Photocatalysis-Assisted Absorption-Based Ultrasensitive As3+ Sensing Using an LRET-Driven UV–Vis–NIR Upconversion System

We developed an eco-friendly photochemical sensor based on Er3+/Yb3+-codoped Ag2MoO4 upconversion nanoparticles (UCNPs) decorated with MnO2 (cod-AMO-3/MnO2) for the selective and ultrasensitive detection of As3+ in water. The sensor uses metronidazole (MNZ) degradation kinetics as a simple absorption-based sensing platform for As3+, eliminating the need for complex instrumentation or costly reagents. The cod-AMO-3/MnO2 nanocomposite (NComp) promotes efficient photocatalytic MNZ degradation through photoinduced charge separation facilitated by luminescence resonance energy transfer (LRET). Under optimized conditions, NComp achieved 99% MNZ degradation within 28 min under ultraviolet (UV) irradiation, 99.16% within 63 min under visible (vis) light, and 95.58% within 120 min under near-infrared (NIR) irradiation. Full-spectrum solar irradiation further enhanced the activity, achieving 99.07% degradation within 15 min. The presence of trace As3+ altered the charge separation dynamics of the NComp, producing measurable changes in MNZ degradation kinetics. This enabled selective As3+ detection over a linear range of 0–150 ppb with a detection limit (LOD) of 0.026 ppb, outperforming many traditional detection techniques and aligning closely with our previous photoluminescence-based sensor (LOD: 0.028 ppb). The proposed absorption-based strategy provides a simpler and more accessible alternative to photoluminescence-based detection, demonstrating the potential of UCNP-based nanocomposites for practical arsenic monitoring in water.