Spatial Confinement-Enhanced electrochemiluminescence of Gold nanoclusters in chitosan nanogels and its application for ultrasensitive detection of Aflatoxin B1

Gold nanoclusters (AuNCs), as a category of promising electrochemiluminescence (ECL) emitter, hold great potential for sensing applications. However, its application is still restricted by the relatively low ECL quantum yield and difficult to purification. In this work, AuNCs were confined in a soft chitosan (CS) nanogel matrix (AuNCs@CS) with good biocompatibility via a facile one-pot approach. The as-fabricated AuNCs@CS nanogels showed 2.4-fold ECL intensity relative to that of bare AuNCs without chitosan. The ECL enhancement was attributed to the increased percentage of Au(0) in AuNCs@CS nanogels, the confinement effect of chitosan nanogels, as well as chitosan as a polymer could reduce the diffusion of the radicals and prolong the excited state lifetime of AuNCs in ECL reaction. Moreover, the obtained AuNCs@CS nanogels are stable and easy to be purified by centrifugation. On this basis, a label-free ECL immunosensor for ultrasensitive detection of aflatoxin B1 (AFB1) was developed by using AuNCs@CS nanogels modified fluorine doped tin oxide (FTO) electrode as a sensing interface. The linear range of the proposed immunosensor for AFB1 detection was 3.16 × 10^-14 to 3.16 × 10^-12 g/mL with a detection limit of 9.3 × 10^-15 g/mL, which was at least one order of magnitude lower than the reported ECL biosensor of AFB1. The proposed strategy may be used for the determination of other toxins in the Aflatoxin family if corresponding antibodies are available, which is of great significance for the quality control of Chinese herbal medicine and food safety.