Monitoring β-galactosidase activity by means of scanning electrochemical microscopy

The activity of β-galactosidase from Escherichia coli was characterized by scanning electrochemical microscopy (SECM). β-Galactosidase microspots were patterned by immobilizing biotin-labelled β-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 generation-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 β-galactosidase microspot arrays and the capability of SECM to resolve enzyme activity over individual enzyme microspots were demonstrated.