Low-Triggering-Potential Electrochemiluminescence from Surface-Confined CuInS2@ZnS Nanocrystals and their Biosensing Applications

Electrochemiluminescence (ECL) of low triggering potential is strongly anticipated for ECL assays with less inherent electrochemical interference and improved long-term stability of the working electrode. Herein, effects of the thiol capping agents and the states of luminophores, i.e., the thiol-capped CuInS2@ZnS nanocrystals (CuInS2@ZnS-Thiol), on the ECL triggering potential of CuInS2@ZnS-Thiol/N2H4·H2O were explored on the Au working electrode. The thiol capping agent of glutathione (GSH) not only enabled CuInS2@ZnS-Thiol/N2H4·H2O with the stronger oxidative-reduction ECL than other thiol capping agents but also demonstrated the largest shift for the ECL triggering potential of CuInS2@ZnS-Thiol/N2H4·H2O upon changing the luminophores from the monodispersed state to the surface-confined state. CuInS2@ZnS-GSH/N2H4·H2O exhibited an efficient oxidative-reduction ECL around 0.78 V (vs Ag/AgCl) with CuInS2@ZnS-GSH of the monodispersed state. Upon employing CuInS2@ZnS-GSH as the ECL tag and immobilizing them onto the Au working electrode, the oxidative-reduction ECL of CuInS2@ZnS-GSH/N2H4·H2O was lowered to 0.32 V (vs Ag/AgCl), which was about 0.88 V lower than that of traditional Ru(bpy)32+/TPrA (typically ∼1.2 V, vs Ag/AgCl). The ECL of the CuInS2@ZnS-GSH/N2H4·H2O system with the luminophore of both monodispersed and surface-confined states was spectrally identical to each other, indicating that this surface-confining strategy exhibited negligible effect on the excited state for the ECL of CuInS2@ZnS-GSH. A surface-confined ECL sensor around 0.32 V was fabricated with CuInS2@ZnS-GSH as a luminophore, which could sensitively and selectively determine the K-RAS gene from 1 to 500 pM with a limit of detection at 0.5 pmol L–1 (S/N = 3).