Dual‐Emission Carbon Dots Hybrid for Ratiometric Fluorescence and Visual On‐Site Detection of Carbendazim Residues in Fruits and Vegetables

A ratiometric fluorescence sensor based on dual‐emissive carbon dots (d‐CDs) and a smartphone‐assisted colorimetric platform was developed for the sensitive visual detection of carbendazim (MBC) in complex food matrices. The d‐CDs were obtained by hybridizing blue‐emissive CDs (B‐CDs) and red‐emissive CDs (R‐CDs), showing emission peaks at 430 and 610 nm under 365 nm excitation. In the presence of MBC, the 430 nm emission was quenched by π–π stacking and photoinduced electron transfer (PET), while the 610 nm emission increased due to PET inhibition through amino‐MBC coordination. The fluorescence intensity ratio (F 430 /F 610 ) showed a linear response to MBC from 0 to 2.5 μM, with a detection limit of 0.0209 μM, recoveries of 93.1%–108.7%, and relative standard deviations below 3.5% in real food samples. The smartphone‐assisted method exhibited a distinct color change from dark blue to magenta under a portable UV lamp as the MBC concentration increased for the d‐CDs, allowing for instrument‐free visual semiquantitative analysis with a detection limit of 0.0700 μM. This work contributes to a reliable, portable, and economical method for quantitative and semiquantitative detection of MBC residues in fruits and vegetables, supporting real‐time food safety monitoring.