Adsorptive stripping voltammetric detection of single-stranded DNA at electrochemically modified glassy carbon electrode

Electrochemically modified glassy carbon electrode (GCE) was used to study the electrochemical oxidation and detection of denatured single-stranded (ss) DNA by means of adsorptive stripping voltammetry. The modification of GCE, by electrochemical oxidation at +1.75 V (vs.SCE) for 10 min and cyclic sweep between +0.3 V and -1.3 V for 20 cycles in pH 5.0 phosphate buffer, results in 100-fold improvement in sensitivity for ssDNA detection. We speculated that the modified GCE has a high affinity to single-stranded DNA through hydrogen bond (specific static adsorption). Single-stranded DNA can accumulate at the GCE surface at open circuit and produce a well-defined oxidation peak corresponding to the guanine residues at about +0.80 V in pH 5.0 phosphate buffer, while the native DNA gives no signal under the same condition. ne peak currents are proportional to the ssDNA concentration in the range of 0-18.0 mug mL(-1). The detection limit of denatured ssDNA is ca. 0.2 mug mL(-1) when the accumulation time is 8 min at open circuit. The accumulation mechanism of ssDNA on the modified GCE was discussed.