DNA hybridization sensor based on aurothiomalate electroactive label on glassy carbon electrodes

In this work, a gold complex is used as electroactive label for monitoring hybridization assays on glassy carbon electrodes. Ionic gold is bound to a 30-mer sequence of the SARS (severe acute respiratory syndrome) virus, responsible for the atypical pneumonia, using sodium aurothiomalate. In order to label this single strand, a mixture of sodium aurothiomalate and the strand is prepared. Then, it is incubated for 24 h at 37 °C and, finally, free gold is separated from the labeled strand by a dialysis against a 0.15 M NaCl solution (pH 7.5). The DNA hybridization sensor is designed immobilizing the complementary probe on the pre-treated electrode surface and, then, the hybridization reaction takes place with the gold labeled strand. The electrochemical determination is based on the catalytic effect of electrodeposited gold on the reduction of silver ions. In non-stringent experimental conditions, a limit of detection of 15 fmol (30 μL) is obtained, and discrimination between a complementary oligonucleotide and a three-based mismatch complementary oligonucleotide is achieved. For the discrimination of a single-base mismatch, is needed to use stringent conditions (50% of formamide in the hybridization buffer).