Carbon dots@silica-based dual-emission ratiometric fluorescent sensor for highly selective detection of Cu2+ and thiram

Thiram is a widely used fungicide and pesticide in agriculture, whose ability to form stable complexes with metal ions increases its environmental persistence and pollution risks, posing potential threats to water bodies and food safety. Therefore, it is urgently needed to develop a sensitive method for the detection of thiram and heavy metals. In this work, a ratiometric fluorescent sensor, comprised of blue and yellow carbon dots encapsulated in silica (CDs@SiO₂) composites, was developed for the detection of copper ions (Cu²⁺) and thiram. Upon excitation at 390 nm, the probe exhibited two distinct fluorescent emission peaks at 450 and 580 nm. The addition of Cu²⁺ induced aggregation of yellow carbon dots, enhancing the emission intensity at 580 nm via aggregation-induced emission enhancement, while the inner filter effect simultaneously reduced the emission intensity at 450 nm. This dual mechanism enabled a sensitive response for Cu²⁺ detection. A linear correlation between the F₅₈₀/F₄₅₀ ratio and Cu²⁺ concentration was observed in the range of 0.5 to 115 μM, with a limit of detection (LOD) as low as 0.144 μM. Furthermore, thiram competes with yellow CDs@SiO₂ for Cu²⁺ binding, enabling ratiometric detection of thiram concentrations between 2 and 80 μM with a LOD of 1.76 μM. The sensor also demonstrates excellent selectivity, reproducibility and stability, making it a promising tool for the accurate determination of Cu²⁺ and thiram in real samples.