Redox-Induced Switching of the Viscoelasticity of DNA Layers Observed by using Electrochemical Quartz Crystal Microbalance on the Millisecond Timescale

The interactions of single-stranded DNA (ssDNA) immobilized on gold electrodes with hexammine ruthenium(III) (RuHex) and hexammine cobalt(III) (CoHex) were investigated with chronocoulometric and electrochemical quartz crystal microbalance experiments. The modified surfaces were created by immobilizing ssDNA with tris(dithioserinol) linkers to form a compact, self-assembled monolayer, followed by passivation with 6-mercapto-1-hexanol (MCH). Upon addition of the redox indicator during a potential jump for RuHex and CoHex, we observed a dramatic increase in the frequency response in comparison to the signal observed with only low-ionic-strength hybridization buffer, 10 mM tris(hydroxymethyl)-aminomethane (Tris)/H2SO4 (pH7.4). RuHex and CoHex responded quite differently, even on a millisecond time scale. As the expected mass change is less than a factor of 35 to the observed frequency response, we concluded that the applied potential jumps lead to switching of the DNA layer viscoelasticity.