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

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.