Direct mapping of local redox current density on a monolith electrode by laser scanning

• SEED can quantitatively maps multiple redox reactions on a monolith electrode.
• The signal from SEED enhance as the sensor electrode size reduces.
• SEED can measure non-turnover redox reaction in an immobilized enzyme monolayer on the electrode.
• SEED is a general tool to measure redox voltammogram.
• SEED is benchmarked with cyclic voltammetry (CV) by performing both measurements concomitantly.

An optical method of mapping local redox reaction over a monolith electrode using simple laser scanning is described. As the optical signal is linearly proportional to the maximum redox current that is measured concomitantly by voltammetry, the optical signal quantitatively maps the local redox current density distribution. The method is demonstrated on two types of reactions: (1) a reversible reaction where the redox moieties are ionic, and (2) an irreversible reaction on two different types of enzymes immobilized on the electrode where the reaction moieties are nonionic. To demonstrate the scanning capability, the local redox behavior on a “V-shaped” electrode is studied where the local length scale and, hence, the local current density, is nonuniform. The ability to measure the current density distribution by this method will pave the way for multianalyte analysis on a monolith electrode using a standard three-electrode configuration. The method is called Scanning Electrometer for Electrical Double-layer (SEED).