One-Pot Green Synthesis of Biocompatible Graphene Quantum Dots and Their Cell Uptake Studies

Holistic Investigation of Graphene Quantum Dot Endocytosis

Graphene quantum dots (GQDs) have gained popularity in nano-biotechnology due to their multifunctional delivery and imaging capabilities. The outcome of their therapeutic delivery applications relies on understanding cell internalization routes. Current literature presents often conflicting results based on surveying only a few endocytosis inhibitors. Herein, a holistic approach to cell uptake studies by utilizing six different inhibitors while considering their on- and off-target effects on internalization of the GQDs of different charges is provided. Endocytosis paths are explored by tracking intracellular GQD fluorescence in HeLa or HEK-293 cells. Contrary to the previous assumptions of a singular entry route, findings suggest that GQDs enter the cells through several endocytosis paths with some more prevalent than others. Selectivity between the pathways is based on GQD charge and functional groups. Positively charged nitrogen-doped GQDs (NGQDs) predominantly utilize a fast endophilin-mediated endocytosis (FEME) in HeLa cells with a secondary preference for clathrin-mediated endocytosis (CME). In HEK-293 cells NGQDs internalize via clathrin-independent, glycosylphosphatidylinositol-anchored protein-enriched compartments (CLIC/GEEC) and FEME. Conversely, GQDs with a substantial negative surface charge uptake through CME in HeLa cells. The optimization of these mechanisms can enhance GQD applications in biomedicine, ideally streamlining their translation into the clinic.

Toward a New Understanding of Graphene Oxide Photolysis: The Role of Photoreduction in Degradation Pathway

Graphene oxide (GO) is developed in various applications owing to its fascinating physicochemical properties. However, the weak photostability always leads to inevitable photolysis of GO during the use, storage, and application. Indirect photolysis has a significant impact on the structure of GO via causing fragmentation and degradation, while the pathway can be divided into two stages. In the early stage, photoreduction is the dominant reaction to generate porous reduction GO (PrGO). Then H2O2 breaks PrGO into fragments, and eventually, the fragmented GO is converted into CO2 by OH radicals. The generation of porous structures in early photoreduction is a crucial premise for the subsequent photodegradation, while GO flakes without porous structure cannot be broken by H2O2 and OH. In this work, a deep insight into the indirect photolysis pathway and the committed step is provided, which may bring some advanced ideas for enhancing GO stability in practical application.

Multifaceted role of H2O2 in the solvothermal synthesis of green-emitting nitrogen-doped graphene quantum dots

Fluorescent nitrogen-doped carbon dots (N-GQDs) with long-wavelength emission properties are of increased interest for technological applications. They are widely synthesized through the solvothermal treatment of graphene oxide (GO) using N,N-dimethylformamide (DMF) as a cleaving and doping agent. However, this process simultaneously generates undesired interfering blue-emissive by-products. In this study, we present a straightforward method for synthesizing N-GQDs exclusively exhibiting green fluorescence. The key innovation lies in the addition of hydrogen peroxide (H2O2) to the DMF-driven one-pot solvothermal cleavage process. Systematically controlling the reaction conditions, we elucidate the threefold beneficial role of H2O2: first, it acts as a radical source facilitating the degradation of DMF and the generation of nitrogen-containing radicals, essential for N-GQD formation; second, it prevents the thermal reduction of GO, thus ensuring persistent reaction pathways with DMF-derived radicals; and third, it suppresses the self-reaction of DMF-derived radicals, thereby avoiding the formation of undesired blue-fluorescent by-products. Our findings on the reaction mechanism and the advantageous role of H2O2 open new possibilities for the rational design of N-GQDs genuinely emitting at long wavelengths.

Microwave-Assisted Green Synthesis of Fluorescent Graphene Quantum Dots: Metal Sensing, Antioxidant Properties, and Biocompatibility Insights

Graphene quantum dots (GQDs) are highly valued for their chemical stability, tunable size, and biocompatibility. Utilizing green chemistry, a microwave-assisted synthesis method was employed to produce water-soluble GQDs from Mangifera Indica leaf extract. This approach is efficient, cost-effective, and environmentally friendly, offering reduced reaction times, energy consumption, and uniform particle sizes, and has proven advantageous over other methods. Water-soluble GQDs were synthesized using Mangifera Indica leaf extract, which ranged less than 15 nm in diameter, confirmed by high-resolution transmission electron microscopy with a lattice spacing of 0.34 nm. The GQDs exhibited strong photoluminescence with bright red fluorescence under UV light and excitation-independent emission at 662 nm with excitation wavelengths ranging from 300 to 500 nm, achieving a quantum yield of 10.3%. A peak at 27.2˚ was recorded corresponding to the graphite's (002) plane diffraction peak. Raman spectroscopy confirmed their graphitic nature and sp2 crystallinity, with an intensity ratio of D and G peak ID/IG ratio of 1.12. Biocompatibility assays (MTT and live/dead) showed better results at lower concentrations (1 mg/ml) while higher concentrations (2 mg/ml) showed reduced efficacy. Antioxidant tests revealed increased DPPH scavenging activity with higher GQD concentrations and longer incubation times. The GQDs demonstrated excellent performance as fluorescent biosensors for Ni2⁺ (0.15 ppm) and Fe3⁺ (0.20 ppm), with high selectivity in river water samples, highlighting their potential for environmental and health applications.

Physico-chemical properties and biological evaluation of graphene quantum dots for anticancer drug susceptibility

Graphene quantum dots (GQDs) possess unique optical and biocompatible properties, making them suitable candidates for biomedical and pharmaceutical applications. This study reports the hydrothermal synthesis of pristine-GQD and doped variants: Nitrogen-GQD and Sulfur-GQD. The materials underwent thorough characterization techniques such as UV-vis, fluorescence, XRD, FE-TEM/SEM, EDX, and Raman spectroscopy. The particle sizes of these GQDs range from 2 to 5 nm. We conducted a comprehensive study through MTT assays to evaluate the potential cytotoxic effect of GQD and the doped variants. This study demonstrated their synergistic interactions with an anti-cancer drug, methotrexate (MTX), and also improvement of cytocompatibility in the presence of folic acid (FA). Systematic MD simulations revealed a compacting effect on the dynamic behavior of GQD and its variants in the presence of drugs. Fluorescence spectroscopy and computational modeling suggest non-intercalative surface interactions between GQDs and the drugs. The cytotoxic activity of pristine GQD on HeLa cervical cancer cells is higher than that of N-GQD and S-GQD. When treated with GQD-IC50-MTX-IC50, only 5.6 % of HeLa cells remained viable. The doped variants exhibited bio-compatibility when tested on normal HEK cell lines. Overall, this study emphasizes the potential of GQDs for targeted cancer therapy through an interdisciplinary approach involving material characterization, computational modeling, and biological assays.

A holistic review on red fluorescent graphene quantum dots, its synthesis, unique properties with emphasis on biomedical applications

Graphene quantum dots (GQDs) are an evolving class of carbon-based nanomaterial, seizing tremendous attention owing to their intense optical property, engineered shapes and structures, and good photostability. Being a zero-dimensional form of carbon structure, GQDs have superior photoluminescent behavior, tunable emission and absorption, excellent biocompatibility, low cytotoxicity, hydrophilic nature, modifying surface states. Their water dispersibility and functionalized surface structure, involving heteroatoms and various functional groups onto the surface of GQDs, make them particularly suitable for biological applications. Based on their absolute luminescence properties, GQDs emit blue, green, yellow, and red light under ultraviolet irradiation. Amongst the three colors, red luminescence can achieve deeper penetration of light into tissues, good cellular distribution, bio-sensing property, cell imaging, drug delivery, and serves as a better candidate for photodynamic therapy. The overall objective of this review is to provide a comprehensive overview of the synthesis methods for red fluorescence graphene quantum dots (RF-GQDs), critical comparative analyses of spectral techniques used for their characterization, the tunable photoluminescence mechanisms underpinning red emission, and the significance of chemically functionalizing GQDs' surface edges in achieving red fluorescence are discussed in depth. This review also discusses the effective biological applications and critical challenges associated with RF-GQDs are examined, providing insights into their future potential in clinical and industrial applications.

Structural Features of Carbon Dots and Their Agricultural Potential

Carbon dots (CDs) have drawn attention due to their enticing physical, chemical, and surface properties. Besides, good conductivity, low toxicity, environmental friendliness, simple synthetic routes, and comparable optical properties are advantageous features of CDs. Further, recently, CDs have been explored for biological systems, including plants. Among biological systems, only plants form the basis for sustainability and life on Earth. In this Review, we reviewed suitable properties and applications of CDs, such as promoting the growth of agricultural plants, disease resistance, stress tolerance, and target transportation. Summing up the available studies, we believe that the applications of CDs are yet to be explored significantly for innovation and technology-based agriculture.

Photostability and phototoxicity of graphene quantum dots interacting with red blood cells

Here we discuss fluorescent properties of graphene quantum dots (GQDs) interacting with the membranes of red blood cells. We report the results of spectroscopic, microscopic, and photon-counting measurements of the GQDs in different surroundings for uncovering specific features of the GQD fluorescence, and describe two observed phenomena important for implementation of the GQDs as fluorescent labels and agents for drug delivery. Firstly, the GQDs can suffer from photodegradation but also can be stabilized in the presence of antioxidants (reduced glutathione, N-acetylcysteine, or 1,4-hydroquinone). Secondly, GQDs can accumulate in red blood cell membranes without compromising the viability of the cells but also can induce hemolysis in the presence of visible light. We discuss mechanisms and regimes of the photodegradation, stabilization, interaction of the GQDs with red blood cell membranes, and hemolysis. Notably, photohemolysis for the case is dependent on the light dose and GQD concentration but not caused by the production of reactive oxygen species.

Photothermal therapy using graphene quantum dots

The rapid development of powerful anti-oncology medicines have been possible because of advances in nanomedicine. Photothermal therapy (PTT) is a type of treatment wherein nanomaterials absorb the laser energy and convert it into localized heat, thereby causing apoptosis and tumor eradication. PTT is more precise, less hazardous, and easy-to-control in comparison to other interventions such as chemotherapy, photodynamic therapy, and radiation therapy. Over the past decade, various nanomaterials for PTT applications have been reviewed; however, a comprehensive study of graphene quantum dots (GQDs) has been scantly reported. GQDs have received huge attention in healthcare technologies owing to their various excellent properties, such as high water solubility, chemical stability, good biocompatibility, and low toxicity. Motivated by the fascinating scientific discoveries and promising contributions of GQDs to the field of biomedicine, we present a comprehensive overview of recent progress in GQDs for PTT. This review summarizes the properties and synthesis strategies of GQDs including top-down and bottom-up approaches followed by their applications in PTT (alone and in combination with other treatment modalities such as chemotherapy, photodynamic therapy, immunotherapy, and radiotherapy). Furthermore, we also focus on the systematic study of in vitro and in vivo toxicities of GQDs triggered by PTT. Moreover, an overview of PTT along with the synergetic application used with GQDs for tumor eradication are discussed in detail. Finally, directions, possibilities, and limitations are described to encourage more research, which will lead to new treatments and better health care and bring people closer to the peak of human well-being.

Cancer Therapeutic siRNA Delivery and Imaging by Nitrogen- and Neodymium-Doped Graphene Quantum Dots

While small interfering RNA (siRNA) technology has become a powerful tool that can enable cancer-specific gene therapy, its translation to the clinic is still hampered by the inability of the genes alone to cell transfection, poor siRNA stability in blood, and the lack of delivery tracking capabilities. Recently, graphene quantum dots (GQDs) have emerged as a novel platform allowing targeted drug delivery and fluorescence image tracking in visible and near-infrared regions. These capabilities can aid in overcoming primary obstacles to siRNA therapeutics. Here, for the first time, we utilize biocompatible nitrogen- and neodymium-doped graphene quantum dots (NGQDs and Nd-NGQDs, respectively) for the delivery of Kirsten rat sarcoma virus (KRAS) and epidermal growth factor receptor (EGFR) siRNA effective against a variety of cancer types. GQDs loaded with siRNA noncovalently facilitate successful siRNA transfection into HeLa cells, confirmed by confocal fluorescence microscopy at biocompatible GQD concentrations of 375 μg/mL. While the GQD platform provides visible fluorescence tracking, Nd doping enables deeper-tissue near-infrared fluorescence imaging suitable for both in vitro and in vivo applications. The therapeutic efficacy of the GQD/siRNA complex is verified by successful protein knockdown in HeLa cells at nanomolar siEGFR and siKRAS concentrations. A range of GQD/siRNA loading ratios and payloads are tested to ultimately provide substantial inhibition of protein expression down to 31-45%, comparable with conventional Lipofectamine-mediated delivery. This demonstrates the promising potential of GQDs for the nontoxic delivery of siRNA and genes in general, complemented by multiwavelength image tracking.

Lights and Dots toward Therapy-Carbon-Based Quantum Dots as New Agents for Photodynamic Therapy

The large number of deaths induced by carcinoma and infections indicates that the need for new, better, targeted therapy is higher than ever. Apart from classical treatments and medication, photodynamic therapy (PDT) is one of the possible approaches to cure these clinical conditions. This strategy offers several advantages, such as lower toxicity, selective treatment, faster recovery time, avoidance of systemic toxic effects, and others. Unfortunately, there is a small number of agents that are approved for usage in clinical PDT. Novel, efficient, biocompatible PDT agents are, thus, highly desired. One of the most promising candidates is represented by the broad family of carbon-based quantum dots, such as graphene quantum dots (GQDs), carbon quantum dots (CQDs), carbon nanodots (CNDs), and carbonized polymer dots (CPDs). In this review paper, these new smart nanomaterials are discussed as potential PDT agents, detailing their toxicity in the dark, and when they are exposed to light, as well as their effects on carcinoma and bacterial cells. The photoinduced effects of carbon-based quantum dots on bacteria and viruses are particularly interesting, since dots usually generate several highly toxic reactive oxygen species under blue light. These species are acting as bombs on pathogen cells, causing various devastating and toxic effects on those targets.

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.

Top-down synthesis and enhancing device adaptability of graphene quantum dots

Quantum dots (QD) are rapidly making their way into several application sectors including optoelectronics, and there is a strong need to focus on non-toxic QDs. In this work, we have synthesized graphene QDs in the size range of 1.4-4.2 nm from inexpensive graphite by oxidative cleavage using a sulphuric and nitric acid mixture. A subsequent hydrogen peroxide oxidation step, investigated using two thermal budgets, has resulted in QDs with excellent photoluminescence (PL) intensity. Prolonged, higher temperature oxidation results in smaller size GQDs. X-ray photoelectron spectroscopy analysis confirmed the role of ·OH radicals in the oxidation process and Raman analysis revealed that the higher thermal budget oxidation results in lower defect density. To overcome the challenges in device adaptability due to the inherent acidity in the QDs, a post-synthesis neutralization process was devised. The neutralized GQDs were formed into a film to be used as the active layer in a photodetector device. Fluorescence decay analysis showed there is no significant change in lifetime because of the film formation process. The fabricated GQD photodetector device exhibited high photocurrent under ultraviolet illumination with an ON/OFF ratio of 400% at an applied bias of ±1 V. The device performance underlines the high potential for the non-toxic, top-down synthesized GQDs for application in optoelectronic devices.

Green Synthesis of Blue-Emitting Graphene Oxide Quantum Dots for In Vitro CT26 and In Vivo Zebrafish Nano-Imaging as Diagnostic Probes

Graphene oxide quantum dots (GOQDs) are prepared using black carbon as a feedstock and H₂O₂ as a green oxidizing agent in a straightforward and environmentally friendly manner. The process adopted microwave energy and only took two minutes. The GOQDs are 20 nm in size and have stable blue fluorescence at 440 nm. The chemical characteristics and QD morphology were confirmed by thorough analysis using scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), Fourier transmission infra-red (FT-IR), and X-ray photoelectron spectroscopy (XPS). The biocompatibility test was used to evaluate the toxicity of GOQDs in CT26 cells in vitro and the IC₅₀ was found to be 200 µg/mL with excellent survival rates. Additional in vivo toxicity assessment in the developing zebrafish (Danio rerio) embryo model found no observed abnormalities even at a high concentration of 400 μg/mL after 96 h post fertilization. The GOQDs luminescence was also tested both in vitro and in vivo. They showed excellent internal distribution in the cytoplasm, cell nucleus, and throughout the zebrafish body. As a result, the prepared GOQDs are expected to be simple and inexpensive materials for nano-imaging and diagnostic probes in nanomedicine.

Antioxidative and Photo-Induced Effects of Different Types of N-Doped Graphene Quantum Dots

Due to the increasing number of bacterial infections and the development of resistivity toward antibiotics, new materials and approaches for treatments must be urgently developed. The production of new materials should be ecologically friendly considering overall pollution with chemicals and economically acceptable and accessible to the wide population. Thus, the possibility of using biocompatible graphene quantum dots (GQDs) as an agent in photodynamic therapy was studied. First, dots were obtained using electrochemical cutting of graphite. In only one synthetic step using gamma irradiation, GQDs were doped with N atoms without any reagent. Obtained dots showed blue photoluminescence, with a diameter of 19-89 nm and optical band gap of 3.23-4.73 eV, featuring oxygen-containing, amino, and amide functional groups. Dots showed antioxidative activity; they quenched •OH at a concentration of 10 μg·mL-1, scavenged DPPH• radicals even at 5 μg·mL-1, and caused discoloration of KMnO4 at 30 μg·mL-1. Under light irradiation, dots were able to produce singlet oxygen, which remained stable for 10 min. Photoinduced effects by GQDs were studied on several bacterial strains (Listeria monocytogenes, Bacillus cereus, clinical strains of Streptococcus mutans, S. pyogenes, and S. sangunis, Pseudomonas aeruginosa, and one yeast strain Candida albicans) but antibacterial effects were not noticed.

Surface modification of carbon nitride dots by nanoarchitectonics for better drug loading and higher cancer selectivity

Carbon Dots (CDs) have recently attracted a considerable amount of attention thanks to their well-documented biocompatibility, tunable photoluminescence, and excellent water solubility. However, CDs need further analysis before their potential use in clinical trials. Previously, we reported a new type of carbon nitride dot (CND) that displayed selective cancer uptake traits attributed to structural resemblances between CNDs and glutamine. Here, the effects of surface structural differences on the cellular uptake of CNDs are further investigated to understand their selective cancer cell uptake trend. Beyond enhanced drug loading on modified CNDs, our cytotoxicity, western blotting and bioimaging studies proposed that modified CNDs' cellular uptake mechanism is thoroughly linked with ASCT2 and LAT1 transporters. Therefore, CNDs have a promising trait of selective cancer cell targeting by utilizing highly expressed transporters on cancer cells. Additionally, drug loaded CNDs exhibited improved anti-cancer efficacies towards cancer cells along with good non-tumor biocompatibilities.

Progress on carbon dots and hydroxyapatite based biocompatible luminescent nanomaterials for cancer theranostics

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Biocompatible carbon dots (CDs) and nanohydroxyapatite (nHA) have attracted much attention for the development of optical imaging probes.

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This review discusses the development of CD and nHA based nanomaterials as multifunctional agents for cancer theranostics.

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The effect of synthesis strategies and doping on photoluminescent properties along with tuning of emission in biological window has been briefly reviewed.

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The cancer targeting strategies, biocompatibility and biodistribution of CDs and nHA based luminescent probes is discussed.

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A summary of current challenges and future perspectives is provided.

Despite the significant advancement in cancer diagnosis and therapy, a huge burden remains. Consequently, much research has been diverted on the development of multifunctional nanomaterials for improvement in conventional diagnosis and therapy. Luminescent nanomaterials offer a versatile platform for the development of such materials as their intrinsic photoluminescence (PL) property offers convergence of diagnosis as well as therapy at the same time. However, the clinical translation of nanomaterials faces various challenges, including biocompatibility and cost-effective scale up production. Thus, luminescent materials with facile synthesis approach along with intrinsic biocompatibility and anticancerous activity hold significant importance. As a result, carbon dots (CDs) and nanohydroxyapatite (nHA) have attracted much attention for the development of optical imaging probes. CDs are the newest members of the carbonaceous nanomaterials family that possess intrinsic luminescent and therapeutic properties, making them a promising candidate for cancer theranostic. Additionally, nHA is an excellent bioactive material due to its compositional similarity to the human bone matrix. The nHA crystal can efficiently host rare-earth elements to attain luminescent property, which can further be implemented for cancer theranostic applications. Herein, the development of CDs and nHA based nanomaterials as multifunctional agents for cancer has been briefly discussed. The emphasis has been given to different synthesis strategies leading to different morphologies and tunable PL spectra, followed by their diverse applications as biocompatible theranostic agents. Finally, the review has been summarized with the current challenges and future perspectives.

Carbon Dots: Synthesis, Properties and Applications

Carbon dots (CDs) are known as the rising star of carbon-based nanomaterials and, by virtue of their unique structure and fascinating properties, they have attracted considerable interest in different fields such as biological sensing, drug delivery, photodynamic therapy, photocatalysis, and solar cells in recent years. Particularly, the outstanding electronic and optical properties of the CDs have attracted increasing attention in biomedical and photocatalytic applications owing to their low toxicity, biocompatibility, excellent photostability, tunable fluorescence, outstanding efficient up-converted photoluminescence behavior, and photo-induced electron transfer ability. This article reviews recent progress on the synthesis routes and optical properties of CDs as well as biomedical and photocatalytic applications. Furthermore, we discuss an outlook on future and potential development of the CDs based biosensor, biological dye, biological vehicle, and photocatalysts in this booming research field.

Wide visible-range activatable fluorescence ZnSe:Eu3+/Mn2+@ZnS quantum dots: local atomic structure order and application as a nanoprobe for bioimaging

The development of QDs-based fluorescent bionanoprobe for cellular imaging fundamentally relies upon the precise knowledge of particle-cell interaction, optical properties of QDs inside and outside of the cell, movement of a particle in and out of the cell, and the fate of particle. We reported engineering and physicochemical characterization of water-dispersible Eu³⁺/Mn²⁺ co-doped ZnSe@ZnS core/shell QDs and studied their potential as a bionanoprobe for biomedical applications, evaluating their biocompatibility, fluorescence behaviour by CytoViva dual mode fluorescence imaging, time-dependent uptake, endocytosis and exocytosis in RAW 264.7 macrophages. The oxidation state and local atomic structure of the Eu dopant studied by X-ray absorption fine structure (XAFS) analysis manifested that the Eu³⁺ ions occupied sites in both ZnSe and ZnS lattices for the core/shell QDs. A novel approach was developed to relieve the excitation constraint of wide bandgap ZnSe by co-incorporation of Eu³⁺/Mn²⁺ codopants, enabling the QDs to be excited at a wide UV-visible range. The QDs displayed tunable emission colors by a gradual increase in Eu³⁺ concentration at a fixed amount of Mn²⁺, systematically enhancing the Mn²⁺ emission intensity via energy transfer from the Eu³⁺ to Mn²⁺ ion. The ZnSe:Eu³⁺/Mn²⁺@ZnS QDs presented high cell viability above 85% and induced no cell activation. The detailed analyses of QDs-treated cells by dual mode fluorescence CytoViva microscopy confirmed the systematic color-tunable fluorescence and its intensity enhances as a function of incubation time. The QDs were internalized by the cells predominantly via macropinocytosis and other lipid raft-mediated endocytic pathways, retaining an efficient amount for 24 h. The unique color tunability and consistent high intensity emission make these QDs useful for developing a multiplex fluorescent bionanoprobe, activatable in wide-visible region.

Graphene quantum dots (GQDs) nanoarchitectonics for theranostic application in lung cancer

Lung cancer (LC) is heading up as a substantial cause of mortality worldwide. Despite enormous progress in cancer management, LC remains a crucial problem for oncologists due to the lack of early diagnosis and precise treatment. In this context, numerous early diagnosis and treatment approaches for LC at the cellular level have been developed using advanced nanomaterials in the last decades. Amongst this, graphene quantum dots (GQDs) as a novel fluorescent material overwhelmed the horizons of materials science and biomedical fields due to their multifunctional attributes. Considering the complex nature of LC, emerging diagnostic and therapeutic (Theranostics) strategies using GQDs proved to be an effective way for the current practice in LC. In this line, we have abridged various approaches used in the LC theranostics using GQDs and its surface-engineered motif. The admirable photophysical attributes of GQDs realised in photolytic therapy (PLT), hyperthermia therapy (HTT), and drug delivery have been discussed. Furthermore, we have engrossed the impasse and its effects on the use of GQDs in cancer treatments from cellular level (in vivo-in vitro) to clinical. Inclusively, this review will be an embodiment for the scientific fraternity to design and magnify their view for the theranostic application of GQDs in LC treatment.

Influence of surface charge of graphene quantum dots on their uptake and clearance in melanoma cells

Graphene quantum dots (GQDs) continue to draw interest in biomedical applications. However, their efficacy gets compromised due to their rapid clearance from the body. On one hand, rapid clearance is desired and considered advantageous in terms of their cytocompatibility, but on the other hand, it is a major limitation for their prolonged use as imaging and therapeutic probes. The uptake and clearance of GQDs have been described in vivo, however, their clearance in vitro is still not understood, one of the main reasons being that their uptake and clearance are a cell type-dependent phenomena. Studies on other types of quantum dots revealed the importance of surface charge in their uptake and retention in different cell types. However, the role of surface chemistry in GQD uptake and clearance has not been described previously. Here, we studied the influence of surface charge on GQDs (anionic and cationic) on their uptake and clearance in melanoma cells. Both cationic and anionic GQDs were synthesized using a hydrothermal method to have a relatively consistent size with an aim to study the role of surface charge in their uptake and clearance in isolation by avoiding size-dependent uptake bias. Both GQDs exhibited excellent biocompatibility with cell viability over 90% even at a high concentration of 200 μg mL-1. Using confocal microscopy and flow cytometry, we observed significantly faster and higher uptake of cationic GQDs compared to anionic GQDs. Consequently, relatively rapid clearance was observed in cells treated with anionic GQDs compared to those treated with cationic GQDs, highlighting the role of surface charge on GQDs in their uptake and clearance. Raman analysis of the cleared exocytosed GQDs revealed no sign of biodegradation of either type.

Graphene Quantum Dots by Eco-Friendly Green Synthesis for Electrochemical Sensing: Recent Advances and Future Perspectives

The continuous decrease in the availability of fossil resources, along with an evident energy crisis, and the growing environmental impact due to their use, has pushed scientific research towards the development of innovative strategies and green routes for the use of renewable resources, not only in the field of energy production but also for the production of novel advanced materials and platform molecules for the modern chemical industry. A new class of promising carbon nanomaterials, especially graphene quantum dots (GQDs), due to their exceptional chemical-physical features, have been studied in many applications, such as biosensors, solar cells, electrochemical devices, optical sensors, and rechargeable batteries. Therefore, this review focuses on recent results in GQDs synthesis by green, easy, and low-cost synthetic processes from eco-friendly raw materials and biomass-waste. Significant advances in recent years on promising recent applications in the field of electrochemical sensors, have also been discussed. Finally, challenges and future perspectives with possible research directions in the topic are briefly summarized.

Synthesis of graphene quantum dots and their applications in drug delivery

This review focuses on the recent advances in the synthesis of graphene quantum dots (GQDs) and their applications in drug delivery. To give a brief understanding about the preparation of GQDs, recent advances in methods of GQDs synthesis are first presented. Afterwards, various drug delivery-release modes of GQDs-based drug delivery systems such as EPR-pH delivery-release mode, ligand-pH delivery-release mode, EPR-Photothermal delivery-Release mode, and Core/Shell-photothermal/magnetic thermal delivery-release mode are reviewed. Finally, the current challenges and the prospective application of GQDs in drug delivery are discussed.

Fundamental Understanding of the Formation Mechanism for Graphene Quantum Dots Fabricated by Pulsed Laser Fragmentation in Liquid: Experimental and Theoretical Insight

The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon-based functional materials. In particular, there has been considerable attention on graphene quantum dots (GQDs) derived from multiwalled carbon nanotubes (MWCNTs) by the PLFL process, owing to the low cost and rapid processing time involved. However, a fundamental deep understanding of the formation of GQDs from MWCNTs by PLFL has still not been achieved despite the high demand. In this work, a mechanism for the formation of GQDs from MWCNTs by the PLFL process is reported, through the combination of experimental and theoretical studies. Both the experimental and computational results demonstrate that the formation of GQDs strongly depends on the pulse laser energy. Both methods demonstrate that the critical energy point, where a plasma plume is generated on the surface of the MWCNTs, should be precisely maintained to produce GQDs; otherwise, an amorphous carbon structure is favorably formed from the scattered carbons.

Recent Advances on Graphene Quantum Dots for Bioimaging Applications

Being a zero-dimensional (0D) nanomaterial of the carbon family, graphene quantum dots (GQDs) showed promising biomedical applications owing to their ultra-small size, non-toxicity, biocompatibility, excellent photo stability, tunable fluorescence, and water solubility, etc., thus capturing a considerable attention in biomedical field. This review summarizes the recent advances made in the research field of GQDs and place special emphasis on their bioimaging applications. We briefly introduce the synthesis strategies of GQDs, including top-down and bottom-up strategies. The bioimaging applications of GQDs are also discussed in detail, including optical [fluorescence (FL)], two-photon FL, magnetic resonance imaging (MRI), and dual-modal imaging. In the end, the challenges and future prospects to advance the clinical bioimaging applications of GQDs have also been addressed.

In situ assembly of a graphene oxide quantum dot-based thin-film nanocomposite supported on de-mixed blends for desalination through forward osmosis

In this work, in order to enhance the desalination performance, a unique thin-film composite membrane was designed by in situ assembly of a polyamide (PA)-graphene oxide quantum dot (GQD) framework. This unique assembly was supported on a templated hierarchical porous membrane derived from the de-mixing of a classical UCST (upper critical solution temperature) system consisting of polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA). The de-mixing was achieved by melt processing the blend above the UCST (in the miscible state) and quenching it below UCST. The pore size was controlled by varying the composition in the blends and by etching the PMMA phase. A sandwich architecture was developed by stacking different membranes using polyacrylic acid, as an adhesive, to achieve a gradient in pore size. Pure water flux, dye removal, and desalination experiments were carried out to study the efficacy of this strategy. The stacked membrane (used here as control) showed moderate dye rejection (about 50%) and poor desalination performance. In order to improve the desalination performance, the membranes were suitably modified by depositing a layer of polyamide (PA)-GQD framework obtained using interfacial polymerization. This strategy resulted in efficient salt rejection (more than 94% and 98% for monovalent salt and divalent salt, respectively) when studied through a pressure enhanced osmosis process using a 1000 ppm draw solution, and dye rejection (more than 90% and 85% for methylene blue (MB) and Congo red (CR), respectively) was studied through a cross-flow experimental set up using a 10 ppm feed solution @ 60 psi. Moreover, the antifouling properties of the PA-GQD modified membranes were superior (80%) to those of the control stacked membrane.

Green synthesis, biomedical and biotechnological applications of carbon and graphene quantum dots. A review

Carbon and graphene quantum dots are prepared using top-down and bottom-up methods. Sustainable synthesis of quantum dots has several advantages such as the use of low-cost and non-toxic raw materials, simple operations, expeditious reactions, renewable resources and straightforward post-processing steps. These nanomaterials are promising for clinical and biomedical sciences, especially in bioimaging, diagnosis, bioanalytical assays and biosensors. Here we review green methods for the fabrication of quantum dots, and biomedical and biotechnological applications.

Do biomedical engineers dream of graphene sheets?

During the past few years, graphene has outstandingly emerged as a key nanomaterial for boosting the performance of commercial, industrial and scientific related technologies. The popularity of this novel nanomaterial in biomedical engineering is due to its excellent biological, electronic, optical and thermal properties that, as a whole, surpass the features of commonly used biomaterials and consequently open a wide range of applications so far within the reach of science fiction. In this minireview, the potential of graphene and its based materials in the expanding biomedical field is highlighted with focus on groundbreaking diagnostic, monitoring and therapeutic strategies. Some of the major challenges related to the synthesis and safety of graphene-based materials are also briefly discussed because of their critical importance in bringing this class of carbon materials closer to the clinic.

Biocompatible propulsion for biomedical micro/nano robotics

Micro/Nano robots have shown enormous potential for diverse biomedical applications, such as targeted delivery, in vivo biosensing, minimally invasive surgery and cell manipulation through extending their area of operation to various previously inaccessible locations. The motion of these small-scale robots can be either self-propelled or remotely controlled by some external power sources. However, in order to use them for biomedical applications, optimization of biocompatible propulsion and precise controllability are highly desirable. In this article, the recent progress about the biocompatible propulsion (e.g. self-propulsion, external stimuli based propulsion and bio-hybrid propulsion) techniques for these micro/nano robotic devices are summarized along with their applications, with a special focus on the advantages and disadvantages of different propulsion techniques. The current challenges and future perspectives of these small-scale devices are discussed in the final section.