Multifunctional N-doped fluorescent carbon dots for cholesterol monitoring at ultra-low concentration and dye degradation

Abstract

The modified hydrothermal protocol was used to synthesize N-Doped fluorescent carbon dots (N-FCDs) by utilizing urea (0.4 g) and D‐glucose (0.25 g) as a raw material and used for the determination of cholesterol level in human serum as well as utilized for photocatalytic degradation of methyl orange (MO). The N-FCDs exhibited spherical morphology, well defined lattice structure, with atoms arranged in an ordered manner, resulting in a single contiguous crystalline phase having particle size of 3.5 nm as revealed from TEM analysis. The presence of different functional groups enables its wide range applicability. The effect of different experimental conditions like pH, autoclave time, stability and concentration on the fluoresce intensity (FI) of N-FCDs were examined. Maximum emission at 428 nm followed by excitation at 375 nm was observed for N-FCDs (autoclave; 10 h) dispersed in distilled water at pH ≈ 4. The fluorescent N-FCDs were found to undergo quenching upon complexation with hemoglobin (Hb). The quenched complex upon the reaction with cholesterol increases the fluorescence intensity which was examined as a function of cholesterol concentration (0–100 µM). The N-FCDs were able to detect the cholesterol level up to 1258.8 µg/mL which were in good agreement with results from local pathology lab 1280 µgmL^-1. The N-FCDs was also used for the degradation of methyl orange (MO) dye. Different reaction parameters like time (120 min), pH (4) and catalyst dose (0.1 g) was optimized to get maximum efficiency. The N-FCDs effectively degraded 85 % of the MO at optimized reaction conditions. The heterogeneity of the catalyst and adsorption of the dye was confirmed by Freundlich isotherm model (R² = 0.97). The photocatalyst was used for multiple cycles without a prominent decrease in activity. The result showed that N-FCDs can be used for a variety of applications.