Rapid detection of urine chloride enabled by ion exchange in hydrophilic lead halide perovskite nanocrystals

The rapid and precise detection of chloride ions in biosystems is of great importance for clinical diagnosis. In this work, hydrophilic CsPbBr₃ perovskite nanocrystals (PNCs) with a high photoluminescence (PL) quantum yield (QY) of 59% (0.5 g L^-1) are successfully achieved through the passivation of micellar glycyrrhizic acid (GA), which enables good dispersion of PNCs in ethanol. Due to the ionic nature and halogen-dominated band edge, PNCs exhibit fast ion-exchange and halogen-dependent optical properties. As a result, colloidal GA-capped PNC ethanol solution shows a continuous PL shift once aqueous Cl^- with different concentrations is added. This fluorescence sensor shows a wide linear detection range (2-200 mM) of Cl^-, short response time (∼1 s), and low limit of detection (1.82 mM). Because of the encapsulation of GA, good water and pH stability, and anti-interference performance are observed for the GA-capped PNC-based fluorescence sensor. Our findings provide an insight into the biosensor applications of hydrophilic PNCs.