Highly Luminescent and Water-Stable CsPbCl₃/Mn²⁺/PEG Nanocrystals for Ultrasensitive Detection of 4‑Nitrophenol

Perovskite quantum dots (PQDs) offer high photoluminescence quantum yields. However, their poor stability and aqueous-quenching of fluorescence limit their wider application, especially in biochemical detection. In this work, a simple and highly successful coating strategy was used to encapsulate Mn²⁺-doped CsPbCl₃ PQDs in poly(ethylene glycol) (PEG), effectively increasing the water stability of PQDs. After dispersion in deionized water for 25 days, the CsPbCl₃/Mn²⁺/PEG nanocrystals (NCs) retained 40% of their initial fluorescence intensity. In addition, due to the FRET mechanism, 4-nitrophenol (4-NP) can effectively quench the fluorescence of CsPbCl₃/Mn²⁺/PEG NCs. Therefore, utilizing the excellent water stability of CsPbCl₃/Mn²⁺/PEG NCs and their interaction with 4-NP, a fast and conservative fluorescent probe can be established, which can perform highly selective and ultrasensitive quantitative detection of 4-NP in aqueous solutions. In addition, the molecular weight of PEG used for encapsulation, the fluorescence intensity of CsPbCl₃/Mn²⁺/PEG NCs, and the detection range for 4-NP vary. Fortunately, the detection limits are all lower than the drinking water concentrations allowed by the U.S. Environmental Protection Agency. This study also provides a theoretical basis and methodological support for the subsequent application of PQDs in the detection of water pollutants.