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 and 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.