Hybrid Nanostructure-based Immunosensing for Electrochemical Assay of Escherichia coli as Indicator Bacteria Relevant to the Recycling of Urban Sludge

Effective assay of Escherichia coli ( E. coli ) as indicator bacteria is critical for evaluating the recycling of urban sludge. In this work, we utilized multiwalled carbon nanotube/gold nanoparticle (CNT/AuNP) hybrid nanostructures as sensing electrode to design a novel electrochemical immunosensor for E. coli analysis. Herein, the hybrid nanostructures were fabricated by electrodepositing AuNPs on CNTs surface via multi-potential step technique. The CNT/AuNP hybrids were proved to facilitate the improvement of electrochemical performance for signal amplification, as well as the immobilization of E. coli capture antibody ( c Ab). The sandwich-type system was formed by specific recognition of the immobilized c Ab on CNT/AuNP hybrids to E. coli , followed by the attachment of horseradish peroxidase-conjugated E. coli detection antibody ( d Ab-HRP) to produce the electrochemical immunosensor. On the basis of the dual signal amplification of CNT/AuNP hybrid nanostructures and enzymatic catalysis, the electrochemical immunosensor exhibits an excellent performance for E. coli assay ranging from 2.0 × 10 2 to 2.0 × 10 6 cfu mL −1 . The electrochemical method was also successfully used to evaluate E. coli in urban sludge. The proposed strategy provides a convenient and effective method for E. coli detection, and could become a promising technique for estimating the feasibility of sludge recycling.