Label-free upconversion nanosensor for water safety monitoring of permanganate and dichromate ions

Water contaminated with heavy metal ions poses serious threat to the human health and environment protection. It is imperative to develop analytical tools to detect heavy metal ions. Herein, we propose autofluorescence free SiO₂ modified upconversion nanosensor for label-free and fast determination of MnO₄⁻ and Cr₂O₇²⁻ anions. The highly efficient and multi-colour upconversion luminescence (UCL) of UCNPs@SiO₂ was effectively quenched by MnO₄⁻ and Cr₂O₇²⁻ anions with fast response time of 2 and 1 min, respectively. The UCNPs@SiO₂ nanosensor exhibits linear detection ranges of 0.6–2000, 2–2000 µM with the LOD at 0.15, 0.04 µM for MnO₄⁻ and Cr₂O₇²⁻ anions, respectively. The nanosensor was successfully applied for real lake and tap water samples with satisfactory results. The UCNPs@SiO₂ UCL nanosensor demonstrates autofluorescence free and fast determination of MnO₄⁻ and Cr₂O₇²⁻ anions with high sensitivity, good specificity, low LOD, and wide linear detection range, holding great potential for food and environmental sample sensing.