreover, the optical tip under twenty microns is capable of entering into the stratum corneum without destruction of the large areas of the stratum corneum such as that of ablative means. 
     The method described above can be used to access both chemicals that our inherently found in biological systems and is also conceived to detect chemicals that a subject has been exposed to in the environment. The micro-invasive measurement is of particular advantage since chemicals which have invaded just to the level of the epidermis are still detectable where immediate detoxifying means can be employed to arrest further biological damage. 
     It should also be appreciated that microprobe  301  may be used for continuous analyte monitoring as well as for discrete monitoring. In the continuous mode of operation, the microprobe is secured to the body of the person being monitored such that the distal end of the probe is disposed and remains in the interstitial fluid of the person. The concentration of the desired analyte, such as glucose, is then continually monitored and may be displayed as desired (either continuously or upon demand). 
     In view of the above it will be seen that the various objects and features of the present invention are achieved and other advantageous results obtained. The description of the invention contained herein is illustrative only and should not be taken in a limiting sense.