The activity of beta-galactosidase from Escherichia coli was characterized by scanning electrochemical microscopy (SECM). beta-Galactosidase microspots were patterned by immobilizing biotin-labelled beta-galactosidase on streptavidin-coated paramagnetic beads and depositing the beads as microscopic microspots on a hydrophobic surface. The enzyme activity was mapped with SECM in the gene ration-collection mode by monitoring the oxidation of p-aminophenol formed in the galactosidase-catalyzed hydrolysis at the surface of the beads. The electrochemical properties of the enzyme substrate and product were studied with a platinum ultramicroelectrode, and the imaging conditions were optimised. The suitability of the procedure for forming beta-galactosidase microspot arrays and the capability of SECM to resolve enzyme activity over individual enzyme microspots were demonstrated. (C) 2003 Elsevier B.V. All rights reserved.