Abstract
Carbon dots (CDs) are a particularly useful type of fluorescent nanoparticle that demonstrate biocompatibility, resistance to photobleaching, as well as diversity in composition and characteristics amongst the different types available. There are two main morphologies of CDs: Disk-shaped with 1–3 stacked sheets of aromatic carbon rings and quasi-spherical with a core-shell arrangement having crystalline and amorphous properties. They can be synthesized from various potentially environmentally friendly methods including hydrothermal carbonization, microwaving, pyrolysis or combustion, and are then purified via one or more methods. CDs can have either excitation wavelength-dependent or -independent emission with each having their own benefits in microscopic fluorescent imaging. Some CDs have an affinity for a particular cell type, organelle or chemical. This property allows the CDs to be used as sensors in a biological environment and can even provide quantitative information if the quenching or intensity of their fluorescence is dependent on the concentration of the analyte. In addition to fluorescent imaging, CDs can also be used for other applications including drug delivery, quality control, photodynamic therapy, and photocatalysis.
Highlights
carbon dots (CDs) made from performing combustion do not require any additional surface modification, but the photoluminescent quantum yield is lower than the other techniques [19]
The methods that have been mentioned provide a way to remove unwanted material from the sample, they do not isolate the solid particles from the solution, unless the experimenter is able to isolate the nanoparticles of interest in the precipitant rather than the supernatant when centrifuging [27], an additional step must be taken to remove as much of the solvent as possible such as vacuum filtration or rotary evaporation
Since CDs synthesis occurs at higher temperatures [48], they typically do not degrade within the range of temperatures maintained for homeostasis in a biological environment
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. There can be great variation in the chosen mode of synthesis, and in the type of CD produced, between the selection of starting materials, heating method, and purification method or methods applied to the sample to isolate the CDs or version of CDs of interest [4] Due to their small size and composition, CDs have been proven to be non-toxic within working conditions for microscopic fluorescent imaging [5]. A change in intensity and/or wavelength of emission of CDs while within a sample when the excitation source is unaltered can be an indication of the presence of a particular chemical or environmental condition (temperature, pH, etc.) This behavior by CDs opens up the possibility of their use as biological and chemical sensors. It must be proven that the CDs are able to specify just the chemical or condition of interest and not be influenced by the additional species present
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