Reagents for electrochemical test strips

Inventors

Harding, Ian • Lee, Mary Y. • Tan, Sandie

Assignees

Agamatrix Inc

Abstract

A dry reagent composition that includes an active redox enzyme that oxidizes an analyte as a specific substrate to produce an inactive reduced form of the enzyme; and a salt of ferricyanide provides improved performance in electrochemical test strips such as those used for detection of glucose. The salt of ferricyanide consists of ferricyanide and positively-charged counter ions, and the positively charged counter ions are selected such that the salt of ferricyanide is soluble in water, and such that the salt of ferricyanide or the crystalline phase of the salt of ferricyanide has a solubility in water and/or a lower E0eff at a concentration of 100 mM than potassium ferricyanide. For example, the salt of ferricyanide may be tetramethylammonium ferricyanide.

Core Innovation

The invention provides improved electrochemical test-strip reagents for detecting an analyte using an active redox enzyme that oxidizes the analyte as a specific substrate to produce an inactive reduced form of the enzyme. The reagents include ferricyanide salts intended to enable electrochemical measurement while controlling changes that occur during drying and aging. The document emphasizes ferricyanide with specific positively charged counter ions to improve water solubility while reducing baseline signal growth associated with ferricyanide-to-ferrocyanide conversion.

Changing the positively charged counter ion is described as improving shelf stability by reducing baseline signal growth from ferricyanide-to-ferrocyanide conversion during drying and aging. The text compares alternative ferricyanide salts including tetramethylammonium ferricyanide and rubidium ferricyanide relative to potassium ferricyanide, linking selection to water solubility and to lower effective electrode potential E0eff at a stated condition. The dry reagent composition can be combined with an aqueous liquid carrier to form a liquid composition for use with electrochemical sensing.

The reagents and compositions optionally include additional components that support performance, including non-ferricyanide electron-transfer mediators and zwitterionic buffering agents and zwitterionic wetting agents with defined alkyl tail length. The document describes dry and liquid reagent compositions and electrochemical test strip construction conceptually using non-reactive electrodes, along with analyte testing via applied potential or current. Conceptual reaction schemes and performance comparisons are presented to support selection of ferricyanide salts and the optional mediator, buffer, and wetting chemistry for baseline and current stability after aging.

Claims Coverage

The independent claims cover three inventive features: a specific buffer solution, a method of forming a liquid composition by combining an aqueous liquid carrier with a dry reagent composition containing an active redox enzyme and tris-tetramethylammonium ferricyanide, and the resulting liquid composition containing the same core enzyme and ferricyanide components.

Across the independent claims, the core claim coverage is for a specific enzyme-plus-ferricyanide electrochemical reagent system using tris-tetramethylammonium ferricyanide in a liquid composition formed from an aqueous liquid carrier and a dry reagent composition, together with a separately recited buffer solution using a tetramethylammonium salt of a conjugate base. Dependent claim refinements further direct specific mediator and zwitterionic buffer and wetting components and related performance or structural constraints.

Stated Advantages

Documented Applications