Bioimaging based on fluorescent carbon dots

ZnCl2 Enabled Synthesis of Highly Crystalline and Emissive Carbon Dots with Exceptional Capability to Generate O2⋅–

Carbon dots (CDs), including carbon quantum dots, graphene quantum dots, carbon nanodots, and polymer dots, have gained significant attention due to their unique structural and fluorescence characteristics. This review provides a comprehensive overview of the classification, structural characteristics, and fluorescence properties of CDs, followed by an exploration of various fluorescence sensing mechanisms and their applications in gene detection, nucleolus imaging, and gene delivery. Furthermore, the functionalization of CDs with diverse surface ligand molecules, including dye molecules, nucleic acid probes, and metal derivatives, for sensitive nucleic acid detection is systematically examined. Fluorescence imaging of the cell nucleolus plays a vital role in examining intracellular processes and the dynamics of subcellular structures. By analyzing the mechanism of fluorescence and structure-function relationships inherent in CDs, the nucleolus targeting abilities of CDs in various cell lines have been discussed. Additionally, challenges such as the insufficient organelle specificity of CDs and the inconsistent mechanisms underlying nucleolus targeting have also been highlighted. The unique physical and chemical properties of CDs, particularly their strong affinity toward deoxyribonucleic acid (DNA), have spurred interest in gene delivery applications. The use of nuclear-targeting peptides, polymers, and ligands in conjunction with CDs for improved gene delivery applications have been systematically reviewed. Through a comprehensive analysis, the review aims to contribute to a deeper understanding of the potential and challenges associated with CDs in biomedical applications.

Fluorescent carbon dots have the advantages of good chemical stability, low toxicity, and surface functionalization, which has caused concern. In recent years, polymer carbon dots synthesize by polymer polysaccharides have become a new research hotspot. In this paper, a chitosan-based fluorescent polymer carbon dot material is synthesized by hydrothermal method and used for drug-loading research. We choose chitosan-graft-polyethylene glycol monomethyl ether and citric acid derivatives as the carbon sources for the carbon dots, because chitosan and polyethylene glycol are both a carbon source for carbon dots and a passivation reagent for carbon dots. Then the quantum yield of the polymeric carbon dots is increased. Polymer carbon dots can also retain the molecular structure of polyethylene glycol and chitosan, providing favorable conditions for its application in drug loading. The structural characterization is performed on P(CS-g-mPEG-CA)CDs by IR, UV, X-ray diffraction, photoelectron spectroscopy, transmission electron microscopy and photoluminescence spectra and pH stability test is carried out. The results show that the synthesized P(CS-g-mPEG-CA)CDs has higher fluorescence quantum yield(66.81%), longer fluorescence lifetime(15.247 ns), and better pH stability. Using Doxorubicin as a model drug, a load study was conducted using this polymer carbon dot. The results show that if the degree of substitution of mPEG is 11.9%, the maximum loading rate of polymer carbon dots is 51.3% and the maximum drug release rate is 28.7%. In addition, we also found that drug loading and release could be controlled by the grafting rate of mPEG. In addition, the cytotoxicity of polymer carbon dots on nasopharyngeal carcinoma cells(CNE-2) is evaluated using an MTT assay. The study shows that there is no obvious cytotoxicity of blank P(CS-g-mPEG-CA)CDs, and that the survival rate of CNE-2 cells decreases with the increase of drug-loaded micelles. The results show that the P(CS-g-mPEG-CA)CDs have a certain application prospect in the aspects of fluorescence labeling, drug delivery, fluorescent tracer system and controlled release.

These days, carbon dots (CDs) are the rising stars of nanomaterials. Carbon dots (CDs) are small carbon nanoparticles with the same type of surface passivation (less than 10 nm in size). Researchers found C-dots by accident while purifying single-walled carbon nanotubes (SWCNTs) manufactured using the arc-discharge process. Toxic metal-based quantum dots are being replaced with carbon dots (QDs). Carbon dots are currently being prepared from a variety of natural resources in order to obtain self-passivated products at a reasonable cost. Because of their superior photo physical characteristics, biocompatibility, and low toxicity, carbon dots have prospective applications in bio sensing, bio imaging, and drug administration. Different synthetic processes, precursors, salient properties, and applications were reviewed in this review, as well as some future prospects, obstacles, and possible solutions for future development. Because of their tunable optical characteristics and better biocompatibility, luminous carbon-based nanomaterials have sparked a lot of scientific interest. Different light emission properties of carbon are discussed in this review. Distinct synthesis procedures have resulted in different carbon dots (CDs). Summarized here. The optical properties of CDs that haven't been synthesized yet surface doping and element doping can be used to further control it. CDs are being functionalized for an adjustable band gap. As a result of their luminescent with reduced cytotoxicity and tunable optical characteristics CDs have been thoroughly investigated in terms of their potential uses in biomedicine, such as analytical sensors, and instruments for bioimaging. Fluorescent carbon dots are a new type of nanomaterial from the carbon family. Green CDs, which have attracted a lot of attention from researchers because of their better water solubility, high biocompatibility, and eco-friendly nature when compared to chemically generated CDs, can be made from a variety of inexpensive and renewable resources. The presence of heteroatoms on the surface of green CDs in the form of amine, hydroxyl, carboxyl, or thiol functional groups, which can improve their physicochemical qualities, quantum yield, and likelihood of visible light absorption, eliminates the need for additional surface passivation.

Surface functionality and formation mechanisms of carbon and graphene quantum dots

Carbon dots (or carbon quantum dots in some literature reports), generally small carbon nanoparticles with various surface passivation effects, have attracted widespread attention in recent years, with a rapidly increasing number of research publications. The reported studies covered many aspects of carbon dots, from the development of many new synthetic methodologies to an improved mechanistic elucidation and to the exploration of application opportunities, especially for those in the fluorescence imaging of cells and tissues. There have also been significant advances in the establishment of a shared mechanistic framework for carbon dots and other carbon-based quantum dots, graphene quantum dots in particular. In this article, representative recent studies for more efficient syntheses of better-performing carbon dots are highlighted along with results from explorations of their various bioimaging applications in vitro and in vivo. Similar fluorescence properties and potential imaging uses of some graphene quantum dots are also discussed, toward a more consistent and uniform understanding of phenomenologically different carbon-based quantum dots.

Morphological insights into uncompetitive fluorescence of coal-based carbon dots and strategies for improvement

Recent advances in agricultural and marine waste-derived carbon dots for clean energy technologies

Due to the different emission mechanism between fluorescent carbon dots and semiconductor quantum dots (QDs), it is of interest to explore the potential emission in hetero-structured carbon dots/semiconducting QDs. Herein, we design carbon dots coated CdTe QDs (CDQDs) and investigate their inherent emission. We demonstrate switchable emission for the hetero-interactions of the CDQDs. Optical analyses indicate electron transfer between the carbon dots and the CdTe QDs. A heterojunction electron process is proposed as the driving mechanism based on N atom protonation of the carbon dots. This work advances our understanding of the interaction mechanism of the heterostructured CDQDs and benefits the future development of optoelectronic nanodevices with new functionalities.

Carbon nanodots: Mechanisms of photoluminescence and principles of application

Fluorescent carbon dots (FCDs) is the youngest member of the carbon nanoparticles family, having superior features such as tunable fluorescent properties, low toxicity, good water solubility, chemical stability, economical and straightforward synthesis methods, and easy functionalization. In the context of these properties, carbon quantum dots are thought to be potential candidates to replace conventional toxic and expensive semiconductor quantum dots. The application areas of these extraordinary zero-dimensional carbon particles have been getting increased day by day. They have been most widely used in sensing, bioimaging, photocatalysis, and optoelectronics applications. In this present chapter, the historical development of FCDs has been mentioned, and brief information about FCDs and their advantages was given. After then, synthesis methods of the FCDs were mentioned. Fluorescence carbon dots can be obtained from a variety of different precursors. Among them, vegetables and fruit as a carbon source is the primary concern of the current review. The fluorescent carbon dots obtained from vegetables and fruit and their waste as a carbon source have been briefly discussed. Further, their applications have been reviewed.KeywordsCarbon dotsVegetable and fruit wastesSynthesis methodRecyclingReview

Dual emissive carbon dots: Synthesis strategies, properties and its ratiometric sensing applications

Carbon dots (CDs) have outstanding optical properties, biocompatibility, and photostability, making them attractive for imaging applications. A facile and green one-step hydrothermal synthesis method is proposed, which can be safely used in a wide range of applications such as chemical sensing, bioimaging, and optoelectronics. In this study, we report green synthesis of carbon dots from bitter orange juice (Citrus Aurantium) by hydrothermal treatment for the first time. We studied effects of time, temperature, and pH on fluorescence of CDs, characterized them using various spectroscopic and microscopic methods, and evaluated their toxicity to different cell lines. Identifying an optimum reaction condition of 180 ºC for 7 h heating gave CDs that showed pH-dependent fluorescence, with the largest fluorescence at a pH of 7.0. The CDs were 1-2 nm in size with a spherical morphology and negative surface charge. The CDs showed a high quantum yield of 19.9 %, reasonable photostability, excellent water solubility, and long fluorescence lifetime. A one step hydrothermal rout led to various hydrophilic functional groups on the surface of the CDs. Our results showed that the CDs were non-toxic over a large concentration range and effective for imaging of cells, indicating their potential as imaging probes in medical diagnostics and biosensor applications.

Developing highly fluorescent biogenic carbon dots (CDs) as molecular probes and cellular imaging agents with excellent cellular biocompatibility and water dispersibility can advance the scope of CDs in various biomedical applications. The present work aims to produce CDs from biological precursors such as natural amino acids. Due to their molecular recognition properties, the resultant CDs exhibit biocompatibility, polar functional groups, and selective molecule sensing. Microwave (MW)-assisted carbonization of L-tryptophan, L-glutamic acid, and their mixture led to the formation of CDs. However, the CDs derived from the mix of amino acids exhibited strong emission at 450 nm, with a quantum yield of 31.3%, and showed excellent stability under wide pH conditions. These CDs have a crystalline graphitic core, predominantly derived from the carbonization of the aromatic moiety intrinsic to L-tryptophan amino acid, while the partial carbonization of L-glutamic acid led to anchor polar functional groups on the CDs surface. These CDs were established as molecular probes for sensing the biomolecule cysteamine with enhanced sensitivity and remarkable cross-selectivity among the interfering metal ions, anions, and other thiols. To demonstrate these materials' cellular biocompatibility, the cell viability of MCF-7 and fibroblast cells was studied following their exposure to CDs. The studies revealed that the fluorescent CDs did not elicit cytotoxic effects on the cells at elevated concentrations. The CDs from the mixture of amino acids were efficiently internalized by MCF-7 cells, enabling efficient imaging of live cells. Overall, this study developed biogenic and cellular biocompatible CDs with robust luminescent properties and demonstrated their applications in biomolecular sensing, cellular uptake, and imaging.

Chapter 13 - Carbon dots as adsorbents for removal of toxic chemicals