Detection of Attomole Quantitites of DNA Targets on Gold Microelectrodes by Electrocatalytic Nucleobase Oxidation

The electrochemical detection of nucleic acid targets at low concentrations has a number of applications in diagnostics and pharmaceutical research. Self-assembled monolayers of alkanethiol-derivatized oligonucleotides on gold electrodes provide a useful platform for such detectors, and the electrocatalytic oxidation of nucleobases included in the DNA targets is a particularly sensitive method of electrochemical detection. A strategy has been developed for combining these two aspects by substituting either 7,8-dihydro-8-oxoguanine (8G) or 5-aminouridine (5U) into DNA targets. Upon hybridization of targets containing these modified nucleobases, electrocatalytic signals at probe-modified gold electrodes are observed in the presence of Os(bpy)32+, which oxidizes both 8G and 5U upon oxidation to the Os(III) state. Self-assembled monolayers were prepared on both macro (1.6 mm) and micro (25 μm) gold electrodes using published procedures involving C6-terminated alkanethiol oligonucleotides and mercaptohexanol a...