Terbium (III)-referenced N-doped carbon dots for ratiometric fluorescent sensing of mercury (II) in seafood

•Abundant NH2 and COOH group functionalized N-CDs-Tb-DPA as dual-emission sensor.•Electron transfer from COOH of N-CDs to Hg2+ induces the change of surface state.•Hg2+ inhibits electron transfer between NH2 and COOH enhancing selectivity.•The compound of Hg2+COO− dominated the affinity of the sensor toward Hg2+.•Lower limit of detection of 37 nM. A ratiometric fluorescence (FL) sensor was fabricated by coordinating 2, 6-pyridinedicarboxylic acid (DPA) sensitized Tb3+ (Tb-DPA) with NH2 and COOH on the surface of the N-doped carbon dots (N-CDs) for detecting Hg2+ in seafood. The sensor exhibited two FL emissions at 436 nm (N-CDs) as the response signal and at 543 nm (Tb-DPA) as the reference signal when excited at 290 nm. After adding Hg2+, the FL emission at 436 nm was significantly quenched and the FL emission at 543 nm was negligibly changed. The electron transfer (ET) between COO− of N-CDs and Hg2+ led to the FL quenching of N-CDs. The FL ratio (F436/F543) exhibited a good linear relationship in the Hg2+ concentrations of 1161.51 μM with a low limit of detection (LOD) of ~37 nM. The sensor presented high selectivity, satisfactory accuracy and precision toward Hg2+ in seafood with recoveries of 86.45–114.47% and RSDs of 0.20–1.92%.