Dual-Mode Lateral Flow Assay for Simultaneous Quantification of Antibiotic and Bacteria

Simultaneous detection of chemical and biological contaminants in complex samples remains a major analytical challenge. Here, we present a dual-mode lateral flow assay (LFA) based on magnetic-SiO₂-fluorescent probes (Fe@Si@QDs) possessing dual "enrichment-signal amplification" functions. The platform integrates both sandwich and competitive formats, enabling ultrasensitive and quantitative detection of a representative antibiotic (gentamicin) and pathogen (Escherichia coli O157) on a single test strip. The Fe@Si@QDs probe incorporates a SiO₂ interlayer between the 180 nm Fe₃O₄ core and outer quantum dots (QDs), effectively suppressing fluorescence inner-filter effects from the magnetic core while enhancing probe dispersibility and chromatographic mobility. Antibody-functionalized Fe@Si@QDs facilitate efficient cocapture of both microorganisms and antibiotics, enabling precise quantitative detection through fluorescence signal enhancement on the microbial test line and attenuation on the small-molecule test line. The developed LFA method achieved detection limits of 36 cfu/mL for E. coli O157 (E. coli O157) and 2.05 pg/mL for gentamicin (GEN), offering at least a 500-fold sensitivity improvement over conventional colorimetric-LFA methods. Validation with real environmental and food samples demonstrated excellent reliability and stability, underscoring the platform's broad applicability for on-site, household, and laboratory use.