Surface-Defect-Induced and Synergetic-Effect-Enhanced NIR-II Electrochemiluminescence of Au–Ag Bimetallic Nanoclusters and Its Spectral Sensing

Aqueous electrochemiluminescence (ECL) in the second near-infrared biowindow (NIR-II, 900–1700 nm) was anticipated for ECL evolution and spectral multiplexing. Herein, aqueous and monochromatic ECL with a single emission peak beyond 900 nm was achieved by employing methionine (Met)-capped Au–Ag bimetallic nanoclusters (BNCs) as luminophores and triethanolamine (TEOA) as a coreactant. The Met-capped Au–Ag BNCs with surface-defect-induced PL around 756 nm were water-soluble and synthesized via doping Met-capped Au NCs with Ag in a doping-in-growth way. By extensively exploiting the red-shifting nature of surface-defect-induced ECL to PL and the synergetic-effect-enhanced ECL of BNCs, physically surface-confined Au–Ag BNCs exhibited efficient NIR-II ECL around 906 nm in aqueous medium. A spectrum-based NIR-II ECL immunoassay around 915 nm was also achieved by immobilizing the Au–Ag BNCs onto an electrode surface via forming a sandwich immunocomplex, which could selectively determine CA125 from 5 × 10–4 to 1 U/mL with a detection limit of 5 × 10–5 U/mL (S/N = 3). The combined strategy of surface-defect-induced ECL and synergetic-effect-enhanced ECL would enable promising biorelated application of NIR-II ECL.