CA2218008C - Use of thermochromic liquid crystals in reflectometry based diagnostic methods - Google Patents
Use of thermochromic liquid crystals in reflectometry based diagnostic methods Download PDFInfo
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- CA2218008C CA2218008C CA002218008A CA2218008A CA2218008C CA 2218008 C CA2218008 C CA 2218008C CA 002218008 A CA002218008 A CA 002218008A CA 2218008 A CA2218008 A CA 2218008A CA 2218008 C CA2218008 C CA 2218008C
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
- G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
- G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
- G01N33/543—Immunoassay; Biospecific binding assay; Materials therefor with an insoluble carrier for immobilising immunochemicals
- G01N33/54366—Apparatus specially adapted for solid-phase testing
- G01N33/54373—Apparatus specially adapted for solid-phase testing involving physiochemical end-point determination, e.g. wave-guides, FETS, gratings
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/8483—Investigating reagent band
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T436/00—Chemistry: analytical and immunological testing
- Y10T436/11—Automated chemical analysis
- Y10T436/112499—Automated chemical analysis with sample on test slide
Abstract
Disclosed is a method for improving the accuracy of temperature sensitive diagnostic assays which are carried out using reflectance spectrometers to detect color changes in a solid test system which has been contacted with a fluid test system suspected of containing an analyte whose presence and/or concentration is being sought. The improvement involves determining the temperature of the solid test material by measuring the reflectance of a thermochromic liquid crystal in close proximity to the solid test material and correcting the result of the assay for a change in temperature from a pre-selected nominal temperature.
Description
USE OF THERMOCHROMIC LIQUID CRYSTALS
IN REFLECTOMETRY BASED DIAGNOSTIC METHODS
Background of the Invention The present invention is concerned with diagnostic test strips and an improved method for reading them by means of a reflectance spectrometer.
Test strips for the analysis of components in a liquid such as human body fluid are well known. Typically such strips are made of an absorbant material in which there is ab-sorbed a reagent system which responds to the presence of an analyte in the test fluid with a visually detectable signal such as a change in color. This change in color, which ap-pears in one or more test field of the strip, can be the re-sult of an enzymatic reaction in which a redox dye is oxidized or reduced to produce the colored response. Alternatively, the strip is made of a material through which the analyte and labeled antibodies specific therefor can flow to form ana-lyte/labeled antibody conjugates which are captured in a spe-cific detection zone of the strip to provide a detectable re-sponse representing the concentration of the analyte in the fluid test sample.
While the detectable response obtained using such strips can be observed visually to obtain a qualitative or semi-quantitative measure of the analyte in the test sample, greater quantitation and faster, more reliable handling of multiple test strips can be realized by instrumentally reading the developed strips. Such instrumental reading is usually accomplished by the use of a reflectance spectrometer which determines the intensity of the reflection from the test field surface. This sort of instrument determines the intensity of the reflected light in the developed strip by illuminating the strip with light at one angle (typically 90°), detecting the reflected light at a different angle (typically 45°) and se-lecting the measured color or wavelength range at either the source or the detector.
Since the spectrometer is programmed to take the ref lec-tance reading at a particular point in time and the intensity of the visually detectable signal can vary with a change in ambient temperature, because the reaction rate and/or equilib-rium are often temperature dependent, there is a need for some means by which temperature variations can be factored out of the assay.
The present invention involves the use of thermochromic liquid crystals in conjunction with the reading of test strips by spectrophotometric means to aid in correcting the readout of the spectrophotometer for variations in ambient tempera-ture. The use of thermochromic liquid crystals (TLCs) in re-search and testing is becoming increasingly widespread par-ticularly in the areas of flow visualization and heat transfer studies. The TLCs react to changes in temperature by changing color as their name implies. They typically have chiral (twisted) molecular structures and consist of optical mixtures of organic chemicals. The proper name for these materials is cholesteric or chiral nematic liquid crystals. The term cho-lesteric is historical and is derived from the fact that the first materials to show the characteristic properties and structure of thermochromic liquid crystals were esters of cho-lesterol. However, many optically active chemicals and mix-tures thereof which are not related to cholesterol or other sterols also exhibit the cholesteric liquid crystal structure.
TLC mixtures can be divided into 2 distinct types according to their chemical compositions. These types are cholesteric, i.e. formulations comprised entirely of cholesterol and other sterol related chemicals and chiral nematic, i.e. formulations comprised entirely of non-sterol based chemicals. A third category of TLCs arises from the fact that cholesteric and chiral nematic chemicals can be mixed together to provide for-mulations which exhibit a continuum of physical and chemical properties somewhere between those of their pure cholesteric and pure chiral nematic precursors.
TLCs exhibit colors by selectively reflecting incident white light. Conventional temperature sensitive mixtures turn from colorless (black against black background) to red at a given temperature and, as the temperature increases, pass through the other colors of the visible spectrum in sequence (orange, yellow, green, blue, violet) before turning colorless (black) again at yet higher temperatures. Since the color changes are reversible, the color sequence is reversed upon cooling. TLCs can be used in a number of different forms such as unsealed liquids which are essentially oils with the con-sistence at their working temperatures being between that of a thin oil and a viscous paste which are applied in thin uniform films, microencapsulated forms in which droplets of the TLC
are surrounded by a continuous polymer coating or coated sheets in which a thin film of the liquid crystal is sand-wicked between a transparent polymer sheet as substrate and a black absorbing background.
Summary of the Invention The present invention involves an improvement to a spec-trophotometric test for the presence and/or concentration of an analyte in a fluid test sample when a temperature sensitive assay is employed. This type of assay can be used with any type of system which provides a spectrophotometricly detect-able color change upon contacting a solid test material with a fluid sample containing the analyte. The improvement involves detecting the temperature of the solid test material by spec-trophotometrically measuring the reflectance of a thermochro-mic liquid crystal in close proximity to the solid test mate-rial. After the temperature is determined, the results of the assay are compensated for any change in temperature from a pre-selected nominal temperature which the test material has undergone.
Brief Description of the Drawings FIG. 1 illustrates a TLC affixed to an instrument table.
FIG. 2 illustrates changes in reflectance when TLC is applied to a MylarTM backing.
FIG. 3 illustrates the determination of temperature as a function of reflectance.
FIG. 4 illustrates the correlation of the TLC response with a probe.
FIGS. 5 and 6 illustrate the sensitivity of reflectance measurements to temperature.
4a FIG. 7 illustrates the linear regression of the Delta (factor change) as a function of decode measurement.
Description of the Invention The present invention is a means for correcting for changes in ambient temperature pursuant to the spectropho-tometric reading of test strips which, when contacted with an analyte in a fluid test sample, provide a spectrophotometricly detectable response. When this response is subject to influ-ence by ambient temperature changes, so that the spectropho-tometric reading will be skewed to give inaccurate results, use of the technique of this invention provides a means for factoring out inaccuracies in the reading which can be applied to existing spectrophotometers with only minimal changes to the hardware being required. The technique is applicable to both the traditional colorimetric type of assay strip, in which a redox dye is caused to change color by an enzymatic reaction, or the more recently introduced immunochroma-tographic strips in which a ligand labeled with a visually de-tectable marker combines with an analyte to provide a visually detectable response. Both of these techniques, and particu-larly the later, are quite sensitive to changes in ambient temperature, and, in the absence of some means of correcting for temperature variations, may provide skewed results. One such assay is the test for urobilinogen; abnormally high lev-els of which in urine can be indicative of hemolytic and he-patic diseases, biliary obstruction and other bile duct dys-functions. The standard method for detecting urobilinogen in urine employs the Ehrlich reaction which utilizes an aqueous solution of p-dimethylaminobenzenealdehyde or p-diethyl-aminobenzaldehyde and hydrochloric acid. In the presence of urobilinogen, there is produced a complex with the Ehrlich reagent which exhibits absorption in the visible spectrum.
This reaction is particularly sensitive to variations in ambi-ent temperature. In the immunochromatographic type assay, the labeled ligand and/or a binding partner thereof, must flow along a strip of porous support material and bind with an im-mobilized binding partner to provide a visually detectable signal in a particular zone of the strip which signal is in-dicative of the analyte's presence and/or concentration in the test fluid. Immunochromatography assays are not always sensi-tive to temperature in a normal ambient range. However, in certain instances, such as the test for deoxypyridinoline (Dpd) in urine, the Dpd antibodies are quite sensitive to changes in temperature. This temperature sensitivity will vary, depending on the particular analyte being sought, which makes it difficult to predict the temperature sensitivity of Ab-An reactions. With enzymes or other typical chemical reac-tions, the turnover rate increases approximately 2-fold with every 10°C rise in temperature due to the increase in the mo-lecular encounter rate with increasing temperature. While there is no turnover for an Ab-An reaction, the encounter rate would normally be expected to increase with temperature. In addition, the Ab and An molecular configuration may undergo numerous changes with temperature variation which would alter the reaction rate.
Increased precision in diagnostic assays conducted with these strips is achievable with careful temperature control.
Of course, temperature control can be maintained by conducting the assays in an environmentally controlled testing area.
This, however, is not always satisfactory because the backfit-ting of existing reflectance spectrometers with temperature control devices, such as electronic temperature sensors, would be bulky and, in many cases, cost prohibitive. Such tempera-ture control would also involve the use of heater elements and an enhanced power supply, all of which would increase the bulk and power requirements of the instrument. The presently dis-closed invention provides compensation for temperature fluc-tuations through temperature measurement using thermochromic liquid crystals and compensation for the change in temperature through modification of the spectrophotometer's software.
Temperature sensing is through reflectance measurements of a thermochromic liquid crystal having the appropriate char-acteristics. Suitable TLCs for use in the present invention undergo a visible color change as a function of temperature.
The most suitable color change is an increase or decrease in the TLCs optical reflectance as recorded through one of the filters of a reflectance spectrometer having multiple detec-tors for identifying reflected light at various wavelengths.
All TLCs undergo a color change from Black > Color >
Black (assuming a black background which is usually the case).
Thus, the instrumental recording of this change must be within some range in the color changing region, which is located in a position which can be scanned by the instrument's readhead.
Placement of the TLC could be on the test strip itself in or-der to coordinate the temperature adjustment with a particular assay and to ensure that the TLC has not been in place longer than its long term stability would suggest. Most conveniently the TLC is placed on the instrument's specimen tray just above the top end of the slot for receiving the test strip as illus-trated by Fig. 1. Referring to Fig. 1, the specimen tray 10 which is normally equipped with a white calibration strip 12 and a strip placement insert 14 is also provided with a TLC 16 located just above the top of the insert for strip placement.
The instrument's software is modified to cause the spec-trometer to read the liquid crystal and translate its re-flected color into a temperature measurement by a predeter-mined mathematical relationship. For example the reflectance of a TLC material affixed to the table of a CLINITEK~ 50 uri-nalysis instrument is read through the instrument's green and red filters and the reflectance values from each of the fil-ters is combined. This combined numerical value is then used to compute the temperature by using a preestablished relation-ship between the combined red and green reflectance measure-ments and the table temperature. The modified software and the thermochromic liquid crystal can be installed by the own-ers of existing instruments thereby updating them to take ad-vantage of the temperature compensating system of the present invention. The system can, of course, be incorporated into new spectrometers before they are sold. This technique is preferable to adding the feature of temperature compensated chemistry to new or existing reflectometry based medical ana-lyzers. The use of TLCs allows the manufacturer of the ana-lyzer to provide the temperature compensation feature at lit-tle additional cost and avoid the use of wire ribbons to the specimen table and/or avoid the need for circuit board modifi-cations. The instruments are updated by simply affixing the TLC to the appropriate location and modifying the software.
Through the use of reflectance measurements of a tempera-ture dependent area or pad (TLC), the measurements are related to temperature and used to correct for temperature dependent reagents where temperature control is not available.
The TLC can be applied to each individual test strip or to the instrument as previously described. A number of varia-tions of normal TLC sheet manufacturing are possible for variations in application. If it is desirable to put the TLC
directly on the reagent carrier or on components of the in-strument, a TLC slurry can be screen printed directly onto the desired location thereby rendering the positioning of the TLC
adaptable to a number of locations, shapes and sizes. For greater precision, a number of TLCs can be placed anywhere on the table or strip to allow a wider temperature range to be tracked for better accuracy in a narrow range. Typically each TLC would have a unique temperature signal. The preferred method is to place a single wide temperature range TLC affixed to a portion of the instrument table between the white cali-bration chip and the strip placement area as shown in Fig. 1 to most accurately record the temperature of the test strip.
The instrument's software is designed to translate the reflectance and color of the TLC into temperature. The fol-lowing example mathematically describes how the urobilinogen algorithm values changed as a function of temperature. In this case, the values were linear allowing a delta decode to be computed for each of the analyte levels where delta decode refers to a change in the decode as a function of temperature for each of the analyte levels tested. The delta decode val-ues were looked at in terms of a factor change over a 6°C dif-ference between 30 and 24°C. The 24°C level was chosen as the nominal temperature since this is the most common environ-mental temperature at which the instruments will be used and the factor difference, as plotted in Fig. 7, does not appear to be linear. All other temperatures were normalized to this nominal temperature. As non-linearity would require a more complex equation, the normalization at the middle temperature rather than at one of the extremes results in less of a bias at either one of the temperature extremes. As indicated by the example, the temperature dependent error in the urobilino-gen test was reduced by the temperature correction method of the present invention.
The method of practicing the present invention is further illustrated by the following examples.
Example I
Samples of TLC coated onto a Mylar'"backing with different levels of TLC were obtained from two separate vendors. These were specialized materials made for use in the present inven-tion which are designated here as A and B. The temperature dependence of one of the TLC samples (A) was tested on a CLINITEK~ 100 instrument from Bayer Diagnostics using the fol-lowing procedure:
The TLC was applied to the Mylar~" backing by multiple passes with a wire rod followed by spreading the material with the rod. The greatest changes in reflectance were noted when the largest amount of TLC (as indicated by the number of passes) was added to the Mylar~". This is illustrated by Fig.
2. This illustrates the need for careful quality control to ensure that the thickness of TLC applied to the test strips or instrument remains consistent from strip to strip or instru-ment to instrument.
The other TLC (B) was tested in a similar manner. The B
material gave a response which, while visually more distinct, gave less of a signal difference between thicknesses. The problem with this TLC was that it underwent too large of a color change in the temperature range of interest. It is dif-ficult to deal with reflectance changes which are both in-creasing and decreasing within a given temperature region.
Although the A material showed less visible change, the fact that the reflectance would only decrease as the temperature increased was advantageous from the instrumental prospective.
This TLC could not be used to monitor temperatures below 18°C
due to a strong decrease in reflectance below this tempera-ture.
To ensure that no hysterisis effect, i.e. the observed reflectance was dependent on whether the temperature was in-creasing or decreasing, was being noted, data were collected using both TLCs with the temperature changing in both direc-tions.
Example II
Additional data supporting the efficacy of using thermo-chromic liquid crystals as a method for determining tempera-ture in conjunction with the spectrophotometric reading of an analysis strip is graphically represented by Fig. 3. The data were collected over a two day period in an environmental cham-ber which was cycled repeatedly between 18°C and 30°C with a constant relative humidity of 40~. Temperatures were recorded every 5 minutes from three different positions in relation to the TLC which was affixed to the spectrometer's specimen ta-ble. A CLINITEK~ CT50 instrument was used in conjunction with a program that would initiate a reading every 5 minutes fol-lowed by collection of the TLC reflectance data along with the table, board and ambient temperatures. The table temperature came from an embedded probe at the tip position of the strip adjacent to the TLC position. The board temperature came from a temperature sensor which was on the circuit board near the readhead of the instrument. The ambient temperature came from a probe about 1 foot away from the instrument. Data were col-lected for over 31 hours (a total of 374 data points) The signals obtained from each of the instruments IR, red, green and blue sensors were collected at each time point and plotted in Fig. 3. The ~ reflectance through the IR fil-ter showed little or no change. The change in the red, green and blue filter signals as a function of temperature are shown in Fig. 3. The combined red and green signal was used since a greater signal change between 18 and 30°C could be obtained.
Using these data and a 2 polynomial regression fit through the data points, there was developed an equation by which the re-flectance values through the red and green filters of the in-strument could be converted to temperature. This equation is:
TLC temperature = 38.068 - 0.0883 (Rg+Rb) + 0.0000775 (Rg+Rb)z where Rg is the $ reflectance through the green filter and Rb is the % reflectance through the red filter.
The relationship between the TLC reflectance response and the temperature to obtain the above equation was obtained by using an IBM compatible computer connected through a serial port connection to a Baytech Multiport controller. Output from a Cole-Palmer scanning thermocouple and output from a CLINITEK~ CT50 instrument was matched through the Baytech con-troller. The output from the CT50 included reflectance read-ings through the red, green, blue and IR filters. The output from the scanning thermocouple included temperature readings from a probe approximately one foot from the instrument which was embedded in the table as described above and attached to the main circuit board close to the readhead of the instru-ment. Specialized software programmed in Visual Basic as used to initiate the 5 minute readings by the instrument and to ob-tain and match all of the datastreams.
The data set out in Fig. 4 represent the correlation of the TLC response (the summation of the green filter reflec-tance and the red filter reflectance) with that of the probe embedded in the table adjacent to the affixed TLC material.
From Fig. 4 it can be determined that even under rapidly fluc-tuating temperatures there is good correlation between the temperatures recorded by the probe and those which are re-corded by the TLC. Under these rapidly fluctuating environ-mental conditions the correlation between the TLC and the probe measuring the ambient air temperature were less robust.
Fig. 4 correlates the TLC recorded temperature to that of the table temperature probe. The correlation shows a RZ of 0.998 and a Sy.X (standard deviation of the line) of 0.203 where Rz is the squared regression coefficient which shows the correla-tion between two measurements with the value of 1 demonstrat-ing a perfect correlation with a value of 0 demonstrating no correlation at all between the two measurements. This indi-cates that within a 95% confidence limit, the correlation be-tween the TLC and table probe is within half a degree.
For optimal results the TLC needs to be quite close to the test strip. There is typically a small temperature gradi-ent within the instrument itself which, at least in a rapidly fluctuating temperature environment, would cause 1-3°C tem-perature difference. Accordingly, the TLC is preferably placed on the test strip itself or on the specimen table near the strip as illustrated in Fig. 1.
Example III
The temperature correcting ability of a reflectance read TLC is demonstrated by this example in which the urobilinogen pad of a MULTISTIX SG~ strip was tested over several tempera-tures from 18 to 30°C. The results of this reagent pad are known to be sensitive to temperature as indicated by the prod-uct insert. The reflectance measurements are sensitive to temperatures as shown in Figs. 5 and 6 using calibrated solu-tions containing 0 and 4 mg/dL urobilinogen in the fluid test sample. In all cases the decode, i.e. the algorithm result from the instrument, measurements (where decode is equal to the reflectance values obtained from green/IR filters of a CLINITEK~ 50 spectrophotometer) show a negative response to-ward increases in temperature and appear to be linear. The factor change per degree change from 24°C is calibrated by us-ing:
Delta~pact°r change) = 1-Decode3oc/Decodez4c This relationship is shown in Fig. 7 and is nearly lin-ear. No difference was found when the factor difference was computed at a lower temperature. The above relationship was then used to calculate a corrected decode as a function of temperature using the following equation:
Decode~orrectea = Decode/ { 1 + ( Decode*Slope + Intercept ) * ( Taotuai -24 ) }
where Slope - -2.94~l0E-05 and Intercept - 0.0287 wherein these values were calculated from the linear regression of the Delta~p8ctor change) Per °C from 24°C versus decode measurement in Fig. 7.
The results of this calculation are set out in Table 1.
Table 1 UrobiiinopsnOECOOE
1 ldL1 . Uneorrocted . OECOOE
. Cor~ecad Max-Min Avp. SD Max-Min Avp. ValueSO
( Value p 41.4 831 12.9 8.6 837 2.8 ( 1 58.7 727.6 18.7 15 731 4.2 4 86.9 1540.1 23.5 18.9 540.9 6.3 As indicated by Table 1, a significant reduction in the error (in terms of standard deviation) on the order of about 4-fold is achieved by applying the TLC temperature correction to the data with no change in the average decode measurement.
This demonstrates that TLC obtained temperature data can be used to significantly reduce the temperature induced error in cases where temperature control is not practical or available.
The present invention operates on the principle of meas-uring the reflectance of the TLC material through a reflec-tance meter. One or a combination of reflected wavelengths is chosen such that a unique value for a given temperature is ob-tained. As the TLC material's color changes from black ->
color -> black with increasing temperature, it is desirable to limit the detected temperature range to an area where one or a combination of wavelength values give a numerical value.
The reflectance of the TLC material is calibrated by relating these unique values to a given temperature and deriving an equation which allows the numerical calculation of temperature when only the reflectance of the TLC material is known. The temperature of the TLC material will be the same as or close to the temperature of the solid test material when the two are maintained in sufficiently close proximity. The accuracy of the temperature determining method may decrease as the TLC ma-terial and solid test material are separated by increasing distances. An example of such calibration is given by Fig. 4.
Temperature effects of the immunological or chemical re-action at given analyte levels are determined throughout the analyte range in which detection is desired. The chemical or immunological reactivity can be expressed in any form such as units, mg or any other form in which the data of Figs. 5 and 6 are expressed as decode. A relationship between the decode value, which is a measure of the chemical or immunological re-activity, to that of temperature can be drawn from the rela-tionships shown in Figs. 5 and 6. As shown in Fig. 7, it is desirable to fixate the factor change in the decode value to the mid point of the desired temperature range in order to minimize bias in the calculations relating the decode to the temperature change.
Once the relationship has been established for a given lot of reagents and a given temperature range, the measured decode value is adjusted by the factor difference established for that decode value and the deviation of the temperature from the nominal value. This relationship can be any mathe-matical equation which allows the calculation of corrected de-code from a measured decode and temperature measurement. In the present example, that relationship is described by a lin-ear line with a slope of -2.94~110E-05 and intercept of 0.0287. Accordingly, a measured decode value of 600 is cor-rected for temperature effects by software which uses the equation and computes the value of 563 for a corrected decode value of 562. An established relationship residing in the software between decode and analyte level is then used to pro-vide the analyte concentration in the sample.
IN REFLECTOMETRY BASED DIAGNOSTIC METHODS
Background of the Invention The present invention is concerned with diagnostic test strips and an improved method for reading them by means of a reflectance spectrometer.
Test strips for the analysis of components in a liquid such as human body fluid are well known. Typically such strips are made of an absorbant material in which there is ab-sorbed a reagent system which responds to the presence of an analyte in the test fluid with a visually detectable signal such as a change in color. This change in color, which ap-pears in one or more test field of the strip, can be the re-sult of an enzymatic reaction in which a redox dye is oxidized or reduced to produce the colored response. Alternatively, the strip is made of a material through which the analyte and labeled antibodies specific therefor can flow to form ana-lyte/labeled antibody conjugates which are captured in a spe-cific detection zone of the strip to provide a detectable re-sponse representing the concentration of the analyte in the fluid test sample.
While the detectable response obtained using such strips can be observed visually to obtain a qualitative or semi-quantitative measure of the analyte in the test sample, greater quantitation and faster, more reliable handling of multiple test strips can be realized by instrumentally reading the developed strips. Such instrumental reading is usually accomplished by the use of a reflectance spectrometer which determines the intensity of the reflection from the test field surface. This sort of instrument determines the intensity of the reflected light in the developed strip by illuminating the strip with light at one angle (typically 90°), detecting the reflected light at a different angle (typically 45°) and se-lecting the measured color or wavelength range at either the source or the detector.
Since the spectrometer is programmed to take the ref lec-tance reading at a particular point in time and the intensity of the visually detectable signal can vary with a change in ambient temperature, because the reaction rate and/or equilib-rium are often temperature dependent, there is a need for some means by which temperature variations can be factored out of the assay.
The present invention involves the use of thermochromic liquid crystals in conjunction with the reading of test strips by spectrophotometric means to aid in correcting the readout of the spectrophotometer for variations in ambient tempera-ture. The use of thermochromic liquid crystals (TLCs) in re-search and testing is becoming increasingly widespread par-ticularly in the areas of flow visualization and heat transfer studies. The TLCs react to changes in temperature by changing color as their name implies. They typically have chiral (twisted) molecular structures and consist of optical mixtures of organic chemicals. The proper name for these materials is cholesteric or chiral nematic liquid crystals. The term cho-lesteric is historical and is derived from the fact that the first materials to show the characteristic properties and structure of thermochromic liquid crystals were esters of cho-lesterol. However, many optically active chemicals and mix-tures thereof which are not related to cholesterol or other sterols also exhibit the cholesteric liquid crystal structure.
TLC mixtures can be divided into 2 distinct types according to their chemical compositions. These types are cholesteric, i.e. formulations comprised entirely of cholesterol and other sterol related chemicals and chiral nematic, i.e. formulations comprised entirely of non-sterol based chemicals. A third category of TLCs arises from the fact that cholesteric and chiral nematic chemicals can be mixed together to provide for-mulations which exhibit a continuum of physical and chemical properties somewhere between those of their pure cholesteric and pure chiral nematic precursors.
TLCs exhibit colors by selectively reflecting incident white light. Conventional temperature sensitive mixtures turn from colorless (black against black background) to red at a given temperature and, as the temperature increases, pass through the other colors of the visible spectrum in sequence (orange, yellow, green, blue, violet) before turning colorless (black) again at yet higher temperatures. Since the color changes are reversible, the color sequence is reversed upon cooling. TLCs can be used in a number of different forms such as unsealed liquids which are essentially oils with the con-sistence at their working temperatures being between that of a thin oil and a viscous paste which are applied in thin uniform films, microencapsulated forms in which droplets of the TLC
are surrounded by a continuous polymer coating or coated sheets in which a thin film of the liquid crystal is sand-wicked between a transparent polymer sheet as substrate and a black absorbing background.
Summary of the Invention The present invention involves an improvement to a spec-trophotometric test for the presence and/or concentration of an analyte in a fluid test sample when a temperature sensitive assay is employed. This type of assay can be used with any type of system which provides a spectrophotometricly detect-able color change upon contacting a solid test material with a fluid sample containing the analyte. The improvement involves detecting the temperature of the solid test material by spec-trophotometrically measuring the reflectance of a thermochro-mic liquid crystal in close proximity to the solid test mate-rial. After the temperature is determined, the results of the assay are compensated for any change in temperature from a pre-selected nominal temperature which the test material has undergone.
Brief Description of the Drawings FIG. 1 illustrates a TLC affixed to an instrument table.
FIG. 2 illustrates changes in reflectance when TLC is applied to a MylarTM backing.
FIG. 3 illustrates the determination of temperature as a function of reflectance.
FIG. 4 illustrates the correlation of the TLC response with a probe.
FIGS. 5 and 6 illustrate the sensitivity of reflectance measurements to temperature.
4a FIG. 7 illustrates the linear regression of the Delta (factor change) as a function of decode measurement.
Description of the Invention The present invention is a means for correcting for changes in ambient temperature pursuant to the spectropho-tometric reading of test strips which, when contacted with an analyte in a fluid test sample, provide a spectrophotometricly detectable response. When this response is subject to influ-ence by ambient temperature changes, so that the spectropho-tometric reading will be skewed to give inaccurate results, use of the technique of this invention provides a means for factoring out inaccuracies in the reading which can be applied to existing spectrophotometers with only minimal changes to the hardware being required. The technique is applicable to both the traditional colorimetric type of assay strip, in which a redox dye is caused to change color by an enzymatic reaction, or the more recently introduced immunochroma-tographic strips in which a ligand labeled with a visually de-tectable marker combines with an analyte to provide a visually detectable response. Both of these techniques, and particu-larly the later, are quite sensitive to changes in ambient temperature, and, in the absence of some means of correcting for temperature variations, may provide skewed results. One such assay is the test for urobilinogen; abnormally high lev-els of which in urine can be indicative of hemolytic and he-patic diseases, biliary obstruction and other bile duct dys-functions. The standard method for detecting urobilinogen in urine employs the Ehrlich reaction which utilizes an aqueous solution of p-dimethylaminobenzenealdehyde or p-diethyl-aminobenzaldehyde and hydrochloric acid. In the presence of urobilinogen, there is produced a complex with the Ehrlich reagent which exhibits absorption in the visible spectrum.
This reaction is particularly sensitive to variations in ambi-ent temperature. In the immunochromatographic type assay, the labeled ligand and/or a binding partner thereof, must flow along a strip of porous support material and bind with an im-mobilized binding partner to provide a visually detectable signal in a particular zone of the strip which signal is in-dicative of the analyte's presence and/or concentration in the test fluid. Immunochromatography assays are not always sensi-tive to temperature in a normal ambient range. However, in certain instances, such as the test for deoxypyridinoline (Dpd) in urine, the Dpd antibodies are quite sensitive to changes in temperature. This temperature sensitivity will vary, depending on the particular analyte being sought, which makes it difficult to predict the temperature sensitivity of Ab-An reactions. With enzymes or other typical chemical reac-tions, the turnover rate increases approximately 2-fold with every 10°C rise in temperature due to the increase in the mo-lecular encounter rate with increasing temperature. While there is no turnover for an Ab-An reaction, the encounter rate would normally be expected to increase with temperature. In addition, the Ab and An molecular configuration may undergo numerous changes with temperature variation which would alter the reaction rate.
Increased precision in diagnostic assays conducted with these strips is achievable with careful temperature control.
Of course, temperature control can be maintained by conducting the assays in an environmentally controlled testing area.
This, however, is not always satisfactory because the backfit-ting of existing reflectance spectrometers with temperature control devices, such as electronic temperature sensors, would be bulky and, in many cases, cost prohibitive. Such tempera-ture control would also involve the use of heater elements and an enhanced power supply, all of which would increase the bulk and power requirements of the instrument. The presently dis-closed invention provides compensation for temperature fluc-tuations through temperature measurement using thermochromic liquid crystals and compensation for the change in temperature through modification of the spectrophotometer's software.
Temperature sensing is through reflectance measurements of a thermochromic liquid crystal having the appropriate char-acteristics. Suitable TLCs for use in the present invention undergo a visible color change as a function of temperature.
The most suitable color change is an increase or decrease in the TLCs optical reflectance as recorded through one of the filters of a reflectance spectrometer having multiple detec-tors for identifying reflected light at various wavelengths.
All TLCs undergo a color change from Black > Color >
Black (assuming a black background which is usually the case).
Thus, the instrumental recording of this change must be within some range in the color changing region, which is located in a position which can be scanned by the instrument's readhead.
Placement of the TLC could be on the test strip itself in or-der to coordinate the temperature adjustment with a particular assay and to ensure that the TLC has not been in place longer than its long term stability would suggest. Most conveniently the TLC is placed on the instrument's specimen tray just above the top end of the slot for receiving the test strip as illus-trated by Fig. 1. Referring to Fig. 1, the specimen tray 10 which is normally equipped with a white calibration strip 12 and a strip placement insert 14 is also provided with a TLC 16 located just above the top of the insert for strip placement.
The instrument's software is modified to cause the spec-trometer to read the liquid crystal and translate its re-flected color into a temperature measurement by a predeter-mined mathematical relationship. For example the reflectance of a TLC material affixed to the table of a CLINITEK~ 50 uri-nalysis instrument is read through the instrument's green and red filters and the reflectance values from each of the fil-ters is combined. This combined numerical value is then used to compute the temperature by using a preestablished relation-ship between the combined red and green reflectance measure-ments and the table temperature. The modified software and the thermochromic liquid crystal can be installed by the own-ers of existing instruments thereby updating them to take ad-vantage of the temperature compensating system of the present invention. The system can, of course, be incorporated into new spectrometers before they are sold. This technique is preferable to adding the feature of temperature compensated chemistry to new or existing reflectometry based medical ana-lyzers. The use of TLCs allows the manufacturer of the ana-lyzer to provide the temperature compensation feature at lit-tle additional cost and avoid the use of wire ribbons to the specimen table and/or avoid the need for circuit board modifi-cations. The instruments are updated by simply affixing the TLC to the appropriate location and modifying the software.
Through the use of reflectance measurements of a tempera-ture dependent area or pad (TLC), the measurements are related to temperature and used to correct for temperature dependent reagents where temperature control is not available.
The TLC can be applied to each individual test strip or to the instrument as previously described. A number of varia-tions of normal TLC sheet manufacturing are possible for variations in application. If it is desirable to put the TLC
directly on the reagent carrier or on components of the in-strument, a TLC slurry can be screen printed directly onto the desired location thereby rendering the positioning of the TLC
adaptable to a number of locations, shapes and sizes. For greater precision, a number of TLCs can be placed anywhere on the table or strip to allow a wider temperature range to be tracked for better accuracy in a narrow range. Typically each TLC would have a unique temperature signal. The preferred method is to place a single wide temperature range TLC affixed to a portion of the instrument table between the white cali-bration chip and the strip placement area as shown in Fig. 1 to most accurately record the temperature of the test strip.
The instrument's software is designed to translate the reflectance and color of the TLC into temperature. The fol-lowing example mathematically describes how the urobilinogen algorithm values changed as a function of temperature. In this case, the values were linear allowing a delta decode to be computed for each of the analyte levels where delta decode refers to a change in the decode as a function of temperature for each of the analyte levels tested. The delta decode val-ues were looked at in terms of a factor change over a 6°C dif-ference between 30 and 24°C. The 24°C level was chosen as the nominal temperature since this is the most common environ-mental temperature at which the instruments will be used and the factor difference, as plotted in Fig. 7, does not appear to be linear. All other temperatures were normalized to this nominal temperature. As non-linearity would require a more complex equation, the normalization at the middle temperature rather than at one of the extremes results in less of a bias at either one of the temperature extremes. As indicated by the example, the temperature dependent error in the urobilino-gen test was reduced by the temperature correction method of the present invention.
The method of practicing the present invention is further illustrated by the following examples.
Example I
Samples of TLC coated onto a Mylar'"backing with different levels of TLC were obtained from two separate vendors. These were specialized materials made for use in the present inven-tion which are designated here as A and B. The temperature dependence of one of the TLC samples (A) was tested on a CLINITEK~ 100 instrument from Bayer Diagnostics using the fol-lowing procedure:
The TLC was applied to the Mylar~" backing by multiple passes with a wire rod followed by spreading the material with the rod. The greatest changes in reflectance were noted when the largest amount of TLC (as indicated by the number of passes) was added to the Mylar~". This is illustrated by Fig.
2. This illustrates the need for careful quality control to ensure that the thickness of TLC applied to the test strips or instrument remains consistent from strip to strip or instru-ment to instrument.
The other TLC (B) was tested in a similar manner. The B
material gave a response which, while visually more distinct, gave less of a signal difference between thicknesses. The problem with this TLC was that it underwent too large of a color change in the temperature range of interest. It is dif-ficult to deal with reflectance changes which are both in-creasing and decreasing within a given temperature region.
Although the A material showed less visible change, the fact that the reflectance would only decrease as the temperature increased was advantageous from the instrumental prospective.
This TLC could not be used to monitor temperatures below 18°C
due to a strong decrease in reflectance below this tempera-ture.
To ensure that no hysterisis effect, i.e. the observed reflectance was dependent on whether the temperature was in-creasing or decreasing, was being noted, data were collected using both TLCs with the temperature changing in both direc-tions.
Example II
Additional data supporting the efficacy of using thermo-chromic liquid crystals as a method for determining tempera-ture in conjunction with the spectrophotometric reading of an analysis strip is graphically represented by Fig. 3. The data were collected over a two day period in an environmental cham-ber which was cycled repeatedly between 18°C and 30°C with a constant relative humidity of 40~. Temperatures were recorded every 5 minutes from three different positions in relation to the TLC which was affixed to the spectrometer's specimen ta-ble. A CLINITEK~ CT50 instrument was used in conjunction with a program that would initiate a reading every 5 minutes fol-lowed by collection of the TLC reflectance data along with the table, board and ambient temperatures. The table temperature came from an embedded probe at the tip position of the strip adjacent to the TLC position. The board temperature came from a temperature sensor which was on the circuit board near the readhead of the instrument. The ambient temperature came from a probe about 1 foot away from the instrument. Data were col-lected for over 31 hours (a total of 374 data points) The signals obtained from each of the instruments IR, red, green and blue sensors were collected at each time point and plotted in Fig. 3. The ~ reflectance through the IR fil-ter showed little or no change. The change in the red, green and blue filter signals as a function of temperature are shown in Fig. 3. The combined red and green signal was used since a greater signal change between 18 and 30°C could be obtained.
Using these data and a 2 polynomial regression fit through the data points, there was developed an equation by which the re-flectance values through the red and green filters of the in-strument could be converted to temperature. This equation is:
TLC temperature = 38.068 - 0.0883 (Rg+Rb) + 0.0000775 (Rg+Rb)z where Rg is the $ reflectance through the green filter and Rb is the % reflectance through the red filter.
The relationship between the TLC reflectance response and the temperature to obtain the above equation was obtained by using an IBM compatible computer connected through a serial port connection to a Baytech Multiport controller. Output from a Cole-Palmer scanning thermocouple and output from a CLINITEK~ CT50 instrument was matched through the Baytech con-troller. The output from the CT50 included reflectance read-ings through the red, green, blue and IR filters. The output from the scanning thermocouple included temperature readings from a probe approximately one foot from the instrument which was embedded in the table as described above and attached to the main circuit board close to the readhead of the instru-ment. Specialized software programmed in Visual Basic as used to initiate the 5 minute readings by the instrument and to ob-tain and match all of the datastreams.
The data set out in Fig. 4 represent the correlation of the TLC response (the summation of the green filter reflec-tance and the red filter reflectance) with that of the probe embedded in the table adjacent to the affixed TLC material.
From Fig. 4 it can be determined that even under rapidly fluc-tuating temperatures there is good correlation between the temperatures recorded by the probe and those which are re-corded by the TLC. Under these rapidly fluctuating environ-mental conditions the correlation between the TLC and the probe measuring the ambient air temperature were less robust.
Fig. 4 correlates the TLC recorded temperature to that of the table temperature probe. The correlation shows a RZ of 0.998 and a Sy.X (standard deviation of the line) of 0.203 where Rz is the squared regression coefficient which shows the correla-tion between two measurements with the value of 1 demonstrat-ing a perfect correlation with a value of 0 demonstrating no correlation at all between the two measurements. This indi-cates that within a 95% confidence limit, the correlation be-tween the TLC and table probe is within half a degree.
For optimal results the TLC needs to be quite close to the test strip. There is typically a small temperature gradi-ent within the instrument itself which, at least in a rapidly fluctuating temperature environment, would cause 1-3°C tem-perature difference. Accordingly, the TLC is preferably placed on the test strip itself or on the specimen table near the strip as illustrated in Fig. 1.
Example III
The temperature correcting ability of a reflectance read TLC is demonstrated by this example in which the urobilinogen pad of a MULTISTIX SG~ strip was tested over several tempera-tures from 18 to 30°C. The results of this reagent pad are known to be sensitive to temperature as indicated by the prod-uct insert. The reflectance measurements are sensitive to temperatures as shown in Figs. 5 and 6 using calibrated solu-tions containing 0 and 4 mg/dL urobilinogen in the fluid test sample. In all cases the decode, i.e. the algorithm result from the instrument, measurements (where decode is equal to the reflectance values obtained from green/IR filters of a CLINITEK~ 50 spectrophotometer) show a negative response to-ward increases in temperature and appear to be linear. The factor change per degree change from 24°C is calibrated by us-ing:
Delta~pact°r change) = 1-Decode3oc/Decodez4c This relationship is shown in Fig. 7 and is nearly lin-ear. No difference was found when the factor difference was computed at a lower temperature. The above relationship was then used to calculate a corrected decode as a function of temperature using the following equation:
Decode~orrectea = Decode/ { 1 + ( Decode*Slope + Intercept ) * ( Taotuai -24 ) }
where Slope - -2.94~l0E-05 and Intercept - 0.0287 wherein these values were calculated from the linear regression of the Delta~p8ctor change) Per °C from 24°C versus decode measurement in Fig. 7.
The results of this calculation are set out in Table 1.
Table 1 UrobiiinopsnOECOOE
1 ldL1 . Uneorrocted . OECOOE
. Cor~ecad Max-Min Avp. SD Max-Min Avp. ValueSO
( Value p 41.4 831 12.9 8.6 837 2.8 ( 1 58.7 727.6 18.7 15 731 4.2 4 86.9 1540.1 23.5 18.9 540.9 6.3 As indicated by Table 1, a significant reduction in the error (in terms of standard deviation) on the order of about 4-fold is achieved by applying the TLC temperature correction to the data with no change in the average decode measurement.
This demonstrates that TLC obtained temperature data can be used to significantly reduce the temperature induced error in cases where temperature control is not practical or available.
The present invention operates on the principle of meas-uring the reflectance of the TLC material through a reflec-tance meter. One or a combination of reflected wavelengths is chosen such that a unique value for a given temperature is ob-tained. As the TLC material's color changes from black ->
color -> black with increasing temperature, it is desirable to limit the detected temperature range to an area where one or a combination of wavelength values give a numerical value.
The reflectance of the TLC material is calibrated by relating these unique values to a given temperature and deriving an equation which allows the numerical calculation of temperature when only the reflectance of the TLC material is known. The temperature of the TLC material will be the same as or close to the temperature of the solid test material when the two are maintained in sufficiently close proximity. The accuracy of the temperature determining method may decrease as the TLC ma-terial and solid test material are separated by increasing distances. An example of such calibration is given by Fig. 4.
Temperature effects of the immunological or chemical re-action at given analyte levels are determined throughout the analyte range in which detection is desired. The chemical or immunological reactivity can be expressed in any form such as units, mg or any other form in which the data of Figs. 5 and 6 are expressed as decode. A relationship between the decode value, which is a measure of the chemical or immunological re-activity, to that of temperature can be drawn from the rela-tionships shown in Figs. 5 and 6. As shown in Fig. 7, it is desirable to fixate the factor change in the decode value to the mid point of the desired temperature range in order to minimize bias in the calculations relating the decode to the temperature change.
Once the relationship has been established for a given lot of reagents and a given temperature range, the measured decode value is adjusted by the factor difference established for that decode value and the deviation of the temperature from the nominal value. This relationship can be any mathe-matical equation which allows the calculation of corrected de-code from a measured decode and temperature measurement. In the present example, that relationship is described by a lin-ear line with a slope of -2.94~110E-05 and intercept of 0.0287. Accordingly, a measured decode value of 600 is cor-rected for temperature effects by software which uses the equation and computes the value of 563 for a corrected decode value of 562. An established relationship residing in the software between decode and analyte level is then used to pro-vide the analyte concentration in the sample.
Claims (12)
1. In an assay for the presence and/or concentration of an analyte in a fluid test sample in which the presence and/or concentration of the analyte is determined by measuring a color change in a solid test material using a reflectance spectrometer after the test material has been contacted with the fluid test sample and wherein assay results vary with changes in temperature of the solid test material, the improvement which comprises using the reflectance spectrometer to determine the temperature of the solid test material by measuring the reflectance of a thermochromic liquid crystal in close proximity to the solid test material and correcting the results of the assay for deviation in temperature of the solid test material from a pre-selected nominal temperature.
2. The assay of claim 1 wherein the solid test material is a strip of an absorbant material having absorbed therein a reagent system which responds to the presence of the analyte in the fluid test sample with a visually detectable color change.
3. The assay of claim 1 wherein the thermochromic liquid crystal is of the cholesteric, chiral nematic or a combination thereof.
4. The assay of claim 1 wherein the color change in the solid test material is caused by an enzymatic reaction with the analyte which changes the color of a redox dye carried by the solid test material.
5. The assay of claim 1 wherein the color change in the solid test material is caused by the interaction of a ligand having a visually detectable marker with the analyte.
6. The assay of claim 1 wherein the analyte is urobilinogen and the fluid test sample is urine.
7. The assay of claim 1 wherein the thermochromic liquid crystal is located on the solid test material.
8. The assay of claim 1 wherein the reflectance spectrometer has a specimen table for placement of the solid test material and the thermochromic liquid crystal and solid test material are located on the specimen table directly adjacent to each other.
9. The assay of claim 1, wherein the temperature of the solid test material is determined by:
i) measuring the reflectance of the thermochromic liquid crystal through the reflectance spectrometer;
ii) comparing the measured reflectance of the thermochromic liquid crystal to a first standard curve by:
a) measuring a standard reflectance of the thermochromic liquid crystal at a plurality of standard temperatures to provide a first unique reflectance value for said plurality of standard temperatures;
b) deriving an equation of the first standard curve which allows numerical calculation of a temperature of the thermochromic liquid crystal, when only the measured reflectance of the thermochromic liquid crystal is known; and iii) solving the equation to obtain the temperature of the solid test material.
i) measuring the reflectance of the thermochromic liquid crystal through the reflectance spectrometer;
ii) comparing the measured reflectance of the thermochromic liquid crystal to a first standard curve by:
a) measuring a standard reflectance of the thermochromic liquid crystal at a plurality of standard temperatures to provide a first unique reflectance value for said plurality of standard temperatures;
b) deriving an equation of the first standard curve which allows numerical calculation of a temperature of the thermochromic liquid crystal, when only the measured reflectance of the thermochromic liquid crystal is known; and iii) solving the equation to obtain the temperature of the solid test material.
10. The assay of claim 9, wherein the assay results of the analyte concentration in the fluid test sample are corrected for a change in temperature by:
i) measuring the reflectance of the solid test material through the reflectance spectrometer;
ii) comparing the measured reflectance of the solid test material to a second standard curve obtained by:
a) measuring the reflectance of the solid test material at a plurality of standard temperatures and standard analyte concentrations to provide a second unique reflectance value for said plurality of standard temperatures and said standard analyte concentrations;
b) deriving an equation of the second standard curve which allows numerical calculation of a correction for a change in temperature of the solid test material; and with the results of step iii) of claim 9, iii) solving the equation of the second standard curve to obtain temperature corrected assay results of the analyte concentration in said fluid test sample.
i) measuring the reflectance of the solid test material through the reflectance spectrometer;
ii) comparing the measured reflectance of the solid test material to a second standard curve obtained by:
a) measuring the reflectance of the solid test material at a plurality of standard temperatures and standard analyte concentrations to provide a second unique reflectance value for said plurality of standard temperatures and said standard analyte concentrations;
b) deriving an equation of the second standard curve which allows numerical calculation of a correction for a change in temperature of the solid test material; and with the results of step iii) of claim 9, iii) solving the equation of the second standard curve to obtain temperature corrected assay results of the analyte concentration in said fluid test sample.
11. The assay of claim 1 wherein the temperature of the solid test material is determined by;
i) measuring the reflectance of the thermochromic liquid crystal ("TLC") material through the reflectance spectrometer;
ii) choosing one or a combination of the reflected wavelengths to provide a unique value for a given temperature;
iii) calibrating the reflectance of the TLC material by relating the unique value to a given temperature;
iv) deriving an equation which allows the numerical calculations of temperature when only the reflectance of the TLC material is known, and v) solving the equation to obtain the temperature.
i) measuring the reflectance of the thermochromic liquid crystal ("TLC") material through the reflectance spectrometer;
ii) choosing one or a combination of the reflected wavelengths to provide a unique value for a given temperature;
iii) calibrating the reflectance of the TLC material by relating the unique value to a given temperature;
iv) deriving an equation which allows the numerical calculations of temperature when only the reflectance of the TLC material is known, and v) solving the equation to obtain the temperature.
12. The assay of claim 11 wherein the results of the assay are corrected for a change in temperature by:
i) measuring the reflectance of the solid test material through the reflectance spectrometer;
ii) choosing one or a combination of the reflected wavelengths to provide a unique value for a given analyte concentration;
iii) determining the relationship between the color of the solid test material as reported by the reflectance spectrometer and the temperature of the solid test material for various analyte concentrations throughout the range of analyte concentration of interest;
iv) calculating a temperature factor difference in the reported color for each of the various analyte concentrations;
v) determining the corrected color value reported by the spectrometer by adjusting the color value for the temperature factor difference and deviation of the temperature from the nominal value;
vi) determining the corrected color value from the measured color and temperature; and vii) determining the analyte concentration in the fluid test sample from the corrected color value.
i) measuring the reflectance of the solid test material through the reflectance spectrometer;
ii) choosing one or a combination of the reflected wavelengths to provide a unique value for a given analyte concentration;
iii) determining the relationship between the color of the solid test material as reported by the reflectance spectrometer and the temperature of the solid test material for various analyte concentrations throughout the range of analyte concentration of interest;
iv) calculating a temperature factor difference in the reported color for each of the various analyte concentrations;
v) determining the corrected color value reported by the spectrometer by adjusting the color value for the temperature factor difference and deviation of the temperature from the nominal value;
vi) determining the corrected color value from the measured color and temperature; and vii) determining the analyte concentration in the fluid test sample from the corrected color value.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/773,269 US5972715A (en) | 1996-12-23 | 1996-12-23 | Use of thermochromic liquid crystals in reflectometry based diagnostic methods |
| US08/773,269 | 1996-12-23 |
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| CA2218008A1 CA2218008A1 (en) | 1998-06-23 |
| CA2218008C true CA2218008C (en) | 2005-03-01 |
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| CA002218008A Expired - Fee Related CA2218008C (en) | 1996-12-23 | 1997-10-10 | Use of thermochromic liquid crystals in reflectometry based diagnostic methods |
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| US (1) | US5972715A (en) |
| EP (1) | EP0851229B1 (en) |
| JP (1) | JPH10206411A (en) |
| AU (1) | AU718044B2 (en) |
| CA (1) | CA2218008C (en) |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011085728A1 (en) * | 2010-01-13 | 2011-07-21 | Flowsion Aps | Microfluidic system comprising a light emitting device |
Families Citing this family (79)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5972715A (en) * | 1996-12-23 | 1999-10-26 | Bayer Corporation | Use of thermochromic liquid crystals in reflectometry based diagnostic methods |
| US6036924A (en) | 1997-12-04 | 2000-03-14 | Hewlett-Packard Company | Cassette of lancet cartridges for sampling blood |
| US6391005B1 (en) | 1998-03-30 | 2002-05-21 | Agilent Technologies, Inc. | Apparatus and method for penetration with shaft having a sensor for sensing penetration depth |
| DE19952215C2 (en) * | 1999-10-29 | 2001-10-31 | Roche Diagnostics Gmbh | Test element analysis system |
| US6780296B1 (en) * | 1999-12-23 | 2004-08-24 | Roche Diagnostics Corporation | Thermally conductive sensor |
| US6612901B1 (en) * | 2000-06-07 | 2003-09-02 | Micron Technology, Inc. | Apparatus for in-situ optical endpointing of web-format planarizing machines in mechanical or chemical-mechanical planarization of microelectronic-device substrate assemblies |
| DE10032015A1 (en) | 2000-07-01 | 2002-01-10 | Roche Diagnostics Gmbh | Test strip analysis unit for bodily fluid, employs temperature history correction system which will not drain batteries |
| DE10057832C1 (en) | 2000-11-21 | 2002-02-21 | Hartmann Paul Ag | Blood analysis device has syringe mounted in casing, annular mounting carrying needles mounted behind test strip and being swiveled so that needle can be pushed through strip and aperture in casing to take blood sample |
| US8641644B2 (en) | 2000-11-21 | 2014-02-04 | Sanofi-Aventis Deutschland Gmbh | Blood testing apparatus having a rotatable cartridge with multiple lancing elements and testing means |
| US9795747B2 (en) | 2010-06-02 | 2017-10-24 | Sanofi-Aventis Deutschland Gmbh | Methods and apparatus for lancet actuation |
| US7041068B2 (en) | 2001-06-12 | 2006-05-09 | Pelikan Technologies, Inc. | Sampling module device and method |
| US7981056B2 (en) | 2002-04-19 | 2011-07-19 | Pelikan Technologies, Inc. | Methods and apparatus for lancet actuation |
| US9226699B2 (en) | 2002-04-19 | 2016-01-05 | Sanofi-Aventis Deutschland Gmbh | Body fluid sampling module with a continuous compression tissue interface surface |
| ES2357887T3 (en) | 2001-06-12 | 2011-05-03 | Pelikan Technologies Inc. | APPARATUS FOR IMPROVING THE BLOOD OBTAINING SUCCESS RATE FROM A CAPILLARY PUNCTURE. |
| AU2002348683A1 (en) | 2001-06-12 | 2002-12-23 | Pelikan Technologies, Inc. | Method and apparatus for lancet launching device integrated onto a blood-sampling cartridge |
| EP1404232B1 (en) | 2001-06-12 | 2009-12-02 | Pelikan Technologies Inc. | Blood sampling apparatus and method |
| US8337419B2 (en) | 2002-04-19 | 2012-12-25 | Sanofi-Aventis Deutschland Gmbh | Tissue penetration device |
| US9427532B2 (en) | 2001-06-12 | 2016-08-30 | Sanofi-Aventis Deutschland Gmbh | Tissue penetration device |
| WO2002100460A2 (en) | 2001-06-12 | 2002-12-19 | Pelikan Technologies, Inc. | Electric lancet actuator |
| US7316700B2 (en) | 2001-06-12 | 2008-01-08 | Pelikan Technologies, Inc. | Self optimizing lancing device with adaptation means to temporal variations in cutaneous properties |
| US6780602B2 (en) * | 2001-11-01 | 2004-08-24 | Microbiosystems, Limited Partnership | Taxonomic identification of pathogenic microorganisms and their toxic proteins |
| US7371247B2 (en) | 2002-04-19 | 2008-05-13 | Pelikan Technologies, Inc | Method and apparatus for penetrating tissue |
| US8702624B2 (en) | 2006-09-29 | 2014-04-22 | Sanofi-Aventis Deutschland Gmbh | Analyte measurement device with a single shot actuator |
| US7229458B2 (en) | 2002-04-19 | 2007-06-12 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US7901362B2 (en) | 2002-04-19 | 2011-03-08 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US7291117B2 (en) | 2002-04-19 | 2007-11-06 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US7674232B2 (en) | 2002-04-19 | 2010-03-09 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US7175642B2 (en) | 2002-04-19 | 2007-02-13 | Pelikan Technologies, Inc. | Methods and apparatus for lancet actuation |
| US9248267B2 (en) | 2002-04-19 | 2016-02-02 | Sanofi-Aventis Deustchland Gmbh | Tissue penetration device |
| US7547287B2 (en) | 2002-04-19 | 2009-06-16 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US7909778B2 (en) | 2002-04-19 | 2011-03-22 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US9314194B2 (en) | 2002-04-19 | 2016-04-19 | Sanofi-Aventis Deutschland Gmbh | Tissue penetration device |
| US7481776B2 (en) | 2002-04-19 | 2009-01-27 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US8784335B2 (en) | 2002-04-19 | 2014-07-22 | Sanofi-Aventis Deutschland Gmbh | Body fluid sampling device with a capacitive sensor |
| US8221334B2 (en) | 2002-04-19 | 2012-07-17 | Sanofi-Aventis Deutschland Gmbh | Method and apparatus for penetrating tissue |
| US7648468B2 (en) | 2002-04-19 | 2010-01-19 | Pelikon Technologies, Inc. | Method and apparatus for penetrating tissue |
| US7892183B2 (en) | 2002-04-19 | 2011-02-22 | Pelikan Technologies, Inc. | Method and apparatus for body fluid sampling and analyte sensing |
| US7297122B2 (en) | 2002-04-19 | 2007-11-20 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US7491178B2 (en) | 2002-04-19 | 2009-02-17 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US9795334B2 (en) | 2002-04-19 | 2017-10-24 | Sanofi-Aventis Deutschland Gmbh | Method and apparatus for penetrating tissue |
| US8579831B2 (en) | 2002-04-19 | 2013-11-12 | Sanofi-Aventis Deutschland Gmbh | Method and apparatus for penetrating tissue |
| US7708701B2 (en) | 2002-04-19 | 2010-05-04 | Pelikan Technologies, Inc. | Method and apparatus for a multi-use body fluid sampling device |
| US8267870B2 (en) | 2002-04-19 | 2012-09-18 | Sanofi-Aventis Deutschland Gmbh | Method and apparatus for body fluid sampling with hybrid actuation |
| US7331931B2 (en) | 2002-04-19 | 2008-02-19 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US7232451B2 (en) | 2002-04-19 | 2007-06-19 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US7717863B2 (en) | 2002-04-19 | 2010-05-18 | Pelikan Technologies, Inc. | Method and apparatus for penetrating tissue |
| US7976476B2 (en) | 2002-04-19 | 2011-07-12 | Pelikan Technologies, Inc. | Device and method for variable speed lancet |
| US8574895B2 (en) | 2002-12-30 | 2013-11-05 | Sanofi-Aventis Deutschland Gmbh | Method and apparatus using optical techniques to measure analyte levels |
| EP1443325A1 (en) * | 2003-02-01 | 2004-08-04 | Roche Diagnostics GmbH | System and method for determining a coagulation parameter |
| US7850621B2 (en) | 2003-06-06 | 2010-12-14 | Pelikan Technologies, Inc. | Method and apparatus for body fluid sampling and analyte sensing |
| WO2006001797A1 (en) | 2004-06-14 | 2006-01-05 | Pelikan Technologies, Inc. | Low pain penetrating |
| WO2005033659A2 (en) | 2003-09-29 | 2005-04-14 | Pelikan Technologies, Inc. | Method and apparatus for an improved sample capture device |
| US9351680B2 (en) | 2003-10-14 | 2016-05-31 | Sanofi-Aventis Deutschland Gmbh | Method and apparatus for a variable user interface |
| US20060257929A1 (en) * | 2003-11-12 | 2006-11-16 | Microbiosystems, Limited Partnership | Method for the rapid taxonomic identification of pathogenic microorganisms and their toxic proteins |
| US7822454B1 (en) | 2005-01-03 | 2010-10-26 | Pelikan Technologies, Inc. | Fluid sampling device with improved analyte detecting member configuration |
| US8668656B2 (en) | 2003-12-31 | 2014-03-11 | Sanofi-Aventis Deutschland Gmbh | Method and apparatus for improving fluidic flow and sample capture |
| US8828203B2 (en) | 2004-05-20 | 2014-09-09 | Sanofi-Aventis Deutschland Gmbh | Printable hydrogels for biosensors |
| EP1765194A4 (en) | 2004-06-03 | 2010-09-29 | Pelikan Technologies Inc | Method and apparatus for a fluid sampling device |
| US8652831B2 (en) | 2004-12-30 | 2014-02-18 | Sanofi-Aventis Deutschland Gmbh | Method and apparatus for analyte measurement test time |
| EP1909103A4 (en) * | 2005-07-14 | 2011-05-04 | Panasonic Corp | Analyzer and analyzing method |
| US20070132898A1 (en) * | 2005-11-04 | 2007-06-14 | Union College | Light transmission based liquid crystal temperature sensor |
| ES2712778T3 (en) | 2007-05-30 | 2019-05-14 | Ascensia Diabetes Care Holdings Ag | Method and system to manage health data |
| EP2203725A4 (en) | 2007-10-15 | 2011-04-20 | Bayer Healthcare Llc | Method and assembly for determining the temperature of a test sensor |
| US9386944B2 (en) | 2008-04-11 | 2016-07-12 | Sanofi-Aventis Deutschland Gmbh | Method and apparatus for analyte detecting device |
| PL2380009T3 (en) | 2008-12-18 | 2015-07-31 | Bayer Healthcare Llc | Assembly for determining the temperature of a test sensor |
| US9375169B2 (en) | 2009-01-30 | 2016-06-28 | Sanofi-Aventis Deutschland Gmbh | Cam drive for managing disposable penetrating member actions with a single motor and motor and control system |
| JP2012520994A (en) * | 2009-03-20 | 2012-09-10 | エフ．ホフマン−ラ ロシュ アーゲー | Test elements and methods for measuring body fluids |
| WO2010144441A1 (en) * | 2009-06-08 | 2010-12-16 | Bayer Healthcare Llc | Method and assembly for determining the temperature of a test sensor |
| US8965476B2 (en) | 2010-04-16 | 2015-02-24 | Sanofi-Aventis Deutschland Gmbh | Tissue penetration device |
| CN102375055A (en) * | 2010-08-19 | 2012-03-14 | 中国人民解放军军事医学科学院微生物流行病研究所 | Multiplex detection immune chromatography chip |
| CN103635568B (en) | 2011-06-24 | 2016-04-27 | 株式会社日立高新技术 | Nucleic acid amplifier and nucleic acid analyzer |
| US9063091B2 (en) | 2012-04-06 | 2015-06-23 | Ixensor Inc. | Test strips and method for reading test strips |
| US9778200B2 (en) | 2012-12-18 | 2017-10-03 | Ixensor Co., Ltd. | Method and apparatus for analyte measurement |
| EP3578959A3 (en) * | 2013-01-07 | 2020-02-26 | Ixensor Co., Ltd. | Method for reading test strips |
| US20140273270A1 (en) * | 2013-03-14 | 2014-09-18 | Polymer Technology Systems, Inc. | Direct temperature measurement of a test strip |
| WO2016123610A1 (en) * | 2015-01-30 | 2016-08-04 | Polymer Technology Systems, Inc. | Systems and methods for temperature correction in test strips for enzyme detection |
| WO2021138902A1 (en) * | 2020-01-10 | 2021-07-15 | 上海泰辉生物科技有限公司 | Point-of-care testing system for immunochromatographic strip |
| US20230046089A1 (en) * | 2021-08-13 | 2023-02-16 | Palo Alto Research Center Incorporated | Method and system for measuring the temperature of a thermochromic liquid crystal |
| CN117031164B (en) * | 2023-08-10 | 2024-03-26 | 国网山东省电力公司临沂供电公司 | Dry-type air-core reactor operating temperature intelligent supervision system based on data analysis |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3697297A (en) * | 1970-10-22 | 1972-10-10 | Ncr Co | Gelatin-gum arabic capsules containing cholesteric liquid crystal material and dispersions of the capsules |
| US4310577A (en) * | 1979-08-24 | 1982-01-12 | Liquid Crystal Products, Inc. | Liquid crystal film laminate |
| DE3135196A1 (en) * | 1981-09-05 | 1983-03-17 | Merck Patent Gmbh, 6100 Darmstadt | METHOD, MEANS AND DEVICE FOR DETERMINING BIOLOGICAL COMPONENTS |
| DK0485549T3 (en) * | 1990-06-04 | 1996-03-11 | Behring Diagnostics Inc | Analytical assay |
| WO1994000763A1 (en) * | 1992-06-24 | 1994-01-06 | Akzo Nobel N.V. | Method for determining multiple immunocomplexes on one surface using spectroscopy |
| EP0730760A1 (en) * | 1993-11-25 | 1996-09-11 | Technobiochip | Potentiometric biosensors, control and applications thereof |
| US5547283A (en) * | 1994-11-01 | 1996-08-20 | Kronberg; James W. | Optical temperature sensor using thermochromic semiconductors |
| US5972715A (en) * | 1996-12-23 | 1999-10-26 | Bayer Corporation | Use of thermochromic liquid crystals in reflectometry based diagnostic methods |
-
1996
- 1996-12-23 US US08/773,269 patent/US5972715A/en not_active Expired - Lifetime
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1997
- 1997-10-10 CA CA002218008A patent/CA2218008C/en not_active Expired - Fee Related
- 1997-12-10 EP EP97121706A patent/EP0851229B1/en not_active Expired - Lifetime
- 1997-12-10 DE DE69717065T patent/DE69717065T2/en not_active Expired - Lifetime
- 1997-12-10 ES ES97121706T patent/ES2186836T3/en not_active Expired - Lifetime
- 1997-12-19 JP JP9349858A patent/JPH10206411A/en active Pending
- 1997-12-22 AU AU48551/97A patent/AU718044B2/en not_active Ceased
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011085728A1 (en) * | 2010-01-13 | 2011-07-21 | Flowsion Aps | Microfluidic system comprising a light emitting device |
Also Published As
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|---|---|
| EP0851229A1 (en) | 1998-07-01 |
| US5972715A (en) | 1999-10-26 |
| AU4855197A (en) | 1998-06-25 |
| DE69717065D1 (en) | 2002-12-19 |
| ES2186836T3 (en) | 2003-05-16 |
| DE69717065T2 (en) | 2003-10-09 |
| CA2218008A1 (en) | 1998-06-23 |
| EP0851229B1 (en) | 2002-11-13 |
| AU718044B2 (en) | 2000-04-06 |
| JPH10206411A (en) | 1998-08-07 |
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