With the possible use of DNA in molecular electronic applications as either a scaffold for conducting wires  or a conducting wire itself , the need to assemble and detect DNA on metal electrodes has emerged. Whilst the use of fluorescent tags to detect DNA on non-metallic surfaces is widely applied in DNA microarrays, using the same technique on metallic surfaces proves difficult owing to electronic quenching of fluorescence by the close proximity of the metal surface .
Using a colorimetric detection method, we are able to detect biotinylated oligonucleotides hybridised to thiolated complementary strands bound to a gold surface. Bulk concentrations down to 10-9 M of biotinylated oligonucleotides were detectable. Unlike previous colorimetric detection methods [4,5], our method has the advantage of providing spatial information of the binding event, which is of higher resolution than that of an optical microscope. In addition it can also be used on a metal surface, unlike previous colorimetric detection methods. We are able to detect biotinylated single-stranded DNA from a solution containing a maximum number of only 7000 molecules on a microarray size spot (approx. 40 µm diameter, see Figure). This is equivalent to a minimum detectable surface coverage of 7×108 molecules per cm2, assuming that all the 7000 molecules in the solution hybridise to the surface. The real minimum detectable surface coverage is probably even one or two orders of magnitude lower, making our detection mechanism much more sensitive than, for example, surface plasmon resonance amplified by gold nanoparticles.
E. Braun, Y. Eichen, U. Sivan and G. Ben-Yoseph Nature1998, 391, 775.
Y.A. Berlin, A.L. Burin and M.A. Ratner Supperlattice. Microst.2000, 28, 241.