Mediator stabilized reagent compositions and methods for their use in electrochemical analyte detection assays

A dry reagent composition comprising:

• an enzyme;
• a redox mediator;
• an enzyme cofactor;
• and
• a mediator-stabilizing buffer comprising a polycarboxylic acid having at least two carboxylic acid groups, present in an amount in the range of 0.01% wt/wt to 40% wt/wt sufficient to stabilize said redox mediator during storage of the dry reagent composition, wherein said mediator-stabilizing buffer has a low binding affinity for divalent metal ions, said low binding affinity for divalent metal ions being at least 2-fold less than a divalent metal ion binding affinity of an enzyme/cofactor complex formed from the enzyme and the cofactor of the dry reagent mixture.

An electrochemical cell comprising a dry reagent composition that includes:

• an enzyme;
• a redox mediator;
• an enzyme cofactor;
• and
• a mediator-stabilizing buffer comprising a polycarboxylic acid having at least two carboxylic acid groups, present in an amount in the range of 0.01% wt/wt to 40% wt/wt sufficient to stabilize said redox mediator during storage of the dry reagent composition, wherein said mediator-stabilizing buffer has a low binding affinity for divalent metal ions, said low binding affinity for divalent metal ions being at least 2-fold less than a divalent metal ion binding affinity of an enzyme/cofactor complex formed from the enzyme and the cofactor of the dry reagent mixture.

A method for making an electrochemical test strip, the method comprising:

• making an electrochemical strip that includes:
• a dry reagent composition with:
• an enzyme;
• a redox mediator;
• an enzyme cofactor;
• and
• a mediator-stabilizing buffer comprising a polycarboxylic acid having at least two carboxylic acid groups, present in an amount in the range of 0.01% wt/wt to 40% wt/wt sufficient to stabilize said redox mediator during storage of the dry reagent composition, wherein said mediator-stabilizing buffer has a low binding affinity for divalent metal ions, said low binding affinity for divalent metal ions being at least 2-fold less than a divalent metal ion binding affinity of an enzyme/cofactor complex formed from the enzyme and the cofactor of the dry reagent mixture.

A method for determining the concentration of an analyte in a sample, said method comprising:

• (a) applying said sample to an electrochemical cell comprising a dry reagent composition that includes:
• an enzyme;
• a redox mediator;
• an enzyme cofactor;
• and
• a mediator-stabilizing buffer comprising a polycarboxylic acid having at least two carboxylic acid groups, present in an amount in the range of 0.01% wt/wt to 40% wt/wt sufficient to stabilize said redox mediator during storage of the dry reagent composition, wherein said mediator-stabilizing buffer has a low binding affinity for divalent metal ions, said low binding affinity for divalent metal ions being at least 2-fold less than a divalent metal ion binding affinity of an enzyme/cofactor complex formed from the enzyme and the cofactor of the dry reagent mixture;
• (b) detecting an electrical signal produced by said cell;
• and
• (c) relating said detected electrical signal to the concentration of said analyte in said sample.