Aspartic acid assisted one-step synthesis of stable CsPbX@Asp-CsPbX by in situ growth in NH-MIL-53 for ratiometric fluorescence detection of 4-bromophenoxybenzene.

A molecularly imprinted ratiometric fluorescent sensor was synthesized for the detection of 4-bromophenoxybenzene (BDE-3) based on perovskite quantum dots and metal organic framework. First, aspartic acid (Asp) was introduced during the synthesis of perovskite CsPbX for the formation of a core-shell structure of CsPbX@Asp-CsPbX. Due to the protection of the shell layer CsPbX, the stability of the core CsPbX was improved significantly. Compared to CsPb(BrI), the ultraviolet and thermal stabilities of CsPb(BrI)@Asp-CsPb(BrI) were increased by 26 times and 32 times, respectively, and, compared to CsPbBr, these stabilities of CsPbBr@Asp-CsPbBr were increased by 3 times and 13 times, respectively. The water stabilities of CsPb(BrI)@Asp-CsPb(BrI) and CsPbBr@Asp-CsPbBr were greatly improved too. Then, a ratiometric fluorescence sensor was constructed by in situ growth of CsPb(BrI)@Asp-CsPb(BrI) in metal organic framework (NH-MIL-53) for the detection of BDE-3, in which the orange fluorescence of CsPb(BrI)@Asp-CsPb(BrI) (614 nm) was regarded as the reference signal and the cyan fluorescence of NH-MIL-53 (494 nm) was used as the fluorescence response signal. To improve the selectivity of the sensor, the molecular imprinting polymer (MIP) was modified on the NH-MIL-53 and an imprinting factor of 3.17 was obtained. Under 365 nm light excitation, the fluorescent response signal at 494 nm was quenched gradually by BDE-3 in the range 11.4 to 68.5 nmol/L, while the reference signal at 614 nm remained unchanged. The limit of detection and limit of quantification were 3.35 and 11.2 nmol/L, respectively, and the fluorescent color of the sensor changed gradually from cyan to green to orange, which illustrated that the developed sensor has an ability to recognize BDE-3 specifically, a good anti-interference ability, and a sensitively visual detection ability. Moreover, the sensor was successfully applied to the BDE-3 detection in polyethylene terephthalate plastic bottle, polyvinyl chloride plastic bag, and circuit board with satisfactory recoveries (96.3-108.1%) and low relative standard deviations (5%). The preparation processes of NH-MIL-53, NH-MIL-53-CsPb(BrI)@Asp-CsPb(BrI), and the MIP-NH-MIL-53-CsPb(BrI)@Asp-CsPb(BrI) composites.