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/cm), 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⁻.