Inner Filter Effect (IFE)-Based Fluorescent Sensing and Quantification of p-Nitrophenol (p-NP) Using N, S-Doped Carbon Dots (N, S-CDs)

p-Nitrophenol (p-NP) is widely used in industrial applications for synthesis of large number of commercially valued products. However, it is dangerous to humans and aquatic life due to its toxicity. In this study, DL-Malic acid, L-Histidine, and L-Cysteine were utilized as sources of carbon, nitrogen, and sulfur respectively to establish a simple, cost-effective, and one-step hydrothermal synthetic process for nitrogen and sulfur-doped carbon dots (N, S-CDs), as a high-performance fluorescent sensor for selective measurement of p-NP based upon Inner filter effect (IFE). The synthesized CDs were subjected to characterization by TEM, FT-IR, XRD, UV–vis, and fluorescence spectroscopy techniques. The developed N, S-CDs exhibited LOD of 0.064 µM and a robust linear response extending from 0.1 to 120 µM. The CDs demonstrated remarkable photostability on exposure to varied environmental factors; including pH, salt, and UV light. The selectivity of sensor was demonstrated by analyzing p-NP response in presence of its analogues and several cations and anions. Results from the analysis of seawater and tap water showed recoveries varying from 98 to 103.8% with RSD of 1.1 to 2%. Moreover, the N, S-CDs offered ease of preparation and operation compared with HPLC, requiring less sophisticated equipment and shorter analysis times.