Carbon dots (CDs) being a new type of carbon‐based nanomaterial have attracted intensive interest from researchers owing to their excellent biophysical properties. CDs are a class of fluorescent carbon nanomaterials that have emerged as a promising alternative to traditional quantum dots and organic dyes in applications including bioimaging, sensing, and optoelectronics. CDs possess unique optical properties, such as tunable emission, facile synthesis, and low toxicity, making them attractive for many applications in biology, medicine, and environmental areas. The synthesis of CDs is achievable by a variety of methods, including bottom‐up and top‐down approaches, involving the use of different carbon sources and surface functionalization strategies. However, understanding the fluorescence mechanism of CDs remains a challenge. Various mechanistic models have been proposed to explain their origin of luminescence. This review summarizes the recent developments in the synthesis and functionalization of CDs and provides an overview of the current understanding of the fluorescence mechanism.
Synthesis Mechanisms, Structural Models, and Photothermal Therapy Applications of Top-Down Carbon Dots from Carbon Powder, Graphite, Graphene, and Carbon Nanotubes
In this study, top-down syntheses of carbon dots (CDs) from four different carbon precursors, namely, carbon nano powders, graphite, graphene, and carbon nanotubes, were carried out. Systematic study demonstrated that the optical properties and surface functionalities of the CDs were quite similar and mainly influenced by the synthesis method, while the sizes, morphologies, chemical compositions, and core structures of the CDs were heavily influenced by the carbon precursors. On the basis of these studies, the formation processes and structural models of these four top-down CDs were proposed. The cell cytotoxicity and photothermal conversion efficiency of these CDs were also carefully evaluated, demonstrating their potential applications in photothermal therapy.
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- Award ID(s):
- 2041413
- NSF-PAR ID:
- 10350462
- Date Published:
- Journal Name:
- International Journal of Molecular Sciences
- Volume:
- 23
- Issue:
- 3
- ISSN:
- 1422-0067
- Page Range / eLocation ID:
- 1456
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
Carbon dots (CDs) are emerging as the material of choice in a range of applications due to their excellent photoluminescence properties, ease of preparation from inexpensive precursors, and low toxicity. However, the precise nature of the mechanism for the fluorescence is still under debate, and several molecular fluorophores have been reported. In this work, a new blue fluorophore, 5-oxopyrrolidine-3-carboxylic acid, was discovered in carbon dots synthesized from the most commonly used precursors: citric acid and urea. The molecular product alone has demonstrated interesting aggregation-enhanced emission (AEE), making it unique compared to other fluorophores known to be generated in CDs. We propose that this molecular fluorophore is associated with a polymer backbone within the CDs, and its fluorescence behavior is largely dependent on intermolecular interactions with the polymers or other fluorophores. Thus, a new class of non-traditional fluorophores is now relevant to the consideration of the CD fluorescence mechanism, providing both an additional challenge to the community in resolving the mechanism and an opportunity for a greater range of CD design schemes and applications.more » « less
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In this study, carbon dots are synthesized hydrothermally from loblolly pine using top-down and bottom-up processes. The bottom-up process dialyzed carbon dots from hydrothermally treated process liquid. Meanwhile, hydrochar was oxidized into carbon dots in the top-down method. Carbon dots from top-down and bottom-up processes were compared for their yield, size, functionality, and quantum properties. Furthermore, hydrothermal treatment temperature and residence time were evaluated on the aforementioned properties of carbon dots. The results indicate that the top-down method yields higher carbon dots than bottom-up in any given hydrothermal treatment temperature and residence time. The size of the carbon dots decreases with the increase in reaction time; however, the size remains similar with the increase in hydrothermal treatment temperature. Regarding quantum yield, the carbon dots from the top-down method exhibit higher quantum yields than bottom-up carbon dots where the quantum yield reaches as high as 48%. The only exception of the bottom-up method is the carbon dots prepared at a high hydrothermal treatment temperature (i.e., 260 °C), where relatively higher quantum yield (up to 18.1%) was observed for the shorter reaction time. Overall, this study reveals that the properties of lignocellulosic biomass-derived carbon dots differ with the synthesis process as well as the processing parameters.more » « less
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Force sensors play an important role in the biomedical devices industry, especially in motion- and pressure-related devices. Such sensors are designed to collect force or pressure data by converting it into electrical signals. The data can then be sent to and analyzed by a local or cloud-based processing unit. It is vital that the sensors can be fabricated in a way that time efficiency, cost efficiency, and quality are all maximized. The advent of three-dimensional (3D) printing has greatly facilitated prototyping and customized manufacturing, as compared to older crafting methods (such as welding and woodworking), 3D printing requires less skill and involves less costly materials making it much more time- and cost-efficient. Technological advancements have also improved the quality of the actual sensing materials used in sensor-based devices, and notably, carbon-based materials have become increasingly favored for use as sensing elements. In the presented sensor, the modern sensor fabrication methods of 3D printing and using carbon materials as sensing elements are combined. The sensor presented as a proof of the above concepts is a cantilever flex sensor. The sensor consists of a 30 mm-long cantilever extending from a 2.5 mm-thick wall, with a second wall of the same thickness parallel to the cantilever. After designing this structure and printing it using a 3D printer, the top surface of the cantilever was coated with a thin layer of conductive carbon paste and two copper wires were stripped and soldered to a pair of copper alligator clips, to be used for testing purposes. To test the sensor, the two copper wires were clipped onto the sensor (Figure 1A) and each wire was connected to a multimeter probe on the end opposite of the alligator clip. Then, using a set of four through holes in the parallel wall (along with a slotted rod), the tip of the cantilever was pressed down to an angle of 5, 10, 15, or 20 degrees (Figures 1B, 1C, 1D, and 1E, respectively) below the original plane of the cantilever and held there for 2 minutes. The resistance between the ends of the cantilever was measured throughout each trial by the multimeter, and the results (Figure 1F) for each angle were compiled and analyzed to determine the effect of each depression angle on impedance change, and thus, the overall effectiveness of the sensor. In the future, a notable improvement would be miniaturizing the sensor to facilitate in integration of the sensor in wearable and biomedical devices.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/ijms23031456
