Microelectrode array (MEA) devices were employed to investigate the direct electrochemistry of three redox proteins, namely: horse heart cytochrome c, amicyanin from Thiobacillus versutus and amicyanin from Paracoccus denitrificans. Cyclic voltammetric experiments were carried out with arrays of 15 x 15 square-shaped gold microdisks of 5 mum in dimension. The gold microelectrodes were defined by a photoresist or silicon nitride coating as the insulating layer. The occurrence of well-behaved, steady-state responses of the redox proteins only at MEAs fabricated with photoresist may be explained by a model which assumes that one component of the photoresist acts as a facilitator enabling electron transfer between the microelectrodes and the protein molecules. It could be shown that the photoresist facilitates the electrochemistry of positively and negatively charged proteins. The formal redox potentials of both types of amicyanin were studied over a range of solution pH. In agreement with previous studies, the formal redox potentials increased with decreasing pH because of the redox inactivity of amicyanin in the Cu-I state at low pH. These experiments demonstrated that photoresist-coated MEAs can be employed as versatile tools to gain insight into the properties of redox biomacromolecules. (C) 2000 Elsevier Science B.V. All rights reserved.