Selective detection of mercury ions based on tin oxide quantum dots: performance and fluorescence enhancement model

Abstract

The superiority of fluorescence-based methods in the metal ion detection is well established; however, the quantum dot (QD) fluorescent probes currently used for mercury ions (Hg²⁺) have many limitations, such as a narrow detection range and environmental toxicity. In this work, environment-friendly tin oxide (SnO₂) quantum dots were prepared and applied as a fluorescent sensor for the selective determination of Hg²⁺. The synthesized SnO₂ QDs showed excellent performance in Hg²⁺ ion detection, with a broad linear range of 10⁻²–10⁵ μM and a low detection limit of 5 nM. Remarkably, SnO₂ QDs illustrated high selectivity to Hg²⁺ ions without interference from other metal ions. Furthermore, the mechanism of fluorescence enhancement in SnO₂ QDs was based on the ratio of non-radiative electrons, and the density of active Sn vacancies was further explained. A mathematical model is proposed to interpret the mechanism of the adsorptive process during Hg²⁺ detection, thereby providing a quantitative understanding of the fluorescence sensing principle of semiconductor QDs. This work demonstrates the promising application of SnO₂ QDs for convenient, highly sensitive and low-cost determination of Hg²⁺ ions in experimental and actual conditions.