HK1066597A - Multiwavelength readhead for use in the determination of analytes in body fluids - Google Patents

Description

Multi-wavelength read head for analyte determination in body fluids

Technical Field

The present invention relates generally to test systems for determining the concentration of an analyte in a biological sample, and more particularly, to an optical read head for determining the concentration of an analyte in a biological sample.

Background

It is often necessary to rapidly obtain a blood sample and perform an analysis of the blood sample. One example of the need to obtain a blood sample is associated with a blood glucose monitoring system that must be frequently used by a user to monitor the user's blood glucose level.

Those with irregular blood glucose levels are medically required to self-monitor their blood glucose levels on a regular basis. Irregularities in blood glucose levels can be caused by a variety of causes including disease, such as diabetes. The purpose of monitoring blood glucose concentration levels is to determine the blood glucose concentration level and then take corrective action based on whether its level is too high or too low to bring the level back within a normal range. There are serious implications of not performing a corrective action. When blood glucose levels fall too low-a condition known as hypoglycemia-a person becomes nervous, frail and distressing. The person's judgment is impaired and eventually falls over. People also become seriously ill when blood glucose levels are too high, a condition known as hyperglycemia. Both conditions, hypoglycemia and hyperglycemia, are potentially life-threatening acute diseases.

One method of monitoring a person's blood glucose level is to carry a portable handheld blood glucose testing device. The portable nature of these devices allows users to conveniently test their blood glucose levels wherever they may be. Typically, these devices utilize either electrochemical or colorimetric tests. In electrochemical analysis, the reagent is designed to react with glucose in the blood to generate an oxidation current on an electrode disposed in a reaction region. The current is directly proportional to the glucose concentration in the blood of the user. In a colorimetric assay, the reagents are designed to produce a colorimetric response indicative of the blood glucose concentration level of the user. The colorimetric reaction is then read by an optical instrument integrated into the test device.

Disadvantages associated with optical instruments for reading colorimetric reactions include size, low signal throughput, and accuracy errors caused in part by the mechanical alignment (or misalignment) sensitivity of the optical elements. These problems are further compounded when the optical instrument needs to read at more than one wavelength. Providing multiple wavelengths mixes these problems because prior art devices produce light at each wavelength with different light emitting elements, such as light emitting diodes. It is difficult and expensive to align multiple leds to provide identical illumination to the sample area. Misalignment and source geometry variations result in light from each led having a different radiance and a different radiance distribution as it passes through the sample. What is needed, therefore, is an apparatus that can illuminate a sample with light of multiple wavelengths, wherein each beam having a different wavelength has substantially uniform radiance and radiance distribution across the sample.

Disclosure of Invention

A readhead for use in determining the concentration of an analyte in a sample includes a reading area for receiving a sample, a light source including a plurality of light emitting elements for outputting light at a plurality of wavelengths, a light guide having an input end and an output end, a lens for receiving light from the output end of the light guide and illuminating the sample with a substantially parallel beam of light, and a detector for detecting light from the sample in response to illuminating the sample. The input end of the light pipe is optically connected with the light source and is used for receiving the light output by the plurality of light-emitting elements. The input end of the light pipe has a center that is offset from a center of at least one of the plurality of light emitting elements. The light pipe directs a substantial portion of the light received from the light source to an output end of the light pipe.

The above summary of the present invention is not intended to describe each embodiment, or every aspect, of the present invention. Additional features and advantages of the invention will be apparent from the detailed description set forth below, the drawings, and the claims.

Brief Description of Drawings

FIG. 1 is a functional block diagram of a multi-wavelength transmittance readhead according to one embodiment of this invention.

FIG. 2 is an alternative embodiment of the readhead shown in FIG. 1.

FIG. 3a is another alternative embodiment of the readhead shown in FIG. 1.

FIG. 3b is another alternative embodiment of the readhead shown in FIG. 1.

FIGS. 4 and 5 are graphs of light modeled illumination intensity profiles of the light source output of the readhead shown in FIG. 1 with and without the light pipe, respectively.

Fig. 6a, 6b and 6c are simulated intensity distribution scatter plots of the light beams output from the sample aperture of the readhead of fig. 1, detected at distances of 2, 5 and 10 mm from the sample aperture, respectively, where the light guide of the readhead has a circular cross-section.

Figures 7a, 7b and 7c are simulated intensity distribution scatter plots of the light beams output from the sample aperture of the readhead of figure 1, detected at distances of 2, 5 and 10 mm from the sample aperture, respectively, in which the light guide of the readhead has a square cross-section.

FIG. 8 is a functional block diagram of a multi-wavelength reflectivity readhead according to an alternative embodiment of this invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Detailed description of illustrative embodiments

Turning now to the drawings and first to FIG. 1, a multi-wavelength readhead 10 according to one embodiment of this invention is shown. In use, the readhead 10 is included in a portable hand-held glucose testing device for measuring the glucose concentration in a body fluid of a patient (also a user in a self-test application). In particular, the readhead 10 is used to measure a colorimetric reaction when a reagent reacts with an analyte. The readhead 10 of the present invention is used to measure the extent of reagent colour change caused by the reaction. The degree of reagent color change is indicative of the concentration of an analyte (e.g., glucose, fructosamine, hemoglobin Alc, cholesterol, etc.) in the body fluid. Colorimetric tests are described in detail in U.S. Pat. No. 5,5723284, entitled "control solution and method for the Performance of an electrochemical device for determining the concentration of an analyte in blood", which is incorporated herein by reference in its entirety. Colorimetric tests are also described in detail in U.S. Pat. Nos. 6181417B1 (entitled "photometric reading head with light conditioning disk"), 5518689 (entitled "light diffuse reflectance reading head"), and 5611999 (entitled "light diffuse reflectance reading head"), each of which is incorporated herein by reference in its entirety.

According to one embodiment of the present invention, the readhead 10 includes a light source that includes a surface mounted light emitting diode 12 ("SMD LED"). The SMDLED12 is mounted on a printed circuit board 14 ("PCB") which may include electronic circuitry for operating a device incorporating the readhead 10 of the present invention. The SMDLED12 is a multi-wavelength SMDLED that outputs light of a plurality of wavelengths, for example, red, green, and blue. According to one embodiment, a surface mount device includes a red LED for outputting red light having a wavelength in the range of about 600nm to about 670nm, a green LED for outputting green light having a wavelength in the range of about 520nm to about 580nm, and a blue LED for outputting blue light having a wavelength in the range of about 360nm to about 450 nm. According to another embodiment, red light has a wavelength of about 625nm, green light has a wavelength of about 565nm and blue light has a wavelength of about 430 nm. According to yet another alternative embodiment of the invention, the surface mount device includes an infrared LED for outputting infrared light having a wavelength in a range of about 800nm to about 1000 nm. An SMD LED suitable for use with the readhead 10 is available from Kingbright Corporation of City of Industry, Calif., model AAA3528 EMBBSGC. According to another embodiment, the light source may include other types of light sources besides LEDs, for example, a composite packaged LED, a chip on composite interposer, or a laser diode may be used as the light source for outputting light at multiple wavelengths.

The light at multiple wavelengths output by the SMD LED12 illuminates the sample as will be described in further detail below. Because the intermediate wavelength can be used to correct for errors in the specific wavelength used to evaluate the sample, instrument performance is improved by illuminating the sample with light at multiple wavelengths. For example, when the sample is blood, the particular wavelength of light is absorbed to a greater extent by naturally occurring chromophores (e.g., hemoglobin) in the range of about 400nm to about 600nm (and other ranges). The accuracy of colorimetric measurements is limited by the absorption caused by unknown levels of interfering absorbants. For example, the hematocrit content of blood is known to vary over a wide range from sample to sample and from subject to subject. If a pure interstitial fluid sample is obtained, the hematocrit content reaches zero. The strong absorption of hemoglobin in hematocrit results in a generally variable "background" absorption that cannot be distinguished from the altered absorption of the associated colorimetric reagents. However, appropriate selection of the auxiliary wavelength may be used to compensate for the measurement at the relevant wavelength, for example by the ratio of the absorption values at the two wavelengths. In addition, multiple auxiliary wavelengths may be used to compensate for other phenomena that interfere with absorption measurements, such as mechanical eccentricity, scattering changes from the sample, and scattering changes from the scattering film in diffuse reflectance measurements.

The SMD LED12 inputs light into a light pipe 16 to direct the light to the sample. According to one embodiment of the invention, the molding is made of an optically transparent material, such as polyacrylic acid. In other embodiments, light pipe 16 is molded from other optically transparent materials, such as polycarbonate, or polyester. The light emitted by the SMD LED12 is reflected from the SMD LED12 off a white conical reflector 13 in the SMD LED 12. Light is guided along the light guide 16 by total internal reflection. The light pipe 16 advantageously delivers a large amount of light at its output end 18 that is input into the light pipe 16 by the SMD LED 12. According to one embodiment of the invention, light pipe 16 has a square cross-section with an area of about 2.3mm by 2.3mm, and a length of about 5 cm. According to one embodiment of the invention, the conical reflector 13 of the SMD LED12 has a diameter of about 2.4 mm. The close coupling of the SMD LED12 and the light pipe 16 results in 92% of the light output by the SMD LED12 being captured by the light pipe 16.

The light guide 16 depicted in fig. 3a and 3b is curved to illustrate that the light guide 16 may be molded as follows: which has one or more turns of about 90 degrees without significant attenuation of the intensity of the transmitted light and without significant interruption in the illumination distribution of the transmitted light. This characteristic of light pipe 16 allows light source 12 and the illuminated sample to be placed along a non-linear illumination path. In alternative embodiments, light pipe 16 is positioned along a non-linear path having any angle other than a right angle.

The light pipe 16 transmits light from the SMD LED12 to a calibration optic disposed on an output end 18 of the polyacrylic light pipe 16. The collimating optics include a body having a collimating aperture 20, and a collimating lens 22 that outputs a substantially parallel beam of light. The substantially parallel beam is directed through a sample aperture 24 disposed in the other body to reduce the diameter of the parallel beam-this narrow substantially parallel beam is marked with reference numeral 26. A collimating lens 22 suitable for use with the readhead 10 of the embodiment shown in FIG. 1 is available from Edmundandriral Optics of Barrington, N.J., No. NT45-117, and is a glass plano-convex lens having a focal length of 3 mm.

The parallel light beam 26 exiting the sample aperture 24 is directed onto a biological sample (e.g., blood, intracellular material, extracellular fluid, interstitial fluid, combinations thereof, and the like) disposed in a read zone 30 of a sample space (format) 32. The biological sample includes an analyte that reacts with a reagent also disposed in the read zone. (reagents are placed in the read zone 30 prior to each use). According to one embodiment of the invention, the sample space 32 collects a sample from a patient. For example, a fingertip of a patient is pierced and a drop of blood is taken on the fingertip of the patient. The space 32 is brought into contact with a drop of blood and blood is collected by a capillary channel (not shown), e.g., by drawing blood to the reading zone 30 of the space 32 where an analyte in the blood (e.g., glucose) reacts with a reagent disposed in the reading zone 30 of the space 32. Alternatively, the biological sample is placed directly in the read zone 30 by a separate collection device.

Alternatively, a biological sample (e.g., blood) containing an analyte (e.g., glucose) can also be harvested using a test strip having a reagent disposed therein. The blood moves to the test sensor and the analyte reacts with the reagent to produce a colorimetric reaction. Test sensors are inserted into the read zone 30 of the read head 10 for analysis. In the embodiment of the readhead 10 shown in FIG. 1, in which light transmitted through a sample is measured, at least a portion of the structure of the test sensor in which the colorimetric reaction occurs is constructed of a substantially optically transparent material. In the embodiment of the readhead 100 shown in FIG. 8, where light reflected from the sample is measured as discussed below, the rear side of the test sensor where the colorimetric reaction occurs should be constructed of a diffusely reflective material, while the front side of the test strip should be constructed of a substantially optically transparent material. Such a configuration allows light to illuminate the sample and reflect from the sample.

Referring back to FIG. 1, the substantially parallel light beam 26 directed onto the sample at the spatially disposed read zone 30 is transmitted through the sample and through the read zone 30 to the detector 34. The transmitted light signature is referenced 36. Because light is transmitted through the space, the space 32 is constructed of an optically transparent material such that the space 32 does not significantly alter or attenuate the transmitted light 36. The space 32 may be molded from an optically transparent material, such as polyacrylic, polycarbonate, or polyester.

Light 36 transmitted through the sample is received by a detector 34, which outputs a signal indicative of the received light. A CMOS monolithic detector/amplifier from Texas advanced optoelectronic Solutions, inc., model TAOS TSL250R is suitable for use as the detector 34 according to one embodiment of the present invention. Signals indicative of the received light are output by detector 34 onto leads (not shown) electrically connected to the electronics of the device housing readhead 10.

The signal output by the detector is compared with a reference signal stored in a memory (not shown) of the device housing the readhead 10. The reference signal is obtained by illuminating the reading zone 30 before placing the sample in the reading zone 30. The reference signal is then compared to the signal obtained from the light transmitted through the sample. The difference in light absorption between the two is used to determine the concentration of a particular analyte in the sample to be assessed.

According to one embodiment of the invention, the readhead 10 has a structure of the following dimensions: a light pipe 16, constructed of polyacrylic acid, having a square cross-section of about 2.3mm by 2.3mm and a length of about 5 cm; the collimating aperture 24 has a diameter of about 0.76 mm; the sample aperture 24 has a diameter of about 0.5mm resulting in a beam of about 0.75mm diameter for illuminating the read zone 30, the read zone 30 being located about 2mm from the sample aperture 24. The dimensions of the readhead 10 may vary according to alternative embodiments of this invention, and a description of specific dimensions is provided by way of example. The elements may be accordingly graded to provide more LED wavelengths and/or beam shapes and sizes in various alternative embodiments according to the invention.

Referring now to FIG. 2, in accordance with an alternative embodiment of the readhead 10, the detector 34 and other electronics of the device containing the readhead 10 are located on a PCB 14. As the transmitted light is output from the space 32, the light holes 37 receive the transmitted light 36 and input the light into optical fibers 38, which duct the transmitted light into detectors 34 mounted on the PCB 14. An optical fiber 38 suitable for use with the readhead 10 of the embodiment shown in FIG. 2 is available from Edmund Idustial Optics of Barrington, N.J., under the number NT 02-535. This embodiment provides the advantage of having the electronics placed on the same PCB14 and in the same location in the device.

Referring now to FIG. 3a, yet another alternative embodiment of the readhead 10 is shown. As discussed in an alternative embodiment in relation to fig. 2, the embodiment shown in fig. 3a includes the smd led12 and the detector 34 both mounted on the PCB 14. However, in the embodiment of the readhead 10 shown in FIG. 3a, the light pipe 16 is bent or deformed to transmit light from the SMD LEDs 12 (disposed on the PCB 14) to the detector 34 (also disposed on the PCB 14). An advantage of the embodiment of the readhead 10 shown in fig. 3 is that it is constructed from a reduced number of components, for example, eliminating the wires (not shown) from the detector 34 to the PCB14 associated with fig. 1, or the optical fiber 38 associated with fig. 2. Having the non-linear light pipe of fig. 3 is useful in applications where a linear light pipe is not allowed due to space constraints.

Referring now to FIG. 3b, yet another alternative embodiment of the readhead 10 is shown. The readhead of figure 3b is similar to that of figure 1. However, the light pipe 16 in the embodiment of fig. 3b includes two substantially 90 degree turns along its path between the SMD LED12 and the output end 18 of the light pipe 16.

The read head 10 provides the advantage that it supplies an increased light flux from the light source to the read zone 30. Flux is throughThe intimate coupling between the backlight (e.g., SMD LED 12) and the light pipe 16 is enhanced. Uniform illumination at the output end 18 of the light pipe 16 also increases the light level at the collimating aperture 20. Good signal levels are maintained by the collimating optics, using micro-optics to substantially collimate the light. According to one embodiment, the substantially parallel sample beam 26 is reduced to about 0.75mm in diameter over a sample of about 1mm in diameter without reducing the signal to an unacceptable level. Lighttools using an emulated readhead 10^Signal flux evaluation of the software model predicted a current of about 384nA at a wavelength of about 680nm at the detector.

Mechanical alignment variations of the optical elements can cause problems with transmission accuracy. Sample beam diameter, divergence, intensity distribution and sample position can all contribute to accuracy errors. These problems are particularly prevalent when transmittance readings at two or three wavelengths are required. The readhead 10 of the present invention reduces these types of errors. In particular, the square shaped light pipe 16 reduces beam geometry and intensity variations associated with multi-wavelength light output by the plurality of LEDs using the SMD LEDs 12. LED dies of the SMD LED12 that do not output light on the common axis can cause an uneven intensity distribution output of the SMD LED 12. One or more of the LED dies of the SMD LEDs 12 will be offset from the center of the input end of the light pipe 16. However, due to its low cost and ability to output multi-wavelength light, an SMD LED12 with multiple dies is desirable. The inventors have found that a polyacrylic light pipe 16 having a square cross-section produces a uniform illumination distribution at the output end 18 of the light pipe 16 for each wavelength, despite the LED die of the SMD LEDs 12 being offset from the center of the light pipe 16. In addition, this arrangement results in substantially the same beam diameter, divergence and collimation regardless of the wavelength of the light output by the SMD LEDs 12.

Referring now to FIGS. 4 and 5, the readhead 10 of FIG. 1 utilizes LightTools on a computer^And (4) simulating a software model. The graph shows the intensity of illumination across the front of the detector 34 along its X-axis and Y-axis that requires the light pipe 16 (fig. 5) and does not require the light pipe 16 (fig. 4). The LED dies in the SMD LEDs 12 are modeled as slave SMD LED12 groupsIs offset by about 0.43mm (to illustrate three LED dies in an SMD LED, each offset by about 0.43mm from the center in the SMD LED group). FIG. 4 shows that when light pipe 16 is removed, the illumination distribution along the Y-axis of detector 34 is relatively non-uniform and includes "hot spots" (i.e., regions of relatively high intensity). Along the X-axis of the detector, the intensity distribution is somewhat uniform, however, the intensity is lower due to the absence of the light pipe 16.

As can be seen in fig. 5, the addition of light pipe 16 results in a significant increase in illumination distribution and intensity across the front of detector 34, at least in part due to the continuous sidewall reflection within light pipe 16. The inventors have found that at least 5cm has a thickness of about 2.3mm²The cross-section of the light pipe significantly increases the amount of internal reflection at the sidewalls to produce uniform illumination at the output end 18 of the light pipe 16.

The inventors have also found that light pipes with a square cross-section give better results than light pipes with a round cross-section. Referring now to fig. 6 and 7, intensity profiles for the read head 19 (fig. 1) are shown. However, the readhead 10 used in connection with FIG. 6 provides a light pipe 16 having a circular cross-section (about 2.3mm in diameter), whereas the readhead 10 used in connection with FIG. 7 employs a light pipe 16 having a square cross-section (about 2.3mm by 2.3 mm). Fig. 6 and 7 each include three intensity profiles associated with three different detectors positioned at 2, 5 and 10 millimeters from the sample pupil 24. A round light pipe (fig. 6) produces a non-uniform intensity distribution on each of the three detectors, with a different distribution on each detector. A square light pipe (fig. 7) produces a substantially uniform intensity distribution on each of the three detectors. Irradiance of the circular light guide is about 4.9 mu W/cm²Irradiance of a square light pipe of about 6.8 μ W/cm². Thus, the square light pipe 16 results in a greater amount of light being transmitted to the sample and a more uniform illumination distribution regardless of the distance between the sample aperture and the detector.

Referring to FIG. 8, a multi-wavelength diffuse reflectance readhead ("reflectance readhead") 100 according to an alternative embodiment of this invention is shown. Like the multi-wavelength transmittance readhead 10 shown in FIGS. 1-3, the reflectance readhead 100 includes an SMD LED12 mounted on a PCB14 for inputting multi-wavelength light to a light pipe 16. The light is guided by total internal reflection along the light guide 16 to the collimating optics, which comprise a collimating aperture 20 and a collimating lens 22 that outputs a substantially parallel light beam 26 to the sample space 102. Light 26 illuminates a sample placed in read zone 108 of sample space 102. The sample space 102, or at least the read zone 108 of the space, is made of a diffusely reflecting film, such as paper or polystyrene film. According to one embodiment of the present invention, the light pipe 16 of the reflectivity readhead 100 has a square cross-section similar to that described in connection with the transmissivity readhead 10 of FIG. 1.

Light 26 scatters away from the sample, and this scattered light is designated as reference number 110. Scattered light 110 includes light reflected from the surface of the sample, light reflected from the interior of the sample, and light reflected off of sample reading zone 108 of space 102. Some of the scattered light 110 is collected by an optical fiber 114 that channels the collected scattered light back to the detector 34. According to one embodiment of the invention, the optical fiber 114 has a numerical aperture of about 0.51, which translates into an observable region defined as an acceptance cone of approximately 30 degrees for observing a sample of about 1 mm. The scattered light 110 that falls into the acceptance cone of the fiber 114 is transmitted back through the conduit to the detector 34.

Mechanical alignment variations of the optical elements cause problems with diffuse reflection accuracy. Further, sample beam diameter, divergence, intensity distribution and position all affect the error. These types of errors and problems are factors that directly affect the accuracy of the reflectivity-based system. Several elements of the reflectivity read head 100 contribute to reducing these types of errors. A light pipe 16 with a square cross-section reduces the geometrical variation of the light beam. The SMD LED12 outputs a non-uniform intensity distribution, which is leveled by the light pipe 16, resulting in a substantially uniform beam diameter, divergence and collimation for each wavelength across the sample, regardless of the LED die location in the SMD LED 12. Light pipe 16 allows for continuous sidewall reflection within light pipe 16 which results in a substantially uniform irradiance distribution.

The use of diffuse reflectance is also sensitive to accuracy problems caused by the high sensitivity of the sample. Sample height sensitivity refers to the amount of reflectivity change caused by the read position or height of sample space 102. For example, the sample position varies between the sample and the meter, and each position causes a change in reflectivity corresponding to the nominal sample position, resulting in accuracy errors. Reduced sample height sensitivity performance is achieved by illuminating the sample in the reading zone 108 with collimated light 26. The collimated light produces less variation in the illumination read zone 108 as the sample moves toward and away from the nominal read height. Similarly, the sample tilt sensitivity is also reduced by illuminating the sample with collimated light 26. Sample tilt refers to the orientation of the sample within the read zone 108. For example, the sample at the read zone 108 may not remain perpendicular to the beam 26, and variations in tilt may cause performance problems. Furthermore, as discussed above, the close coupling of the light pipe 16 and the smd led12 allows the light pipe 16 to collect a large portion (about 92%) of the light output by the smd led 12.

While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Claims (67)

1. A readhead for determining an analyte concentration in a sample, comprising:

a reading zone for receiving a sample;

a plurality of light emitting elements for outputting light at a plurality of wavelengths;

a light pipe having an input end and an output end, the input end optically connected with the plurality of light-emitting elements to receive light output by the plurality of light-emitting elements, the input end having a center offset from a center of at least one of the plurality of light-emitting elements, the light pipe directing a majority of the received light to the output end;

a lens for receiving light from the output end of the light pipe and illuminating the sample with a substantially parallel beam of light; and

a detector for detecting light from the sample in response to illuminating the sample.

2. The readhead of claim 1, wherein the detector detects light transmitted through the sample.

3. The readhead of claim 1, wherein the detector detects light reflected by the sample.

4. The readhead of claim 1, wherein the read zone is constructed of a substantially optically transparent material.

5. The readhead of claim 1, wherein the read zone comprises an optically reflective surface.

6. The readhead of claim 1, wherein the light pipe is made of a polymer.

7. The readhead of claim 6, wherein the polymer is polyacrylic acid.

8. The readhead of claim 1, wherein the light pipe follows a substantially linear path between the input end and the output end.

9. The readhead of claim 1, wherein the light pipe follows a path having at least one substantially right angle between the input end and the output end.

10. The readhead of claim 1, wherein the light pipe has a length of at least 5 centimeters.

11. The readhead of claim 1, wherein the light pipe has a substantially square cross-section.

12. The readhead of claim 1, wherein the plurality of light emitting elements are disposed in a surface mount device.

13. The readhead of claim 1, further comprising a printed circuit board, wherein the detector and the light emitting element are mounted on the printed circuit board.

14. The readhead of claim 1, further comprising an optical fiber for transmitting light from the sample to the detector.

15. The readhead of claim 1, wherein the substantially parallel light beam illuminating the sample has a substantially uniform cross-section.

16. The readhead of claim 1, further comprising a body having a collimating aperture for reducing the diameter of light output from the output end of the light pipe, the body being positioned between the output end of the light pipe and the lens.

17. The readhead of claim 1, further comprising a body having a sample aperture for reducing the diameter of the substantially parallel light illuminating the sample, the body having the sample aperture positioned between the lens and the reading area.

18. The readhead of claim 1, wherein the plurality of light emitting elements for outputting light at a plurality of wavelengths comprises three light emitting elements.

19. The readhead of claim 18, wherein one of the three light emitting elements outputs red light.

20. The readhead of claim 18, wherein one of the three light emitting elements outputs green light.

21. The readhead of claim 18, wherein one of the three light emitting elements outputs blue light.

22. The readhead of claim 18, wherein one of the three light emitting elements outputs light having a wavelength in the range of between about 600nm and about 670 nm.

23. The readhead of claim 18, wherein one of the three light emitting elements outputs light having a wavelength in the range between about 520nm and about 520 nm.

24. The readhead of claim 18, wherein one of the three light emitting elements outputs light having a wavelength in the range between about 360nm and about 450 nm.

25. The readhead of claim 18, wherein one of the three light emitting elements outputs infrared light.

26. The readhead of claim 18, wherein one of the three light emitting elements outputs light having a wavelength in the range between about 800nm and about 1000 nm.

27. The readhead of claim 1, wherein the sample is a biological sample.

28. The readhead of claim 27, wherein the biological sample is blood.

29. A device for measuring an analyte concentration in a biological sample, the device comprising:

a test strip for receiving a biological sample, the test strip including a reaction zone having a reagent that reacts with the biological sample for producing a colorimetric reaction indicative of the concentration of an analyte in a blood sample;

a test strip receiving area for receiving at least the test strip reaction area; and

a readhead for measuring the degree of color change in a colorimetric reaction, the readhead comprising:

a light source including a plurality of light emitting elements for outputting light at a plurality of wavelengths;

a light pipe having an input end and an output end, the input end optically connected with the light source to receive light output by the plurality of light-emitting elements, the input end having a center offset from a center of at least one of the plurality of light-emitting elements, the light pipe guiding a majority of the received light to the output end;

a collimating lens for receiving light from the output end of the light pipe and illuminating the reaction area of the test strip with a substantially parallel beam of light; and

a detector for detecting light from a reaction zone in a test strip containing a biological sample including an analyte that reacts with a reagent.

30. The apparatus of claim 29, wherein the detector detects light transmitted through the reaction sample.

31. The apparatus of claim 29, wherein the detector detects light reflected from the reaction sample.

32. The apparatus of claim 29, wherein the light pipe is made of polyacrylic acid.

33. The apparatus of claim 29 wherein the light pipe follows a substantially linear path between the first end and the second end of the light pipe.

34. The apparatus of claim 29 wherein the light pipe follows a path having at least one substantially right angle between the first end and the second end of the light pipe.

35. The apparatus of claim 29, wherein the light pipe has a substantially square cross-section.

36. The device of claim 29, wherein the light source is a surface mount device.

37. The apparatus of claim 29, wherein each of the plurality of light emitting elements is a light emitting diode.

38. The apparatus of claim 29, further comprising a printed circuit board, wherein the detector and the light source are mounted on the printed circuit board.

39. The apparatus of claim 29, further comprising an optical fiber for transmitting light from the reaction sample to the detector.

40. The apparatus of claim 29, wherein the substantially parallel beam of light illuminating the biological sample has a substantially uniform cross-section.

41. The apparatus of claim 29 further comprising a body having a collimating aperture for reducing the diameter of light output from the output end of the light pipe, the body being disposed between the output end of the light pipe and the collimating lens.

42. The apparatus of claim 29, further comprising a body having a sample light aperture for reducing a diameter of the substantially parallel light illuminating the sample, the body having the sample light aperture disposed between the collimating lens and the reading zone.

43. The apparatus of claim 29, wherein the plurality of light-emitting elements for outputting light at a plurality of wavelengths comprises three light-emitting elements.

44. The device of claim 43, wherein one of the three light emitting elements outputs red light.

45. The device of claim 43, wherein one of the three light emitting elements outputs green light.

46. The device of claim 43 wherein one of the three light emitting elements outputs blue light.

47. The device of claim 43, wherein one of the three light-emitting elements outputs light having a wavelength in a range between about 600nm and about 670 nm.

48. The device of claim 43, wherein one of the three light-emitting elements outputs light having a wavelength in a range between about 520nm and about 520 nm.

49. The device of claim 43, wherein one of the three light-emitting elements outputs light having a wavelength in a range between about 360nm and about 450 nm.

50. A method for determining the concentration of an analyte in a biological sample using a multi-wavelength read head to measure a colorimetric reaction between the analyte and a reagent in the biological sample, the method comprising:

reacting a biological sample comprising an analyte with a reagent in a read zone of a read head;

illuminating a reading zone with a plurality of light beams having a plurality of wavelengths;

transmitting a plurality of light beams to a reading zone with a light pipe;

substantially collimating the light beam prior to illuminating the sample; and

detecting an optical response of a sample to the illumination reading zone, the sample comprising an analyte that has reacted with the reagent.

51. The method of claim 50, wherein detecting further comprises detecting light transmitted through the reacted sample in the read zone.

52. The method of claim 50, wherein detecting further comprises detecting light reflected from the reacted sample in the reading zone.

53. The method of claim 50, wherein substantially collimating further comprises reducing a diameter of the plurality of light beams with a collimating aperture disposed within the body.

54. The method of claim 50, wherein the read zone is comprised of a substantially optically transparent material.

55. The method of claim 50, wherein the read zone comprises an optically reflective surface.

56. The method of claim 50, further comprising reducing a diameter of the substantially parallel beam with a sample aperture disposed in the body.

57. The method of claim 50 wherein the light pipe has a substantially square cross-section.

58. The method of claim 50 wherein the light pipe is comprised of polyacrylic acid.

59. The method of claim 49, wherein illuminating further comprises illuminating the read zone with three beams of light.

60. The method of claim 59, wherein one of the three beams of light comprises red light.

61. The method of claim 59, wherein one of the three beams of light comprises green light.

62. The method of claim 59 in which one of the three beams of light comprises blue light.

63. The method of claim 59, wherein one of the three beams of light comprises light having a wavelength in a range between about 600nm and about 670 nm.

64. The method of claim 59, wherein one of the three beams of light comprises light having a wavelength in a range between about 520nm and about 520 nm.

65. The method of claim 59, wherein one of the three beams of light comprises light having a wavelength in a range between about 360nm and about 450 nm.

66. The readhead of claim 18, wherein one of the three light emitting elements outputs infrared light.

67. The readhead of claim 18, wherein one of the three light emitting elements outputs light having a wavelength in the range between about 800nm and about 1000 nm.