Microwave-assisted synthesis of fluorescent silicon quantum dots for ratiometric sensing of Hg (II) based on the regulation of energy transfer

Abstract

The rapid and sensitive detection of Hg2+ is highly required to protect the environmental safety and human healthy. In the present work, a ratiometric fluorescent sensing platform, consisting of silicon quantum dots (SiQDs), Rox-labelled DNA (Rox-DNA), and Exonuclease III (Exo III), is developed for the accurate detection of Hg2+. As for fluorescent probe, we report the first use of glutathione as reduction reagent for the microwave synthesis of SiQDs, achieving the facile (using a house-hold microwave oven) and rapid (within 8 min) synthesis. Such SiQDs show pH-independent spectra and reversible fluorescent behavior with temperature. Moreover, experimental results revealed that the electrostatic interaction-induced aggregation of Rox-DNA and SiQDs facilitated the occurring of energy transfer (ET). And detection principle based on the regulation of ET between Rox and SiQDs with Exo III was designed for analysis. ET effect resulted in the fluorescent fading of Rox while that of SiQDs kept stable. For analysis, the addition of Hg2+ led to the formation of double-stranded Rox-DNA via T-Hg2+-T. Exo III would cut these double-stranded DNA to release Rox and Hg2+, thereby impeding the ET effect and recovering the fluorescent of Rox. Such SiQDs/Rox-DNA/Exo III ratiometric fluorescent sensing platform exhibited a linear response concentration range of 0.02 nM–10 nM with a detection limit of 0.01 nM. It was successfully used to analyze the water and soil samples. The reliability was validated by ICP-MS. Our work should promote the practical application of ratiometric fluorescent assay.