Carbon-based sensors for the detection of ascorbic acid (AA) and ferric ions have drawn a great deal of attention recently, owing to their excellent optical properties and good biocompatibility for biological applications. In this work, a series of nitrogen-doped carbon dots (NCDs) were fabricated by a microwave-assistant approach with a combination of dl-malic acid and urea as precursors. Under optimal experimental conditions, NCDs with an average size of 4.52 ± 0.05 nm were prepared, containing amino N and C–N functional groups on the surface of carbon cores. Optical analysis showed that the NCDs exhibited excitation-dependent and concentration-dependent emission properties. A single emission at 450 nm was observed with two luminescent centers at 280 and 370 nm for concentrations ranging from 0.02 to 0.08 mg/mL. Moreover, the NCDs were further used as a fluorescence sensor to detect AA and Fe3+ in solution. From the metal ion sensing research, Fe3+ demonstrated significant quenching abilities on NCDs with a detection limit of 1.9 μM. More importantly, the NCDs also showed an excellent quenching response by AA through the static quenching mechanism and inner filter effect with a detection limit of 2.6 μM. Additionally, the low cell toxicity against MA104 and 293T cells from both monkeys and humans were affirmed, respectively. Therefore, the NCDs developed in the present work provide a “turn-off” strategy for the highly sensitive detection of AA and Fe3+ ions and can be potentially applied in both environmental and biological systems.
Carbon dots (CDs) have caught enormous attention owing to their distinctive properties, such as their high water solubility, tunable optical properties, and easy surface modification, which can be generally used for the detection of heavy metals and organic pollutants. Herein, nitrogen and fluorine co-doped carbon dots (NFCDs) were designed via a rapid, low-cost, and one-step microwave-assisted technique using DL-malic acid and levofloxacin. The NFCDs emitted intense green fluorescence under UV lighting, and the optical emission peak at 490 nm was observed upon a 280 nm excitation, with a high quantum yield of 21.03%. Interestingly, the spectral measurements illustrated excitation-independent and concentration-independent single-color fluorescence owing to the presence of nitrogen and fluorine elements in the surface functional groups. Additionally, the NFCDs were applied for the selective detection of Fe3+ and ascorbic acid based on the “turn-off” mode. The detection limits were determined as 1.03 and 4.22 µM, respectively. The quenching mechanisms were explored using the static quenching mechanism and the inner filter effect. Therefore, a NFCDs fluorescent probe with single color emission was successfully developed for the convenient and rapid detection of Fe3+ and ascorbic acid in environments.
The basic principles of systematical thinking with an eye to its application take optimization as the primary objective. Based on the principle of integrity of the system as the most significant and essential feature, study style construction is considered to be system engineering. And in connection with the principle of relevance for the system, study style construction is characterized by and reflected in the whole process of education instead of a kind of temporary, periodic and partial work. All aspects of work are involved in colleges and universities, which are in need of active coordination, participation and support of all parts. Therefore, total study style construction should be advocated. According to the principle of hierarchy for the system, we also need to attach importance to the personality development of students while emphasizing comprehensive quality of all-round development.
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