This work designed an ultrasensitive electrochemical immunosensor for microcystin-LR (MC-LR) detection using gold nanoparticle functional polypyrrole microsphere (AuNP/PPyMS) as a novel signal tag to induce silver enhancement for signal amplification. The dispersed polypyrrole microsphere (PPyMS) synthesized with a chemical oxidative polymerization was used to load AuNP for labeling signal antibodies, which enhanced the detection signal due to large surface area. The proposed MC-LR immunosensor was constructed by coating a polyethylene glycol film on a carbon nanotubes modified electrode and then immobilizing MC-LR antigen on the film. With a competitive immunoassay format, coated MC-LR competed for MC-LR antibody with added target MC-LR to form antibody-antigen immunocomplex. Subsequently, the immunocomplex reacted with AuNP/PPyMS labeled signal antibodies. The MC-LR immunoreaction monitoring was achieved by the electrochemical stripping signal of the deposited silver catalyzed by AuNP/PPyMS. AuNP/PPyMS-mediated silver enhancement along with carbon nanotubes-promoted electron transfer led to high detection sensitivity of MC-LR. Under optimal conditions, the MC-LR immunoassay had a wide linear range of 0.25 ng L-1 to 50 μg L-1 , low detection limit of 0.1 ng L-1 , and good precision, reproducibility and stability. The designed amplification strategy has potential application in the ultrasensitive electrochemical detection of other algae toxins.

was used as a tracing tag to label signal antibody, which induced silver deposition for anodicstripping analysis. The immunosensor was constructed by immobilizing capture antibody on carbon nanohorns modified electrode with the aid of polyethylene glycol film. Through a sandwich-type immunoreaction, Au/Bi 2 S 3 NRs tags were captured on the immunoconjugates to induce a silver deposition process. The electrochemical stripping signal of the deposited silver was used to monitor the immunoreaction. The Au/Bi 2 S 3 NRs-mediated silver enhancement along with the carbon nanohorns-promoted electron transfer led to high detection sensitivity of E. coli O157:H7 antigen. Under the optimal conditions, the immunosensor exhibited a wide linear dependence on the logarithm of the concentration of E. coli ranging from 40 to 2.0 × 10 6 cfu mL −1 with a detection limit of 6 cfu mL −1 . Moreover, the proposed sensor was successfully applied in the detection of E. coli O157:H7 in real samples indicating its possibility in practical application.