Cobalt ion doping to improve electrochemiluminescence emisssion of gold nanoclusters for sensitive NIR biosensing

Screening highly efficient luminophores has attracted considerable attention in bioanalysis. To improve the emission efficiency of nanoclusters (NCs), this work designed an ion doping strategy for regulating the electcrochemiluminesent (ECL) emisssion of gold nanoclusters (AuNCs). This strategy could be conveniently performed by doping cobalt ions (Co2+) in cysteamine and N-acetyl-L-cysteine stabilized AuNCs, which not only generated tunable hole-injection channels for the ECL emission, but also reduced the superficial defects to promote electron transfer through the synergetic effect of Au and Co2+. The obtained Co2+-AuNCs displayed 0.2 V lower anodic emission potential and double ECL efficiency and intensity in the near-infrared region (NIR) compared to the AuNCs. Benefitting from the enhanced NIR ECL emission and the excellent biocompatibility of Co2+-AuNCs, as well as the lowered background interference, a sensitive “signal-on” immunosensor using neuron specific enolase (NSE) as a model analyte was proposed. This ECL biosensing method showed a limit of detection (LOD) of 0.16 fg/mL (S/N = 3), a linear range from 0.5 fg/mL to 1 ng/mL, excellent specificity and good practicability, demonstrating the excellent ECL performance of Co2+-AuNCs in bioanalysis. This work provides a way to modulate the ECL features of NCs-based luminophores and improve the performance of ECL bioassay.