Promising Mercaptobenzoic Acid-Bridged Charge Transfer for Electrochemiluminescence from CuInS2@ZnS Nanocrystals via Internal Cu+/Cu2+ Couple Cycling.

Screening novel electrochemiluminescence (ECL) systems with less inherent interference is strongly anticipated for ECL evolution. Herein, near-infrared ECL (∼730 nm) with an ultralow triggering potential of 0.45 V (vs Ag/AgCl) is achieved under physiological conditions with 4-mercaptobenzoic acid (MBA) and citrate capped CuInS2@ZnS (CIS@ZnS) nanocrystals (NCs), which is promising for less autofluorescence and electrochemical interference. Cu+ species within the CIS@ZnS NCs can be electrochemically oxidized at 0.45 V to form internal Cu2+ defects, while the capping agent MBA can bridge a direct charge transfer between the oxidized NCs and the traditional coreactant tripropylamine (TPrA) for weak ECL at 0.45 V. When hydrazine hydrate is adopted as coreactant, CIS@ZnS NCs/hydrazine hydrate exhibits 8k-fold enhanced oxidative-reduction ECL via the internal Cu+/Cu2+ couple cycling at 0.45 V in comparison to CIS@ZnS NCs/TPrA. This work opens a way to enhance the radiative charge transfer of NCs.