Abstract
We have utilized protective oligonucleotides to modify DNA fragments with osmium tetroxide complexes without compromising their ability to hybridize with immobilized thiol-linked probe-SAMs on gold electrodes. Due to reversible voltammetric signals of Os(VI/IV), this method allowed sensitive electrochemical hybridization detection of short (25 bases) and long (120 bases) thymine-containing DNA targets. The detection limit was 3.2 nM for the long target. We found an optimum 40 degrees C hybridization temperature for the short target. No interference by noncomplementary DNA was observed. At least 10 repetitive hybridization experiments at the same probe-SAM were possible with thermal denaturation in between. Such use of protective strands could be useful also for other types of DNA recognition and even for other DNA-modifying agents. Moreover, it is possible to produce electrochemically active oligonucleotides (targets and reporter probes) in ones own laboratory in a simple way.
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