Abstract:
An optical biosensor has a first enclosure with a pathogen recognition surface, including a planar optical waveguide and grating located in the first enclosure. An aperture is in the first enclosure for insertion of sample to be investigated to a position in close proximity to the pathogen recognition surface. A laser in the first enclosure includes means for aligning and means for modulating the laser, the laser having its light output directed toward said grating. Detection means are located in the first enclosure and in optical communication with the pathogen recognition surface for detecting pathogens after interrogation by the laser light and outputting the detection. Electronic means is located in the first enclosure and receives the detection for processing the detection and outputting information on the detection, and an electrical power supply is located in the first enclosure for supplying power to the laser, the detection means and the electronic means.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to biosensors and more specifically to biosensors that are portable, are simple to use and operate, and cost much less than current biosensors available on the market. This invention was made with Government support under Contract No. W-7405-ENG-36 awarded by the U.S. Department of Energy. The Government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Biosensors are devices that detect chemical or biological species with high selectivity on the basis of molecular recognition. Biosensor technology has grown rapidly over the last several years, and incorporates technological improvements in a variety of disciplines, including biochemical methodologies (e.g., organic synthesis, molecular biology) and electronics. The potential market for application of biosensor technology is enormous and includes detection and diagnostics in the health care industry and environmental monitoring.  
         [0003]     Although biosensor systems are available for the detection of various bacteria, toxins, and viruses, the devices themselves can be difficult to operate, very expensive, and generally not portable. However, immunochromatographic assays can be taken in the field using test strips sometimes called “smart tickets.” These test strips, currently manufactured by Tetracore, Inc., currently located at 11 Firstfield Road, Suite C, Gaithersburg, Md. 20878, and Alexeter currently located in Chicago, Ill. area, and others, are relatively simple to use by placing a sample onto a test strip. If the sample has a sufficiently high concentration of a pathogen, the results can be observed by sight. However, if the pathogen concentration is lower, the results must be read by a relatively large instrument, usually at a base location. These assays are not very sensitive or accurate, as they suffer from problems with cross reactivity, resulting in a high rate of false positives.  
         [0004]     The operations required to use the conventional biosensor systems typically involve multiple steps that are very precise and intricate. For example, the biosensor operations may require washing the sample multiple times, followed by mixing several different reagents with the sample; all at precise times and in precise amounts. These processes provide opportunities for the introduction of errors and, thus, the biosensor results are prone to error. The processes also require time to complete and may take up to a few days to yield results. In some cases, for instance with Hantavirus infection, the time required for detection may be longer than the minimum time required to administer successful treatment. In fact, the diagnosis may arrive too late for any type of treatment to be effective.  
         [0005]     Currently, there are only a few small, hand-held biosensor systems available for field-testing, such as the previously described test strips. Often, test samples must be brought into the lab from the field or from a remote location. Not only does the transportation take time, which may be very limited, but also the process of transportation may contaminate the sample. Often, the sample itself may present a potential health hazard to those transporting it. In some cases, it may not be possible to transport the sample to a laboratory, such as during combat or in other emergency situations.  
         [0006]     Additionally, conventional biosensors systems often require highly trained personnel to operate them, although the above-described test strips are relatively simple to use, they suffer from certain problems. Only very highly skilled personnel are able to perform the chemical processes involved in preparing and analyzing the samples that are required to complete the testing using these systems. The amount of skill required limits the number of potential biosensor system operators. In emergencies, there may be fewer personnel available to operate the equipment and perform the testing. Therefore, the lack of trained personnel available to analyze the samples can become a bottleneck to rapid turnaround times when timely results are imperative.  
         [0007]     U.S. Pat. No. 6,136,611 entitled, “Assay Methods and Apparatus”, issued Oct. 24, 2000, to Saaski et al., describes an optical assay apparatus that includes a light source module and an optical sensing element coupled by an interrogation module. The light source module produces light having propagation angles ranging from a lower, non-zero limit. This is accomplished by including an obscuration that blocks low propagation angle light. The sensing element includes a reflector portion and a sensing fiber portion. The reflector portion receives, as incident light, the light produced by the light source module and produces, as reflected light, light having an approximately constant propagation angle, preferably just less than the critical angle of the sensing fiber. The sensing element also includes a lens position that collimates signal recovery light collected by the sensing fiber. The interrogation module includes a window containing a light source optical fiber that transmits light from the light source module to the sensing element. The light source fiber has an angled end with a reflective surface to form a right-angle reflector and is embedded within the window in a slot containing an opaque material for absorbing back-scattered light. The sensing fiber may be appropriately adapted for evanescent-wave or surface plasmon resonance sensing operations.  
         [0008]     Although the apparatus described in patent &#39;611 provides a method for detecting certain biological material, the apparatus itself has not been optimized to provide a simplistic method of operation. There are still several complex steps in the process that require an expert&#39;s attention in order to render accurate results. For example, the sample cell used in the testing process must be completely dehydrated after the insertion of the sample before testing may begin. There are also several reagents that must be added to the sample for processing. The apparatus described in patent &#39;611 also fails to provide a portable optical biosensor system that may be used in the field as well as in a lab. Finally, the components and materials used in the apparatus described in patent &#39;611 are bulky and expensive. Therefore, the system described in patent &#39;611 does not provide a simple to use, portable, and inexpensive method of testing for the presence of certain biological material in a sample.  
         [0009]     Therefore, it is an object of the present invention to provide an integrated optical biosensor apparatus that is simple to operate so that an individual who is not highly technically trained can produce accurate results in a timely manner.  
         [0010]     It is another object of this invention to provide an integrated optical biosensor apparatus that is smaller than conventional biosensor systems and that is sufficiently portable to operate in the field and point of care settings.  
         [0011]     It is yet another object of this invention to provide an integrated optical biosensor apparatus that is inexpensive to build, purchase, and maintain.  
       SUMMARY OF THE INVENTION  
       [0012]     In order to achieve the objects and purposes of the present invention, and in accordance with its objectives, an optical biosensor comprises a first enclosure with a pathogen recognition surface, including a planar optical waveguide and grating located in the first enclosure. An aperture is in the first enclosure for insertion of sample to be investigated to a position in close proximity to the pathogen recognition surface. A laser in the second enclosure includes means for aligning and means for modulating the laser, the laser having its light output directed toward said grating. Detection means are located in the second enclosure and in optical communication with the pathogen recognition surface for detecting pathogens after interrogation by the laser light and outputting the detection. Electronic means is located in the second enclosure and receives the detection for processing the detection and outputting information on the detection, and an electrical power supply is located in the second enclosure for supplying power to the laser, the detection means and the electronic means.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate an embodiment of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:  
         [0014]      FIG. 1A  is an isometric view of a hand-held, portable, integrated optical biosensor apparatus.  
         [0015]      FIG. 1B  is a top view of the hand-held, portable, integrated optical biosensor apparatus.  
         [0016]      FIG. 1C  is an isometric view of a sample cartridge that holds a sample cell for testing and a sample cartridge cover.  
         [0017]      FIG. 1D  is a bottom view of the sample cartridge and sample cartridge cover.  
         [0018]      FIG. 2  is a block diagram of the overall integrated optical biosensor system.  
         [0019]      FIG. 3  illustrates an example method of operation for the integrated optical biosensor system.  
         [0020]      FIG. 4A  is data measured using the IOBS sample cartridge and a commercial fiber optic spectrometer for detection. The spectral curves measured by the fiber optic spectrometer illustrate the relative changes in emission intensity of the 575-nm wavelength yellow fluorescent dye and the 625-nm wavelength red fluorescent dye in response to successive injections of 2.5 nM cholera toxin.  
         [0021]      FIG. 4B  shows IOBS apparatus  100  bandpass filter relationship to the spectra. IOBS apparatus  100  measures the filtered detector responses and does not measure the entire spectra. In this embodiment the use of filtered detectors was selected over a fiber optic spectrometer to provide for a reduction both in instrument size and cost.  
         [0022]      FIG. 4C  shows IOBS apparatus  100  bandpass filter relationship to the spectra. IOBS apparatus  100  measures the filtered detector responses and does not measure the entire spectra. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0023]     The present invention provides an apparatus for optically detecting the presence of various biological materials using simple and inexpensive components that yields accurate results quickly and with relatively little human intervention. The invention is most easily understood through reference to the drawings.  
         [0024]      FIG. 1A  shows an isometric view of an integrated optical biosensor (IOBS) apparatus  100 . IOBS apparatus  100  further includes an LCD display  110 , a keypad  115 , a serial RS-232 port  120  for communication with a PC (not shown), a battery low indicator  125 , a battery charging indicator  130 , a power switch  135 , a horizontal laser alignment wheel  140 , a vertical laser alignment wheel  145 , and a DC power plug  150 .  
         [0025]      FIG. 1B  shows a top view of IOBS apparatus  100  further including a sample cartridge port  155 , covered by a sample cartridge cover  175 .  
         [0026]      FIG. 1C  shows a top view of a sample cartridge  160 , further including an injection port  170 , sample cartridge cover  175 , and a viewing window  165 . In addition, sample cartridge  160  contains a fluid cell, optical waveguide transducers, a recognition surface, and sample waste reservoir.  
         [0027]     The recognition surface (described more specifically below) is deposited onto a planar optical waveguide, which is an optically transparent material that guides light along its length. The optical waveguide has a higher index of refraction than the recognition surface, and than the substrate onto which it is deposited.  
         [0028]      FIG. 1D  shows a bottom view of sample cartridge  160 , sample cartridge cover  175 , and viewing window  165 . LCD display  110  is a 4-line-by-20-character unit in this example. However, other suitable inexpensive LCD displays are commercially available that would perform adequately. LCD display  110  may also display information from keypad  115  inputs. LCD display  110  has a high-contrast, super-twist, yellow-green screen with a backlight for easy viewing. It may also be used in low light or dark environments, which may be useful in emergencies.  
         [0029]     Keypad  115  is a 3-by-4-character keypad containing a matrix keypad of 12 keys. Other types of keypads may be used without changing the spirit of the invention. User inputs to keypad  115  control certain functions of IOBS apparatus  100 . A menu-driven program allows the user to select various menu options using keypad  115 . For example, after power-up, the user may be asked to enter a number on keypad  115  corresponding to the task he or she wishes to perform, such as calibrating a sample cell, testing a sample, or storing data from a recent test.  
         [0030]     RS-232 port  120 , battery low indicator  125 , battery charging indicator  130 , power switch  135 , horizontal laser alignment wheel  140 , vertical laser alignment wheel  145 , DC power plug  150 , sample cartridge port  155 , viewing window  165 , injection port  170 , and sample cartridge cover  175  are functionally described with reference to  FIGS. 2 and 3 .  
         [0031]      FIG. 2  shows a block diagram of an IOBS system  200 . IOBS system  200  includes sample cartridge  160 , which further includes a recognition surface  205 , a sample containment area  208 , and a planar optical waveguide  210  (as described above). Recognition surface  205  is formed on the surface of planar optical waveguide  210 , and includes receptive material selected to interact with certain biological, biochemical or chemical substances contained within a sample to be analyzed. For example, the receptive material may be natural or man made antibodies, antigens or chemical ligands. In one embodiment, recognition surface  205  can have a membrane such as a phospholipid bilayer (an organic two-layered membrane) to create an artificial cell surface. For implementation using a recognition membrane Natural or Man-made receptors for a specific protein are attached to the artificial cell surface using synthetic anchors. This is more specifically described in U.S. patent application Ser. No. 10/104,158, filed Mar. 21, 2002, by Schmidt et al. for “Generic Membrane Anchoring System,” which is included herein for all purposes.  
         [0032]     Conjugated to each man-made receptor is one of two kinds of reporter dye molecules: a donor fluorophore or and acceptor fluorophore. The membrane based assay is more specifically described in U.S. Pat. No. 6,297,059, issued Oct. 2, 2001, for “Triggered Optical Biosensor,” which is included herein for all purposes. The membrane based assay using an optical waveguide as a transducer is more specifically described in U.S. patent application Ser. No. 09/598,882, filed Jun. 21, 2000, for “Optical Biosensor and Method for Detecting a Multivalent Target Molecule,” which is included herein for all purposes. However, other recognition surfaces with receptive materials (or assays) that also produce fluorescent changes upon the binding of a targeted pathogen could be used as well. For example the recognition surface  205  may be comprised of a self-assembled monolayer (SAM) having man-made or natural receptors attached to the SAM surface using flexible length linkers with reporter dyes attached close to the receptors.  
         [0033]     Planar optical waveguide  210  sits on a substrate  220  onto which diffraction grating  215  has been etched. A sample waste reservoir  225  is coupled to sample containment area  208 . A laser  230  shines a laser beam  235  through the substrate  220  onto the diffraction grating  215 . Laser  230  must be properly aligned via a laser alignment  240 , using horizontal laser alignment wheel  140 , and vertical laser alignment wheel  145 . In order to efficiently couple laser beam  235  into planar optical waveguide  210  the angle of laser beam  235  with respect to diffraction grating  215  must match the resonant angle for excitation to occur so a minor adjustment of laser  230  with respect to planar optical waveguide  210  may be required. In the future, mass manufacture of waveguides with tight tolerances for waveguide and grating manufacture will eliminate the need for these adjustments. A laser modulation  245  controls power to laser  230 . In one embodiment, laser  230  is an inexpensive, commercially available, 1-mW, 532-nm laser diode attenuated to 200 uW to reduce photo-bleaching of the reporter dyes and provide an eye-safe exposure/class IIIa laser. Other laser wavelengths may be used, and are determined by the excitation spectra of the fluorescent dyes selected. For example, 632-nm laser diodes may also be used with fluorescent dyes that can be excited by this wavelength. Laser  230  is also very low power and may be operated from a battery-sourced power supply.  
         [0034]     Detector PCB  250  includes a reference detector  255 , a 570-nm band pass filter  260   a  connected to silicon photodiode  260   b  that feeds to gated integrator/preamplifier  260 , and a 632.8-nm band pass filter  265   b  connected to silicon photodiode  265   b  that feeds to gated integrator/preamplifier  265 . Other bandpass filters may be used, and are selected according to the emission wavelength of the dyes selected for any particular application. The silicon photodiodes  260   b ,  265   b  may be a Hamamatsu S1227-16BR silicon photodiode, for example; however, the invention is not limited to that specific part, and one skilled in the art may substitute a similarly functioning device that is optimized for sensitivity in the visible range.  
         [0035]     The information gathered by 632.8-nm gated integrator/preamplifier  265 , 570-nm gated integrator/preamplifier  260 , and reference detector  255  is delivered via signal wires to a system electronics PCB  270 . System electronics PCB  270  includes a microprocessor  275 , a power distribution and battery control  280 , and front-end electronics  285 . Front-end electronics  285  includes circuitry to receive analog light-intensity measurement information from detector PCB  250  and to amplify, filter, and convert the signals to a multi-bit, digital form that may then be processed by microprocessor  275 .  
         [0036]     Microprocessor  275  includes software to facilitate the functions of IOBS system  200 . Having an internal controller saves space, allows the system to be portable, eliminates many compatibility and timing issues associated with external processing, and saves design time. Microprocessor  275  includes a CPU, memory, oscillator, watchdog timer, USART, and I/O interfaces incorporated within a single integrated circuit chip. In one embodiment, microprocessor  275  is a microcontroller, for example, a PIC 18C452. However, the invention is not limited to the use of a specific type of processor, and any suitable processing device may be used. For this example, microprocessor  275  has RAM available for variable storage and ROM for program storage. Microprocessor  275  controls all functions of IOBS apparatus  100  and is integrated with other hardware devices including, but not limited to, LCD display  110 , keypad  115 , and RS-232 port  120 . Microprocessor  275  communicates serially with LCD display  110  using an RS-232 protocol.  
         [0037]     In addition to inputs from keypad  115 , IOBS apparatus  100  may also be coupled to PC software  295  via RS-232 port  120 . The associated PC software  295  allows a user to implement all available functions without using keypad  115 . This provides the user with a friendly PC GUI in a virtual push button fashion.  
         [0038]     Therefore, IOBS apparatus  100  may be operated using keypad  115  and LCD display  120  on the front panel, or it may be operated using a serial interface to a PC running, for example, LABVIEW®  295  software. VISUAL BASIC® among other programs could also be used. (LABVIEW® is a software system that can be used). In addition to providing a GUI, computer interface  295  also provides the means for downloading all data that has been stored within the non-volatile memory of microprocessor  275 . The data may then be processed using other traditional PC software applications.  
         [0039]     Power distribution and battery control  280  functions to regulate the power supply to IOBS system  200 . Since IOBS system  200  is designed to be portable, it is powered by an internal battery  290 , such as a lithium-ion battery, when AC power is not available. Battery  290  provides stand-alone operation for up to six hours. An external AC/DC power supply plugged into DC power plug  150  may also be used at any time. A standard, commercially available 15-volt, 28-watt AC-to-DC converter (not shown) is used to provide DC power supply operation and recharge internal battery  290 . Internal circuitry in power distribution and battery control  280  detects the presence of DC power plug  150  and automatically switches from battery power. Power distribution and battery control  280  charges internal battery  290  when DC power plug  150  is being used. Battery low indicator  125  illuminates when internal battery  290  is low. Battery charging indicator  130  is lit when internal battery  290  is charging. Battery charging indicator  130  turns off when internal battery  290  is fully charged.  
         [0040]     The following method describes an example method of operation using IOBS apparatus  100 : 
         FIG. 3  is a method  300  of operating IOBS apparatus  100  for a cholera toxin test sample. 
 
 Step  305 : Inserting Clean Sample Cartridge 
       
 
         [0042]     In this step, the operator inserts clean (i.e., not previously used for testing purposes) sample cartridge  160  into sample cartridge port  155  of IOBS apparatus  100 . Method  300  proceeds to step  310 .  
         [0000]     Step  310 : Aligning Laser  
         [0043]     In this step, the user looks through viewing window  165  to ensure that laser beam  235  is properly aligned with diffraction grating  210  Using horizontal laser alignment wheel  140  and vertical laser alignment wheel  145 , the user aligns laser  230  to the correct position indicated. To align the laser two methods may be used: (1) the user opens viewing window  165  and adjusts laser alignment wheels  140  and/or  145  to produce a streak of laser light parallel with the long dimension of viewing window  165 . Laser alignment wheels  140  and/or  145  are adjusted until a maximum intensity is observed. (2) The user observes a numerical readout obtained from digitized signal intensity of reference detector  255  converted in microprocessor  275  to a numerical readout on the LCD display and adjusts laser alignment wheels  140  and/or  145  until a maximum value is obtained. Method  300  proceeds to step  315 .  
         [0000]     Step  315 : Calibrating Sample Cartridge  
         [0044]     In this step, the user selects “calibrate cell” either from the menu list on keypad  115  or from the GUI interface on a connected PC via computer interface  295 . Each new sample cartridge  160  must be calibrated before an accurate test may be performed. Laser beam  235 , now properly aligned, is coupled into planar optical waveguide  210  via diffraction grating  215  exciting recognition surface  205 . Recognition surface  205  contains optically tagged receptors that are deposited on planar optical waveguide  210 . The optical detection electronics on detector PCB  250  begin taking emission intensity readings from sample containment area  208 . This provides a control basis for comparison of the fluorescence emission of the 575-nm and 625-nm dyes before and after the sample has been injected.  
         [0045]     At present, the system operator is responsible for ensuring that a calibration step is performed for each new sample cartridge  160  inserted. However, automated methods of ensuring proper calibration of new sample cartridges  160  include a simple pressure switch that is installed into sample cartridge port  155  that sends a signal to microprocessor  275  when the sensor detects the removal of a sample cartridge  160  followed by the insertion of a new sample cartridge  160 . This would indicate to system software that a calibration must be completed before testing may commence. Method  300  proceeds to step  320 .  
         [0000]     Step  320 : Injecting Sample  
         [0046]     Once laser  230  and sample cartridge  160  have been calibrated, IOBS apparatus  100  is ready to test the sample. The sample is injected into sample containment area  208  via injection port  170 , forcing buffer fluid (not shown) in sample containment area  208  to be injected into sample waste reservoir  225 . The buffer fluid is there to protect recognition surface  205  until such a time as a sample is injected. Sample waste reservoir  225  is a containment area that ensures that no hazardous materials leave hermetically sealed sample cartridge  160 . Method  300  then proceeds to step  325 .  
         [0000]     Step  325 : Starting Test  
         [0047]     In this step, the user depresses the key on keypad  115  corresponding to “start test,” or the user may select a “begin test” button on LabView computer interface  295 . Current methods involve the user injecting the sample then depressing the correct keys on keypad  115  or LabView computer interface  295  to begin testing. Automated methods to determine sample injection include the use of a plunger device attached to sample waste reservoir  225  such that as sample waste reservoir  225  fills with buffer solution during injection when the plunger is displaced. Once sample waste reservoir  225  fills completely, the plunger is in a position to trigger either a position sensor or a pressure sensor that, in turn, marks time zero in microprocessor  275 . Method  300  proceeds to step  330 .  
         [0000]     Step  330 : Measuring Light Emissions Data  
         [0048]     In this step, the filter electronics on detector PCB  250  begin taking emission intensity readings from sample containment area  208 . Recognition surface  205  contains optically tagged receptors that are deposited on planar optical waveguide  210 . Once recognition surface  205  has received the sample, laser beam  235  is coupled into optical planar waveguide  210 , exciting recognition surface  205 . In one embodiment, the binding of the targeted toxin to multiple receptors that are labeled with reporter dyes triggers fluorescent resonant energy transfer (FRET) to provide a change in fluorescence emission in the 575-nm and 625-nm dyes. The reduced emission in the 575-nm dye and the increased emission in the 625-nm dye is a measure of the concentration of bound toxin in recognition surface  205 . Method  300  proceeds to step  335 .  
         [0000]     Step  335 : Is Test Complete? 
         [0049]     In this decision step, Method  300  checks to see if the test is complete. If yes, the test stops automatically and method  300  proceeds to step  340 ; if no, method  300  returns to step  330 .  
         [0000]     Step  340 : Analyzing Results  
         [0050]     In this step, IOBS apparatus  100  indicates the presence or absence of the target. If the target is detected, IOBS apparatus  100  indicates a concentration level. The IOBS detection algorithms in microprocessor  275  measure the change in relative intensities of fluorescence emission over time and determine the concentration of toxin based on the fluorescence change. It is understood that, although this embodiment uses the specific wavelengths of light mentioned herein, it is possible to design alternate embodiments of the IOBS that would use alternate reporter dyes requiring laser excitation of a different wavelength, that, in turn, would result in fluorescence emissions of different wavelengths. Method  300  proceeds to step  345 .  
         [0000]     Step  345 : Disposing of Used Cartridge  
         [0051]     In this step, the user ejects sample cartridge  160  and disposes of it in a medical waste receptacle. Method  300  is therefore ended.  
         [0052]      FIG. 4A  and  FIG. 4B  are graphs that further explain the emission comparisons. The graphs depict the results of a typical cholera toxin detection test using IOBS apparatus  100 . The graphs are different representations of the measured fluorescence output of the sample cell in response to successive injections of 2.5 nM solutions of cholera toxin.  
         [0053]      FIG. 4A  is data measured using the IOBS sensor cartridge and a commercial fiber optic spectrometer depicting the relative changes in intensity of the evanescence of the 575-nm wavelength yellow fluorescent dye and the 625-nm wavelength red fluorescent dye. The relative intensity of the 575-nm wavelength decreases with successive injections of 2.5 nM cholera toxin while the relative intensity of the 625-nm wavelength increases, showing the presence of cholera toxin in the sample.  
         [0054]      FIG. 4B  shows IOBS apparatus  100  bandpass filter relationship to the spectra. IOBS apparatus  100  measures the filtered detector responses and does not measure the entire spectra. In this embodiment the use of filtered detectors was selected over a fiber optic spectrometer to provide for a reduction both in instrument size and cost.  
         [0055]      FIG. 4C  is a graph of the ratio of yellow wavelength intensity to red wavelength intensity as measured by the IOBS instrument resulting from successive injections of 2.5 nM solutions of cholera toxin.  
         [0056]     In summary, the present invention provides a hand-held, portable, battery-operated, simple, and inexpensive device and method for detecting the presence of toxins, in this case a cholera toxin, in a timely manner. The detection of cholera takes approximately five minutes using IOBS apparatus  100 . In emergency situations, this timesaving may be extremely important. It is also important to note that no added reagents, washing, mixing, agitating, or any other type of chemical processing was necessary to complete the test. A user inserts a clean sample cartridge  160  into IOBS apparatus  100 . Sample cartridge  160  is then calibrated and the sample is injected via injection port  170 .  
         [0057]     The test begins at the press of a button and completes in fewer than ten minutes. The user simply disposes of the used cartridge in a medical waste receptacle. No other processing or waiting is required and the results are very accurate, since there has been little opportunity for the introduction of errors. The tests may be completed in the field or in other uncontrolled environments. When battery power begins to diminish, battery low indicator  125  notifies the user. DC power may be used instead of battery power. Battery  290  is recharged automatically using DC power plug  150  for ease of maintenance and to ensure future operation of IOBS apparatus  100 .  
         [0058]     The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.