Chemical timer for a visual test strip

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.

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.

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.

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.