Oxygen reduction mediated by single nanodroplets containing attomoles of vitamin B12: electrocatalytic nano-impacts method.

We report the use of single Vitamin B12 nanodroplets to mediate the reduction of oxygen in neutral buffer. Electron transfer to single Vitamin B12 nanodroplets is observed using the nano-impacts method and shown to be quantitative. The mechanism of mediated oxygen reduction by single VB12 droplets is revealed as via both Co(II) and Co(I) reduced from Co(III) in VB12 through one or two electron transfer followed by the four-electron reduction of oxygen.