Quenched fluorometric analysis of nevirapine and 4-nitrophenol in S,N-doped carbon dots derived from avocado seeds

Water contamination from pharmaceutical residues, such as nevirapine (NVP), and industrial phenolic pollutants, like 4-nitrophenol (4-NP), has become widespread. The fluorescence of sustainable carbon dots (S,N-FCDs) was significantly quenched by either NVP or 4-NP at 420 nm. Besides metronidazole at a 10-fold concentration higher than the target analytes, no other commonly found environmental contaminants interfered with the detection of either NVP or 4-NP. The quantitative aspects of NVP or 4-NP using S,N-FCD fluorescence quenching were fully investigated. The new fluorometric sensing of NVP (pH = 4) showed a wide linear concentration range of 5-1500 ppb (y = 8.67 × 10^-3 [NVP] + 0.975), with an estimated LOD and LOQ of 4.8 ppb and 13.4 ppb, respectively. Similarly, independent fluorometric calibration measurements for 4-NP (pH = 7) were linear in the range of 0.5-1500 ppb (y = 1.77 × 10^-3 [4-NP] + 1.109), with an estimated LOQ and LOD value of 3.4 ppb and 11.4 ppb, respectively. The enhanced absorption of 4-NP at 400 nm when mixed with S,N-CDs also exhibited two linear correlations between absorbance and 4-NP concentration in the 20-1500 ppb range (y = 4.7 × 10^-4 [4-NP] + 0.26) and in the 0.5-20 ppb range (y = 1.741 × 10^-2 [4-NP] + 0.01096), with LOD and LOQ values (derived from the wider and more precise calibration range) of 0.11 ppb and 0.38 ppb, respectively. These quantitative methods for NVP or 4-NP demonstrated acceptable recoveries (88-103%) in spiked river water samples. Thus, the S,N-FCDs can be used for the quantitative detection of these two analytes down to ppb levels in samples where the two analytes do not coexist, with high accuracy, sensitivity, and selectivity, and can be applied to complex environmental samples.