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 (cAb). The sandwich-type system was formed by specific recognition of the immobilized cAb on CNT/AuNP hybrids to E. coli, followed by the attachment of horseradish peroxidase-conjugated E. coli detection antibody (dAb-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 × 102 to 2.0 × 106 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.