Preparation of Fluorescent "on-off-on" Carbon Quantum Dots and Their Application to the Detection of Fe 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 Fe 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 Fe to Fe, 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 Fe and AA with strong antijamming capability. The LOD for Fe concentrations in the ranges of 0 to 30 µM and 30 to 100 µM were 0.3 µM and 0.76 µM, respectively. The LOD for AA concentrations in the ranges of 0 to 82.5 µM and 82.5 to 172.5 µM were 3.93 µM and 1.63 µM, respectively. Spiking recoveries of Fe in tap water, AA in orange juice and tomato juice were 87.93 ∼ 101.13%, 86.77 ∼ 105.15% and 86.43 ∼ 103.80%, respectively. Meanwhile, k-CQDs also showed good potential for anti-counterfeiting encryption.