Since its popularization in the 1990's, the diazonium reduction reaction has gained prolific status as a method of carbon surface functionalization. However, its usefulness is limited by its tendency to passivate surfaces through the formation of multilayers which inhibit the access of analytes or redox mediators to the electrode surface. Precise control over the diazonium reduction reaction is required to limit the surface passivation associated with diazonium reduction, and by extension the reaction's viability in the preparation of electrochemical sensors. Previously published efforts have achieved approximate monolayer coverage through the use of chemical reagents or electrochemical techniques. Presented here is a method of controlling the diazonium reduction reaction that requires no additional reagents, is fast, simple, and tunable from sparse sub-monolayer coverage through multilayer formation. Monolayer to sub-monolayer coverage has been confirmed through the use of atomic force microscopy, and intact functional group delivery has been confirmed through x-ray photoelectron spectroscopy. Electrochemical passivation has been investigated through cyclic voltametric interrogation with a surface-sensitive redox couple (ferri/ferrocyanide) and was found to be within acceptable limits. Control of the diazonium reduction reaction's extent is achieved through manipulation of the parameters input during grafting which limit charge transfer, effectively dictating the number of molecules which are attached to the electrode. Monolayer coverages are achieved on bulk electrode surfaces in a matter of milliseconds, and coverage growth follows predictable trends. This precise and tunable control increases the usefulness of the diazonium reduction reaction in applications requiring preservation of the electrochemical properties of modified surface, such as in the fabrication of electrochemical biosensors.

Precise and tunable electrochemical control of the diazonium reduction reaction for sub-monolayer surface coverage

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