Promising Electrochemiluminescence from CuInS2/ZnS Nanocrystals/Hydrazine via Internal Cu(I)/Cu(II) Couple Cycling.

Screening a novel electrochemiluminescence (ECL) system is crucial to ECL evolution. Herein, an efficient ECL system with less interference and environmental concern under physiological condition is developed via a unique internal Cu(I)/Cu(II) couple cycling amplified strategy by employing the glutathione- and citrate-capped copper indium sulfide (CIS)/ZnS nanocrystals (NCs) as electrochemiluminophore and N2H4·H2O as co-reactant. CIS/ZnS NCs can be electrochemically injected with valence band (VB) hole at 0.46 and 0.87 V (vs Ag/AgCl), and then achieve the same hole-injected states by relocalizing VB holes with the Cu(I) species inside of CIS/ZnS NCs to form internal Cu(II) defects, while each N2H4·H2O molecule can be successively oxidized to two more reducing species N2H3• and N2H2 around 0.10 V, and inject conduction band (CB) electron onto CIS/ZnS NCs for triple times. The internal Cu(I)/Cu(II) couple cycling involved radiative-charge recombination between these VB hole and CB electron eventually enables two efficient near-infrared ECL processes (around 731 nm) at 0.55 and 0.87 V, in which each single nanocrystal may participate in multiple ECL reaction cycles to produce multiple photons for amplified ECL, similar to the tris(bipyridyl)ruthenium(III) based ECL system. The low-triggering-potential ECL process at 0.55 V can be utilized to selectively determine Cu(II) with a wide linear range from 10 and 1500 nM and a limit of detection of 5 nM (S/N = 3). This work presents a NCs engineering and co-reactant selecting combined strategy for further ECL evolution.