Electrochemical behavior of methylene blue at bare and DNA-modified silver solid amalgam electrodes

Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used for a voltammetric study of methylene blue (MB) at a mercury meniscus-modified silver solid amalgam electrode (m-AgSAE). Electrochemical impedance spectroscopy (EIS) was used for the verification and comparison of results. DPV offered sensitive detection of MB (in 0.1 mol L-1 phosphate buffer of pH 7.0) at both a bare and a DNA-modified silver amalgam electrode. MB gives a specific cathodic signal related to the reduction of this redox intercalator. This signal is significantly higher at the DNA-modified than at the unmodified silver amalgam electrode, which is in correspondence with the changes in charge transfer resistance values obtained from Nyquist plots. The concentration of double-stranded DNA (dsDNA) to form a layer (0.1 mg mL(-1)), the time of the dsDNA spontaneous immobilization on the surface of the electrode (1 min), the concentration of MB (1 x 10(-5) mol L-1), and the time of the accumulation of MB into the dsDNA layer (1 min) were optimized for further biosensor development and applications.