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.
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