Dual‐Mode Selective Detection of <i>E. coli</i> in Water via Benzoquinone‐Redox‐Mediated Electrochemical Immunosensing

Rapid and reliable detection of Escherichia coli ( E. coli ) in water is critical for safeguarding public health. We developed a dual‐mode biosensor that integrates p‐benzoquinone (BQ)‐mediated colorimetric prescreening with antibody‐based electrochemical quantification using screen‐printed gold electrodes (SPGEs). BQ serves a dual role by generating a visible color change through its enzymatic reduction by viable E. coli and by participating in a reversible redox cycle that enhances faradaic response during electrochemical analysis. The biosensing platform was validated using E. coli ATCC 25922 together with broad‐serotype polyclonal anti‐ E. coli O/K antibodies, which enable species‐level recognition. Under optimized conditions (6.0 mM BQ, 25 µg/mL antibody), the sensor achieved a wide linear range from 10 1 to 10 9 CFU/mL with a detection limit of 0.57 CFU/mL. Repeatability was excellent (1.51% RSD), and specificity tests demonstrated clear discrimination between viable E. coli , nontarget bacteria ( S. aureus ), and nonviable cells. This dual‐selectivity strategy, combining metabolic activity with molecular recognition, offers a rapid and portable approach for on‐site microbial water quality monitoring.