Rapid Synthesis of Non-Toxic, Water-Stable Carbon Dots Using Microwave Irradiation

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

Carbon dots (CDs) are a new category of crystalline, quasi-spherical fluorescence, “zero-dimensional” carbon nanomaterials with a spatial size between 1 nm to 10 nm and have gained widespread attention in recent years. Green CDs are carbon dots synthesised from renewable biomass such as agro-waste, plants or medicinal plants and other organic biomaterials. Plant-mediated synthesis of CDs is a green chemistry approach that connects nanotechnology with the green synthesis of CDs. Notably, CDs made with green technology are economical and far superior to those manufactured with physicochemical methods due to their exclusive benefits, such as being affordable, having high stability, having a simple protocol, and being safer and eco-benign. Green CDs can be synthesized by using ultrasonic strategy, chemical oxidation, carbonization, solvothermal and hydrothermal processes, and microwave irradiation using various plant-based organic resources. CDs made by green technology have diverse applications in biomedical fields such as bioimaging, biosensing and nanomedicine, which are ascribed to their unique properties, including excellent luminescence effect, strong stability and good biocompatibility. This review mainly focuses on green CDs synthesis, characterization techniques, beneficial properties of plant resource-based green CDs and their biomedical applications. This review article also looks at the research gaps and future research directions for the continuous deepening of the exploration of green CDs.

Background: Silent onset and metastasis in tissues make cancer the most devastating illness globally. Monitoring the growth of the tumour and delivering drugs to specific tissues are some of the major issues associated with treatment. However, with an improved understanding of tumour microenvironments and advancements in nanocarriers of drugs, novel nano-targeting pathways that can be utilised by nanocarriers have been developed. Carbon Dots, with their tiny size and outstanding physicochemical features, are an emerging category of carbon nanostructures that have attracted a lot of curiosity. Objective: Multitudinous attempts and extensive studies have been undertaken by many researchers regarding the synthesis of Carbon Dots and their applications in various fields. These studies have explained that the synthesised Carbon Dots have versatile surface functionalities, high luminescence, and excellent biocompatibility. This article focuses on recent developments in synthesis approaches, carbon precursors used, and applications of Carbon Dots, specifically within the biomedical field, with a particular focus on cancer. Results: Carbon dots synthesised from a variety of precursors can act as prominent candidates for bioimaging and drug carriers and are used in cancer phototherapy. In this article, Carbon Dots are summarised based on their bright luminescent properties, distinct structure, drug loading capacity, and near-infrared (NIR) emission. Conclusion: Carbon dots, employed as tumour theranostics, can serve as an alternative to synthetic fluorescent dyes. They fulfil the role of bioimaging agents and facilitate the precise delivery of drugs to cancer cells. Additionally, they exhibit excellence as phototherapeutic agents, featuring high nearinfrared (NIR) emission and minimal side effects.

Carbon dots (CDs) are a type of carbon nanomaterials (CNMs) with unique properties, including ultrasmall size, excellent water dispersibility, tunable photoluminescence, easy surface funcionalization, low toxicity, and biocompatibility. Owing to their attractive characteristics, CDs have drawn significant interest across diverse application fields. Nowadays, the massive production, consumption, and random disposal of plastics result in accumulation of tremendous non-biodegradable plastic wastes in landfills and natural ecosystems, which could potentially induce environmental pollution and impose threat to human health and ecosystem. The carbon-rich nature of plastic wastes makes them become appealing carbonaceous feedstocks for the fabrication of CDs at low production cost. However, studies focused on this field are still in the preliminary stage, with enormous possibilities remaining to be explored regarding the optimization of synthetic approaches and CD applications in various essential areas. Therefore, this thesis aims at upgrading non-degradable plastic wastes into valuable CDs through eco-friendly and facile synthetic approaches and further investigating their potential applications in the fields of analytical detection and agriculture. Firstly, exhausted RO membrane modules were utilized as feedstocks to produce valuable pyrolysis products and CDs through thermochemical conversion followed by H2O2-assisted hydrothermal method. The synthetic approach of CDs was optimized via adjustments of carbon precursor size, H2O2 concentration, and reaction time. The resultant CDs possess desired properties including excellent water dispersibility, narrow size distribution of 1.3–6.8 nm, high stability, and strong blue fluorescence with a quantum yield of 6.24%. The feasibility of obtained CDs for Fe3+ determination in different water samples is validated and the possible detection mechanism is investigated. Secondly, we successfully achieved the conversion of waste polyethylene terephthalate (PET) bottles into CDs and used them as seed nano-priming agents for green pea seeds. It was found CD priming could efficiently facilitate seed germination and seedling growth of pea plants at all applied concentrations (0.25-2 mg/mL). CD treatment also upregulated multiple biochemical parameters in the plant system favorable for pea development, including root vigor, chlorophyll content, carbohydrate content, and antioxidant enzyme activities. Furthermore, comparative studies of CDs and carbon nanotubes (CNTs) derived from waste plastics were then conducted to investigate their respective effects on pea plant development as nano-priming agents. Different from the previous study which was carried out in a hydroponic system, this study implemented pea cultivation in soil culture treated with or without salt stress (200 mM NaCl). The results demonstrated that both CNMs could promote seed germination and seedling growth and enhance salt tolerance of the plant. A certain degree of surface destruction was observed from the seed coat primed with CDs and CNTs, which could be induced by surface erosion and mechanical interaction, respectively. Besides, it was found that under equivalent concentrations, CDs and CNTs triggered plant response at varying levels and ultimately resulted in variable pea seedling development and salt tolerance. This study provides new insights of implementing CNMs derived from plastic wastes as seed priming agents for agricultural practices, such as saline stress amelioration. Overall, the above studies are expected to offer alternative options for waste management using waste-to-material strategy, thereby contributing to the development of a resilient and reliable circular economy framework.

Metal-doped and hybrid carbon dots: A comprehensive review on their synthesis and biomedical applications

Nucleic acid transfer has shown significant potential in the treatment of bone damage because of its long lasting local effect and lower cost. Nonviral vectors, such as nanomaterials, with higher biocompatibility are increasedly applied in the study of bone defect repair. Carbon dots with various reactive groups on the surface not only provide a unique surface to carry therapeutic genes, but also some carbon dots have been reported to promote osteogenic differentiation. The bone regeneration effect of carbon dots in vivo, however, is rarely investigated. MiR-2861 has revealed osteogenic differentiation effects. In the current study, we created ascorbic acid-PEI carbon dots (CD), which were able to carry miR-2861, by the microwave-assisted pyrolysis method. Results demonstrated that CD had excellent fluorescence stability leading to good fluorescence imaging in vitro and in vivo. CD was efficiently internalized into bone marrow stromal cells (BMSCs) through the clathrin-mediated endocytosis pathway and distributed in the mitochondria, endoplasmic reticulum, lysosome, and nucleus. Results from alkaline phosphatase staining, alizarin red staining, and reverse transcription real-time PCR (RT-QPCR) showed that our CD indeed had osteogenic effects in vitro. Flow cytometry data indicated that CD could efficiently deliver miR-2861 into BMSCs in vitro, and CD carrying miR-2861 (CD@miR) had the strongest osteogenic effects. Analyses of hematology, serum biochemistry, and histology showed that CD and CD@miR did not have cytotoxicity and had higher biocompatibility in vivo. Most interestingly, CD and miR-2861 in the CD@miR could act synergistically to promote osteogenic differentiation in vitro and new bone regeneration in vivo remarkably. Our results clearly indicate that the osteogenic CD delivering osteogenic therapeutic gene, miR-2861, can obtain much stronger bone regeneration ability, suggesting that our CD has great potential in future clinical application.

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.

Green and microwave-assisted synthesis of carbon dots and application for visual detection of cobalt(II) ions and pH sensing

PurposeThis paper aims to develop carbon dots using whey as a valuable resource and to create a sustainable and biocompatible nanomaterial with potential applications in a variety of fields owing to its unique optical properties and antimicrobial capabilities, which are frequently used as sensing agents for detecting specific molecules in food, environmental and biomedical applications. Versatility of carbon dots (CDs) allows the utilization of these dots for a wide range of applications in areas such as food safety, antibacterial properties, production of composite polymers for food packaging, treatment of different diseases and detection of food-borne pathogens. Owing to their high brightness, low toxicity and excellent biocompatibility, CDs have attracted significant interest in food safety. This is also a cutting-edge technology that bids new ideas for treating various diseases.Design/methodology/approachLiterature review related to using whey as the carbon source for synthesis of CDs was collected and studied from different sources like Google Scholar, Research Gate, online journals available at library of Banaras Hindu University, Web of Science and Scopus. A database of more than 100 scientific sources from different sources was made as per the headings and sub headings of the paper.FindingsWhey generated as a by-product from the cheese industry contained a good amount of carbon and nitrogen that can be used for the fabrication of CDs. CDs produced using whey exhibited great photostability, high sensitivity and outstanding biocompatibility and also showed that Fe3+ ions could be quickly, sensitively and extremely selectively detected in an aqueous solution of CDs, with a revealing limit of 0.409 µM in the linear range of 0–180 µM. CDs are a promising area of study to a key component of next-generation multifunctional nanomaterials, promoting creativity, sustainability and useful solutions across a variety of industries, including health care and energy. The susceptibility of S. typhimurium (Gram-negative) was found to be higher than that of L. monocytogenes (Gram-positive) bacteria with MIC and MBC of 500 and 1000 µL/mL, respectively.Originality/valueWhey-derived CDs are an environmentally beneficial substitute for conventional additives and their biocompatibility guarantees that they adhere to food safety regulations. In light of the future, the green volarization of dairy waste for the synthesis of CDs is consistent with the increasing worldwide focus on environmental responsibility and sustainability.

Crosslinked chitosan embedded TiO2 NPs and carbon dots-based nanocomposite: An excellent photocatalyst under sunlight irradiation

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.

Subject of study. The study focuses on luminescent carbon nanoparticles, specifically carbon dots, based on citric acid, formamide, and various chiral molecules. Aim of study. The aim is to assess the influence of chiral molecules used in the synthesis of carbon dots on optical transitions in the long-wavelength spectral region and to investigate the mechanism underlying the circular dichroism signal of these nanoparticles. Method. Carbon dot samples were synthesized using two methods: (i) a one-step solvothermal synthesis of carbon dots from citric acid, formamide, and various chiral molecules and (ii) a two-step method involving the solvothermal synthesis of achiral carbon dots from citric acid and formamide, followed by surface treatment with L-cysteine. Absorption and luminescence spectroscopy methods were employed to study the chemical structure and optical properties of the carbon dots. The chiroptical properties of the obtained samples were analyzed using circular dichroism spectroscopy. Main results. The addition of various chiral molecules to a mixture of precursors during one-step synthesis enabled the fabrication of carbon dots with different chemical compositions, including variations in surface groups and types of emission centers in the spectral region of 350–700 nm. The use of L-phenylglycine and L-tryptophan in the one-step synthesis was shown to lead to the formation of nanoparticles with optical transitions in both short- and long-wavelength regions of the spectrum. The addition of L-glutathione during the one-step synthesis resulted in the formation of carbon dots with short-wavelength emission, while the addition of L-cysteine did not alter the emission characteristics of achiral carbon dots based on citric acid and formamide. The optical properties of the chiral carbon dots obtained using the two-step synthesis method with L-cysteine remained unchanged compared with those of the achiral carbon dots synthesized from citric acid and formamide. The circular dichroism spectra of all the samples showed a signal at ∼250nm, which was attributed to the derivatives of the chiral precursors attached to the surface of the nanoparticles, irrespective of the preparation method. Practical significance. Chiral carbon dots hold promise in biomedicine as sensors, luminescent biomarkers, and other applications due to their biocompatibility and non-toxicity. The results obtained in this work will serve as a foundation for the further fabrication and investigation of chiral carbon nanoparticles with long-wavelength luminescence.

Comparison between hydrothermal and microwave-assisted synthesis of carbon dots from biowaste and chemical for heavy metal detection: A review

Long‐lifetime room‐temperature phosphorescence (RTP) materials are important for many applications, but they are highly challenging materials owing to the spin‐forbidden nature of triplet exciton transitions. Herein, a facile, quick and gram‐scale method for the preparation of ultralong RTP (URTP) carbon dots (CDs) was developed via microwave‐assisted heating of ethanolamine and phosphoric acid aqueous solution. The CDs exhibit the longest RTP lifetime, 1.46 s (more than 10 s to naked eye) for CDs‐based materials to date. The doping of N and P elements is critical for the URTP which is considered to be favored by a n→π* transition facilitating intersystem crossing (ISC) for effectively populating triplet excitons. In addition, possibilities of formation of hydrogen bonds in the interior of the CDs may also play a significant role in producing RTP. Potential applications of the URTP CDs in the fields of anti‐counterfeiting and information protection are proposed and demonstrated.

Polyethyleneimine-functionalized carbon dots and their precursor co-immobilized on silica for hydrophilic interaction chromatography