Coal as an abundant source of graphene quantum dots

Twenty Years of Graphene: From Pristine to Chemically Engineered Nano-Sized Flakes

It is a celebratory moment for graphene! This year marks the 20th anniversary of the discovery of this amazing material by Geim and Novoselov. Curiously, it coincides with the century mark of graphite's layered structure discovery. Since the discovery of graphene with the promise that its outstanding properties would change the world, society often wonders where is graphene? In this context, their discoverers said in 2005, "despite the reigning optimism about graphene-based electronics, "graphenium" microprocessors are unlikely to appear for the next 20 years". Today, possibilities for graphene are endless! It can be used in electronics, photonics, fuel cells, energy storage, artificial intelligence, biomedicine, and even cultural heritage or sports. Additionally, the electronic properties of this material have been modified in fascinating ways. Bilayer graphene sheets have been found to be superconductive when twisted at a "magic angle", leading to a new and exciting field of research known as "moiré quantum materials" or "twistronics". Additionally, small graphene fragments with nanometer sizes undergo a quantum confinement effect of electrons, affording semiconductive materials with applications in optoelectronics. Organic synthesis allows the preparation of molecules with a graphene-like pattern with total control of the shape and size, exhibiting a big catalog of chiroptical and optoelectronic properties. This perspective shows some of the fascinating milestones raised in the field of graphene-like materials from a chemical point of view, including functionalization strategies employed to chemically modify the topology and the properties of pristine graphene as well as the rising molecular graphenes.

Harnessing coal and coal waste for environmental conservation: A review of photocatalytic materials

Fossil fuels, especially coal, have played a pivotal role in driving technological and economic advancements over the past century, though accompanied by numerous environmental challenges. Rapid progress in green and sustainable energy sources, including tidal, wind, and solar energy, coupled with growing environmental concerns, the conventional coal industry is experiencing a sustained decline in both size and financial viability. This situation necessitates the urgent adoption of advanced approaches to coal utilization. Beyond serving as an energy source, coal and its by-products, known as coal waste, can serve as valuable resources for the development of advanced materials, including photocatalysts. The advancement of photocatalytic materials derived from coal and coal waste can capitalize on these natural carbon and mineral sources, providing a viable solution to numerous environmental challenges. Currently, research in this domain remains in its early stages, with existing studies primarily focusing on specific types of photocatalysts or particular aspects of the fabrication process. Therefore, available coal-based and coal waste-based photocatalytic materials were systematically examined and categorized into six types according to their composition and dimensional/structural characteristics. Each type of photocatalytic material was introduced, along with common fabrication and characterization technologies. Representative works were discussed in detail to highlight the unique features of different types of coal-based and coal waste-based photocatalytic materials. Furthermore, the promising applications of these materials in environmental protection and pollution treatment were summarized, while also addressing the challenges and prospects in this research field. This review comprehensively overviews the fundamental knowledge and recent advancements in photocatalytic materials derived from coal and coal waste, with the goal of catalyzing the development of next generation photocatalysts and contributing to the transformation of the conventional coal industry.

Development and challenge of coal-based nanocarbon materials and their application in water treatment: a review

Under the dual pressures of environmental protection and energy security, the development and application of coal-based nanocarbon materials, supported by the technical concepts of molecular chemical engineering and nanomaterial science, is of significant importance for achieving the high-value clean utilization of coal. Furthermore, it serves as an effective means to assist in the realization of dual carbon goals. Coal, with its abundant reserves, high carbon content, and aromatic and hydrogenated aromatic groups, exhibits great advantages and potential in the synthesis of nanocarbon materials. In addition to its applications in traditional power and chemical industries, coal-based nanocarbon materials also demonstrate significant value in the field of environmental pollution control. This article succinctly summarizes the preparation methods and properties of coal-based carbon nanotubes, coal-based carbon quantum dots, and coal-based graphene, elucidates their current applications in water pollution control and governance, and anticipates their development trends in water pollution control, aiming to provide support for the clean and efficient utilization of coal and water pollution control.

Graphene Quantum Dots from Natural Carbon Sources for Drug and Gene Delivery in Cancer Treatment

Cancer therapy is constantly evolving, with a growing emphasis on targeted and efficient treatment options. In this context, graphene quantum dots (GQDs) have emerged as promising agents for precise drug and gene delivery due to their unique attributes, such as high surface area, photoluminescence, up-conversion photoluminescence, and biocompatibility. GQDs can damage cancer cells and exhibit intrinsic photothermal conversion and singlet oxygen generation efficiency under specific light irradiation, enhancing their effectiveness. They serve as direct therapeutic agents and versatile drug delivery platforms capable of being easily functionalized with various targeting molecules and therapeutic agents. However, challenges such as achieving uniform size and morphology, precise bandgap engineering, and scalability, along with minimizing cytotoxicity and the environmental impact of their production, must be addressed. Additionally, there is a need for a more comprehensive understanding of cellular mechanisms and drug release processes, as well as improved purification methods. Integrating GQDs into existing drug delivery systems enhances the efficacy of traditional treatments, offering more efficient and less invasive options for cancer patients. This review highlights the transformative potential of GQDs in cancer therapy while acknowledging the challenges that researchers must overcome for broader application.

Carbon dots-based fluorescent probe for detection of foodborne pathogens and its potential with microfluidics

Concern about food safety triggers demand on rapid, accurate and on-site detection of foodborne pathogens. Among various fluorescent probes for detection, carbon dots (CDs) prepared by carbonization of carbon-rich raw materials show extraordinary performance for their excellent and tailorable photoluminescence property, as well as their facilely gained specificity by surface customization and modification. CDs-based fluorescent probes play a crucial role in many pathogenic bacteria sensing systems. In addition, microfluidic technology with characteristics of portability and functional integration is expected to combine with CDs-based fluorescent probes for point-of-care testing (POCT), which can further enhance the detection property of CDs-based fluorescent probes. Here, this paper reviews CDs-based bacterial detection methods and systems, including the structural modulation of fluorescent probes and pathogenic bacteria detection mechanisms, and describes the potential of combining CDs with microfluidic technology, providing reference for the development of novel rapid detection technology for pathogenic bacteria in food.

Carbon Dots: A Review with Focus on Sustainability

Carbon dots (CDs) are an emerging class of nanomaterials with attractive optical properties, which promise to enable a variety of applications. An important and timely question is whether CDs can become a functional and sustainable alternative to incumbent optical nanomaterials, notably inorganic quantum dots. Herein, the current CD literature is comprehensively reviewed as regards to their synthesis and function, with a focus on sustainability aspects. The study quantifies why it is attractive that CDs can be synthesized with biomass as the sole starting material and be free from toxic and precious metals and critical raw materials. It further describes and analyzes employed pretreatment, chemical-conversion, purification, and processing procedures, and highlights current issues with the usage of solvents, the energy and material efficiency, and the safety and waste management. It is specially shown that many reported synthesis and processing methods are concerningly wasteful with the utilization of non-sustainable solvents and energy. It is finally recommended that future studies should explicitly consider and discuss the environmental influence of the selected starting material, solvents, and generated byproducts, and that quantitative information on the required amounts of solvents, consumables, and energy should be provided to enable an evaluation of the presented methods in an upscaled sustainability context.

Leveraging Non-Radiative Transitions in Asphaltenes-Derived Carbon Dots for Cancer Photothermal Therapy

Cancer photothermal therapy leverages the capability of photothermal agents to convert light to heat for cancer cell ablation and necrosis. However, most conventional photothermal agents (Au, CuS, Pd, mesoporous silica nanoparticles, and indocyanine green dye) either face scalability challenges or photobleached upon prolonged irradiation which jeopardizes practical applications. Here, asphaltenes-derived carbon dots (ACDs, 5 nm) are rationally engineered as a low-cost and photostable photothermal agent with negligible in vivo cytotoxicity. The abundant water-solvating functional groups on the ACDs surface endows them with excellent water re-dispersibility that outperforms those of most commercial nanomaterials. Photothermal therapeutic property of the ACDs is mechanistically described by non-radiative transitions of excited electrons at 808 nm via internal conversions and vibrational relaxations. Consequently, the ACDs offer cancer photothermal therapy in mice within 15 days post-exposure to one-time near infrared irradiation. This pioneering study showcases the first utilization of asphaltenes-based materials for cancer therapy and is expected to arouse further utilization of such materials in various cancer theranostics.

Carbon Dot Synthesis and Purification: Trends, Challenges and Recommendations

Carbon dots (CDs) have rapidly emerged as a new family of carbon-based nanomaterials since their initial discovery two decades ago. Numerous appealing properties, such as precursor and synthesis process flexibility, tunable photoluminescence, and good biocompatibility, have enabled their widespread applications in sensing, catalysis, energy, and biomedical fields. As the field expands, notable efforts have recently focused on mechanistically elucidating the structural formation and optical behavior of CDs. However, the absence of "clean" CDs presents a major obstacle to achieving a solid understanding of these aspects. Often, the claimed CDs are, in fact, a mixture of small molecules, oligomers, nano-sized aggregates, or even microparticles. Such coexistence of impurities markedly impacts the physicochemical properties of resulting CD-based mixtures, hampering the resolution of key mechanistic questions. Here, we aim to address this fundamental shortcoming of the field, going beyond the customary focus of the existing reviews that predominantly cover synthesis, optical performance, and application prospects. We begin with an overview of CD synthesis and then thoroughly examine the purification methods, including filtration, dialysis, electrophoresis, and chromatography. The insights provided here will guide the researchers towards obtaining high-quality CDs, employing proper combinations of available tools, and ultimately paving the way for more demanding applications.

The Emerging Star of Carbon Luminescent Materials: Exploring the Mysteries of the Nanolight of Carbon Dots for Optoelectronic Applications

Carbon dots (CDs), a class of carbon-based nanomaterials with dimensions less than 10 nm, have attracted significant interest since their discovery. They possess numerous excellent properties, such as tunability of photoluminescence, environmental friendliness, low cost, and multifunctional applications. Recently, a large number of reviews have emerged that provide overviews of their synthesis, properties, applications, and their composite functionalization. The application of CDs in the field of optoelectronics has also seen unprecedented development due to their excellent optical properties, but reviews of them in this field are relatively rare. With the idea of deepening and broadening the understanding of the applications of CDs in the field of optoelectronics, this review for the first time provides a detailed summary of their applications in the field of luminescent solar concentrators (LSCs), light-emitting diodes (LEDs), solar cells, and photodetectors. In addition, the definition, categories, and synthesis methods of CDs are briefly introduced. It is hoped that this review can bring scholars more and deeper understanding in the field of optoelectronic applications of CDs to further promote the practical applications of CDs.

Fluorescent carbon dots for sensing applications: a review

Luminescent carbon dots (CDs) are important class of nanomaterials with fantastic photoluminescence (PL) properties, great biocompatibility, extraordinary solubility in water, minimal expense, and so on. There are many methods for their preparation and they are mainly classed into two groups, top-down and bottom-up approaches. In order to understand the origin of fluorescence in quantum CDs, three mechanisms have been proposed namely molecular state, surface state, and quantum confinement phenomenon. Fluorescent CDs have significant application in the fields of biochemical sensing, photocatalysis, bioimaging, delivery of drugs, and other related fields. In this review article the application of quantum dots as detecting component, for the sensing of different targets, has been summed up. In fact, the detection of several analytes including, anions, cations, small molecules, polymers, cells, and microscopic organisms has been discoursed. Moreover, the future aspects of CDs as detecting resources have been explored.

Construction of N-doped carbon encapsulated Mn2O3/MnO heterojunction for enhanced lithium storage performance

Owing to high theoretical capacity, low cost and abundant availability, manganese oxides are widely viewed as promising anodes for lithium-ion batteries (LIBs). Nonetheless, their practical application is significantly hindered by poor electrical conductivity, sluggish reaction kinetics and substantial volume change. In this work, an ingenious polypyrrole encapsulation followed by pyrolysis strategy is proposed to produce N-doped carbon encapsulated Mn2O3/MnO heterojunction (Mn2O3/MnO@NC) by using mechanically ground Mn3O4/C3N4 mixture as the precursor. The results show that the selection of precursor plays a pivotal role in the successful preparation of Mn2O3/MnO@NC hybrid. It is revealed that the uniform encapsulation by N-doped carbon significantly enhances the conductivity and structural stability of the final product. Concurrently, the Mn2O3/MnO heterojunction within the resultant hybrid exhibits a unique quantum-dot size, which effectively shortens ion transport pathways and exposes the active sites for lithium storage. Additionally, experimental observations and theoretical calculations demonstrate that the built-in electric fields generated at the interfaces of Mn2O3/MnO heterojunction accelerate the charge transfer and ion diffusion, thereby enhancing the electrochemical reaction kinetics. As a result, the Mn2O3/MnO@NC hybrid displays much enhanced lithium storage performance. Evidently, our work offers a good guidance for the design and synthesis of advanced transition metal oxide/carbon anodes for LIBs.

A review on synthesis, properties, and biomedical applications of graphene quantum dots (GQDs)

A new type of 0-dimensional carbon-based materials called graphene quantum dots (GQDs) is gaining significant attention as a non-toxic and eco-friendly nanomaterial. GQDs are nanomaterials composed of sp2hybridized carbon domains and functional groups, with their lateral size less than 10 nm. The unique and exceptional physical, chemical, and optical properties arising from the combination of graphene structure and quantum confinement effect due to their nano-size make GQDs more intriguing than other nanomaterials. Particularly, the low toxicity and high solubility derived from the carbon core and abundant edge functional groups offer significant advantages for the application of GQDs in the biomedical field. In this review, we summarize various synthetic methods for preparing GQDs and important factors influencing the physical, chemical, optical, and biological properties of GQDs. Furthermore, the recent application of GQDs in the biomedical field, including biosensor, bioimaging, drug delivery, and therapeutics are discussed. Through this, we provide a brief insight on the tremendous potential of GQDs in biomedical applications and the challenges that need to be overcome in the future.

Designing cellulose nanofibrils/carbon dots intelligent label with colorimetric and fluorescent dual responsiveness for real-time monitoring of food freshness

This study utilized 1,2,4-triaminobenzene dihydrochloride and NaOH as precursors to prepare the pH optical sensor based on carbon dots (CDs). By incorporating CDs into pineapple peel cellulose nanofibrils (CNF) matrix, an intelligent label (CNF/CDs label) with colorimetric and fluorescent dual responsiveness was created for real-time monitoring of food freshness. The CNF/CDs labels exhibited remarkable sensitivity and recognizability towards pH changes from 1 to 12. They also demonstrated excellent reversibility during acid-alkali cycling. Moreover, these labels exhibited exceptional responsiveness to the alkaline and acidic gas environments formed by ammonium hydroxide and acetic acid solutions, respectively. These responses were visually distinguishable through visible color changes and ultraviolet (UV) fluorescence alterations. Encouragingly, the developed labels were successfully applied to monitor the freshness of prawns and fruits, enabling timely assessment of food freshness levels. The dual-mode response of color and fluorescence provided double assurance for the accuracy of the results.

Synthesis mechanism from graphene quantum dots to carbon nanotubes by ion-sputtering assisted chemical vapor deposition

We present the first work of the synthesis mechanism from graphene quantum dots (GQDs) to carbon nanotubes (CNTs) by an ion-sputtering assisted chemical vapor deposition. During the annealing process, a Pt thin film deposited by the ion-sputtering was dewetted and agglomerated to form many nanometer-sized particles, leading to Pt nanoparticles (PtNPs) that can act as catalysts for creating carbon allotropes. The shape of the allotropes can be effectively tailored from GQDs to CNTs by controlling three key parameters such as the dose of catalytic ions (D), amounts of carbon source (S), and thermal energy (T). In our work, it was clearly proved that the growth control from GQDs to CNTs has a comparably proportional relationship with D and S, but has a reverse proportional relationship with T. Furthermore, high-purity GQDs without any other by-products and the CNTs with the cap of PtNPs were generated. Their shapes were appropriately controlled, respectively, based on the established synthesis mechanism.

High-performance cementitious composites containing nanostructured carbon additives made from charred coal fines

Carbon-based nanomaterials, such as carbon nanoplatelets, graphene oxide, and carbon quantum dots, have many possible end-use applications due to their ability to impart unique mechanical, electrical, thermal, and optical properties to cement composites. Despite this potential, these materials are rarely used in the construction industry due to high material costs and limited data on performance and durability. In this study, domestic coal is used to fabricate low-cost carbon nanomaterials that can be used economically in cement formulations. A range of chemical and physical processing approaches are employed to control the size, morphology, and chemical functionalization of the carbon nanomaterial, which improves its miscibility with cement formulations and its impact on mechanical properties and durability. At loadings of 0.01 to 0.07 wt.% of coal-derived carbon nanomaterial, the compressive and flexural strength of cement samples are enhanced by 24% and 23%, respectively, in comparison to neat cement. At loadings of 0.02 to 0.06 wt.%, the compressive and flexural strength of concrete composites increases by 28% and 21%, respectively, in comparison to neat samples. Additionally, the carbon nanomaterial additives studied in this work reduce cement porosity by 36%, permeability by 86%, and chloride penetration depth by 60%. These results illustrate that low-loadings of coal-derived carbon nanomaterial additives can improve the mechanical properties, durability, and corrosion resistance of cement composites.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Carbon Dots and Their Polymeric Nanocomposites: Insight into Their Synthesis, Photoluminescence Mechanisms, and Recent Trends in Sensing Applications

Carbon dots (CDs), a novel class of carbon-based nanoparticles, have received a lot of interest recently due to their exceptional mechanical, chemical, and fluorescent properties, as well as their excellent photostability and biocompatibility. CDs' emission properties have already found a variety of potential applications, in which bioimaging and sensing are major highlights. It is widely acknowledged that CDs' fluorescence and surface conditions are closely linked. However, due to the structural complexity of CDs, the specific underlying process of their fluorescence is uncertain and yet to be explained. Because of their low toxicity, robust and wide optical absorption, high chemical stability, rapid transfer characteristics, and ease of modification, CDs have been recognized as promising carbon nanomaterials for a variety of sensing applications. Thus, following such outstanding properties of CDs, they have been mixed and imprinted onto different polymeric components to achieve a highly efficient nanocomposite with improved functional groups and properties. Here, in this review, various approaches and techniques for the preparation of polymer/CDs nanocomposites have been elaborated along with the individual characteristics of CDs. CDs/polymer nanocomposites recently have been highly demanded for sensor applications. The insights from this review are detailed sensor applications of polymer/CDs nanocomposites especially for detection of different chemical and biological analytes such as metal ions, small organic molecules, and several contaminants.

Engineering functionalization and properties of graphene quantum dots (GQDs) with controllable synthesis for energy and display applications

Graphene quantum dots (GQDs), a new type of 0D nanomaterial, are composed of a graphene lattice with sp2 bonding carbon core and characterized by their abundant edges and wide surface area. This unique structure imparts excellent electrical properties and exceptional physicochemical adsorption capabilities to GQDs. Additionally, the reduction in dimensionality of graphene leads to an open band gap in GQDs, resulting in their unique optical properties. The functional groups and dopants in GQDs are key factors that allow the modulation of these characteristics. So, controlling the functionalization level of GQDs is crucial for understanding their characteristics and further application. This review provides an overview of the properties and structure of GQDs and summarizes recent developments in research that focus on their controllable synthesis, involving functional groups and doping. Additionally, we provide a comprehensive and focused explanation of how GQDs have been advantageously applied in recent years, particularly in the fields of energy storage devices and displays.

A Fluorescent Carbon Nanoparticle for Photodynamic Cell Therapy via Rapid Non-Endocytic Uptake

Although photodynamic therapy is a promising approach for cancer treatment, it has limited clinical application due to the poor performance of conventional photosensitizers. In this study, we present a carbon nanoparticle-based photosensitizer for efficient photodynamic cell therapy. The nanoparticles have been synthesized from a steel industry-based waste material, exhibiting strong fluorescence in the visible region, rapidly entering the cell via non-endocytic uptake, and localizing within the mitochondria. Light exposure of nanoparticle-labeled cells offers efficient photodynamic therapy and induces cytotoxicity. Overall, this study highlights the utility of carbon nanoparticles in efficient photodynamic therapy via rapid cellular uptake and subcellular targeting.

Carbon Dots: From Synthesis to Unraveling the Fluorescence Mechanism

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.

Weathered coal-based carbon dots modified by organic amine for enhanced crystallinity and toughness of poly(lactic acid) film

Poly(lactic acid) (PLA) has its own limitations in terms of slow crystallization rate and low crystallinity during processing, resulting in poor toughness and thermal stability, which seriously restricts the practical application of PLA. Blending nanoparticles into the PLA matrix is an effective way to improve PLA crystallization. In this study, carbon dots (CDs) were prepared by green oxidation using weathered coal as carbon source and then surface-modified with dodecylamine (DDA) and octadecylamine (ODA). Modified CDs (MCDs)/PLA composite films were prepared using MCDs as filler to improve the crystallinity and toughness of PLA films. The results showed that the improvement effect of ODA-modified CDs (ODACDs) was better than that of DDA-modified CDs (DDACDs). The crystallinity of PLA composite film (0.05 wt% ODACDs) was increased from 7.20% (pure PLA film) to 35.44%, and its elongation at break was increased by 5.01 times compared with that of the pure PLA film. Moreover, thermogravimetric analysis suggested that the thermal stability of MCDs/PLA films was also improved. The results of simultaneous rheology and in-situ FTIR analysis as well as molecular dynamics simulations confirmed that MCDs had a strong interaction with PLA molecules, which promoted the crystallization of PLA film, thereby improving its toughness and thermal stability.

Preparation and Biotoxicity of Coal-Based Carbon Dot Nanomaterials

Coal-based Carbon Dots (C-CDs) have gradually become a research focus due to the abundant raw materials and low preparation cost. Still, before coal-based carbon dots are widely used, a systematic biological toxicity study is the basis for the safe utilization of C-CDs. However, the level of toxicity and the mechanism of toxicity of C-CDs for organisms are still unclear. To ensure the safe utilization of C-CDs, the present study investigated C-CD nanomaterials as stressors to probe their biotoxic effects on plant, bacterial, and animal cells as well as the photocatalytic oxidative properties of C-CDs. The results showed that low concentrations of C-CDs could promote various growth indicators of wheat, and high concentrations of C-CDs had significant inhibitory effects on wheat growth; C-CDs had significant toxic effects on (S. aureus) at specific concentrations and were light-related; meanwhile, at concentrations of 1-5000 μg/mL, C-CDs were almost not toxic to HeLa cells; however, when irradiated at 365 nm, even low concentrations of C-CDs were toxic to cells by the mechanism that C-CDs could generate singlet oxygen (1O2) by photocatalytic oxidation under 365 nm excitation light, resulting in enhanced toxicity of C-CDs to cells.

Carbon Nanostructured Immunosensing of Anti-SARS-CoV-2 S-Protein Antibodies

The rampant spread and death rate of the recent coronavirus pandemic related to the SARS-CoV-2 respiratory virus have underscored the critical need for affordable, portable virus diagnostics, particularly in resource-limited settings. Moreover, efficient and timely monitoring of vaccine efficacy is needed to prevent future widespread infections. Electrochemical immunosensing poses an effective alternative to conventional molecular spectroscopic approaches, offering rapid, cost-effective, sensitive, and portable electroanalysis of disease biomarkers and antibodies; however, efforts to improve binding efficiency and sensitivity are still being investigated. Graphene quantum dots (GQDs) in particular have shown promise in improving device sensitivity. This study reports the development of a GQD-functionalized point-of-contamination device leveraging the selective interactions between SARS-CoV-2-specific Spike (S) Protein receptor binding domain (RBD) antigens and IgG anti-SARS-CoV-2-specific S-protein antibodies at screen-printed carbon electrode (SPCE) surfaces. The immunocomplexes formed at the GQD surfaces result in the interruption of the redox reactions that take place in the presence of a redox probe, decreasing the current response. Increased active surface area, conductivity, and binding via EDC/NHS chemistry were achieved due to the nanomaterial inclusion, with 5 nm, blue luminescent GQDs offering the best results. GQD concentration, EDC/NHS ratio, and RBD S-protein incubation time and concentration were optimized for the biosensor, and inter- and intra-screen-printed carbon electrode detection was investigated by calibration studies on multiple and single electrodes. The single electrode used for the entire calibration provided the best results. The label-free immunosensor was able to selectively detect anti-SARS-CoV-2 IgG antibodies between 0.5 and 100 ng/mL in the presence of IgM and other coronavirus antibodies with an excellent regression of 0.9599. A LOD of 2.028 ng/mL was found, offering comparable findings to the literature-reported values. The detection sensitivity of the sensor is further compared to non-specific IgM antibodies. The developed GQD immunosensor was compared to other low-oxygen content carbon nanomaterials, namely (i) carbon quantum dot (CQD), (ii) electrochemically reduced graphene oxide, and (iii) carbon black-functionalized devices. The findings suggest that improved electron transfer kinetics and increased active surface area of the CNs, along with surface oxygen content, aid in the detection of anti-SARS-CoV-2 IgG antibodies. The novel immunosensor suggests a possible application toward monitoring of IgG antibody production in SARS-CoV-2-vaccinated patients to study immune responses, vaccine efficacy, and lifetime to meet the demands for POC analysis in resource-limited settings.

Asphaltene-Derived Graphene Quantum Dots for Controllable Coatings on Glass, Fabrics, and Aerogels

Graphene quantum dots (GQDs) derived from natural asphaltene byproducts can produce controlled hydrophobic or hydrophilic interfaces on glass, fabrics, and aerogels. A set of facile solvent extraction methods were used to isolate and chemically prepare materials with different surface functionalities from a commercially derived asphaltene precursor. The organic-soluble fraction was used to create hydrophobic and water-repellent surfaces on glass and cotton fabrics. The GQD solutions could also penetrate the pores of a silica aerogel, rendering it hydrophobic. Alternatively, by extracting the more polar fraction of the GQDs and oxidizing their surfaces, we also demonstrate strongly hydrophilic coatings. This work shows that naturally abundant GQD-containing materials can produce interfaces with the desired wettability properties through a straightforward tuning of the solvent extraction procedure. Owing to their natural abundance, low toxicity, and strong fluorescence, asphaltene-derived GQDs could thus be applied, in bulk, toward a wide range of tunable surface coatings. This approach, moreover, uses an important large-scale hydrocarbon waste material, thereby offering a sustainable alternative to the disposal of asphaltene wastes.

Coal waste-derived synthesis of yellow oxidized graphene quantum dots with highly specific superoxide dismutase activity: characterization, kinetics, and biological studies

The disintegration of coal-based precursors for the scalable production of nanozymes relies on the fate of solvothermal pyrolysis. Herein, we report a novel economic and scalable strategy to fabricate yellow luminescent graphene quantum dots (YGQDs) by remediating unburnt coal waste (CW). The YGQDs (size: 7-8 nm; M.W: 3157.9 Da) were produced using in situ "anion-radical" assisted bond cleavage in water (within 8 h; at 121 °C) with yields of ∼87%. The presence of exposed surface and edge groups, such as COOH, C-O-C, and O-H, as structural defects accounted for its high fluorescence with εmax ∼530 nm at pH 7. Besides, these defects also acted as radical stabilizers, demonstrating prominent anti-oxidative activity of ∼4.5-fold higher than standard ascorbic acid (AA). In addition, the YGQDs showed high biocompatibility towards mammalian cells, with 500 μM of treatment dose showing <15% cell death. The YGQDs demonstrated specific superoxide dismutase (SOD) activity wherein 15 μM YGQDs equalled the activity of 1-unit biological SOD (bSOD), measured using the pyrogallol assay. The Km for YGQDs was ∼10-fold higher than that for bSOD. However, the YGQDs retained their SOD activity in harsh conditions like high temperatures or denaturing reactions, where the activity of bSOD is completely lost. The binding affinity of YGQDs for superoxide ions, measured from isothermal calorimetry (ITC) studies, was only 10-fold lower than that of bSOD (Kd of 586 nM vs. 57.3 nM). Further, the pre-treatment of YGQDs (∼10-25 μM) increased the cell survivability to >75-90% in three cell lines during ROS-mediated cell death, with the highest survivability being shown for C6-cells. Next, the ROS-induced apoptosis in C6-cells (model for neurodegenerative diseases study), wherein YGQDs uptake was confirmed by confocal microscopy, showed ∼5-fold apoptosis alleviation with only 5 μM pretreatment. The YGQDs also restored the expression of pro-inflammatory Th1 cytokines (TNF-α, IFN-γ, IL-6) and anti-inflammatory Th2 cytokines (IL-10) to their basal levels, with a net >3-fold change observed. This further explains the molecular mechanism for the antioxidant property of YGQDs. The high specific SOD activity associated with YGQDs may provide the cheapest alternative source for producing large-scale SOD-based nanozymes that can treat various oxidative stress-linked disorders/diseases.

From Pristine to Heteroatom-Doped Graphene Quantum Dots: An Essential Review and Prospects for Future Research

Graphene quantum dots (GQDs) are carbon-based zero-dimensional materials that have received considerable scientific interest due to their exceptional optical, electrical, and optoelectrical properties. Their unique electronic band structures, influenced by quantum confinement and edge effects, differentiate the physical and optical characteristics of GQDs from other carbon nanostructures. Additionally, GQDs can be synthesized using various top-down and bottom-up approaches, distinguishing them from other carbon nanomaterials. This review discusses recent advancements in GQD research, focusing on their synthesis and functionalization for potential applications. Particularly, various methods for synthesizing functionalized GQDs using different doping routes are comprehensively reviewed. Based on previous reports, current challenges and future directions for GQDs research are discussed in detail herein.

Carbon Dots for Electroluminescent Light-Emitting Diodes: Recent Progress and Future Prospects

Carbon dots (CDs), as emerging carbon nanomaterials, have been regarded as promising alternatives for electroluminescent light-emitting diodes (LEDs) owing to their distinct characteristics, such as low toxicity, tuneable photoluminescence, and good photostability. In the last few years, despite remarkable progress achieved in CD-based LEDs, their device performance is still inferior to that of well-developed organic, heavy-metal-based QDs, and perovskite LEDs. To better exploit LED applications and boost device performance, in this review, a comprehensive overview of currently explored CDs is presented, focusing on their key optical characteristics, which are closely related to the structural design of CDs from their carbon core to surface modifications, and to macroscopic structural engineering, including the embedding of CDs in the matrix or spatial arrangement of CDs. The design of CD-based LEDs for display and lighting applications based on the fluorescence, phosphorescence, and delayed fluorescence emission of CDs is also highlighted. Finally, it is concluded with a discussion regarding the key challenges and plausible prospects in this field. It is hoped that this review inspires more extensive research on CDs from a new perspective and promotes practical applications of CD-based LEDs in multiple directions of current and future research.

Flexible genosensors based on polypyrrole and graphene quantum dots for PML/RARα fusion gene detection: A study of acute promyelocytic leukemia in children

Acute promyelocytic leukemia (APL) in children is associated with a favorable initial prognosis. However, minimal residual disease (MRD) follow-up remains poorly defined, and relapse cases are concerning due to their recurrent nature. Thus, we report two electrochemical flexible genosensors based on polypyrrole (PPy) and graphene quantum dots (GQDs) for label-free PML-RARα oncogene detection. Atomic force microscopy (AFM), scanning electron microscope (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to characterize the technological biosensor development. M7 and APLB oligonucleotide sequences were used as bioreceptors to detect oncogenic segments on chromosomes 15 and 17, respectively. AFM characterization revealed heterogeneous topographical surfaces with maximum height peaks for sensor layers when tested with positive patient samples. APLB/Genosensor exhibited a percentage change in anode peak current (ΔI) of 423 %. M7/Genosensor exhibited a ΔI of 61.44 % for more concentrated cDNA samples. The described behavior is associated with the biospecific recognition of the proposed biosensors. Limits of detection (LOD) of 0.214 pM and 0.677 pM were obtained for APLB/Genosensor and M7/Genosensor, respectively. The limits of quantification (LOQ) of 0.648 pM and 2.05 pM were estimated for APLB/Genosensor and M7/Genosensor, respectively. The genosensors showed reproducibility with a relative standard deviation of 7.12 % for APLB and 1.18 % for M7 and high repeatability (9.89 % for APLB and 1.51 % for M7). In addition, genetic tools could identify the PML-RARα oncogene in purified samples, plasmids, and clinical specimens from pediatric patients diagnosed with APL with high bioanalytical performance. Therefore, biosensors represent a valuable alternative for the clinical diagnosis of APL and monitoring of MRD with an impact on public health.

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

Plasma-Enabled Graphene Quantum Dot Hydrogel-Magnesium Composites as Bioactive Scaffolds for In Vivo Bone Defect Repair

Bioactive and mechanically stable metal-based scaffolds are commonly used for bone defect repair. However, conventional metal-based scaffolds induce nonuniform cell growth, limiting damaged tissue restoration. Here, we develop a plasma nanotechnology-enhanced graphene quantum dot (GQD) hydrogel-magnesium (Mg) composite scaffold for functional bone defect repair by integrating a bioresource-derived nitrogen-doped GQD (NGQD) hydrogel into the Mg ZK60 alloy. Each scaffold component brings major synergistic advantages over the current alloy-based state of the art, including (1) mechanical support of the cortical bone and calcium deposition by the released Mg2+ during degradation; (2) enhanced uptake, migration, and distribution of osteoblasts by the porous hydrogel; and (3) improved osteoblast adhesion and proliferation, osteogenesis, and mineralization by the NGQDs in the hydrogel. Through an in vivo study, the hybrid scaffold with the much enhanced osteogenic ability induced by the above synergy promotes a more rapid, uniform, and directional bone growth across the hydrogel channel, compared with the control Mg-based scaffold. This work provides insights into the design of multifunctional hybrid scaffolds, which can be applied in other areas well beyond the demonstrated bone defect repair.

Solid-State Phosphors from Coal-Derived Carbon Quantum Dots

With unique optical and chemical properties, carbon quantum dots (CQDs) find tremendous applications in chemistry, biology, and materials science to medicine. To expand the applicability of coal-derived CQDs from the liquid to solid state, we herein report the sustainable synthesis of solid phosphors from coal-derived CQDs using poly(vinyl alcohol) (PVA) and silica (SiO₂) as an organic and inorganic matrix. Two coal-derived CQDs were obtained using an eco-friendly ultrasonic-assisted wet oxidation method. The structural and chemical properties of the CQDs were extensively investigated and compared with commercial CQDs. The coal-derived CQDs exhibited blue fluorescence with 8.9 and 14.9% quantum yields. The CQDs were found to be self-co-doped with nitrogen and sulfur heteroatoms through surface and edge functional groups. Solid-state fluorescence of PVA/CQD composite films confirmed that the CQDs retained their excellent blue emission in a dry solid matrix. A facile one-pot sol-gel method was employed to fabricate SiO₂/CQD phosphors with the unique fluorescence emission. Due to their special structural features, coal-derived CQDs favored the heterogeneous nucleation and rapid formation of SiO₂/CQD phosphors. Further, coal-derived CQDs caused high-intensity white light emission with CIE coordinates of (0.312, 0.339) by endowing a suitable band gap structure in a SiO₂/CQD solid phosphor for potential optical applications.

Advances in Structural Modifications and Properties of Graphene Quantum Dots for Biomedical Applications

Graphene quantum dots (GQDs) are carbon-based, zero-dimensional nanomaterials and unique due to their astonishing optical, electronic, chemical, and biological properties. Chemical, photochemical, and biochemical properties of GQDs are intensely being explored for bioimaging, biosensing, and drug delivery. The synthesis of GQDs by top-down and bottom-up approaches, their chemical functionalization, bandgap engineering, and biomedical applications are reviewed here. Current challenges and future perspectives of GQDs are also presented.

Coal-Based Carbon Nanomaterials: En Route to Clean Coal Conversion toward Net Zero CO2

As the world is committed to reach carbon peak by 2030 and net zero by 2050, the use of coal as an energy source is facing unprecedented challenges. According to the International Energy Agency (IEA), global annual coal demand is estimated to drop from more than 5640 million tonnes of coal equivalent (Mtce) in 2021 to 540 Mtce in 2050 under the net zero emission scenario, mostly being replaced by renewable energy such as solar and wind. Therefore, the coal industry is vigorously seeking alternative applications to keep it thriving, and nanotechnology can be one of the contributors. Herein, the challenges to coal-based carbon nanomaterials syntheses are outlined, along with a path toward commercialization. Coal-based carbon nanomaterials can be promising contributors to the concept of clean coal conversion, initiating its migration from an energy source to a high-value-added carbon source.

Synthesis of Graphene Quantum Dot Magnesium Hydroxide Nanocomposites and Investigation of Their Antioxidant and Antimicrobial Activities

In this paper, we synthesized graphene quantum dots magnesium hydroxide nanocomposites (GQDs/Mg(OH)₂). The synthesized nanocomposites were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Malvern Zetasizer. The antimicrobial and antioxidant properties of the obtained GQDs/Mg(OH)₂ nanocomposites were investigated. GQDs/Mg(OH)₂ nanocomposites have MIC values of 15.625 μg/mL against fungi (C. metapsilosis and C. parapsilosis) and 62.5 μg/mL against Gram (+) (S. pneumonia and E. faecalis) and Gram (-) (E. coli). The synthesized GQDs/Mg(OH)₂ nanocomposites showed moderate antioxidant activity. The results showed that at 100-µg/mL GQDs/Mg(OH)₂ nanocomposite concentration, the H₂O₂ scavenging activity was 62.18%.

Current trends in carbon-based quantum dots development from solid wastes and their applications

Urbanization and a massive population boom have immensely increased the solid wastes (SWs) generation and are expected to reach 3.40 billion tons by 2050. In many developed and emerging nations, SWs are prevalent in both major and small cities. As a result, in the current context, the reusability of SWs through various applications has taken on added importance. Carbon-based quantum dots (Cb-QDs) and their many variants are synthesized from SWs in a straightforward and practical method. Cb-QDs are a new type of semiconductor that has attracted the interest of researchers due to their wide range of applications, which include everything from energy storage, chemical sensing, to drug delivery. This review is primarily focused on the conversion of SWs into useful materials, which is an essential aspect of waste management for pollution reduction. In this context, the goal of the current review is to investigate the sustainable synthesis routes of carbon quantum dots (CQDs), graphene quantum dots (GQDs), and graphene oxide quantum dots (GOQDs) from various types SWs. The applications of CQDs, GQDs, and GOQDs in the different areas are also been discussed. Finally, the challenges in implementing the existing synthesis methods and future research directions are highlighted.

Codoping g-C3N4 with boron and graphene quantum dots: Enhancement of charge transfer for ultrasensitive and selective photoelectrochemical detection of dopamine

The development of superior photoelectrochemical (PEC) sensors for biosensing has become a major objective of PEC research. However, conventional PEC-active materials are typically constrained by a weak photocurrent response owing to their limited surface-active sites and high electron-hole recombination rate. Here, a boron and graphene quantum dots codoped g-C₃N₄ (named GBCN) as PEC sensor for highly sensitive dopamine (DA) detection was fabricated. GBCN exhibited the greatest photocurrent response and PEC activity compared to free g-C₃N₄ and g-C₃N₄ doped with boron. The proposed PEC sensor for DA determination exhibited a broad linear range (0.001-800 μM) and a low detection limit (0.96 nM). In particular, a sensitivity up to 10.3771 μA/μM/cm² was seen in the case of GBCN. The high PEC activity can be attributed to the following factors: (1) the boron and graphene quantum dots co-doping significantly increased the specific surface area of g-C₃N₄, providing more adsorption sites for DA; (2) the dopants extended the absorption intensity of g-C₃N₄, red-shifting the absorption from 470 to 540 nm; and (3) the synergism of boron and graphene quantum dots efficiently boosted the photogenerated electrons migration from the conduction band of g-C₃N₄ to graphene quantum dots, facilitating charge separation. In addition, GBCN also exhibited good anti-interference ability and stability. This research may shed light on the creation of a highly sensitive and selective PEC platform for detecting biomolecules.

Eco-Friendly and Sustainable Pathways to Photoluminescent Carbon Quantum Dots (CQDs)

Carbon quantum dots (CQDs), a new family of photoluminescent 0D NPs, have recently received a lot of attention. They have enormous future potential due to their unique properties, which include low toxicity, high conductivity, and biocompatibility and accordingly can be used as a feasible replacement for conventional materials deployed in various optoelectronic, biomedical, and energy applications. The most recent trends and advancements in the synthesizing and setup of photoluminescent CQDs using environmentally friendly methods are thoroughly discussed in this review. The eco-friendly synthetic processes are emphasized, with a focus on biomass-derived precursors. Modification possibilities for creating newer physicochemical properties among different CQDs are also presented, along with a brief conceptual overview. The extensive amount of writings on them found in the literature explains their exceptional competence in a variety of fields, making these nanomaterials promising alternatives for real-world applications. Furthermore, the benefits, drawbacks, and opportunities for CQDs are discussed, with an emphasis on their future prospects in this emerging research field.

Natural resources for sustainable synthesis of nanomaterials with anticancer applications: A move toward green nanomedicine

Today, researchers have focused on the application of environmentally-benign and sustainable micro- and nanosystems for drug delivery and cancer therapy. Compared to conventional chemotherapeutics, advanced micro- and nanosystems designed by applying abundant, natural, and renewable feedstocks have shown biodegradability, biocompatibility, and low toxicity advantages. However, important aspects of toxicological assessments, clinical translational studies, and suitable functionalization/modification still need to be addressed. Herein, the benefits and challenges of green nanomedicine in cancer nanotherapy and targeted drug delivery are cogitated using nanomaterials designed by exploiting natural and renewable resources. The application of nanomaterials accessed from renewable natural resources, comprising metallic nanomaterials, carbon-based nanomaterials, metal-organic frameworks, natural-derived nanomaterials, etc. for targeted anticancer drug delivery and cancer nanotherapy are deliberated, with emphasis on important limitations/challenges and future perspectives.

Sustainable Preparation of Graphene Quantum Dots for Metal Ion Sensing Application

Over the past several years, graphene quantum dots (GQDs) have been extensively studied in water treatment and sensing applications because of their exceptional structure-related properties, intrinsic inert carbon property, eco-friendly nature, etc. This work reported on the preparation of GQDs from the ethanolic extracts of eucalyptus tree leaves by a hydrothermal treatment technique. Different heat treatment times and temperatures were used during the hydrothermal treatment technique. The optical, morphological, and compositional analyses of the green-synthesized GQDs were carried out. It can be noted that the product yield of GQDs showed the maximum yield at a reaction temperature of 300 °C. Further, it was noted that at a treatment period of 480 min, the greatest product yield of about 44.34% was attained. The quantum yields of prepared GQDs obtained after 480 min of treatment at 300 °C (named as GQD/300) were noted to be 0.069. Moreover, the D/G ratio of GQD/300 was noted to be 0.532 and this suggested that the GQD/300 developed has a nano-crystalline graphite structure. The TEM images demonstrated the development of GQD/300 with sizes between 2.0 to 5.0 nm. Furthermore, it was noted that the GQD/300 can detect Fe³⁺ in a very selective manner, and hence the developed GQD/300 was successfully used for the metal ion sensing application.

Reduced Graphene Oxide Quantum Dot Light Emitting Diodes Fabricated Using an Ultraviolet Light Emitting Diode Photolithography Technique

Graphene quantum dots usually suffer from serious fluorescence quenching in aggregates and the solid state due to easy agglomeration and aggregation-induced quenching, which seriously restrict their practical applications. An ingenious strategy to kill three birds with one stone, the ultraviolet (UV) photolithography technique, was studied, and blue-emitting reduced graphene oxide quantum dot (rGOQD)-based light emitting diodes (LEDs) with efficient solid state emission were first fabricated using UV photolithography. First, rGOQDs were prepared by the in situ photoreduction of GOQDs by using the photoinitiator phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide with 395 nm UV LED exposure. Furthermore, rGOQD/photoresist patterns were prepared under the same conditions. Meanwhile, the in situ photoreduction of GO in the aforementioned photoresist to rGO was realized by UV photolithography to improve the conductivity of the rGOQD/photoresist films. Additionally, the in situ photoreduction of GOQDs in different surroundings was studied, with the results showing that GOQDs are more easily photoreduced in ionic liquids and that the photoluminescence spectrum obtained for rGOQDs exhibits a 70 nm blueshift with a narrow full-width at half-maximum compared to GOQDs.

Eco-Friendly Sustainable Synthesis of Graphene Quantum Dots from Biowaste as a Highly Selective Sensor

Graphene quantum dots (GQDs) have generated a great deal of scientific interest due to their bright fluorescence, good biocompatibility, minimal toxicity and fascinating physicochemical features. However, the ultimate issues regarding the acidic contaminations and high synthesis cost of GQDs remain open challenges for their real-world applications. Herein, we report an eco-friendly, acid-free and sustainable method for the preparation of GQDs using a cost-efficient, and renewable carbon source, 'biomass-waste', which simultaneously solves the risk of contamination from strong acids and high expenditure initiated by expensive precursors. The results demonstrate that GQDs possess a size range of 1-5 nm with an average size of ~3 ± 0.4 nm and a thickness of ~1 nm consisting of 1-3 layers of graphene. As-prepared GQDs demonstrate fascinating size-dependent optical properties and considerable surface grafting. Due to their intriguing optical properties, these GQDs are employed as fluorescence probes to detect ferric ions. A focused and sensitive sensor is developed with a detection limit down to 0.29 µM. This study emphasizes the need for using a reasonably green process and an inexpensive biomass precursor to create high-value GQDs that hold great potential for use in photocatalytic, bioimaging and real-world sensing applications.

Luminescent Carbon Dots from Wet Olive Pomace: Structural Insights, Photophysical Properties and Cytotoxicity

Carbon nanomaterials endowed with significant luminescence have been synthesized for the first time from an abundant, highly localized waste, the wet pomace (WP), a semi-solid by-product of industrial olive oil production. Synthetic efforts were undertaken to outshine the photoluminescence (PL) of carbon nanoparticles through a systematic search of the best reaction conditions to convert the waste biomass, mainly consisting in holocellulose, lignin and proteins, into carbon dots (CDs) by hydrothermal carbonization processes. Blue-emitting CDs with high fluorescence quantum yields were obtained. Using a comprehensive set of spectroscopic tools (FTIR, Raman, XPS, and ¹H/¹³C NMR) in combination with steady-state and time-resolved fluorescence spectroscopy, a rational depiction of WP-CDs structures and their PL properties was reached. WP-CDs show the up-conversion of PL capabilities and negligible cytotoxicity against two mammalian cell lines (L929 and HeLa). Both properties are excellent indicators for their prospective application in biological imaging, biosensing, and dynamic therapies driven by light.

Study on the microstructure of the symbiosis of coal-based graphene and coal-based graphene quantum dots: preparation and characterization

Coal-based graphene sheets (GS) and coal-based graphene quantum dots (GQDs) are usually prepared separately. In this paper, symbiosis of coal-based GS and coal-based GQDs was successfully prepared with our proposed preparation method by using three raw coals with different reflectance (collected from Qinshui coalfield, Shanxi Province) as carbon sources. The results showed that coal-based GS and coal-based GQDs can exist stably in the symbiosis and are distributed in different layers, and the GQDs are freely distributed between layers of GS. The average number of GS (N_ave) in the three symbiosis is about 7 and the average interlayer spacing (d₀₀₂) is about 0.3887 nm. The average diameter of GQDs in the three symbiosis is about 4.255 nm and the averaged₀₀₂is about 0.230 nm. The averageN_aveof the three symbiosis was about 3 and the averaged₀₀₂is about 0.361 nm. The morphology and crystal parameters of symbiosis is more similar to that of graphene, the elements are only carbon and oxygen. In the prepared symbiosis, the higher the reflectance of raw coal, the smoother the lattice skeleton and the less vortex-layer structure of GS, and the larger the diameter and the denser the six membered ring of GQDs. The C and O functional groups of the prepared symbionts are similar. The higher the reflectance of coal, the higher the content of C-C/C=C. Under ultraviolet light, the prepared products all emit blue, and the higher the reflectance of coal, the higher the ultraviolet absorption, and the stronger the fluorescence intensity.

Yellow-Emitting Carbon Dots for Selective Fluorescence Imaging of Lipid Droplets in Living Cells

This study shows a one-pot preparation of carbon dots by a solvothermal method in ethylene glycol. The carbon dots show yellow-colored fluorescence emission in water. The carbon dots showed distinct preference to be present in the hydrophobic environment which was evident from their efficient transfer from aqueous phase to organic phase. They were also found to locate themselves in the vesicle bilayer and micelle core. This inherent lipophilic character of these carbon dots has been successfully utilized for the selective imaging of lipid droplets inside the living cells. The selective imaging of lipid droplets was confirmed by similar staining patterns with other staining dyes and the starvation study.

A fluorescence digital image-based method using carbon quantum dots to evaluate the compliance of a biocidal agent

In this work, a simple, low-cost and easy-to-handle analytical procedure based on carbon quantum dots (CQDs) is proposed to check commercially available formulated microbicides that are used to mitigate the transmission of viruses, such as SARS-COV-2, or bacterial diseases. For this purpose, CQDs were synthesized via pyrolysis using citric acid and ethylenediamine as precursors to produce an intense fluorescence that is used to measure the concentration of hypochlorite, an important biocidal agent present in sanitizing mats, by quenching mechanisms. The characterization of the CQDs was performed using IR spectrophotometry, UV-Vis spectrophotometry, spectrofluorometry, thermogravimetric analysis, scanning electron microscopy, dynamic light scattering, X-ray diffraction, energy-dispersive spectroscopy, and zeta potential measurements. For analytical purposes, fluorescence was measured in a UV chamber irradiated using an LED with the maximum emission at 350 nm. A smartphone was coupled to the UV chamber to measure the fluorescence quenching due to the presence of hypochlorite, and further the digital images were decomposed by RGB data using free software. Tests of pH, CQD concentration and stability of the fluorescence emitted were performed. The stability study of the fluorescence emitted by the CQD solution showed a relative standard deviation lower than 5.0%. The fluorescence digital image-based (FDIB) method resulted in a linear range from 17.44 μmol L^-1 to 90.0 μmol L^-1 with an LOD of 3.30 μmol L^-1 for the determination of hypochlorite using a microplate made of PLA (polylactic acid) customized using a 3D printer. Furthermore, the hypochlorite concentration was tested in situ for its compliance in a sanitizing mat, in a real use situation (daily, a group of four people, each one kept their feet on the mat for 30 s). After 2.5 h, the monitored concentration of hypochlorite was 0.04953% (w/v) or 7.63 mmol L^-1, and therefore, it was inefficient to act as a sanitizing agent. Thus, for the first time in the literature, an FDIB method with CQDs is used to verify in situ microbicide practices with a fast and low-cost analytical procedure.