Development of silver-doped carbon dots sensor derived from lignin for dual-mode fluorometric and spectrophotometric determination of valsartan in a bulk powder and a commercial product

Doping of carbon dots (CDs) with heteroatoms has garnered growing attention in recent years as a useful method of controlling their physicochemical properties. In this study, a new dual-mode sensor based on silver-doped CDs (AgCDs) derived from lignin was developed for fluorometric and spectrophotometric determination of valsartan (VAL). The analysis of AgCDs revealed a structure that closely resembled graphene oxide, with the successful doping of Ag. The mean particle size of AgCDs was 3.50 ± 0.89 nm and it exhibited a reasonable fluorescence quantum yield of 28.1 %. The emission at 612 nm of AgCDs is quenched by VAL after being excited at 275 nm due to a combination of dynamic and static quenching mechanisms. The enhancement in the absorbance of AgCDs upon the addition of the medication was measured at 275 nm. The most favorable circumstances for the dual-mode sensing were achieved with a pH of 8 and a volume of 0.10 mL of AgCDs. The measurements were conducted using fluorometry after 3 min at 10 °C, followed by spectrophotometry after 7 min at 20 °C. The fluorometric data indicated a linear response within the range of 2.0-50.0 μg/mL, while the spectrophotometric results showed a dynamic range of 5.0-100.0 μg/mL. The limits of detection (LODs) were 0.57 and 1.38 μg/mL for the fluorometric and spectrophotometric methods, respectively. The limits of quantification (LOQs) were 1.72 and 4.19 μg/mL for the fluorometric and spectrophotometric methods, respectively. The nano sensor efficiently assessed the presence of VAL in pharmaceutical tablets and produced a favorable outcome with the mean of recovery of 98.91 % and 99.76 % with relative standard deviation (RSD%) of 0.79 and 0.78 for the fluorometric and spectrophotometric methods, respectively.