Amperometry and Electrochemical Sensors

Amperometry measures the current flowing at a fixed electrode potential to quantify an electroactive analyte, forming the basis of many practical electrochemical sensors and biosensors.

Definition

An electroanalytical technique in which the current at an electrode held at a constant potential is measured and related to the concentration of an electroactive species, often through a chemically selective sensing layer.

Scope

This topic covers amperometric detection: holding an electrode at a potential where the analyte reacts and recording the resulting diffusion-controlled current, the design of biosensors that couple enzymatic recognition to electrochemical transduction, the Clark oxygen electrode, mediated and direct electron-transfer schemes, and the analytical figures of merit of these devices. It spans clinical, environmental, and point-of-care sensing.

Core questions

• How does the current at a fixed potential report the concentration of an analyte?
• How do enzyme-based biosensors convert a specific chemical recognition event into an electrical signal?
• What roles do mediators and electrode modification play in amperometric sensing?
• What determines the sensitivity, selectivity, and response time of an amperometric sensor?

Key theories

Diffusion-limited amperometric current

At a potential past the analyte's redox wave, the steady current is controlled by the rate of analyte diffusion to the electrode and is proportional to bulk concentration, giving a linear analytical signal.

Enzyme-electrode transduction

A selective enzyme generates or consumes an electroactive species in proportion to the target analyte; detecting that species amperometrically, often via a redox mediator, gives a selective and quantitative sensor, as in glucose biosensors.

Clinical relevance

Amperometric biosensors dominate point-of-care diagnostics, most prominently blood-glucose monitoring for diabetes, and extend to lactate, oxygen, and other clinical analytes as well as environmental pollutant detection, valued for rapid, low-cost, miniaturizable measurement.

History

Clark's oxygen electrode (1956) and the Clark–Lyons enzyme-electrode concept (1962) launched amperometric biosensing; the field matured through mediated electron transfer and the commercial success of disposable glucose strips from the 1980s onward.

Key figures

• Leland C. Clark
• Joseph Wang
• Adam Heller

Seminal works

• wang2006
• wang2008
• bard2001

Frequently asked questions

How does a glucose sensor produce an electrical current from sugar?

An enzyme such as glucose oxidase reacts with glucose and, directly or through a mediator, transfers electrons to the electrode; the resulting current is proportional to the glucose concentration in the sample.

What is the difference between amperometry and voltammetry?

Voltammetry varies the potential and records current as a curve, whereas amperometry holds the potential constant and monitors current over time, making it well suited to continuous quantitative sensing of a single analyte.