Direct anodic electrografting of Osmium complexes on Indium tin oxide

Indium tin oxide (ITO) is a widely used electrode material in electrochemical biosensors owing to its beneficial characteristics such as transparency and chemical inertness. The exceptionally sluggish kinetics of heterogeneous electron transfer in ITO provides an exceptionally low background current, making electron mediators essential for electrochemical sensors. However, the chemical modification of ITO with molecular mediators is still challenging. Few straightforward and credible methods are available to obtain sufficiently thin mediator films firmly anchored on the ITO without losing its inherent benefits, including low background current and transparency. This study demonstrated the anodic electrografting of three osmium complexes, which allowed the formation of molecular mediator monolayers on ITO. The densely packed monolayer of osmium complexes retained their reversible redox processes over hundreds of potential cycles. We confirmed electron mediation by the modified electrodes for 4-aminophenol oxidation, suggesting a simple protocol for developing ITO-based biosensors functionalized with molecular mediators.