Excitation-dependent ratiometric fluorescence response to mercury ion based on single hexagonal boron nitride quantum dots

Since a vast majority of mercury ion (Hg2+)-responsive fluorescence probes suffer from significant false positive interference in practical applications originating from their fluorescence quenching mechanism, it is still a challenge to develop a fluorescence enhancement sensor for its assay. In this work, single hexagonal boron nitride quantum dots (BNQDs)-based probe was presented for Hg2+ assay in a fluorescence enhancement-based ratiometric manner. When Hg2+ was present, the BNQDs exhibited a new fluorescence emission peak located at 560 nm under 280 nm excitation, while the original blue fluorescence of the probe at 461 nm was quenched, realizing a ratiometric fluorescence response to Hg2+. Furthermore, it is found that fluorescence enhancement at 560 nm was dramatically suppressed under 365 nm excitation, the mechanism behind this phenomenon has been explored by experiments and relevant theories. In addition to high selectivity and detection sensitivity with LOD of 0.7 nM, the prepared probe successfully demonstrated its accuracy in Hg2+ detection in environmental water samples. Moreover, the probe could be adopted for paper sensor design, and an accurate and reliable cell phone-based portable platform was demonstrated for Hg2+ assay with LOD of 1.9 nM, suggesting its potential in point-of-care detection application.