Nitrogen-doped and sulfur, nitrogen co-doped carbon dots (CDs) were synthesized by solid-state, solvent-free, microwave synthesis technique at 250 oC. CDs were synthesized using citric acid as carbon precursor and urea...

The utilization of ultrathin Mn-metal−organic framework (Mn-UMOF) nanosheets for oxidase-like nanozyme activity has been demonstrated. The Mn-UMOF exhibited superior nanozyme activity to oxidize chromogenic TMB and ABTS than the bulk Mn-BMOF. Based on this fact, a platform for the colorimetric sensing of L-cysteine (L-cys) has been established over the detection of other amino acids and natural compounds such as urea and glucose. In addition, the Mn-UMOF has the capability of catalyzing the oxidation of amplex red to the fluorescent first oxidized product, which has been used to develop a fluorescence turn-off sensor for the selective sensing of L-cys.

In recent years, optical sensing based on nanomaterials has emerged as a prospective strategy for monitoring environmental pollution in water. In this context, carbon nanostructures have received increasing attention due to their unique optoelectronic and physiochemical properties. To this end, nanocarbon such as carbon nanotubes, graphene, and carbon dots have been used to develop proof‐of‐concept opto‐chemical sensors for emerging aquatic contaminants, including pesticides, bacterial pathogens, and pharmaceuticals residues. These optical sensors have attracted significant research interest in nanotechnology, material science, and the detection of aquatic pollutants. However, the practical application for detecting contaminants is still limited because of cost‐effectiveness, sensitivities, and selectivity toward the diverse pollutants. This review examines the current trends and challenges in designing and applying carbon nanostructure‐based optical sensors for detecting aquatic contaminants. Finally, a critical perspective on the field and future research directions is provided.