Acid-assisted ultrasonic preparation of nitrogen-doped MXene quantum dots for the efficient fluorescence “off-on-off” detection of Zn(II) in water and oxalic acid in vegetables

[Display omitted] •N-MQDs are prepared via an acid-assisted ultrasonic process at room temperature.•N-MQDs show selective fluorescence enhancement to Zn(II) by ICT effect, LOD = 0.127 μM.•OA can selectively recover the N-MQDs/Zn(II) fluorescence with a LOD of 0.883 μM.•N-MQDs are applied for Zn(II) and OA detection in actual water and vegetable samples. A novel fluorescence “off-on-off” probe was presented to detect Zn(II) and oxalic acid (OA) based on nitrogen-doped MXene quantum dots (N-MQDs), which were synthesized by an ultrasound approach at room temperature with nitric acid and ethylenediamine. These N-MQDs displayed small size (