An addressable electrode array was used for the production of acid at sufficient concentration to allow deprotection of the dimethoxytrityl (DMT) protecting group from an overlaying substrate bound to a porous reaction layer. Containment of the generated acid to an active electrode of 100 micron diameter was achieved by the presence of an organic base. This procedure was then used for the production of a DNA array, in which synthesis was directed by the electrochemical removal of the DMT group during synthesis. The product array was found to have a detection sensitivity to as low as 0.5 pM DNA in a complex background sample.

Procedures and results are described for multiplexed immunochemical assays using semiconductor microchips. The microchips used here are miniaturized arrays of individually addressable microelectrodes controlled by active CMOS circuitry. Electrode densities exceed 1000 per cm(2). The array chips are coated with a porous reaction layer material to provide a 'biofriendly' milieu overlaying the electrode array. Biotin is linked covalently to regions within the porous reaction layer proximate to selected microelectrodes. Covalent linkage is accomplished using reagents that are generated in situ by the microelectrodes. The covalent linkage of biotin within the porous reaction layer allowed traditional streptavidin (SA)-based immunoassay formats to be used on the biochips.Biochips were used to develop multiplexed assay formats for biological entities over a wide size range - from small organic molecules to cells. Sandwich immunoassays were used for larger entities and competitive immunoassays for smaller molecules. Detection of analytes was accomplished using fluorophore-tagged antibodies and epifluorescent microscopy. Results from a broad range of analytes are presented. (C) 2001 Elsevier Science BN. All rights reserved.