Aggregation and surface-state modulated fluorescence quenching of lemon-derived carbon quantum dots for the sensitive...

4-Aminophenol (4-AP) is the primary degradation product of paracetamol (PA), resulting from its hydrolytic cleavage within the human body and is known for its nephrotoxic, hepatotoxic, and teratogenic nature. Its enhanced levels may cause mutagenic responses and DNA damage in living organisms; therefore, the accurate detection of 4-AP is important for public health monitoring. In this study, a facile, green, and one-step approach for the synthesis of carbon quantum dots (CQDs) using lemon juice as a sustainable carbon precursor and avoiding toxic reagents and harsh conditions is reported to efficiently quantify 4-AP in aqueous media. The prepared CQDs were comprehensively characterized by UV-visible spectroscopy, zeta potential, DLS, FTIR spectroscopy, Raman spectroscopy, XRD, and FESEM. Furthermore, to enhance detection performance, the fluorescence intensity of CQDs was optimized by varying the excitation wavelength, concentrations of CQDs and 4-AP, pH and ionic strengths. The probe exhibited good fluorescence stability over a wide pH range and in the presence of different salts (NaCl, KCl, and MgCl₂) and superior selectivity even in the presence of several potential interfering species. Moreover, high sensitivity towards 4-AP was demonstrated, with a superior limit of detection (0.71 µM) and a wide linear detection range (50 to 2500 µM). The practical applicability of the probe was further validated through spiked serum samples, demonstrating satisfactory recovery rates and good reproducibility. Overall, the proposed method provides a robust platform for the detection of 4-AP and demonstrates strong potential for applications in clinical research, diagnostics as well as biomedical and environmental monitoring.