Sequential Detection of Hg²⁺ and TNT Using a Nitrogen‐Doped Polymeric Carbon Dots On–Off–On Fluorescence Sensor

Abstract

This work presents a fluorescence sensor based on nitrogen‐doped carbon dots (N‐CDs) utilized for sequential detection of Hg2+ and TNT. The N‐CDs were produced by a simple and efficient hydrothermal process involving the combination of black bean extract with citric acid (CA) and ethylenediamine (EDA). The resulting N‐CDs exhibit a steady blue fluorescence with a significant quantum yield of 12%. We conducted a thorough investigation into the mechanism by which the fluorescence of NCDs is reduced in the presence of Hg2+. Our analyses, which included Stern–Volmer quenching tests, confirmed the development of a stable complex between N‐CDs and Hg2+. When the NCDs‐Hg2+ complex was exposed to TNT, the fluorescence was selectively restored. This sequential “on–off–on” sensing capacity allows for efficient monitoring of both Hg2+ and TNT, demonstrating good sensitivity and selectivity. The sensor has a low detection limit (LOD) of 3.1 and 46 nM for Hg2+ ions and TNT in a linear range of 0–40 and 0–30 μM, respectively. This study emphasizes the potential application of N‐CDs for detecting heavy metals and explosives at the same time. It highlights their usefulness in sophisticated environmental sensing technologies that are suitable for important applications.