Fe₃O₄@Au nanoparticles as labels for electrochemical immunodetection of E. coli in water

Fe₃O₄@Au nanoparticles were synthesized in this paper. The surface of nanoparticles was modified with horseradish peroxidase(HRP)-anti-E. coli antibody for amplified electrochemical immunoassay of E. coli. Poly-thionine(PTH) film was electro-polymerized on the GCE as an electron-transfer mediator. Gold nanoparticles(GNPs) on the PTH film constructed an effective antibody immobilization matrix. Using the typical sandwich type immmunoassay, E. coli could be detected according to the H₂O₂ reduction currents catalyzed by HRP labeled on anti-E. coli antibody. The method allowed quantitative determination of E. coli concentration from 50 to 1×10⁵ cfu/mL, with a detection limit of 20 cfu/mL. By introducing pre-enrichment steps, a concentration of 2 cfu/mL E. coli was detected with this method.