Highly stable ionic liquid-modified Cs3Bi2Cl9 quantum dots for highly selective detection of ofloxacin

• Green modification strategy: Ionic liquid was used to modify the surface of lead-free Cs₃Bi₂Cl₉ PQDs, which effectively enhanced its stability and sensing selectivity. • Excellent optical stability: The modified quantum dots can still maintain 77 % of the initial fluorescence intensity after 40 days of sealed storage at room temperature. • Potential for environmental monitoring applications: This study provides a feasible engineering path for the development of environmentally friendly and scalable perovskite-based optical sensing technologies. The imidazole ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) was employed as a surface ligand to synthesize Cs₃Bi₂Cl₉ perovskite quantum dots (CBC-PQDs) via ligand-assisted reprecipitation, yielding an emission peak at 431 nm. Modification with [BMIM][PF₆] improved both photostability and sensing performance. After 40 d of sealed storage at room temperature, [BMIM][PF₆]-functionalized PQDs ([BMIM][PF₆]-PQDs) retained 77% of their initial photoluminescence intensity, corresponding to a 67% enhancement relative to pristine CBC-PQDs. [BMIM][PF₆]-PQDs exhibited a linear detection range of 1-100 μmol/L for ofloxacin (OFLO) with a limit of detection of 18.49 μmol/L, representing a 212% increase in sensitivity compared to unmodified CBC-PQDs. The enhanced response is attributed to hydrogen-bonding interactions between OFLO polar groups and surface hydroxyl/imidazole on the quantum dots. In real water matrices, OFLO recovery rates ranged from 95.82% to 107.36%. This study provides a scientific basis for using IL as a ligand to enhance the performance of CBC-PQDs, and lays a foundation for the future development of sensors for trace OFLO in water.