Chitosan/SiO2-encapsulated gold nanoclusters as a dual-signal fluorescence sensor for sensitive detection of 2-nitroaniline and fluazinam in environmental and food samples

Metal nanoclusters have emerged as promising fluorescence nanomaterials, yet their practical sensing applications remain constrained by limited stability and suboptimal luminescence efficiency. We report a strategically designed nanocomposite, chitosan/silica-encapsulated gold nanoclusters (Au NCs/CSNPs), which integrates three functional components into the fluorescence sensing platform. Unlike conventional encapsulation strategies that merely serve as protective shells, our chitosan-functionalized silica matrix achieves multiple synergistic functions, where rigid confinement enhances quantum yield and photostability, chitosan-induced improvement analyte accessibility, and the tailored composite microenvironment enables analyte-specific response modulation. Remarkably, Au NCs/CSNPs exhibit opposite fluorescence responses toward two distinct contaminants, with enhancement for 2-nitroaniline (2-NA) and quenching for fluazinam (Flu), enabling selective detection with low limits of detection of 52.2 nM for 2-NA and 45.7 nM for Flu. Mechanistic studies reveal that this dual-response behavior originates from distinct pathways including excited-state rigidification for 2-NA versus static quenching coupled with the inner filter effect for Flu. The sensor demonstrates excellent selectivity and practical applicability in environmental and food matrices. This work establishes a new paradigm for nanocluster-based sensors where the encapsulating matrix is not merely protective but functionally integrated to achieve tunable multi-analyte sensing capabilities. Graphical abstract