Fluorescent carbon dots from mono- and polysaccharides: synthesis, properties and applications

Advances in the study of the biological activity of polysaccharide-based carbon dots: A review

Carbon dots have attracted worldwide interest due to their customizable nature, luminescent properties, and exceptional biocompatibility. In particular, biomass-derived carbon dots have attracted attention for their environmentally friendly and cost-effective synthesis. Recent research looks into how polysaccharides can be used to make carbon dots. Using them as starting materials for nanomaterials has benefits in terms of structure, morphology, and doping elements. Although research has extensively examined the optical properties of carbon dots, their potential biological applications have not been thoroughly investigated. This review mainly summarises the cytotoxicity and biological functions of polysaccharide-based carbon dots (e.g. agar, alginate, cellulose, carrageenan, chitosan, chitosan, starch, gelatin, etc.), such as antioxidant, antibacterial and anti-tumor functions, highlighting the different scenarios of the methods of preparation of carbon dots. The applications of carbon dots in food, biomedical sciences, soil fertilization, and power generation are highlighted by reviewing the low toxicity of carbon dots with safety and biocompatibility in human contact. Finally, the importance and challenges of polysaccharide-based carbon dots and the prospects and research directions of polysaccharide-based carbon dots are explained by comparing them with other nanomaterials.

Sweet Janus Particles: Multifunctional Inhibitors of Carbohydrate-Based Bacterial Adhesion

Escherichia coli and other bacteria use adhesion receptors, such as FimH, to attach to carbohydrates on the cell surface as the first step of colonization and infection. Efficient inhibitors that block these interactions for infection treatment are multivalent carbohydrate-functionalized scaffolds. However, these multivalent systems often lead to the formation of large clusters of bacteria, which may pose problems for clearing bacteria from the infected site. Here, we present Man-containing Janus particles (JPs) decorated on one side with glycomacromolecules to target Man-specific adhesion receptors of E. coli. On the other side, poly(N-isopropylacrylamide) is attached to the particle hemisphere, providing temperature-dependent sterical shielding against binding and cluster formation. While homogeneously functionalized particles cluster with multiple bacteria to form large aggregates, glycofunctionalized JPs are able to form aggregates only with individual bacteria. The formation of large aggregates from the JP-decorated single bacteria can still be induced in a second step by increasing the temperature and making use of the collapse of the PNIPAM hemisphere. This is the first time that carbohydrate-functionalized JPs have been derived and used as inhibitors of bacterial adhesion. Furthermore, the developed JPs offer well-controlled single bacterial inhibition in combination with cluster formation upon an external stimulus, which is not achievable with conventional carbohydrate-functionalized particles.

Baicalin functionalized PEI-heparin carbon dots as cancer theranostic agent

The worldwide prevalence of cancer and its significantly rising risks with age have garnered the attention of nanotechnology for prompt detection and effective therapy with minimal or no adverse effects. In the current study, heparin (HP) polymer derived heteroatom (N, S-) co-doped CDs were synthesized using hydrothermal synthesis method to efficiently deliver natural anticancer compound baicalin (BA). Heparin carbon dots (HCDs) were passivated with polyethylenimine (PEI) to improve its fluorescence quantum yield. The surface passivation of CDs by polycationic PEI polymer not only facilitated loading of BA, but also played a crucial role in the pH-responsive drug delivery. The sustained release of BA (up to 80 %) in mildly acidic pH (5.5 and 6.5) conditions endorsed its drug delivery potential for cancer-specific microenvironments. BA-loaded PHCDs exhibited enhanced anticancer activity as compared to BA/PHCDs indicating the effectiveness of the nanoformulation, Furthermore, the flow cytometry analysis confirmed that BA-PHCDs treated cells were arrested in the G2/M phase of cell cycle and had a higher potential for apoptosis. Bioimaging study demonstrated the excellent cell penetration efficiency of PHCDs with complete cytoplasmic localization. All this evidence comprehensively demonstrates the potency of BA-loaded PHCDs as a nanotheranostic agent for cancer.

Comprehensive advances in the synthesis, fluorescence mechanism and multifunctional applications of red-emitting carbon nanomaterials

Red emitting fluorescent carbon nanomaterials have drawn significant scientific interest in recent years due to their high quantum yield, water-dispersibility, photostability, biocompatibility, ease of surface functionalization, low cost and eco-friendliness. The red emissive characteristics of fluorescent carbon nanomaterials generally depend on the carbon source, reaction time, synthetic approach/methodology, surface functional groups, average size, and other reaction environments, which directly or indirectly help to achieve red emission. The importance of several factors to achieve red fluorescent carbon nanomaterials is highlighted in this review. Numerous plausible theories have been explained in detail to understand the origin of red fluorescence and tunable emission in these carbon-based nanostructures. The above advantages and fluorescence in the red region make them a potential candidate for multifunctional applications in various current fields. Therefore, this review focused on the recent advances in the synthesis approach, mechanism of fluorescence, and electronic and optical properties of red-emitting fluorescent carbon nanomaterials. This review also explains the several innovative applications of red-emitting fluorescent carbon nanomaterials such as biomedicine, light-emitting devices, sensing, photocatalysis, energy, anticounterfeiting, fluorescent silk, artificial photosynthesis, etc. It is hoped that by choosing appropriate methods, the present review can inspire and guide future research on the design of red emissive fluorescent carbon nanomaterials for potential advancements in multifunctional applications.

Carbon Quantum Dots Based on Marine Polysaccharides: Types, Synthesis, and Applications

The marine environment offers a vast array of resources, including plants, animals, and microorganisms, that can be utilized to extract polysaccharides such as alginate, carrageenan, chitin, chitosan, agarose, ulvan, porphyra, and many more. These polysaccharides found in marine environments can serve as carbon-rich precursors for synthesizing carbon quantum dots (CQDs). Marine polysaccharides have a distinct advantage over other CQD precursors because they contain multiple heteroatoms, including nitrogen (N), sulfur (S), and oxygen (O). The surface of CQDs can be naturally doped, reducing the need for excessive use of chemical reagents and promoting green methods. The present review highlights the processing methods used to synthesize CQDs from marine polysaccharide precursors. These can be classified according to their biological origin as being derived from algae, crustaceans, or fish. CQDs can be synthesized to exhibit exceptional optical properties, including high fluorescence emission, absorbance, quenching, and quantum yield. CQDs' structural, morphological, and optical properties can be adjusted by utilizing multi-heteroatom precursors. Moreover, owing to their biocompatibility and low toxicity, CQDs obtained from marine polysaccharides have potential applications in various fields, including biomedicine (e.g., drug delivery, bioimaging, and biosensing), photocatalysis, water quality monitoring, and the food industry. Using marine polysaccharides to produce carbon quantum dots (CQDs) enables the transformation of renewable sources into a cutting-edge technological product. This review can provide fundamental insights for the development of novel nanomaterials derived from natural marine sources.

Polysaccharide-based C-dots and polysaccharide/C-dot nanocomposites: fabrication strategies and applications

C-dots are a new class of materials with vast applications. The synthesis of bio-based C-dots has attracted increasing attention in recent years. Polysaccharides being the most abundant natural materials with high biodegradability and no toxicity have been the focus of researchers for the synthesis of C-dots. C-dots obtained from polysaccharides are generally fabricated via thermal procedures, carbonization, and microwave pyrolysis. Small size, photo-induced electron transfer (PET), and highly adjustable luminosity behavior are the most important physical and chemical properties of C-dots. However, C-dot/polysaccharide composites can be introduced as a new generation of composites that combine the features of both C-dots and polysaccharides having a wide range of applications in biomedicines, biosensors, drug delivery systems, etc. This review demonstrates the features, raw materials, and methods used for the fabrication of C-dots derived from different polysaccharides. Furthermore, the properties, applications, and synthesis conditions of various C-dot/polysaccharide composites are discussed in detail.

Investigation of the role of pH and the stoichiometry of the N-dopant in the luminescence, composition and synthesis yield of carbon dots

Carbon dots (CDs) are carbon-based nanoparticles with very attractive luminescence features, which simplicity and flexibility of their fabrication can lead to an endless number of CDs with distinct properties and applications. High fluorescence quantum yields (QY_FL) are generally a necessary feature for various applications of CDs. One commonly employed strategy to improve the fluorescence properties of CDs is heteroatom-doping using precursors containing desired heteroatoms (with focus on N-doping). In this work, we report the synthesis and systematic investigation of an array of N-doped CDs, obtained from the dry heating of solid mixtures of glucose and urea in different molar ratios with two main objectives: to study the role of stoichiometry in the optical properties and composition of CDs and to investigate the formation of possible alkaline-responsive nanoparticles and the potential of this procedure for obtaining CDs with higher synthesis yields. We have characterized the optical properties of this diverse array of glucose and urea-based CDs using both UV-Vis and fluorescence spectroscopies. In addition, we have also examined the CDs by using high-resolution transmission electron microscopy (HR-TEM) and X-Ray photoelectron (XPS) spectroscopy, as well as by assessing the thermal stability of the nanoparticles. We have found that this fabrication process generates two types of CDs, one readily soluble in water and other only soluble at basic pH. The latter was characterized by higher synthesis yields, and lower QY_FL and thermal stability, when compared with those of the former. Furthermore, the stoichiometry of the N-dopant does not appear to be correlated with the QY_FL of the obtained CDs. This study provides novel information that should be useful for the future rational development of CDs with higher QY_FL and synthesis yields.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Carbon-based glyco-nanoplatforms: towards the next generation of glycan-based multivalent probes

Cell surface carbohydrates mediate a wide range of carbohydrate-protein interactions key to healthy and disease mechanisms. Many of such interactions are multivalent in nature and in order to study these processes at a molecular level, many glycan-presenting platforms have been developed over the years. Among those, carbon nanoforms such as graphene and their derivatives, carbon nanotubes, carbon dots and fullerenes, have become very attractive as biocompatible platforms that can mimic the multivalent presentation of biologically relevant glycosides. The most recent examples of carbon-based nanoplatforms and their applications developed over the last few years to study carbohydrate-mediate interactions in the context of cancer, bacterial and viral infections, among others, are highlighted in this review.

Multifunctional nanoparticles based on marine polysaccharides for apremilast delivery to inflammatory macrophages: Preparation, targeting ability, and uptake mechanism

Hydrophobic drug encapsulation inside targeted nanoparticles can enhance accumulation in inflamed sites, limit toxicity to healthy tissue, and improve pharmacokinetics compared to free drug dosing. This study reports a functionalized marine polysaccharide nanoparticle with a controlled release, targeting abilities, and in-situ imaging properties. Carbon dots functionalized Enteromorpha polysaccharide/Mannose/Methionine functionalized Chitosan (CDs.EP/Man/Meth.Cs) NPs could deliver apremilast to inflammatory macrophages and Caco-2 intestinal cells as an in vitro model for application in oral drug delivery to cure IBD. The nanoparticles were simply a polyelectrolyte complex between cationic functionalized chitosan and anionic polysaccharide of Enteromorpha prolifera. Functionalized polysaccharides and the prepared NPs were well characterized. The functionalized nanoparticles could overcome the limitation of poor drug bioavailability and showed a high loading capacity of (45 %) with a controlled release of about (74.5 %). Confocal laser scanning imaging showed higher cellular uptake of the modified nanoparticles than that of the unmodified nanoparticles in LPS-activated RAW 264.7 macrophages and Caco-2 cells. The effect of functionalization on the cellular uptake targetability was assessed using spectrofluorometric measurements after mannose competition. Anti-inflammatory activity of apremilast-loaded NPs is more elevated than the free drug. These results suggest the feasibility of using functionalized EP/Cs nanoparticles in IBD oral drug delivery.

Preparing Colour-Tunable Tannic Acid-Based Carbon Dots by Changing the pH Value of the Reaction System

Biomass carbon dots (CDs) have the characteristics of being green, nontoxic, inexpensive, and simple to prepare, and they can be used in luminescence-related fields. In this study, red, green, and blue luminescent CDs were synthesised by a simple hydrothermal method under alkaline, neutral, and acidic conditions using TA as carbon source and o-phthalaldehyde as blend. The unique optical properties of these CDs are due to the differences in their degrees of conjugation, which can be controlled by the pH value of the reaction system. These three kinds of biomass CDs have good applications in light-emitting diodes (LEDs). By mixing biomass CDs with epoxy resin, warm, and cold white LEDs with Commission Internationale de l'Elcairage (CIE) coordinates (0.35, 0.36) were successfully constructed on extremely stable multicolour CDs. This study shows that these biomass CDs are a promising material for white LED lighting.

Aminoglycoside-mimicking carbonized polymer dots for bacteremia treatment

Bacteremia and associated bacterial sepsis are potentially fatal and occur when the host response to microbial invasion is impaired or compromised. This motivated us to develop carbonized polymer dots (CPDs_Man/AA) from a mixture of mannose (Man) and positively charged amino acids [AAs; lysine, arginine (Arg), or histidine] through a one-step mild pyrolysis procedure, which effectively inhibited drug-resistant bacterial strains isolated from septic patients. The as-prepared CPDs_Man/AA showed broad-spectrum antibacterial activity, including multidrug-resistant bacteria, even in human plasma. The minimal inhibitory concentration of CPDs_Man/Arg is ca. 1.0 μg mL^-1, which is comparable to or lower than those of other tested antibiotics (e.g., ampicillin, gentamicin, and vancomycin). In addition to directly disrupting bacterial membranes, the CPDs_Man/Arg feature a structure similar to aminoglycoside antibiotics that could bind to 16S rRNA, thereby blocking bacterial protein synthesis. In vitro cytotoxic and hemolytic assays demonstrated the high biocompatibility of the CPDs_Man/AA. In addition, in vivo studies on methicillin-resistant Staphylococcus aureus-infected mice treated with the CPDs_Man/Arg showed a significant decrease in mortality-even better than that of antibiotics. Overall, the synthesis of the CPDs_Man/AA is cost-efficient, straightforward, and effective for treating bacteremia. The polymeric features of the CPDs_Man/Arg, including cationic charges and specific groups, can be recognized as a safe and broad-spectrum biocide to lessen our reliance on antibiotics to treat systemic bacterial infections in the future.

Ultra-sensitive and selective fluorescence approach for estimation of elagolix in real human plasma and content uniformity using boron-doped carbon quantum dots

Elagolix (ELX) is an orally administered non-peptidic GnRH antagonist that has been approved by the Food and Drug Administration in 2018 for the treatment of endometriosis pain. A sensitive and selective method for estimating elagolix (ELX) in human plasma and content uniformity was developed and validated. The spectrofluorimetric technique was used to investigate ELX utilizing boron-doped carbon quantum dots (B@CQDs). After gradually adding ELX, the quantum dots fluorescence was enhanced with LOQ of 1.74 ng mL⁻¹, the calibration curve between ELX and corresponding fluorescence intensity was found over a range of 4–100 ng mL⁻¹. The method was successfully applied in real human plasma with pharmacokinetic study and content uniformity test. The pharmacokinetic parameters as C_max were found to be 570 ± 5.32 ng. mL⁻¹ after 1 h, t_1/2 was found to be 6.50 h, and AUC was found to be 1290 ± 30.33 ng. h. mL⁻¹. B@CQDs were characterized using variety of instruments. The strategy is simple to implement in clinical labs and therapeutic drug monitoring systems.

Measuring the refractive index and sub-nanometre surface functionalisation of nanoparticles in suspension

Direct measurements to determine the degree of surface coverage of nanoparticles by functional moieties are rare, with current strategies requiring a high level of expertise and expensive equipment. Here, a practical method to determine the ratio of the volume of the functionalisation layer to the particle volume based on measuring the refractive index of nanoparticles in suspension is proposed. As a proof of concept, this technique is applied to poly(methyl methacrylate) (PMMA) nanoparticles and semicrystalline carbon dots functionalised with different surface moieties, yielding refractive indices that are commensurate to those from previous literature and Mie theory. In doing so, it is demonstrated that this technique is able to optically detect differences in surface functionalisation or composition of nanometre-sized particles. This non-destructive and rapid method is well-suited for in situ industrial particle characterisation and biological applications.

Small variations in reaction conditions tune carbon dot fluorescence

The development of robust and reproducible synthetic strategies for the production of carbon dots (CDs) with improved fluorescence quantum yields and distinct emission profiles is of great relevance given the vast range of applications of CDs. The fundamental understanding at a molecular level of their formation mechanism, chemical structure and how these parameters are correlated to their photoluminescence (PL) properties is thus essential. In this study, we describe the synthesis and structural characterization of a range of CDs with distinct physico-chemical properties. The materials were prepared under three minutes of microwave irradiation using the same common starting materials (D-glucosamine hydrochloride 1 and ethylenediamine 2) but modifying the stoichiometry of the reagents. We show that small variation in reaction conditions leads to changes in the fluorescent behaviour of the CDs, especially in the selective enhancement of overlapped fluorescence bands. Structural analysis of the different CD samples suggested different reaction pathways during the CD formation and surface passivation, with the latter step being key to the observed differences. Moreover, we demonstrate that these materials have distinct reversible response to pH changes, which we can be attribute to different behaviour towards protonation/deprotonation events of distinct emission domains present within each nanomaterial. Our results highlight the importance of understanding the reaction pathways that lead to the formation of this carbon-based nanomaterials and how this can be exploited to develop tailored materials towards specific applications.

Carbon Dots Boost dsRNA Delivery in Plants and Increase Local and Systemic siRNA Production

In this work, we obtained carbon dots from glucose or saccharose as the nucleation source and passivated them with branched polyethylenimines for developing dsRNA nanocomposites. The CDs were fully characterized using hydrodynamic analyses, transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The ζ potential determined that the CDs had positive charges, good electrophoretic mobility and conductivity, and were suitable for obtaining dsRNA nanocomposites. DsRNA naked or coated with the CDs were delivered to leaves of cucumber plants by spraying. Quantitation of the dsRNA that entered the leaves showed that when coated with the CDs, 50-fold more dsRNA was detected than when naked dsRNA. Moreover, specific siRNAs derived from the sprayed dsRNAs were 13 times more abundant when the dsRNA was coated with the CDs. Systemic dsRNAs were determined in distal leaves and showed a dramatic increase in concentration when delivered as a nanocomposite. Similarly, systemic siRNAs were significantly more abundant in distal leaves when spraying with the CD-dsRNA nanocomposite. Furthermore, FITC-labeled dsRNA was shown to accumulate in the apoplast and increase its entry into the plant when coated with CDs. These results indicate that CDs obtained by hydrothermal synthesis are suitable for dsRNA foliar delivery in RNAi plant applications.

Carbon dot-based fluorescent antibody nanoprobes as brain tumour glioblastoma diagnostics

The development of efficient and sensitive tools for the detection of brain cancer in patients is of the utmost importance particularly because many of these tumours go undiagnosed until the disease has advanced and when treatment is less effective. Current strategies employ antibodies (Abs) to detect Glial Fibrillary Acid Protein (GFAP) in tissue samples, since GFAP is unique to the brain and not present in normal peripheral blood, and it relies on fluorescent reporters. Herein we describe a low cost, practical and general method for the labelling of proteins and antibodies with fluorescent carbon dots (CD) to generate diagnostic probes that are robust, photostable and applicable to the clinical setting. The two-step protocol relies on the conjugation of a dibenzocyclooctyne (DBCO)-functionalised CD with azide functionalised proteins by combining amide conjugation and strain promoted alkyne-azide cycloaddition (SPAAC) ligation chemistry. The new class of Ab-CD conjugates developed using this strategy was successfully used for the immunohistochemical staining of human brain tissues of patients with glioblastoma (GBM) validating the approach. Overall, these novel fluorescent probes offer a promising and versatile strategy in terms of costs, photostability and applicability which can be extended to other Abs and protein systems.

Recent studies on cellulose-based fluorescent smart materials and their applications: A comprehensive review

The progress of bio-based fluorescent smart materials and their multifunctional applications have attained increasing interest in the recent decades. Cellulose is among the cheapest and widespread raw material on earth which can be modified into diverse useful materials. This review summarizes the chemical modification of cellulose into smart fluorescent materials. This further highlights on the fabrication of the prepared fluorescent materials into films, fibers, paper strips, carbon dots, hydrogels and solutions which are applied for the sensing of toxic metals and anions, pH, bioimaging, common organic solvents, aliphatic and aromatic amines, nitroaromatics, fluorescent printing, coating, and anti-counterfeiting applications. Finally, the discussion about the upcoming investigations, challenges, and options open for the cellulose-based luminescence sensors are communicated. We believe that this review will appeal more and more attention and curiosity for the chemists, biochemists, and chemical engineers working with the synthesis of cellulose-based fluorescent materials for widespread applications.

Fluorescent xylitol carbon dots: A potent antimicrobial agent and drug carrier

Biomolecular carbon dots (CDs) have immense potential for various industries due to exceptional bioactivity, biocompatibility, low toxicity, and biodegradability. In the present work xylitol (Xlt), a natural sweetener produced by microbial fermentation of sugarcane bagasse (71.98% conversion) has been used for CDs preparation by microwave-assisted carbonization in the presence of ethylene diamine (EDA). The resultant xylitol carbon dots (XCDs) were irregular shaped, rough with an average size of 8.88 nm and exhibiting fluorescence between 400 and 450 nm. The presence of EDA preserves the native chemical structure of Xlt even after exposure to microwaves. Purified XCDs were conjugated (AM-XCD) with ketoconazole and tetracycline for fungi and bacteria, respectively. In comparison to Xlt, XCDs have higher inhibitory potential and reduced dosage size of antimicrobials against Cryptococcus neoformans, Candida albicans, Streptococcus pyogenes, and Escherichia coli by 75%, 75%, 87.50%, and 50%, respectively. For Listeria monocytogenes and Salmonella typhi also inhibitory potential was increased by 14.68% and 21.38%. Increased efficacy advocated the improved drug delivery in the presence of XCDs. However, no inhibitory effect was recorded against DU145 (human prostate cancer) and HCT-15 (human colon adenocarcinoma) cell lines. The findings of the current work suggested the possible use of Xlt as an important antimicrobial agent besides an efficient drug carrier in healthcare.

Carbon Dots as an Emergent Class of Antimicrobial Agents

Antimicrobial resistance is a recognized global challenge. Tools for bacterial detection can combat antimicrobial resistance by facilitating evidence-based antibiotic prescribing, thus avoiding their overprescription, which contributes to the spread of resistance. Unfortunately, traditional culture-based identification methods take at least a day, while emerging alternatives are limited by high cost and a requirement for skilled operators. Moreover, photodynamic inactivation of bacteria promoted by photosensitisers could be considered as one of the most promising strategies in the fight against multidrug resistance pathogens. In this context, carbon dots (CDs) have been identified as a promising class of photosensitiser nanomaterials for the specific detection and inactivation of different bacterial species. CDs possess exceptional and tuneable chemical and photoelectric properties that make them excellent candidates for antibacterial theranostic applications, such as great chemical stability, high water solubility, low toxicity and excellent biocompatibility. In this review, we will summarize the most recent advances on the use of CDs as antimicrobial agents, including the most commonly used methodologies for CD and CD/composites syntheses and their antibacterial properties in both in vitro and in vivo models developed in the last 3 years.

Recent advances in multivalent carbon nanoform-based glycoconjugates

Multivalent carbohydrate-mediated interactions are fundamental to many biological processes, including disease mechanisms. To study these significant glycan-mediated interactions at a molecular level, carbon nanoforms such as fullerenes, carbon nanotubes, or graphene and their derivatives have been identified as promising biocompatible scaffolds that can mimic the multivalent presentation of biologically relevant glycans. In this minireview, we will summarize the most relevant examples of the last few years in the context of their applications.

Design and In-silico study of bioimaging fluorescence Graphene quantum dot-Bovine serum albumin complex synthesized by diimide-activated amidation

Graphene quantum dot possesses advantageous characteristics like tunable fluorescence, nanometer size, low cytotoxicity, high biocompatibility enabling them as an ideal material for fluorescence bio-imaging. It exhibits a unique characteristic of DNA cleavage activity enhancer, gene/drug carrier, and anticancer targeting applications. In this article, we discussed the preparation of graphene quantum dot through the bottom-up method. Carbodiimide-activated amidation reactions were used for the functionalization of graphene quantum dot with Bovine Serum Albumin. Fluorescence spectroscopy data showed that the graphene quantum dot has size-dependent fluorescence emission. TEM and AFM studies showed that the size of graphene quantum dot was around 20 nm with narrow size distribution. Carbodiimide-activated amidation conjugation was successful in binding the protein onto graphene quantum dot and these conjugates were characterized by DLS, FTIR, fluorescence spectroscopy, and agarose gel electrophoresis. We also studied the structural-based in-silico molecular dynamic simulation by AutoDock, PyRx, and Discovery Studio Visualizer. Based on the virtual screening analysis and higher negative energy incorporation, it is observed that graphene quantum dot conjugated with bovine serum albumin quickly and formed is highly stable complex, which makes them a potential candidate for future applications in the field of bio-imaging, bio-sensing, gene/drug delivery, and tumor theragnostic.

Recent Progress in Stimuli-Responsive Intelligent Nano Scale Drug Delivery Systems: A Special Focus Towards pH-Sensitive Systems

Stimuli-responsive nanocarriers are gaining much attention due to their versatile multifunctional activities, including disease diagnosis and treatment. Recently, clinical applications of nano-drug delivery systems for cancer treatment pose a challenge due to their limited cellular uptake, low bioavailability, poor targetability, stability issues, and unfavourable pharmacokinetics. To overcome these issues, researchers are focussing on stimuli-responsive systems. Nanocarriers elicit their role through endogenous (pH, temperature, enzyme, and redox) or exogenous (temperature, light, magnetic field, ultrasound) stimulus. These systems were designed to overcome the shortcomings such as non-specificity and toxicity associated with the conventional drug delivery systems. The pH variation between healthy cells and tumor microenvironment creates a platform for the generation of pH-sensitive nano delivery systems. Herein, we propose to present an overview of various internal and external stimuli-responsive behavior-based drug delivery systems. Herein, the present review will focus specifically on the significance of various pH-responsive nanomaterials such as polymeric nanoparticles, nano micelles, inorganic-based pH-sensitive drug delivery carriers such as calcium phosphate nanoparticles, and carbon dots in cancer treatment. Moreover, this review elaborates the recent findings on pH-based stimuli-responsive drug delivery systems with special emphasis on our reported stimuli-responsive systems for cancer treatment.

Comparison Direct Synthesis of Hyaluronic Acid-Based Carbon Nanodots as Dual Active Targeting and Imaging of HeLa Cancer Cells

The present study explores the potential of carbon nanodots (CDs) synthesized from hyaluronic acid using microwave-assisted and furnace-assisted methods as bioimaging agents for cancer cells. The investigation on the effect of microwave-assisted and furnace-assisted times (2 min and 2 h) on determining CD character is dominantly discussed. Various CDs, such as HA-P1 and HA-P2 were, respectively, synthesized through the furnace-assisted method at 270 °C for 2 min and 2 h, whereas HA-M1 and HA-M2 were synthesized with the microwave-assisted method for 2 min and 2 h, respectively. Overall, various CDs were produced with an average diameter, with the maximum absorption of HA-P1, HA-P2, HA-M1, and HA-M2 at 234, 238, 221, and 217 nm, respectively. The photoluminescence spectra of these CDs showed particular emissions at 320 nm and excitation wavelengths from 340 to 400 nm. Several characterizations such as X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and Raman spectroscopy reveal the CD properties such as amorphous structures, existence of D bands and G bands, and hydrophilic property supported with hydroxyl and carboxyl groups. The quantum yields of HA-M1, HA-M2, HA-P1, and HA-P2 were 12, 7, 9, and 23%, respectively. The cytotoxicity and in vitro activity were verified by a cell counting kit-8 assay and confocal laser scanning microscopy, which show a low toxicity with the percentage of living cells above 80%.

Anti-Inflammatory Effect and Cellular Uptake Mechanism of Carbon Nanodots in in Human Microvascular Endothelial Cells

Cardiovascular disease (CVD) has become an increasingly important topic in the field of medical research due to the steadily increasing rates of mortality caused by this disease. With recent advancements in nanotechnology, a push for new, novel treatments for CVD utilizing these new materials has begun. Carbon Nanodots (CNDs), are a new form of nanoparticles that have been coveted due to the green synthesis method, biocompatibility, fluorescent capabilities and potential anti-antioxidant properties. With much research pouring into CNDs being used as bioimaging and drug delivery tools, few studies have been completed on their anti-inflammatory potential, especially in the cardiovascular system. CVD begins initially by endothelial cell inflammation. The cause of this inflammation can come from many sources; one being tumor necrosis factor (TNF-α), which can not only trigger inflammation but prolong its existence by causing a storm of pro-inflammatory cytokines. This study investigated the ability of CNDs to attenuate TNF-α induced inflammation in human microvascular endothelial cells (HMEC-1). Results show that CNDs at non-cytotoxic concentrations reduce the expression of pro-inflammatory genes, mainly Interleukin-8 (IL-8), and interleukin 1 beta (IL-1β). The uptake of CNDs by HMEC-1s was examined. Results from the studies involving channel blockers and endocytosis disruptors suggest that uptake takes place by endocytosis. These findings provide insights on the interaction CNDs and endothelial cells undergoing TNF-α induced cellular inflammation.

The Synthesis and Evaluation of Multivalent Glycopeptoids as Inhibitors of the Adhesion of Candida albicans

Multivalency is a strategy commonly used by medicinal carbohydrate chemists to increase the affinity of carbohydrate-based small molecules for their protein targets. Although this approach has been very successful in enhancing binding to isolated carbohydrate-binding proteins, anticipating the multivalent presentations that will improve biological activity in cellular assays remains challenging. In this work we investigate linear molecular scaffolds for the synthesis of a low valency presentation of a divalent galactoside 1, previously identified by us as an inhibitor of the adhesion of opportunistic fungal pathogen Candida albicans to buccal epithelial cells (BECs). Adhesion inhibition assays revealed that multivalent glycoconjugate 3 is more effective at blocking C. albicans adherence to BECs upon initial exposure to epithelial cells. Interestingly, 3 did not seem to have any effect when it was pre-incubated with yeast cells, in contrast to the original lead compound 1, which caused a 25% reduction of adhesion. In competition assays, where yeast cells and BECs were co-incubated, multivalent glycoconjugate 3 inhibited up to 49% C. albicans adherence in a dose-dependent manner. The combined effect of compound 1 towards both yeast cells and BECs allowed it to achieve over 60% inhibition of the adhesion of C. albicans to BECs in competition assays.

Insights into photoluminescence mechanisms of carbon dots: advances and perspectives

Carbon dots (CDs) are potentially useful in many areas such as bioimaging, light-emitting diodes, and sensing because of their excellent optical properties, high biocompatibility, and low toxicity. Knowledge of their photoluminescence (PL) mechanisms, which have been widely studied, is of significance in guiding the synthesis and promoting applications of CDs with tunable PL emissions. However, the intrinsic mechanism of PL emission remains unclear, and a unified mechanism has not been found because of differences in particle structures. This review generalizes the categories of CDs, noting their structural diversity. Three types of PL mechanism pertaining to structural differences are outlined: internal factors dominated emission (including the conjugation effect, the surface state, and the synergistic effect), external factors dominated emission (including the molecular state and the environment effect), and crosslink-enhanced emission. Optical applications of CDs are also briefly mentioned. Finally, the prospects for research into PL mechanisms are discussed, noting the remaining challenges and directions for future work.

Carbon Dot-NaCl Crystals for White-Light Generation and Fabry-Perot Lasing

Phosphor materials with broad spectral range and an average emission lifetime (20 μs) have been achieved from carbon dots (CDs)-NaCl crystals. A one-pot synthesis pathway has been developed for CDs-NaCl crystals formation at room temperature. Precursor for CDs materials was screened at room temperature by oxidation methodology from different simple sugar molecules. CDs (size less than 10 nm) prepared from the fructose sugar exhibit most intense emission. Utilizing ripe banana peel (contains ∼27% of fructose) as a precursor for the carbon dot formation, white-light emission with a CIE index of (0.29, 0.34) has been achieved from the single source with CDs-NaCl crystals upon excitation at 430 nm. The crystals also function as Fabry-Perot (F-P) mode resonator for lasing, with a laser threshold value of 0.9 mW and a resonating Q-factor of 207. These results outline a new approach for realizing F-P lasing and white light emission from a non-toxic green source with a quick, facile and low-cost synthesis procedure.

Photosynthesis and crop productivity are enhanced by glucose-functionalised carbon dots

From global food security to textile production and biofuels, the demands currently made on plant photosynthetic productivity will continue to increase. Enhancing photosynthesis using designer, green and sustainable materials offers an attractive alternative to current genetic-based strategies and promising work with nanomaterials has recently started to emerge. Here we describe the in planta use of carbon-based nanoparticles produced by low-cost renewable routes that are bioavailable to mature plants. Uptake of these functionalised nanoparticles directly from the soil improves photosynthesis and also increases crop production. We show for the first time that glucose functionalisation enhances nanoparticle uptake, photoprotection and pigment production, unlocking enhanced yields. This was demonstrated in Triticum aestivum 'Apogee' (dwarf bread wheat) and resulted in an 18% increase in grain yield. This establishes the viability of a functional nanomaterial to augment photosynthesis as a route to increased crop productivity.

The analytical and biomedical applications of carbon dots and their future theranostic potential: A review

In recent years, carbon dots (C-dots) have gained appreciable interest owing to their unique optical properties, including tunable fluorescence, stability against photobleaching and photoblinking, and strong fluorescence. Simple and low-cost hydrothermal and electrochemical approaches have been widely used in the preparation of biocompatible and high-quality C-dots. Various C-dots have been used for the quantitation of small analytes, mostly based on analyte induced fluorescence quenching. Depending on the nature of precursors, synthetic conditions (such as reaction temperature and time), and surface conjugation, multi-function C-dots can be prepared and used in diagnostics and therapeutics. Their strong fluorescence and photostability, enables use in cell imaging. Their biological activity from the surface residues and capability of generating reactive oxygen species, have allowed many C-dots to become candidates as antibacterial and anticancer reagents. After suitable conjugation, biocompatible and fluorescent C-dots can be used for diagnostics and therapeutics, thus, showing their great potential in the area of theranostics.

Transport of N-CD and Pre-Sorbed Pb in Saturated Porous Media

Carbon dots (CDs) are a new type of nanomaterials of the carbon family with unique characteristics, such as their small size (e.g., <10 nm), high water solubility, low toxicity, and high metal affinity. Modification of CDs by Nitrogen functional groups (N-CDs) enhances their metal adsorption capacity. This study investigated the influences of pH (4, 6, and 9), ionic strength (1, 50, and 100 mM), and cation valency (Na+ and Ca2+) on the competitive adsorption of Pb to quartz and N-CD surfaces, the transport and retention of N-CDs in saturated porous media, and the capacity of N-CDs to mobilize pre-adsorbed Pb in quartz columns. Pb adsorption was higher on N-CDs than on quartz surfaces and decreased with increases in ionic strength (IS) and divalent cations (Ca2+) concentration. N-CD mobility in quartz columns was highest at pH of 9- and 1-mM monovalent cations (Na+) and decreased with decreases in pH and increases in ionic strength and ion valency. N-CDs mobilized pre-adsorbed Pb from quartz due to the higher adsorption affinity of Pb to N-CD than to quartz surfaces. These findings provide valuable insights into the transport, retention, and risk assessment of lead in the presence of carbon-based engineered nanoparticles.

"Luminescent carbon nanodots: Current prospects on synthesis, properties and sensing applications"

"Nanocarbon science" ignited interest owing to its substantial scope in biomedicine, energy and environment-beneficial applications. Carbon dots (C-dots), a multi-faceted nanocarbon material, emerged as a homologue to graphene and henceforth geared extensive investigation both on its properties and applications. Eximious properties like excitation-wavelength tunable fluorescence emission, up-converted photoluminescence, photon-induced electron transfer, low cytotoxicity, chiroptical behavior, high chemical and photostability set the ground for astounding applications of carbon dots. Abundant availability of raw "green" precursors complementary to other molecular/graphitic precursors make them environmentally benign, inexpensive and ultimately "nanomaterials of the current decade". This review focuses on the synthesis of carbon dots not only from natural sources but also from other carbonaceous precursors and contemplates the inherent but controversial properties. We also aim to garner the attention of readers to the recent progress achieved by C-dots in one of its prestantious area of applications as nanosensors.

Synthesis of glycoconjugates utilizing the regioselectivity of a lytic polysaccharide monooxygenase

Polysaccharides from plant biomass are the most abundant renewable chemicals on Earth and can potentially be converted to a wide variety of useful glycoconjugates. Potential applications of glycoconjugates include therapeutics and drug delivery, vaccine development and as fine chemicals. While anomeric hydroxyl groups of carbohydrates are amenable to a variety of useful chemical modifications, selective cross-coupling to non-reducing ends has remained challenging. Several lytic polysaccharide monooxygenases (LPMOs), powerful enzymes known for their application in cellulose degradation, specifically oxidize non-reducing ends, introducing carbonyl groups that can be utilized for chemical coupling. This study provides a simple and highly specific approach to produce oxime-based glycoconjugates from LPMO-functionalized oligosaccharides. The products are evaluated by HPLC, mass spectrometry and NMR. Furthermore, we demonstrate potential biodegradability of these glycoconjugates using selective enzymes.

Fluorescent Carbon Dots Derived from Vehicle Exhaust Soot and Sensing of Tartrazine in Soft Drinks

Recycling of waste into valuable products plays a significant role in sustainable development. Herein, we report the conversion of vehicle exhaust waste soot into water-soluble fluorescent carbon dots via a simple acid refluxion method. The obtained carbon dots were characterized using microscopic and spectroscopic techniques. Microscopic techniques reveal that the prepared carbon material is spherical in shape with an average particle size of ∼4 nm. Spectroscopic studies exhibited that the carbon dots are emissive in nature, and the emission is excitation-dependent. Further, the prepared carbon dots were successfully utilized as a fluorescent probe for the detection of tartrazine with a limit of detection of 26 nM. The sensitivity of carbon dots has also been realized by the detection of trace amounts of tartrazine in commercial soft drinks. Overall, this work demonstrates the conversion air pollutant soot into value-added fluorescent nanomaterials toward sensing applications.

An integrated effluent free process for the production of 5-hydroxymethyl furfural (HMF), levulinic acid (LA) and KNS-ML from aqueous seaweed extract

This paper demonstrates an integrated zero liquid discharge (ZLD) process for time-dependent recovery of 5-hydroxymethyl furfural (HMF), levulinic acid (LA) and potassium, nitrogen and sulphur rich mother liquor (KNS-ML) - manure from agar/agarose containing seaweed aqueous solution using transition metal-free KHSO₄ as an eco-friendly and reusable catalyst. The selectivity of HMF is higher at 115 °C in 3 h and favorable to LA in 6 h in autoclave conditions. The proposed concept could be fine-tuned for the selective production of 5-HMF (up to 91% yield) or levulinic acid (56% yield) in the presence of the KHSO₄ catalyst. We have also achieved recyclability of KHSO₄ up to nine (09) cycles and the gram-scale reaction has been demonstrated. The (KNS-ML) obtained after nine cycles followed by neutralization with ammonia solution utilized for manure makes the process zero-liquid discharge and more cost-effective. The efficacy of the KNS-ML after nine cycles has been tested on groundnut plants.

Fe(III) doped carbon nanodots with intense green photoluminescence and dispersion medium dependent emission

The preparation and investigation of Fe(III) doped carbon nanodots (CNDs) with intense green photoluminescence and emission dependence on the dispersion medium are reported. Their unusual photoluminescence is especially highlighted in water where the initial blue emission is gradually shifted to intense deep green, while in other common solvents (chloroform, acetone etc.) this behavior has not been observed. Through embedding in a polymer matrix (e.g., PVA) the color transition becomes reversible and dependent on water content, ranging from a full blue emission, when completely dried, to an intense green emission, when wetted. The preparation path of the Fe(III) doped CNDs undergoes two main stages involving the initial obtaining of Fe(III)-N-Hydroxyphthalimide complex and then a thermal processing through controlled pyrolysis. Morphostructural investigations of the prepared Fe(III) doped CNDs were performed through TG, FT-IR, XPS, DLS, TEM and AFM techniques whereas absolute PLQY, steady state and lifetime fluorescence were used to highlight their luminescence properties. The results issued from structural and fluorescence investigations bring new insights on the particular mechanisms involved in CNDs photoluminescence, a topic still open to debate.

Preparation, functionalization and characterization of engineered carbon nanodots

Carbon-based dots (CDs) and their functionalized (nano)composites have recently attracted attention due to their seemingly easy preparation and numerous potential applications, ranging from those in the biomedical field (i.e., imaging and drug delivery) to those in (opto)electronics (i.e., solar cells and LEDs). This protocol details step-by-step procedures for synthesis, purification, functionalization and characterization of nitrogen-doped carbon nanodots (NCNDs), which we have been preparing for the past few years. First, we describe the bottom-up synthesis of NCNDs, starting with the use of molecular precursors (arginine (Arg) and ethylenediamine (EDA)) and making use of microwave-assisted hydrothermal heating. We also provide guidelines for the purification of these materials, through either dialysis or low-pressure size-exclusion chromatography (SEC). Second, we outline post-functionalization procedures for the surface modification of NCNDs, such as alkylation and amidation reactions. Third, we provide instructions for the preparation of NCNDs with different properties, such as color emission, electrochemistry and chirality. Given the fast evolution of preparations and applications of CDs, issues that might arise from artifacts, errors and impurities should be avoided. In this context, the present protocol aims to provide details and guidelines for the synthesis of high-quality nanomaterials with high reproducibility, for various applications. Furthermore, specific needs might require the CDs to be prepared by different synthetic procedures and/or from different molecular precursors, but such CDs can still benefit from the purification and characterization procedures outlined in this protocol. The sample preparation takes various time frames, ranging from 4 to 18 d, depending on the adopted synthesis and purification steps.

In situ synthesis of core-shell carbon nanowires as a potent targeted anticoagulant

We have developed a one-pot synthesis of bio-carbon nanowires from the natural product sodium alginate at low temperature, without using any catalyst, for anticoagulation applications. Sodium alginate is carbonized and sulfated/sulfonated in situ by solid state heating of a mixture of sodium alginate and ammonium sulfite. By regulating the heating temperature and the ratio of ammonium sulfite to sodium alginate, we modulated the degree of sulfation/sulfonation and carbonization, as well as the morphology of the carbon nanomaterials. The core-shell sulfated/sulfonated bio-carbon nanowires (CNWs_Alg@SOx) made by the reaction of a mixture of ammonium sulfite and sodium alginate with a mass ratio of 5 (ammonium sulfite to sodium alginate) at 165 °C for 3 h, exhibit strong inhibition of thrombin activity due to their ultrahigh binding affinity towards it (dissociation constant (K_d) = 8.7 × 10^-11 M). The possible formation mechanism of the carbon nanowires has been proposed. The thrombin-clotting time delay caused by CNWs_Alg@SOx is ∼ 170 times longer than that caused by sodium alginate. Hemolysis and cytotoxicity assays demonstrated the high biocompatibility of CNWs_Alg@SOx. Furthermore, the thromboelastography of whole-blood coagulation and rat-tail bleeding assays further reveal that CNWs_Alg@SOx have a much stronger anticoagulation activity than sodium alginate and naturally sulfated polysaccharides (e.g., fucoidan). Our results suggest that the low-temperature prepared, cost-effective, and highly biocompatible CNWs_Alg@SOx show great potential as an efficient anticoagulant for the prevention and treatment of diseases associated with thrombosis.

Selective photothermal killing of cancer cells using LED-activated nucleus targeting fluorescent carbon dots

The development of effective theranostic probes in cancer therapy is hampered due to issues with selectivity and off-target toxicity. We report the selective LED-photothermal ablation of cervical (HeLa) cancer cells over human dermal fibroblasts (HDF) using a new class of green-emissive fluorescent carbon dots (FCDs). The FCDs can be easily prepared in one pot using cheap and commercial starting materials. Physico-chemical characterization revealed that a surface coating of 2,5-deoxyfructosazine on a robust amorphous core gives rise to the nanomaterial's unique properties. We show that intracellular uptake mostly involves passive mechanisms in combination with intracellular DNA interactions to target the nucleus and that cancer cell selective killing is likely due to an increase in intracellular temperature in combination with ATP depletion, which is not observed upon exposure to either the "naked" core FCDs or the surface components individually. The selectivity of these nanoprobes and the lack of apparent production of toxic metabolic byproducts make these new nanomaterials promising agents in cancer therapy.

Biomolecule-derived quantum dots for sustainable optoelectronics

The diverse chemical functionalities and wide availability of biomolecules make them essential and cost-effective resources for the fabrication of zero-dimensional quantum dots (QDs, also known as bio-dots) with extraordinary properties, such as high photoluminescence quantum yield, tunable emission, photo and chemical stability, excellent aqueous solubility, scalability, and biocompatibility. The additional advantages of scalability, tunable optical features and presence of heteroatoms make them suitable alternatives to conventional metal-based semiconductor QDs in the field of bioimaging, biosensing, drug delivery, solar cells, photocatalysis, and light-emitting devices. Furthermore, a recent focus of the scientific community has been on QD-based sustainable optoelectronics due to the primary concern of partially mitigating the current energy demand without affecting the environment. Hence, it is noteworthy to focus on the sustainable optoelectronic applications of biomolecule-derived QDs, which have tunable optical features, biocompatibility and the scope of scalability. This review addresses the recent advances in the synthesis, properties, and optoelectronic applications of biomolecule-derived QDs (especially, carbon- and graphene-based QDs (C-QDs and G-QDs, respectively)) and discloses their merits and disadvantages, challenges and future prospects in the field of sustainable optoelectronics. In brief, the current review focuses on two major issues: (i) the advantages of two families of carbon nanomaterials (i.e. C-QDs and G-QDs) derived from biomolecules of various categories, for instance (a) plant extracts including fruits, flowers, leaves, seeds, peels, and vegetables; (b) simple sugars and polysaccharides; (c) different amino acids and proteins; (d) nucleic acids, bacteria and fungi; and (e) biomasses and their waste and (ii) their applications as light-emitting diodes (LEDs), display systems, solar cells, photocatalysts and photo detectors. This review will not only bring a new paradigm towards the construction of advanced, sustainable and environment-friendly optoelectronic devices using natural resources and waste, but also provides critical insights to inspire researchers ranging from material chemists and chemical engineers to biotechnologists to search for exciting developments of this field and consequently make an advance step towards future bio-optoelectronics.

Functional nanomaterials to augment photosynthesis: evidence and considerations for their responsible use in agricultural applications

At the current population growth rate, we will soon be unable to meet increasing food demands. As a consequence of this potential problem, considerable efforts have been made to enhance crop productivity by breeding, genetics and improving agricultural practices. While these techniques have traditionally been successful, their efficacy since the 'green revolution' has begun to significantly plateau. This stagnation of gains combined with the negative effects of climate change on crop yields has prompted researchers to develop novel and radical methods to increase crop productivity. Recent work has begun exploring the use of nanomaterials as synthetic probes to augment how plants use light. Photosynthesis in crops is often limited by their ability to absorb and exploit solar energy for photochemistry. The capacity to interact with and optimize how plants use light has the potential to increase the productivity of crops and enable the tailoring of crops for different environments and to compensate for predicted climate changes. Advances in the synthesis and surface modification of nanomaterials have overcome previous drawbacks and renewed their potential use as synthetic probes to enhance crop yields. Here, we review the current applications of functional nanomaterials in plants and will make an argument for the continued development of promising new nanomaterials and future applications in agriculture. This will highlight that functional nanomaterials have the clear potential to provide a much-needed route to enhanced future food security. In addition, we will discuss the often-ignored current evidence of nanoparticles present in the environment as well as inform and encourage caution on the regulation of nanomaterials in agriculture.

Non-Metal-Heteroatom-Doped Carbon Dots: Synthesis and Properties

Carbon dots (CDs) are new materials with applications in bioimaging, optical devices, catalysis, and many other fields. Their advantages, such as ease of large-scale preparation, low-costing precursors, highly tunable photoluminescence, satisfactory biocompatibility, and photostability against photobleaching, make them competitive alternatives to conventional semiconductor-based quantum dots and organic dyes. To overwhelm other luminescent materials in applications, their functionalities still need to be improved in spite of the abovementioned advantages. In recent years, it has been proven that heteroatom doping is an effective approach to improve the optical and electronic performance of CDs by tuning their carbon skeleton matrices and chemical structures. In this review, the development of non-metal-heteroatom-doped CDs, including heteroatom categories, preparation methods, and physicochemical properties, are discussed. Progressive trends in heteroatom-doped CDs are also discussed at the end of this review.

Synthesis of ginsenoside Re-based carbon dots applied for bioimaging and effective inhibition of cancer cells

BACKGROUND

Fluorescent carbon-based nanomaterials have promising properties such as biosensing, cell imaging, tracing and drug delivery. However, carbon dots (CDs) with specific inherent biological functions have not been investigated. Ginsenosides are the components with multiple bioactivities found in plants of the genus Panax, which have attracted a lot of attention for their anticancer effect.

MATERIALS AND METHODS

In this study, we prepared a kind of novel photoluminescent CDs from ginsenoside Re by one-step hydrothermal synthesis method. The conventional methods including transmission electron microscopy, Fourier transform infrared spectroscopy, HPLC and fluorescence spectrum were used for characterization of CDs. In vitro anticancer effect was investigated by cytotoxicity assay, flow cytometry and Western blot analysis.

RESULTS

The as-prepared Re-CDs had an average diameter of 4.6±0.6 nm and excellent luminescent properties. Cellular uptake of Re-CDs was facilitated by their tiny nanosize, with evidence of their bright excitation-dependent fluorescent images. Compared with ginsenoside Re, the Re-CDs showed greater inhibition efficiency of cancer cell proliferation, with lower toxicity to the normal cells. The anticancer activity of Re-CDs was suggested to be associated with the generation of large amount of ROS and the caspase-3 related cell apoptosis.

CONCLUSION

Hopefully, the dual functional Re-CDs, which could both exhibit bioimaging and anticancer effect, are expected to have great potential in future clinical applications.

Practical Three-Minute Synthesis of Acid-Coated Fluorescent Carbon Dots with Tuneable Core Structure

We report a one-pot, three-minute synthesis of carboxylic acid-decorated fluorescent carbon dots (COOH-FCDs) with tuneable core morphology dependent on the surface passivating agent. Mechanism investigations highlighted the presence of key pyrazine and polyhydroxyl aromatic motifs, which are formed from the degradation of glucosamine in the presence of a bifunctional linker bearing acid and amine groups. The novel COOH-FCDs are selective Fe3+ and hemin sensors. Furthermore, the FCDs are shown to be non-toxic, fluorescent bioimaging agents for cancer cells.