Development of an electrochemical immunoassay for rapid detection of E. coli using anodic stripping voltammetry based on Cu@Au nanoparticles as antibody labels

A sensitive electrochemical immunoassay for rapid detection of Escherichia coli has been developed by anodic stripping voltammetry (ASV) based on core-shell Cu@Au nanoparticles (NPs) as anti-E. coli antibody labels. The characteristics of Cu@Au NPs before and after binding with antibody were confirmed by transmission electron microscopy (TEM). After Cu@Au-labeled antibody reacted with the immobilized E. coli on Polystyrene (PS)-modified ITO chip, Cu@Au NPs were dissolved by oxidation to the metal ionic forms, and the released Cu²⁺ ions were determined at GC/Nafion/Hg modified electrode by ASV. The utilization of GC/Nafion/Hg modified electrode could enhance the sensitivity for Cu²⁺ detection with a concentration as low as 9.0 × 10^-12 mol/L. Since Cu@Au NPs labels were only present when antibody reacted with E. coli, the amount of Cu²⁺ directly reflected the number of E. coli. The technique could detect E. coli with a detection limit of 30 CFU/mL and the overall analysis could be completed in 2 h. By introducing a pre-enrichment step, a concentration of 3 CFU/10 mL E. coli in surface water was detected by the electrochemical immunoassay.