Near-infrared excited dual-mode nanoprobes for background-free and on-site detection of 5-hydroxymethylfurfural in food.

5-Hydroxymethylfurfural (HMF) is a potential food contaminant that poses health risks upon long-term intake. While current fluorescence detection technologies show potential applications in HMF analysis, most reported fluorescent probes rely on short-wavelength excitation and single-signal output, which suffer from background fluorescence interference in complex matrices. This study proposed a near-infrared excited multi-output sensing strategy based on upconversion nanoparticles (UCNPs) and p-toluidine-barbituric acid chromogenic system, enabling synergistic luminescent-colorimetric analysis of HMF. This system specifically reacted with HMF, selectively quenching the green upconversion luminescence of the UCNPs while leaving the red upconversion luminescence unaffected, constructing both ratiometric luminescent and colorimetric visual sensing modes. A smartphone-based sensing platform was further developed for portable and sensitive HMF detection, providing a more convenient and sensitive strategy for food safety analysis. This study provided a novel strategy for background-free, highly sensitive, and portable visual detection of food contaminants.