Phage-induced inner filter effect powers sensitive dual-mode detection of E. coli O157:H7.

Escherichia coli O157:H7 is a highly infectious foodborne pathogen requiring rapid and reliable detection. Inner filter effect (IFE)-based sensors offer dual-mode detection but often lack effective localized surface plasmon resonance (LSPR) modulation and signal amplification. Here, we developed a phage-induced IFE dual-mode sensor using engineered M13 phages displaying E. coli-specific peptides on protein P3 and streptavidin-binding peptides on protein P8. Following aptamer-mediated bacterial capture with magnetic beads, streptavidin-coated gold nanoparticles (SA-AuNPs) self-assemble on the phage surface. The ≈3.2 nm spacing between P8 termini brings SA-AuNPs into close proximity, enhancing LSPR and quenching quantum dot fluorescence via the IFE. The high P8 copy number (≈2700) enables multiple IFE events per recognition, thereby amplifying the signal. The sensor exhibits a linear range of 10-10 CFU/mL, a detection limit of 3 CFU/mL, and recoveries of 86.6 % - 110.6 % in spiked food samples, demonstrating excellent selectivity and strong potential for practical application.