Boron and Sulfur-Codoped g-C ₃ N ₄ Nanostructures and Their <scp>l</scp> -Cysteine-Functionalized Quantum Dots for Selective Detection of Triethylamine Gas and Hg ²⁺ /Pb ²⁺ Ions

A facile way of synthesizing boron and sulfur-doped g-C 3 N 4 (BSCN) 2D nanostructures along with their l -cysteine-modified quantum dots (Cys-BSCN QDs) has been reported in this study. BSCN nanosheets have been incorporated in a Cu-based portable interdigitated electrode (IDE) to explore the sensing performance toward triethylamine (TEA) gas at room temperature. The effects of humidity levels have also been investigated. The fabricated sensor enabled highly selective TEA sensing with a low detection limit (LOD) of ∼0.17 ppm, along with fast response and recovery times of 62 and 60 s, respectively. The BSCN-based sensor markedly outperforms the pristine carbon nitride and its boron or sulfur-doped forms. Long-term stability tests demonstrate sensing performance sustained toward 10 ppm TEA with <5% decline over several weeks. The zero-dimensional (0D) form of BSCN (Cys-BSCN QDs) has been utilized as a highly sensitive and selective fluorescence sensor toward toxic metal ions, Hg 2+ and Pb 2+, with LODs of 14.08 and 14.37 nM, respectively. The electronic modulation induced by B/S codoping, combined with cysteine functionalization, generates abundant active sites, making the material a promising platform to be utilized as a multimodal sensor. Highly sensitive sensing of Hg 2+ and Pb 2+ ions in biological fluids, as well as environmental samples, further validates the practical applicability. Additionally, the sensing mechanism of the 2D and 0D forms of the BSCN-based nanoplatform toward TEA gas and Hg 2+ /Pb 2+ ions have also been investigated.