Localized Electrochemistry on a 10 μm Spot on a Monolith Large Electrode: An Avenue for Electrochemical Microarray Analysis

By measurement of the modulation of ions under an ac field at the electrode/electrolyte interface layer (EIL) at a spatial modulation of 0.0001 nm, a quantitative measurement of local redox current on a 10 mu m spot of a working electrode is achieved at a sensitivity of 0.02 nA/spot. The spot is defined by the probe laser beam. We show the principle for two redox ions, [Fe(CN)(6)](3-) and [Ru(NH3)(6)](3+), on a 4 mm(2) Au electrode. The redox peaks from the optical and the electrochemical (cyclic voltammetry (CV)) responses, which are concomitantly measured, are within 0.005 V. The setup is identical to the conventional three-electrode measurement, and the laser beam does not perturb the electrochemical process. We demonstrate high sensitivity to read binding between two single-stranded DNA (ssDNA) on a 10 mu m spot for DNA microarray analysis where the signal is blind to nonspecific binding. Potentially, quantitative combinatorial electrochemistry can be performed on a monolith electrode by scanning the laser beam on the electrode.