A turn-on fluorescent sensor for highly sensitive mercury(ii) detection based on a carbon dot-labeled oligodeoxyribonucleotide and MnO2 nanosheets

Abstract

A novel fluorescent turn-on aptasensor has been developed for the detection of mercuric ions (Hg²⁺) based on carbon dots (CDs) as donor molecules and MnO₂ nanosheets as acceptor molecules. In this work, an effective fluorescent probe was fabricated through the conjugation of a single-stranded oligodeoxyribonucleotide (ssDNA) on the surface of CDs. In the absence of the target Hg²⁺, the CDs labeled with ssDNA were adsorbed on the MnO₂ surface via van der Waals forces. The fluorescence signal of CDs was then quenched by MnO₂ nanosheets via the fluorescence resonance energy transfer (FRET) mechanism. While Hg²⁺ was introduced, the specific affinity interactions between ssDNA and Hg²⁺ could detach CDs-labeled ssDNA (ssDNA-CDs) from the MnO₂ surface because of the production of the thymine–Hg²⁺–thymine (T–Hg²⁺–T) complex, leading to the recovery of the fluorescence intensity. Under the optimal reaction conditions, the fluorescence intensity of CDs enhanced gradually with the increasing concentration of Hg²⁺ ions in the range from 2 to 200 nmol L⁻¹ and the limit of detection was found to be 0.67 nmol L⁻¹. In addition, the proposed strategy developed its application in the determination of Hg²⁺ in real samples with excellent performance. These features illustrated that the designed fluorescent sensing platform is a reliable quantitative candidate for potential applications in biological and analytical fields.