A visual-colorimetric-photothermal multimodal immunoassay for sensitive and quantitative detection of Escherichia coli

Escherichia coli (E. coli) is one of the most common bacterial pathogens encountered in hospital settings, frequently associated with postoperative infections, urinary tract infections, and sepsis. Rapid and accurate detection of E. coli in clinical samples is critical for early diagnosis, timely treatment, and reducing complications, especially in settings where laboratory infrastructure is limited. To address this need, we developed a multimodal lateral flow immunoassay (LFIA) platform that integrates visual, colorimetric, and photothermal readouts for E. coli detection. The assay uses AuPd@Ab1 nanoprobes prepared by conjugating AuPd nanozymes with E. coli-specific antibodies (Ab1). In a sandwich LFIA, the probes accumulate at the test line for visual identification (10³ CFU/mL). Their peroxidase-like activity enables colorimetric quantification via TMB oxidation, with a limit of detection of 20 CFU/mL. Moreover, under 808 nm laser excitation, the AuPd nanozymes produce measurable heat signals that correlate linearly with bacteria population, achieving a photothermal LOD as low as 5 CFU/mL. Validation using clinical samples confirmed the assay's reliability and sensitivity. By integrating multiple readout modes into a simple lateral flow format, this platform improves detection accuracy and offers practical advantages for rapid, bedside E. coli screening. Its multimodal design and low detection thresholds make it a promising tool for early infection control in clinical diagnostics, particularly in resource-limited or emergency care settings.