Preparation of Fluorescent "on-off-on" Carbon Quantum Dots and Their Application to the Detection of Fe3+ and Ascorbic Acid and Information Encryption

Carbon quantum dots are a new type of fluorescent carbon-based nanomaterials, and their excellent properties have provoked a strong research interest. Herein, blue-fluorescent carbon quantum dots (k-CQDs) were successfully synthesized by a simple one-step hydrothermal method using chitosan and ethylenediaminetetraacetic acid as precursors. It was found that Fe3+ could quench the fluorescence of k-CQDs by a dynamic quenching mechanism that increased the positive charge in solution. Due to ascorbic acid (AA) can reduce Fe3+ to Fe2+, the positive charge in solution was reduced and the fluorescence of k-CQDs was restored. Based on the mechanism of the fluorescence "on-off-on", k-CQDs were used for the detection of Fe3+ and AA with strong antijamming capability. The LOD for Fe3+ concentrations in the ranges of 0 to 30 mu M and 30 to 100 mu M were 0.3 mu M and 0.76 mu M, respectively. The LOD for AA concentrations in the ranges of 0 to 82.5 mu M and 82.5 to 172.5 mu M were 3.93 mu M and 1.63 mu M, respectively. Spiking recoveries of Fe3+ in tap water, AA in orange juice and tomato juice were 87.93 similar to 101.13%, 86.77 similar to 105.15% and 86.43 similar to 103.80%, respectively. Meanwhile, k-CQDs also showed good potential for anti-counterfeiting encryption.