The Osmium Tetroxide Bipyridine-labeled DNA Probe: Hairpin Conformations and Characterization of Redox-label Behavior

Osmium tetroxide bipyridine ([OsO₄(bpy)]) is a versatile label for DNA electrochemistry. Here we report our efforts to create an osmium tetroxide-labeled immobilized DNA probe for use in biosensing experiments. Our label is applied in-house, as opposed to many other covalent redox labels used with DNA. We developed an on-electrode labeling method that was able to avoid attack of our disulfide-based linker by the [OsO₄(bpy)]. Our results include two different hairpin-based signal-off hybridization detection assays, each with robust, reproducible signal decrease on binding to complementary target. We also found that 6-mercapto-1-hexanol was able to interact with [OsO₄(bpy)] in a stable manner when assembled at the surface, but was able to remove excess [OsO₄(bpy)], which was found to adsorb strongly to the gold surface, and avoid MCH transformation, when applied after the labeling process. Furthermore, we found an increased adsorption affinity of [OsO₄(bpy)]-labeled DNA onto gold, characterized the redox behavior of adsorbed [OsO₄(bpy)], and determined voltammetric signals on the HMDE of our intact disulfide linker while verifying that this linker is attacked by [OsO₄(bpy)] when in solution.