Construction of a near-infrared excited RhB@UCNPs fluorescent probe for hypochlorite detection

An upconversion luminescence (UCL) nanoprobe is reported for the rapid detection of hypochlorite ions (ClO^-) in complex environments. The probe is fabricated by sensitizing rhodamine B (RhB) on the surface of core@shell upconversion nanoparticles (C/S UCNPs) with the bridging of polyethylene glycol (PEG) molecules. Under 980 nm excitation, the UCL of C/S UCNPs is quenched by RhB through fluorescence resonance energy transfer (FRET), which can be restored by the oxidative cleavage of RhB induced by ClO^-. It is observed that the green emission intensity of RhB-modified C/S UCNPs increases linearly with the concentration of ClO^-, enabling quantitative detection of ClO^-. Moreover, the excitation of C/S UCNPs requires only a low power density (0.09 W/cm²), which minimizes the photodegradation of RhB and stabilizes the FRET process. Under optimized conditions, the detection limit for ClO^- ions in tap water was 5 µg mL⁻¹.