Photogeneration of reagent radicals for detection of ascorbic acid by using highly photoluminescent nitrogen-doped carbon quantum dots

Abstract

An efficient and new hydrothermal method was established to prepare nitrogen-doped carbon quantum dots (N-CQDs) in an autoclave, using citric acid and 3,4-diaminobenzoic acid as precursors. The characterization of N-CQDs was performed by using various spectroscopic and microscopic techniques. The photoluminescence studies revealed that N-CQDs had a high quantum yield of 45.6 %. N-CQDs were used to develop a novel and exciting turn-off–on photoluminescence method for trace detection of ascorbic acid (AA). The photoluminescence of a mixture of N-CQDs and persulfate drastically decreased under UV irradiation in a flow injection setup. When AA was added to the mixture, the reagent radicals were scavenged. Therefore, the photoluminescence intensity was enhanced. Through the competitive mechanism, an efficient method was born to detect AA in some fruits, vegetables, and supplements. The sensing condition was optimized by a univariate procedure and a central composite design (CCD) approach. Under optimum conditions, the photoluminescence response was linear in the range of 0.3–11.5 µmol/L of AA. The AA sensing method exhibited a limit of detection of 0.05 µmol/L. It showed satisfactory sensitivity, repeatability, and accuracy. The AA assay method presented a sample throughput equal to 70 h−1.