Label-Free Electrochemical Biosensing Architecture Based on a Protein-Decorated Pt@BSA Nanocomposite for Sensitive Immunoassay of Pathogenic Escherichia coli O157:H7

Electrochemical immunosensors equipped with high specificity, superior analysis sensitivity, low cost, and convenient operations have been widely applied in the food industry, clinical medicine, biomonitor technique, and environmental protection. Because of the pressing requirements for detecting the pathogen Escherichia coli (E. coli) O157:H7 in various practical systems, an efficient and specific immunosensor was delicately designed based on the Pt@BSA nanocomposite with the surface conjugation of affinity-purified antibody molecules to achieve immune recognition. Amplified signal response toward probe molecules and favorable biocompatibility for bacteria attachment could be obtained at the assembled Pt@BSA biosensing interface. With the formation of immune complexes, specific binding of E. coli O157:H7 cells under a certain concentration range onto the antibody-immobilized interface resulted in electrochemical signal responses at different levels, which could be directly measured by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). Herein, E. coli O157:H7 cells were quantitatively monitored by the DPV technique in a linear concentration range from 2.5 × 101 to 5.0 × 108 cfu mL–1 with a low detection limit of 9 cfu mL–1. This fabricated bacteria immunosensor indicated high specificity for E. coli determination, favorable selectivity among the interfering bacteria, excellent storage stability, satisfactory preparation reproducibility with a relative standard deviation (RSD) of 3.5%, and acceptable detection accuracy in practical food samples, providing a promising approach for ultrasensitive monitoring of hazardous substances and disease markers at an extremely low level in clinical diagnosis.