Chemical timer for a visual test strip
First Claim
1. A chemical timer for a visual-reading reagent test strip for measuring the concentration of glucose in a biological fluid that is applied to the strip, the timer comprising a dry coating ofa) a colored indicator composition,b) a reagent that, when hydrated, reacts with glucose to change the color of the indicator,c) an inhibitor to inhibit the change in color of the indicator, andd) glucose,in which the inhibitor and glucose concentrations in the dry coating are selected so that the glucose, over a predetermined time after the biological fluid is applied to the strip, reacts with the reagent to change the color of the indicator.
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Abstract
A chemical timer for a direct-reading reagent test strip changes color a predetermined time after a biological fluid is applied to the strip. The strip measures the concentration of an analyte in the fluid. The timer is a dry coating of an indicator, an enzyme-containing reagent that when hydrated can react with glucose to change the color of the indicator, an inhibitor to inhibit the change in color of the indicator, glucose, and optionally, an aldose that does not react with the enzyme in the reagent. Preferably, the reagent and glucose are present in excess in the coating, and the time it takes for the timer color to change can be controlled by the inhibitor concentration. The aldose provides timer stability, probably by interfering with glycosylation by the glucose in the dry state.
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Citations
23 Claims
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1. A chemical timer for a visual-reading reagent test strip for measuring the concentration of glucose in a biological fluid that is applied to the strip, the timer comprising a dry coating of
a) a colored indicator composition, b) a reagent that, when hydrated, reacts with glucose to change the color of the indicator, c) an inhibitor to inhibit the change in color of the indicator, and d) glucose, in which the inhibitor and glucose concentrations in the dry coating are selected so that the glucose, over a predetermined time after the biological fluid is applied to the strip, reacts with the reagent to change the color of the indicator.
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9. A method for preparing a chemical timer for a visual-reading reagent test strip for measuring the concentration of glucose in a biological fluid that is applied to the strip, comprising the steps of
a) coating onto a porous membrane a solution of a reagent that, when hydrated, reacts with glucose to form a reaction product, b) drying the coating to form a first layer c) applying onto the first layer a second layer that contains (i) glucose, (ii) an indicator that reacts with the reaction product to cause a color change, and (iii) an inhibitor to inhibit the change in color of the indicator.
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11. A method for measuring the concentration of glucose in a biological fluid comprising the steps of
(a) applying the fluid to a test strip that comprises (i) a plurality of result segments that each change color when contacted with fluid containing at least a predetermined amount of glucose, different from the amount of glucose that causes a change in color of the other segments and (ii) a timer segment that changes color after a time whose duration is substantially independent of the amount of glucose in the fluid and (b) determining the glucose concentration by observing the result segment that has changed color last when the timer segment changes color.
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12. A chemical timer for a visual reading test strip for measuring the concentration of an analyte in a biological fluid that is applied to the strip, the timer comprising a dry coating of
a) a colored indicator composition b) an enzyme-containing reagent that, when hydrated, reacts with an analyte to change the color of the indicator; -
c) an inhibitor to inhibit the change in color of the indicator, d) glucose, and e) an aldose that does not react substantially with the enzyme in the reagent. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method for preparing a chemical timer for a visual reading test strip for measuring the concentration of an analyte in a biological fluid that is applied to the strip, comprising the steps of
a) coating onto a porous membrane a solution of an enzyme-containing reagent that, when hydrated, reacts with an analyte to form a reaction product, b) drying the coating to form a first layer, and c) applying onto the first layer a second layer that contains (i) an indicator that reacts with the reaction product to cause a color change, (ii) an inhibitor to inhibit the change in color of the indicator, (iii) glucose, and (iv) an aldose that does not react substantially with the enzyme in the reagent.
Specification