MCOF-assisted and MnO₂ nanozyme-triggered cascade dual-mode aptasensor for intelligent detection of Salmonella...

Conventional methods for detecting Salmonella Typhimurium in food often require lengthy procedures or specialized instrumentation. We developed a dual-mode aptasensor based on magnetic covalent organic frameworks (MCOFs) and MnO₂ nanozymes. MCOF-AuNPs@apt captures bacteria, followed by MnO₂@apt binding to form sandwich complexes. The retained MnO₂@apt promotes TMB oxidation without added H₂O₂. Subsequent acidification produces yellow TMB²⁺, which etches gold nanorods. Etching shifts the longitudinal plasmon resonance to shorter wavelengths and decreases the photothermal response under 808 nm irradiation, providing complementary multicolor and photothermal readouts. Calculated detection limits were 6.6 and 3.2 CFU/mL for the colorimetric and photothermal modes, respectively. The assay was evaluated in spiked milk and meat infusion. Smartphone-assisted linear discriminant analysis classified independently prepared blinded samples by bacterial concentration with 97.14% accuracy. These results support the platform as a proof-of-concept approach combining complementary dual-mode detection and smartphone-assisted concentration classification.