A new electrochemical approach for detecting target DNA is described. The scheme involves the catalytic oxidation of a cobalt bipyridine “reporter molecule” in solution. Probe/target DNA duplexes (ds-DNA), bound on an ITO electrode, selectively recruit redox catalyst molecules from solution. This surface-bound catalyst “turns on” the redox chemistry of the reporter molecule which is otherwise kinetically inert to oxidation on ITO. The mode of selective catalyst binding is intercalation between base pairs of ds-DNA. With this approach, we demonstrate detection of a 20-mer DNA target oligonucleotide at picomolar concentrations with outstanding signal-to-noise.