Surface‐Plasmonic‐Field‐Induced Photoredox Catalysis and Mediated Electron Transfer for Washing‐Free DNA Detection

Distance‐dependent electromagnetic radiation and electron transfer have been commonly employed in washing‐free fluorescence and electrochemical bioassays, respectively. In this study, we combined the two distance‐dependent phenomena for sensitive washing‐free DNA detection. A distance‐dependent surface plasmonic field induces rapid photoredox catalysis of surface‐bound catalytic labels, and distance‐dependent mediated electron transfer allows for rapid electron transfer from the surface‐bound labels to the electrode. An optimal system consists of a chemically reversible acceptor (Ru(NH3)63+), a chemically reversible photoredox catalyst (eosin Y), and a chemically irreversible donor (triethanolamine). Side reactions with O2 do not significantly decrease the efficiency of photoredox catalysis. Energy transfer quenching between the electrode and the label can be lowered by increasing the distance between them. Washing‐free DNA detection had a detection limit of approximately 0.3 nm in buffer and 0.4 nm in serum without a washing step. Two distance‐dependent phenomena (surface plasmonic field and mediated electron transfer) were combined to enable washing‐free electrochemical DNA detection. The surface plasmonic field decaying exponentially from a gold electrode induced rapid photoredox catalysis of the surface‐bound catalytic label (eosin Y, EY2−), and mediated electron transfer allowed for rapid electron transfer from eosin Y to the Au electrode (see picture; TEOA=triethanolamine).