Reversible detection of Hg(II) in pure water based on thymine modified nitrogen, sulfur co-doped carbon dots combined with antidote

Conventional Hg²⁺ visual sensors are unsustainable, hindering their practical application for improved water quality and health. In order to address this challenge, herein, N, S co-doped carbon nanodots (NS-CDs) were prepared and well characterized, presented the fluorescent monitoring for Hg²⁺ over other metal ions with the limit of detection (LOD) of 0.47 µM. Next, the CDs were successfully modified by thymine without any fluorescence labelling (referred to as T-NS-CDs). The sensitivity to Hg²⁺ cloud be noticeable enhanced due to the formation of T-Hg²⁺-T specific base pairs. Accordingly, the LOD was calculated with values as low as 1.56 nM. Furthermore, Hg²⁺ could be released and complexed with antidote (meso-2,3-dimercaptosuccinic acid) (DMSA-Hg²⁺), being the responsible for the reversible interconversion between T-Hg²⁺-T and DMSA-Hg²⁺. Interestingly, the proposed sensing system also applies to the fluorescent sensing for Hg²⁺ in tap water with satisfactory recoveries (96.97 %-101.38 %, RSD < 2 %). Thus, by simply combination of elemental doping and surface functionalization, the surface state and functionalities of CDs could be tailorable, endowing the fluorometric sensing towards Hg²⁺ in environmental system.