A sensitive visual detection of thiamethoxam based on fluorescence resonance energy transfer from NH2–SiO2@CsPbBr3 to merocyanine configuration of spiropyran

The spiropyran (SP) compound is a typical photochromic compound. Its merocyanine configuration (MC) can accept energy and be excited by visible light, while the closed-loop configuration cannot. In this work, the SP was wrapped in β-cyclodextrin (β-CD-SP) firstly. When it was competitively replaced by thiamethoxam and dissociated out of β-CD, it would be converted to MC, which could be excited by visible light around 550 nm to produce red fluorescence. Here, CsPbBr3 was selected as the energy donor based on the principle of fluorescence resonance energy transfer (FRET). In order to connect with β-CD-SP and improve its stability, CsPbBr3 was wrapped in mesoporous silica, and then the second wrapping was performed to block those mesopores and the amination reaction was carried out (NH2–SiO2@CsPbBr3). Subsequently, NH2–SiO2@CsPbBr3 with green fluorescence (506 nm) was used as the internal standard and excitation light source for MC, and the red fluorescence of MC was used as the response signal to construct a ratiometric fluorescence sensor. When thiamethoxam was added and excited by 365 nm ultraviolet light, the energy would be transferred from NH2–SiO2@CsPbBr3 (506 nm) that emitted green fluorescence to MC, which emitted red fluorescence. So, the fluorescence color changed from green to yellow to red with the addition of the thiamethoxam. This sensor was employed to detect thiamethoxam in soil and yam.