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 μm 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 mm2 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 μm 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.
ASJC Scopus subject areas
- Analytical Chemistry