Low-Triggering-Potential Single-Color Electrochemiluminescence from Bovine Serum Albumin-Stabilized Unary Au Nanocrystals for Immunoassays

Herein, low-triggering-potential (LTP) electrochemiluminescence (ECL) with an onset around 0.0 V (vs Ag/AgCl) is proposed with bovine serum albumin (BSA)-stabilized Au nanocrystals (BSA–AuNCs) as a luminophore and hydrazine hydrate (N2H4) as a coreactant. The BSA–AuNCs/N2H4 system can exhibit efficient LTP-ECL around 0.37 V with the luminophore of both monodispersed and surface-confined states. The LTP-ECL of BSA–AuNCs/N2H4 is a kind of single-color emission with a maximum emission wavelength around 740 nm, which is obviously red-shifted for 80 nm from that of BSA–AuNCs PL, and indicates that the ECL is generated in a surface-defect-involved route instead of the band-gap-engineered route. Importantly, BSA–AuNCs can be utilized as ECL tags to perform sandwich-type immunoassays with acceptable sensitivity and selectivity, which exhibits a wide linear response for determining CA125 from 0.5 to 1000 mU/mL and a limit of detection of 0.05 mU/mL (S/N = 3).