Optimized ferrocene-functionalized ZnO nanorods for signal amplification in electrochemical immunoassay of Escherichia coli

A novel amplified electrochemical immunoassay based on ferrocene (Fc)-functionalized ZnO nanorods (NRs) was developed in the present work. The detection antibody ( d Ab) and Fc were immobilized onto the surface of ZnO NRs, denoted as { d Ab–ZnO–Fc} bioconjugates. The amount of d Ab and Fc in the bioconjugates was investigated using the copper reduction/bicinchoninic acid reaction (BCA protein assay) and inductive coupled plasma-atomic emission spectroscopy (ICP-AES), respectively. Greatly amplified signal was achieved in the sandwich-type immunoassay when d Ab and Fc linked to ZnO NRs at a proper ratio. Using Escherichia coli ( E. coli ) as a model antigen, the designed immunoassay showed an excellent analytical performance, and exhibited a wide dynamic response range of E. coli concentration from 10 2 to 10 6   cfu/mL with a detection limit of 50   cfu/mL ( S / N   =   3). By introducing a pre-enrichment step, the detection of 5   cfu/10   mL E. coli in hospital sewage water was realized. This proposed signal amplification strategy was promising and could be easily extended to monitor other biorecognition events.