Voltammetric Detection of Thrombin by Labeling with Osmium Tetroxide Bipyridine and Binding with Aptamers on a Gold Electrode

This communication reports on electrochemical detection of thrombin based on labeling with osmium tetroxide bipyridine [OsO₄(bipy)]. Tryptophan amino acids can be labeled at the C−C-double bond, and at least some tryptophan moieties are accessible for labeling in thrombin. Using the catalytic hydrogen signal from adsorptive stripping voltammetry performed on hanging mercury drop electrode, we could detect as little as 1.47 nM [OsO₄(bipy)]-modified thrombin. We also tested the binding of [OsO₄(bipy)]-modified thrombin with the classic thrombin binding aptamer (TBA) on gold electrodes. This preliminary study revealed that even after modification, a major part of the affinity was conserved, and that the aptamer self-assembled monolayer (SAM) could be regenerated several times. Molecular simulations confirm that [OsO₄(bipy)]-modified thrombin largely preserves the high binding affinity also of the alternative HD22 aptamer to thrombin, albeit at slightly reduced affinities due to steric hindrance when tryptophans 96 and 237 are labelled. Based on these simulations, compensatory modifications in the aptamer should result in significantly improved binding with labelled thrombin. This combined experimental-computational approach lays the groundwork for the rational design of improved aptamer sensors for analytical applications.