Synthesis of Doped/Hybrid Carbon Dots and Their Biomedical Application

Preventing biofilm formation and eradicating pathogenic bacteria by Zn doped histidine derived carbon quantum dots

Bacterial infections are of major medical concern due to antibiotic resistance. Carbon quantum dots (CDs) have emerged as potentially excellent biomaterials for multifunctional applications due to their low toxicity, outstanding water solubility, high fluorescence, and high biocompatibility. All of these properties allow CDs to be exceptional biomaterials for inhibiting the growth of bacteria and stopping biofilm formation due to their strong binding affinity, cell wall penetration, and solubilizing biofilm in water. Here, we describe a strategy for one-pot synthesis of histidine-derived zinc-doped N-doped CDs (Zn-NCDs) by a hydrothermal method for inhibiting the growth of both Gram-positive and Gram-negative bacteria without harming mammalian cells. The NCDs and Zn-NCDs showed uniform sizes (∼6 nm), crystallinity, good photostability, high quantum yield (76%), and long decay time (∼5 ns). We also studied their utilization for live cell bio-imaging and the antimicrobial properties towards the Gram-positive Staphylococcus aureus and the Gram-negative Pseudomonas aeruginosa. Importantly, the Zn-NCDs could penetrate the biofilm and bacterial cell wall to effectively inhibit the growth of bacteria and subsequently inhibit biofilm formation. Thus, the structure, chemical composition, and low toxicity properties of the newly-developed Zn-NCDs exemplify a promising novel method for the preparation of nano-level antibacterial drugs.

High Quantum Yield Amino Acid Carbon Quantum Dots with Unparalleled Refractive Index

Carbon quantum dots (CQDs) are one of the most promising types of fluorescent nanomaterials due to their exceptional water solubility, excellent optical properties, biocompatibility, chemical inertness, excellent refractive index, and photostability. Nitrogen-containing CQDs, which include amino acid based CQDs, are especially attractive due to their high quantum yield, thermal stability, and potential biomedical applications. Recent studies have attempted to improve the preparation of amino acid based CQDs. However, the highest quantum yield obtained for these dots was only 44%. Furthermore, the refractive indices of amino acid derived CQDs were not determined. Here, we systematically explored the performance of CQDs prepared from all 20 coded amino acids using modified hydrothermal techniques allowing more passivation layers on the surface of the dots to optimize their performance. Intriguingly, we obtained the highest refractive indices ever reported for any CQDs. The values differed among the amino acids, with the highest refractive indices found for positively charged amino acids including arginine-CQDs (∼2.1), histidine-CQDs (∼2.0), and lysine-CQDs (∼1.8). Furthermore, the arginine-CQDs reported here showed a nearly 2-fold increase in the quantum yield (∼86%) and a longer decay time (∼8.0 ns) compared to previous reports. In addition, we also demonstrated that all amino acid based CQD materials displayed excitation-dependent emission profiles (from UV to visible) and were photostable, water-soluble, noncytotoxic, and excellent for high contrast live cell imaging or bioimaging. These results indicate that amino acid based CQD materials are high-refractive-index materials applicable for optoelectronic devices, bioimaging, biosensing, and studying cellular organelles in vivo. This extraordinary RI may be highly useful for exploring cellular elements with different densities.

Carbon dots and their interactions with recognition molecules for enhanced nucleic acid detection

Carbon Dots (C-dots) have exceptional fluorescence and incident wavelength alteration capabilities because of their π-π* electron transitions between the surface-trapped charges. They have clear, considerate and cost-effective applications in the domain of bio-sensing, optical imaging, medical diagnostics, fluorescence chemotherapy, forensics, and environmentology. Advances in the production process of C-dots can change their optical and chemical characteristics, allowing them to interact with a variety of chemicals and ions that can be exploited for the DNA detection in point-of-care devices. In the current scenario of pathogenic disease prevention, metagenomics and industrial processes, alternative genetic material identification is critical. This review focuses on the existing carbon dots-based DNA detection technologies and their interactions with other components such as metallic salts, dyes, and biological chemicals based on their surface charge distribution (positive or negative) employed in the DNA diagnostic devices and biosensors with their operating mechanism regarding their target component. These intriguing scientific discoveries and technologies will be extensively examined to translate them into real-world solutions which will have a significant societal and economic impact on overall well-being and innovation.

Sonochemistry of molten metals

Ultrasonic irradiation of molten metals in liquid media causes dispersion of the metals into suspensions of micro- and nanoparticles that can be separated. This is applicable mainly to low-m_p elemental metals or alloys, but higher m_p elemental metals or alloys were also reported. Among metals, mercury and gallium exhibit especially-low melting points and are thus considered as liquid metals (LMs). Sonication of mercury in aqueous solutions of certain metal ions can cause simultaneous reduction of the ions and reactions between the metals. Gallium can be melted and sonicated in warm water, as well as in aqueous solutions of various solutes such as metal ions and organic compounds, which opened a wide window of interactions between the gallium particles and the solutes. Sonication of molten metals in organic liquids, such as polyethylene glycol (PEG) 400, forms carbon dots (C-dots) doped with nanoparticles of these metals. This review article summarizes the various interactions and reactions that occur upon sonication of metals in liquid media.

Positively Charged Carbon Dots with Antibacterial and Antioxidant Dual Activities for Promoting Infected Wound Healing

Bacterial infection and excess reactive oxygen species are key factors that lead to slow or substantially delayed wound healing. It is crucial to design and develop new nanomaterials with antibacterial and antioxidative capabilities for wound healing. Here, positively charged carbon dots (CDs) are rationally designed and synthesized from p-phenylenediamine and polyethyleneimine by a facile one-pot solvothermal method, which show good biocompatibility in in vitro cytotoxicity, hemolysis assays, and in vivo toxicity evaluation. The positively charged CDs show superior antimicrobial effect against Staphylococcus aureus (S. aureus) at very low concentrations, reducing the risk of wound infection. At the same time, CDs with surface defects and unpaired electrons can effectively scavenge excess free radicals to reduce oxidative stress damage, accelerate wound inflammation-proliferation transition, and promote wound healing. The mouse model of skin infection demonstrates that CDs can effectively promote the wound healing of skin infection without obvious side effects by simply dropping or spraying onto the wound. We believe that the prepared CDs have satisfactory biocompatibility, antioxidant capacity, and excellent antibacterial activity and have great application potential in wound healing.

Functional Carbon Quantum Dots for Ocular Imaging and Therapeutic Applications

Carbon quantum dots (CDs) are a class of emerging carbonaceous nanomaterials that have received considerable attention due to their excellent fluorescent properties, extremely small size, ability to penetrate cells and tissues, ease of synthesis, surface modification, low cytotoxicity, and superior water dispersion. In light of these properties, CDs are extensively investigated as candidates for bioimaging probes, efficient drug carriers, and disease diagnostics. Functionalized CDs represent a promising therapeutic candidate for ocular diseases. Here, this work reviews the potential use of functionalized CDs in the diagnosis and treatment of eye-related diseases, including the treatment of macular and anterior segment diseases, as well as targeting Aβ amyloids in the retina.

Emerging and Versatile Platforms of Metal-Ion-Doped Carbon Dots for Biosensing, Bioimaging, and Disease Therapy

Metal ions possess abundant electrons and unoccupied orbitals, as well as large atomic radii, whose doping into carbon dots (CDs) is a facile strategy to endow CDs with additional physicochemical characteristics. After being doped with metal ions, CDs reveal obvious changes in their optical, electronic, and magnetic properties by adjustments to their electron density distribution and the energy gaps, leading them to be promising and competitive candidates as labeling probes, imaging agents, catalysts, nanodrugs, and so on. In this review, we summarize the fabrication methods of metal-ion-doped CDs (M-CDs), and highlight their biological applications including biosensing, bioimaging, tumor therapy, and anti-microbial treatment. Finally, the challenging future perspectives of M-CDs are analyzed. We hope this review will provide inspiration for further development of M-CDs in various biological aspects, and help readers who are interested in M-CDs and their biological applications.

High reactive oxygen species produced from fluorescence carbon dots for anticancer and photodynamic therapies: A review

High-photoluminescence carbon dots (CDs) were synthesized from various sources and various methods using two approaches, namely bottom up and top down, with emission-dependent excitation wavelength. Electronic transition from the higher-occupied molecular orbital (HOMO) state to the lowest-unoccupied molecular orbital(LUMO) state, surface defect states, wider excitation spectrum, higher quantum yield, efficient energy transfer, and element doping affected the fluorescence properties of CDs. Using 102 references listed in this review, the authors studied the relationship between fluorescence mechanism and reactive oxygen species (ROS) produced for photodynamic therapy (PDT) and materials anticancer applications. We described how the radical atom or ROS work as anticancer therapy and PDT and described the chemical reaction of high-resolution fluorescence CDs. We summarized experimental techniques that are used for producing CDs and discussed their characteristics. Finally, conclusions and future prospects in this field are also discussed. The important characteristics of CD-based design for high ROS may usher in new prospects and challenges for high efficiency and stability of PDT and anticancer therapy. In conclusion, we have provided perspectives and challenges of the future development of CD s.

Folic Acid-Functionalized Graphene Quantum Dots: Synthesis, Characterization, Radiolabeling with Radium-223 and Antiviral Effect against Zika Virus Infection

The use of graphene quantum dots as biomedical devices and drug delivery systems has been increasing. The nano-platform of pure carbon has shown unique properties and is approved to be safe for human use. In this study, we successfully produced and characterized folic acid-functionalized graphene quantum dots (GQD-FA) to evaluate their antiviral activity against Zika virus (ZIKV) infection in vitro, and for radiolabeling with the alpha-particle emitting radionuclide radium-223. The in vitro results exhibited the low cytotoxicity of the nanoprobe GQD-FA in Vero E6 cells and the antiviral effect against replication of the ZIKV infection. In addition, our findings demonstrated that functionalization with folic acid doesn't improve the antiviral effect of graphene quantum dots against ZIVK replication in vitro. On the other hand, the radiolabeled nanoprobe ²²³Ra@GQD-FA was also produced as confirmed by the Energy Dispersive X-Ray Spectroscopy analysis. ²²³Ra@GQD-FA might expand the application of alpha targeted therapy using radium-223 in folate receptor-overexpressing tumors.

Biowaste-Derived Carbon Dots: A Perspective on Biomedical Potentials

Today, sustainable and natural resources including biowastes have been considered attractive starting materials for the fabrication of biocompatible and biodegradable carbon dots (CDs) due to the benefits of availability, low cost, biorenewability, and environmentally benign attributes. These carbonaceous nanomaterials have been widely explored in the field of sensing/imaging, optoelectronics, photocatalysis, drug/gene delivery, tissue engineering, regenerative medicine, and cancer theranostics. Designing multifunctional biowaste-derived CDs with a high efficacy-to-toxicity ratio for sustained and targeted drug delivery, along with imaging potentials, opens a new window of opportunity toward theranostic applications. However, crucial challenges regarding the absorption/emission wavelength, up-conversion emission/multiphoton fluorescence mechanisms, and phosphorescence of these CDs still need to be addressed to attain the maximum functionality and efficacy. Future studies ought to focus on optimizing the synthesis techniques/conditions, evaluating the influence of nucleation/growth process on structures/properties, controlling their morphology/size, and finding the photoluminescence mechanisms. Reproducibility of synthesis techniques is another critically important factor that needs to be addressed in the future. Herein, the recent developments related to the biowaste-derived CDs with respect to their biomedical applications are deliberated, focusing on important challenges and future perspectives.

State-of-the-art developments in carbon quantum dots (CQDs): Photo-catalysis, bio-imaging, and bio-sensing applications

Carbon quantum dots (CQDs), the intensifying nanostructured form of carbon material, have exhibited incredible impetus in several research fields such as bio-imaging, bio-sensing, drug delivery systems, optoelectronics, photovoltaics, and photocatalysis, thanks to their exceptional properties. The CQDs show extensive photonic and electronic properties, as well as their light-collecting, tunable photoluminescence, remarkable up-converted photoluminescence, and photo-induced transfer of electrons were widely studied. These properties have great advantages in a variety of visible-light-induced catalytic applications for the purpose of fully utilizing the energy from the solar spectrum. The major purpose of this review is to validate current improvements in the fabrication of CQDs, characteristics, and visible-light-induced catalytic applications, with a focus on CQDs multiple functions in photo-redox processes. We also examine the problems and future directions of CQD-based nanostructured materials in this growing research field, with an eye toward establishing a decisive role for CQDs in photocatalysis, bio-imaging, and bio-sensing applications that are enormously effective and stable over time. In the end, a look forward to future developments is presented, with a view to overcoming challenges and encouraging further research into this promising field.

Development of Doped Carbon Quantum Dot-Based Nanomaterials for Lubricant Additive Applications

The development of advanced lubricants is essential for the pursuit of energy efficiency and sustainable development. In order to improve the properties of lubricating fluids, high-performance lubricating additives are required. In recent research studies, carbon nanomaterials such as fullerenes, carbon nanotubes, and graphene have been examined as lubricating additives to water or oil. Lubricating oils are well known for the presence of additives, especially friction-reducers and anti-wear additives. As part of this work, we have studied the advancement in the research and development of carbon dot (CD)-based lubricant additives by presenting a number of several applications of CD-based additives. We have also highlighted the friction-reducing properties and anti-wear properties of CDs and their lubrication mechanism along with some challenges and future perspectives of CDs as an additive. CDs are carbon nanomaterials that are synthesized from single-atom-thick sheets containing a large number of oxygen-containing functional groups; they have gained increasing attention as friction-reducing and antiwear additives. CDs have gradually been revealed to have exceptional tribological properties, particularly acting as additives to lubricating base oils. In our final section, we discuss the main challenges, future research directions, and a number of suggestions for a complete functionalized or hybrid doped CD-based material.