One-step hydrothermal synthesis of Na-doped carbon dots for highly selective detection of Hg2+ in aqueous medium

•Na-doped carbon dots (Na-CDs) was synthesized from β-CD and sodium acetate.•Na-CDs was stable in a wide pH range of 3–12.•Na-CDs served selective probe for fluorescence turn-off detection of Hg2+.•Na-CDs responded to Hg2+ rapidly within 10 min by ACQ mechanism.•Na-CDs displayed low detection limit of 34.22 nmol/L for Hg2+. Na-doped carbon dots (Na-CDs) was synthesized by hydrothermal method from β-cyclodextrin and sodium acetate. The Na-CDs was stable at pH 3–12 and after storage for a long time. The Na-CDs served fluorescence sensor for highly selective detection of Hg2+ in aqueous medium with a detection limit of 34.22 nM. The sensing mechanism was based on the aggregation caused fluorescence quenching. The Na-CDs displayed high selectivity and sensitivity towards Hg2+, which supplied a new idea for constructing CDs-based stable fluorescent probes and a novel platform for selective Hg2+ detection.