Sensitive and Specific Detection of Trace Al3+ Ions Using an Upconversion Nanoparticle-Xylenol Orange Complex via the Inner Filter Effect

We have developed a novel fluorescence sensor based on upconversion nanoparticles (UCNPs) for the rapid and sensitive detection of trace aluminum ions (Al³⁺). The sensor utilizes the inner filter effect (IFE) between the UCNPs and the xylenol orange-aluminum complex (XO-Al³⁺), resulting in significant fluorescence quenching at 543 nm upon Al³⁺ binding. This quenching correlates directly with the Al³⁺ concentration, allowing for quantitative detection within a range of 0–30 µM and achieving an ultra-low detection limit of 0.19 µM. Selectivity of the sensor is enhanced by the incorporation of ascorbic acid, which masks interfering Fe³⁺ ions, thus ensuring accurate determination of Al³⁺ even in the presence of other metal ions. The UCNPs-XO sensor exhibits excellent stability, reproducibility, and minimal interference from commonly co-existing substances. This makes it suitable for the detection of Al³⁺ in various matrices, including food products and environmental water samples. Our work offers a significant advancement in Al³⁺ detection, with potential applications in food safety, environmental monitoring, and public health.