Glowing graphene quantum dots and carbon dots: properties, syntheses, and biological 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.

Technical textiles modified with immobilized carbon dots synthesized with infrared assistance

Carbon quantum dots "CQDs" were investigated as photo-luminescent nanomaterials as it advantageous with nontoxicity to be alternative for metallic-nanomaterials in different purposes. Therefore, the presented report demonstrates an innovative strategy for industrialization of antimicrobial/fluorescent cotton textiles via exploitation of "CQDs". Unique/novel infrared-assisted technique was currently investigated for clustering "CQDs" form carboxymethyl cellulose. The successive nucleation of "CQDs" (8.0 nm) was affirmed via infra-red, Raman spectroscopy, NMR, TEM and Zeta-potential analysis. The clustered "CQDs" showed antimicrobial and fluorescent characters. The minimal inhibition concentration for "CQDs" (100 mg/mL) against E. coli and C. albicans showed pathogenic reduction of 96% and 82%, respectively. Fluorescent emission spectra for "CQDs" showed two intense peaks at 415-445 nm. "CQDs" were loaded upon pristine and cationized cotton to prepare CQDs@cotton and CQDs@cationized cotton. While, their physical/mechanical properties (air and water vapor permeabilities, tensile strength and elongation %) and thermal stability (TGA & DTG analysis) were studied. The CQDs@cationized cotton exhibited excellent antimicrobial activity with good durability as after ten repretitive washings, inhibition zone diameter against E. coli, was diminished from 21.0 mm to 14.0 mm. The fluorescent emmision intensity was diminished from 741 to 287 after 10 washing cycles. The produced cotton fabrics could be safely used in the medical and military textiles.

N-Doped Carbon Quantum Dots as Fluorescent Bioimaging Agents

Graphene quantum dots, carbon nanomaterials with excellent fluorescence characteristics, are advantageous for use in biological systems owing to their small size, non-toxicity, and biocompatibility. We used the hydrothermal method to prepare functional N-doped carbon quantum dots (N-CQDs) from 1,3,6-trinitropyrene and analyzed their ability to fluorescently stain various bacteria. Our results showed that N-CQDs stain the cell septa and membrane of the Gram-negative bacteria Escherichia coli, Salmonellaenteritidis, and Vibrio parahaemolyticus and the Gram-positive bacteria Bacillus subtilis, Listeria monocytogenes, and Staphylococcus aureus. The optimal concentration of N-CQDs was approximately 500 ppm for Gram-negative bacteria and 1000 ppm for Gram-positive bacteria, and the exposure times varied with bacteria. N-Doped carbon quantum dots have better light stability and higher photobleaching resistance than the commercially available FM4-64. When excited at two different wavelengths, N-CQDs can emit light of both red and green wavelengths, making them ideal for bioimaging. They can also specifically stain Gram-positive and Gram-negative bacterial cell membranes. We developed an inexpensive, relatively easy, and bio-friendly method to synthesize an N-CQD composite. Additionally, they can serve as a universal bacterial membrane-staining dye, with better photobleaching resistance than commercial dyes.

Quantum dots as a theranostic approach in Alzheimer's disease: a systematic review

Aim: Quantum dots (QDs) are nanoparticles that have an emerging application as theranostic agents in several neurodegenerative diseases. The advantage of QDs as nanomedicine is due to their unique optical properties that provide high sensitivity, stability and selectivity at a nanoscale range. Objective: To offer renewed insight into current QD research and elucidate its promising application in Alzheimer's disease (AD) diagnosis and therapy. Methods: A comprehensive literature search was conducted in PubMed and Google Scholar databases that included the following search terms: 'quantum dots', 'blood-brain barrier', 'cytotoxicity', 'toxicity' and 'Alzheimer's disease'; PRISMA guidelines were adhered to. Results: Thirty-four publications were selected to evaluate the ability of QDs to cross the blood-brain barrier, potential toxicity and current AD diagnostic and therapeutic applications. Conclusion: QD's unique optical properties and versatility to conjugate to various biomolecules, while maintaining a nanoscale size, render them a promising theranostic tool in AD.

Multifaceted Regulation of Potassium-Ion Channels by Graphene Quantum Dots

Graphene quantum dots (GQDs) are emerging as a versatile nanomaterial with numerous proposed biomedical applications. Despite the explosion in potential applications, the molecular interactions between GQDs and complex biomolecular systems, including potassium-ion (K+) channels, remain largely unknown. Here, we use molecular dynamics (MD) simulations and electrophysiology to study the interactions between GQDs and three representative K+ channels, which participate in a variety of physiological processes and are closely related to many disease states. Using MD simulations, we observed that GQDs adopt distinct contact poses with each of the three structurally distinct K+ channels. Our electrophysiological characterization of the effects of GQDs on channel currents revealed that GQDs interact with the extracellular voltage-sensing domain (VSD) of a Kv1.2 channel, augmenting current by left-shifting the voltage dependence of channel activation. In contrast, GQDs form a "lid" cluster over the extracellular mouth of inward rectifier Kir3.2, blocking the channel pore and decreasing the current in a concentration-dependent manner. Meanwhile, GQDs accumulate on the extracellular "cap domain" of K2P2 channels and have no apparent impact on the K+ flux through the channel. These results reveal a surprising multifaceted regulation of K+ channels by GQDs, which might help de novo design of nanomaterial-based channel probe openers/inhibitors that can be used to further discern channel function.

Fluorescent nanoparticles as tools in ecology and physiology

Fluorescent nanoparticles (FNPs) have been widely used in chemistry and medicine for decades, but their employment in biology is relatively recent. Past reviews on FNPs have focused on chemical, physical or medical uses, making the extrapolation to biological applications difficult. In biology, FNPs have largely been used for biosensing and molecular tracking. However, concerns over toxicity in early types of FNPs, such as cadmium-containing quantum dots (QDs), may have prevented wide adoption. Recent developments, especially in non-Cd-containing FNPs, have alleviated toxicity problems, facilitating the use of FNPs for addressing ecological, physiological and molecule-level processes in biological research. Standardised protocols from synthesis to application and interdisciplinary approaches are critical for establishing FNPs in the biologists' tool kit. Here, we present an introduction to FNPs, summarise their use in biological applications, and discuss technical issues such as data reliability and biocompatibility. We assess whether biological research can benefit from FNPs and suggest ways in which FNPs can be applied to answer questions in biology. We conclude that FNPs have a great potential for studying various biological processes, especially tracking, sensing and imaging in physiology and ecology.

Photoluminescence quenching of thermally treated waste-derived carbon dots for selective metal ion sensing

In the present study, carbon-dots (CDs) were derived from the thermal oxidation of an agricultural waste, bitter tea residue, to obtain different sp²/sp³ ratios and electronic structures for metal sensing. The CDs obtained from calcination at 700 °C exhibited the highest photoluminescence (PL) quantum yield (QY) of 11.8% among all the samples treated at different temperatures. These CDs had a high degree of graphitization, which resulted in a strong π-π* electron transition, and hence in a high QY. The strong photoluminescence of the CDs could be used to sense the metal ions Ag⁺, Sr²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, and Sn²⁺ by monitoring their PL intensity at an excitation wavelength of 320 nm. The metals inhibited the PL intensity in the order Ag⁺ > Fe²⁺, Fe³⁺, Ni²⁺ > Sr²⁺, Co²⁺, Cu²⁺, Sn²⁺, which demonstrated that the CDs exhibited high metal ion detection capability and selectivity. The detection of Fe³⁺ using CDs was performed in the range of 10-100 ppm with a LOD (limit of detection) value of 0.380 ppm. Theoretical calculations demonstrated that Ag⁺, Sr²⁺, and Sn²⁺ induced charge transfer excitation and that Fe²⁺ and Ni²⁺ induced d-d transitions via complexation with the sp² clusters. The charge transfer excitation and d-d transitions hindered the π-π* transition of the sp² clusters, leading to a quenching effect. On the other hand, Li⁺, Na⁺, and K⁺ ions did not alter the π-π* transition of the sp² clusters, resulting in a negligible quenching effect. In summary, the oxidation level and electronic structure of CDs derived from bitter tea residue could be tailored, and the CDs were shown to be a facile, sustainable, and eco-friendly material for metal sensing.

Sulfonated glycosaminoglycan bioinspired carbon dots for effective cellular labelling and promotion of the differentiation of mesenchymal stem cells

Although carbon dots (CDs) have been synthesized and applied in a variety of biological fields, such as disease diagnosis and gene/drug delivery, the exploration of facile bioinspired synthesis and applications of CDs is still of great significance. Particularly, recent increasing research has clearly confirmed that nanomaterials can affect a series of physiological behaviors and functions of mesenchymal stem cells (MSCs) (e.g., differentiation and pluripotency). Therefore, it is very important to develop multifunctional nanomaterials to simultaneously realize the cellular labelling and regulation of MSC behaviors in practical applications. Herein, sulfonated glycosaminoglycan-bioinspired CDs as bi-functional nanomaterials were ingeniously designed for cellular imaging and promoting the differentiation of rat bone MSCs (rBMSCs) in different culture media, which simultaneously met the two fundamental requirements in the field of MSC-based treatments (e.g., precisely directing the differentiation of MSCs and effective cellular labeling). These bifunctional CDs were successfully prepared via one-pot hydrothermal synthesis by using d-glucosamine hydrochloride (GA·HCl) and sodium p-styrenesulfonate (NaSS) as the reactants. The synthesized CDs with a uniform particle size (around 4 nm) dispersed well in aqueous solutions and exhibited remarkable fluorescence stability under different conditions. Additionally, cell viability and proliferation results demonstrated that the CDs possessed good biocompatibility, having negligible effects on the self-renewal potential of rBMSCs. The as-prepared CDs presented a cytoplasmatic distribution after being ingested by rBMSCs; thus, they are particularly suitable for cellular imaging. More importantly, the addition of CDs to osteogenic and chondrogenic induction media (OIM and CIM), respectively, was capable of effectively promoting the osteogenic and chondrogenic differentiation of rBMSCs due to the generation of reactive oxygen species (ROS) while having no influence on their pluripotency. In brief, this study not only implements a cellular labeling method based on CDs that were synthesized by a biomimicking strategy, but also paves a new way to regulate the differentiation of MSCs by designing multifunctional nanomaterials; this will enable the extensive development of facile synthesis methods and new applications of CDs and will also provide some research foundations for MSC-based fields.

Nitrogen-doped carbon dots for wash-free imaging of nucleolus orientation

Carbon dots (CDs) are a rising star in the field of cellular imaging, especially cytoplasmic imaging, attributing to the super-stable optical performance and ultra-low biological toxicity. Nucleolus can accurately reflect the expression state of a cell and is strongly linked to the occurrence and development of many diseases, so exploring bran-new CDs for nucleolus-orientation imaging with no-wash technology has important theoretical value and practical significance. Herein, nitrogen-doped carbon dots (N-CDs) with green fluorescence (the relative fluorescence quantum yield of 24.4%) was fabricated by the hydrothermal treatment of m-phenylenediamine and p-aminobenzoic acid. The N-CDs possess small size, bright green fluorescence, abundant surface functional groups, excellent fluorescence stability and good biocompatibility, facilitating that the N-CDs are an excellent imaging reagent for cellular imaging. N-CDs can particularly bind to RNA in nucleoli to enhance their fluorescence, which ensures that the N-CDs can be used in nucleolus-orientation imaging with high specificity and wash-free technique. This study demonstrates that the N-CDs have a significant feasibility to be used for nucleolus-orientation imaging in biomedical analysis and clinical diagnostic applications.

Applications of Carbon Dots (CDs) in Latent Fingerprints Imaging

Carbon dots (CDs), a new member of the carbon-based material family, possess unique properties, such as high fluorescence, non-toxicity, eco-friendliness, stability and cost-effectiveness. These properties helped CDs to receive tremendous attention in various fields, namely, biological, opto-electronic, bio-imaging and energy-related applications. Although CDs are widely explored in bio-imaging and bio-sensing applications, their effectiveness in forensic science and technology is comparatively new. In this review, applications of CDs pertaining to latent FPs recovery since 2015 to 2020 is summarized comprehensively.

Amino acid-functionalized carbon quantum dots for selective detection of Al3+ ions and fluorescence imaging in living cells

Carbon quantum dots (CQDs) are drawing tremendous attention due to their unique photoluminescence property and fascinating functions. Herein, we prepared novel CQDs functionalized with amino acids (AA-CQDs) by a one-pot hydrothermal method for selective detection of Al³⁺ ions and fluorescence imaging. The prepared AA-CQDs exhibit a novel triple-excitation and single-colour emission for fluorescent property. In addition, the AA-CQDs have a high absolute quantum yield (24.23%) and quantum lifetime (13.29 ns). Moreover, the AA-CQDs exhibit high selectivity and sensitivity for Al³⁺ by fluorescence enhancement. In pH 7.4 PBS solution, there was a good linear relation between the fluorescence intensity and the concentration of Al³⁺ in the range of 1-20 μmol L^-1; the limit of detection (3σ) was only 0.32 μmol L^-1. Furthermore, an AA-CQD probe was also utilized for detection of Al³⁺ in living cells based on excellent biocompatibility and endocytosis. Based on the concentration of Al³⁺ ions in cells and apoptosis data, there will be a quick reflect of apoptosis induced by aluminium ions via the fluorescence intensity of the AA-CQD probe. This work will set the stage for developing novel CQD-based biosensors in cell research.

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.

Folic Acid Functionalized Carbon Dot/Polypyrrole Nanoparticles for Specific Bioimaging and Photothermal Therapy

Polypyrrole nanoparticles (PPy-NPs) with excellent near-infrared absorption are commonly used as photothermal therapy (PTT) agents; however, PTT using PPy-NPs has a limitation in that it is difficult to maximize their therapeutic effect because of the lack of specific targeting. In this study, to overcome the difficulty of targeting, folic acid functionalized carbon dots (FA-CDs) with bright green fluorescence properties were combined with carboxylated PPy-NPs via the EDC/NHS coupling reaction to yield a PTT imaging agent. The synthesized FA-CD/PPy-NPs with excellent photostability performed folate receptor (FR) positive HeLa cancer cell imaging by green fluorescence signals of FA-CDs and exhibited high cell viability (above 90%) even at 500 μg/mL. The viability of HeLa cells incubated with 200 μg/mL FA-CD/PPy-NPs was dramatically decreased to 25.02 ± 1.85% by NIR laser irradiation, through photothermal therapeutic effects of FA-CD/PPy-NPs with high photothermal conversion efficiency (η = 40.80 ± 1.54%). The cancer cell death by FA-CD/PPy-NPs was confirmed by fluorescence imaging of FA-CDs as well as live/dead cell staining assay (calcein-AM/PI). These results demonstrate that the FA-CD/PPy-NPs can be utilized as multifunctional theranostic agents for specific bioimaging and treatment of FR-positive cancer cells.

A mitochondria-targeted ratiometric fluorescent nanoprobe for imaging of peroxynitrite in living cells

Peroxynitrite (ONOO^-) is a series of basic biological oxidants involved in physiological and pathological processes. The detection of ONOO^- in biological systems has been challenging due to its extremely short half-life and low steady-state concentration. In this work, a ratiometric fluorescent nanoprobe for ONOO^- was constructed by coupling covalently of graphene quantum dots (GQDs) with cyanine 5.5 (Cy5.5). This nanoprobe (GQD-Cy5.5) could selectively accumulate in mitochondrial, appears two strong fluorescence emission peaks at 520 and 694 nm. In the presence of ONOO^-, the intensity of fluorescence emission peak at 520 nm increased and the intensity of fluorescence emission peak at 694 nm decreased. The ratio (F_{520 nm}/F_{694 nm}) of fluorescence intensity at two emission peaks had a good linear relationship with the concentration of ONOO^- in the range of 0-6.0 μM, and the detection limit was 0.03 μM. The excellent properties of the nanoprobe enable its applications in the ratiometric fluorescence imaging of endogenous ONOO^- in cell mitochondria.

Synthesis of a novel nanocomposite containing chitosan as a three-dimensional printed wound dressing technique: Emphasis on gene expression

In this study, a highly porous three-dimensional (3D)-printed wound healing core/shell scaffold fabricated using poly-lactic acid (PLA). The core of scaffold was composed of hyaluronic acid (HA), copper carbon dots (Cu-CDs), rosmarinic acid, and chitosan hydrogel. Cu-CDs were synthesized using ammonium hydrogen citrate under hydrothermal conditions. Formulation containing 1 mg ml^-1 concentration of Cu-CDs showed an excellent antibacterial activity against gram bacteria. At 0.25 mg ml^-1 of Cu-CDs concentration, scaffold had a good biocompatibility as confirmed by cytotoxicity assay on L929 fibroblast stem cells. in vivo wound healing experiments on groups of rats revealed that after 15 days of treatment, the optimal formulation of composite scaffold significantly improves the wound healing process compared to the PLA scaffold. This finding was confirmed by histological analysis and the relative expression of PDGF, TGF-β, and MMP-1 genes. The biocompatible antibacterial CU-CDS/PLA/HA/chitosan/rosmarinic acid nanocomposite is a promising wound healing scaffold which highly accelerates the process of skin regeneration.

Rapid ex vivo assessment of cancer prognosis by fluorescence imaging of nucleolus using nitrogen doped carbon dots

Cancer severely threatens human health currently, promoting the rapid development of cancer treatment strategies. In addition to cancer therapy, assessment of cancer prognosis, which can evaluate the success with treatment and chances of recovery as well as assist to make subsequent therapeutic schedule, is also remarkably indispensable and important. Conventional technologies can't provide rapid and highly-sensitive assessment of cancer prognosis at cytological level. Herein, an effective nitrogen doped carbon dots with intrinsic nucleolus-targeting capability and high fluorescence quantum yield are synthesized, characterized and employed for fluorescence imaging of nucleolus, which is closely related to the biological alteration of cancer cell. The cancer prognosis thus can be accurately (limit of detection: 50 nM) and rapidly (5 min) assessed at subcellular organelle level from nucleolar characteristics, which are visualized and analyzed by the captured fluorescence images. Outstanding assessment performance endows the proposed technology with great potential for future clinical research.

Nanostructures derived from expired drugs and their applications toward sensing, security ink, and bactericidal material

In this research, a facile and economical route is introduced for the transformation of pharmaceutical waste (i.e., expired medicines) into value-added fluorescent carbon quantum dots (pharmaceutically derived CQDs abbreviated as 'P-CQDs'). The synthesized P-CQDs were identified to have surface functionalities of -OH, C=O, and C=C with an average size of ~2-3 nm and a high quantum yield of 35.3%. The photoluminescence of P-CQDs recorded a maximum optical emission intensity at 2.8 eV (425 nm). The binding of Cu (II) ions by -COOH functionalities on the surface of P-CQDs led to its fluorescence quenching (turn-off) over a wide Cu (II) concentration range of 0.25-50 ppm. The P-CQDs exhibited the detection limit of 0.66 ppm (well below the WHO permissible limit of 2 ppm). The fluorescence intensity of the P-CQDs-Cu (II) complex was recovered from NaHCO_3.Hence, their "off-on" behavior was also explored for security ink applications for information encryption and decryption. Moreover, the rich oxygenated groups on the surface of the P-CQDs were utilized for green synthesis of plasmonic Ag@P-CQDs nanostructures, which were also demonstrated to have enhanced potential as bactericidal materials (e.g., against both E. coli and S. aureus). The overall results of this study are demonstrated to help create new and diverse routes for converting expired drugs into value-added nanostructures.

Investigations of Graphene and Nitrogen-Doped Graphene Enhanced Polycaprolactone 3D Scaffolds for Bone Tissue Engineering

Scaffolds play a key role in tissue engineering applications. In the case of bone tissue engineering, scaffolds are expected to provide both sufficient mechanical properties to withstand the physiological loads, and appropriate bioactivity to stimulate cell growth. In order to further enhance cell-cell signaling and cell-material interaction, electro-active scaffolds have been developed based on the use of electrically conductive biomaterials or blending electrically conductive fillers to non-conductive biomaterials. Graphene has been widely used as functioning filler for the fabrication of electro-active bone tissue engineering scaffolds, due to its high electrical conductivity and potential to enhance both mechanical and biological properties. Nitrogen-doped graphene, a unique form of graphene-derived nanomaterials, presents significantly higher electrical conductivity than pristine graphene, and better surface hydrophilicity while maintaining a similar mechanical property. This paper investigates the synthesis and use of high-performance nitrogen-doped graphene as a functional filler of poly(ɛ-caprolactone) (PCL) scaffolds enabling to develop the next generation of electro-active scaffolds. Compared to PCL scaffolds and PCL/graphene scaffolds, these novel scaffolds present improved in vitro biological performance.

Protein nanoparticles in molecular, cellular, and tissue imaging

The quest to develop ideal nanoparticles capable of molecular, cellular, and tissue level imaging is ongoing. Since certain imaging probes and nanoparticles face drawbacks such as low aqueous solubility, increased ROS generation leading to DNA damage, apoptosis, and high cellular/organ toxicities, the development of versatile and biocompatible nanocarriers becomes necessary. Protein nanoparticles (PNPs) are one such promising class of nanocarriers that possess most of the desirable properties of an ideal nanocarrier for bioimaging applications. PNPs demonstrate high aqueous solubility, minimal cytotoxicity, and multi-cargo loading capacity. They are also amenable to surface-functionalization, as well as modulation of their hydrophobicity and hydrophilicity. The use of PNPs for bioimaging applications has made rapid advancements in the past two decades. Being comparatively less explored, the field opens up a plethora of opportunities and focus areas to engineer ideal bioimaging protein nanocarriers. The use of PNPs as carriers of their natural ligands as well as other heavy metals and fluorescent probes, along with drug molecules for combined theranostic applications has been reported. In addition, surface functionalization to impart specificity of targeting the PNPs has been shown to reduce nonspecific cellular interactions, thus reducing systemic toxicity. PNPs have been explored for their application in imaging of numerous cancers, cardiovascular diseases as well as imaging of the brain using near infrared fluorescence (NIRF) imaging, magnetic resonance imaging (MRI), X-ray computed tomography (CT), positron emission tomography (PET), single-photon emission computed tomography (SPECT), ultrasound (US), and photoacoustic (PA) imaging. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Lateral size of graphene oxide determines differential cellular uptake and cell death pathways in Kupffer cells, LSECs, and hepatocytes

As a representative two-dimensional (2D) nanomaterial, graphene oxide (GO) has shown high potential in many applications due to its large surface area, high flexibility, and excellent dispersibility in aqueous solutions. These properties make GO an ideal candidate for bio-imaging, drug delivery, and cancer therapy. When delivered to the body, GO has been shown to accumulate in the liver, the primary accumulation site of systemic delivery or secondary spread from other uptake sites, and induce liver toxicity. However, the contribution of the GO physicochemical properties and individual liver cell types to this toxicity is unclear due to property variations and diverse cell types in the liver. Herein, we compare the effects of GOs with small (GO-S) and large (GO-L) lateral sizes in three major cell types in liver, Kupffer cells (KCs), liver sinusoidal endothelial cells (LSECs), and hepatocytes. While GOs induced cytotoxicity in KCs, they induced significantly less toxicity in LSECs and hepatocytes. For KCs, we found that GOs were phagocytosed that triggered NADPH oxidase mediated plasma membrane lipid peroxidation, which leads to PLC activation, calcium flux, mitochondrial ROS generation, and NLRP3 inflammasome activation. The subsequent caspase-1 activation induced IL-1β production and GSDMD-mediated pyroptosis. These effects were lateral size-dependent with GO-L showing stronger effects than GO-S. Amongst the liver cell types, decreased cell association and the absence of lipid peroxidation resulted in low cytotoxicity in LSECs and hepatocytes. Using additional GO samples with different lateral sizes, surface functionalities, or thickness, we further confirmed the differential cytotoxic effects in liver cells and the major role of GO lateral size in KUP5 pyroptosis by correlation studies. These findings delineated the GO effects on cellular uptake and cell death pathways in liver cells, and provide valuable information to further evaluate GO effects on the liver for biomedical applications.

Fluorescent Carbon Dots: Fantastic Electroluminescent Materials for Light-Emitting Diodes

Fluorescent carbon dots (CDs) have emerged as fantastic luminescent nanomaterials with significant potentials on account of their unique photoluminescence properties, high stability, and low toxicity. The application of CDs in electroluminescent light-emitting diodes (LEDs) have aroused much interest in recent years. Herein, the state-of-the-art advances of CD-based electroluminescent LEDs are summarized, in which CDs act as active emission layer and interface transport layer materials is discussed and highlighted. Besides, the device structure of CD-based LEDs and preparation methods of CDs are also introduced. Furthermore, the opportunities and challenges for achieving high performance CD-based electroluminescent LED devices are presented. This review article is expected to stimulate more unprecedented achievements derived from CDs and CD-based electroluminescent LEDs, thus further promoting their practical applications in future solid-state lighting and flat-panel displays.

Mechanism of action and cellular responses of HEK293 cells on challenge with zwitterionic carbon dots

Carbon, an extremely versatile element has great demand in the field of nanoscience. Carbon-based nanostructures are exponentially increased due to its wide range of applications in biotechnological and environmental approaches; hence, its safety assessment is of greater concern. In the present study, high quantum yielding zwitterionic carbon dots were synthesized, characterized and its safety assessment at different concentration ranges (50-1600 μgmL^-1) on HEK 293 cells was carried out. Cellular, mitochondrial, lysosomal integrity and ROS generation were assessed using specific fluorochromes.The key cellular event apoptosis was assessed by annexinpropidium iodide staining using imaging flow cytometry. Moreover, the mRNA levels of the apoptotic genes were determined by real-time PCR. The results revealed that the cell viability assays (MTT, NR) and mitochondrial membrane potential were altered on exposure to a higher concentration of zwitterionic CDs for 24 h. Also, annexinpropidiumiodidestaining exhibited an increased percentage of apoptotic cells upon exposure to zwitterionic CDs at higher concentrations. Further, apoptosis was confirmed by significantlyincreased expression of pro-apoptotic gene (Bax) together with decreased expression of Bcl-2/Bax ratio. Collectively, this study suggests that zwitterionic CDs induce apoptosis in HEK 293 at higher concentration and the safe range for its intended application is found to be 50-200 μg/mL.

Fabrication of multi-functional carbon dots based on "one stone, three birds" strategy and their applications for the dual-mode Fe3+ detection, effective promotion on cell proliferation and treatment on ferric toxicosis in vitro

The ingenious design of multi-functional materials to simultaneously achieve the accurate detection of targets and effective treatment of target-related diseases is of great significance for both practical and clinical applications. Accordingly, based on their advantages of facile synthesis and function designability, functional nanomaterials have become promising candidates for integrating multi-functionality into one platform, especially carbon dot (CD)-based materials. Herein, deferoxamine (DFO)-inspired CDs with integrated "sense and treatment" potential were elaborately designed and fabricated via a one-pot hydrothermal synthesis by employing l-aspartic acid (Asp) and 2,5-diaminobenzenesulfonic acid (DABSA) as the reactants. A series of characterization results distinctly confirmed that the synthesized CDs possessed a unique chemical composition, uniform spherical morphology (diameter of around 5 nm) and good dispersibility in aqueous solution, exhibiting excellent fluorescence stability under different conditions. Owing to the complexation interaction between Fe3+ and the functional groups of CDs, the selective and sensitive detection of Fe3+ could be successfully realized through fluorescent and colorimetric dual-mode detection based on the statistic quenching in the initial stage, and subsequently the FRET process. Furthermore, these CDs could be utilized for cellular imaging and effective Fe3+ detection due to their outstanding biocompatibility and cytoplasmatic distribution. More significantly, these DFO-inspired CDs could remarkably promote the proliferation of various mammalian cells. Particularly, the results in this work obviously indicated that this type of CDs could weaken the damage of Fe3+ towards the physiological behaviors of cells, helping the cells to regain their capability of differentiation after ferric toxicosis. Therefore, this work presents an original approach for the design and fabrication of multi-functional materials according to the "one stone, three birds" strategy, which may be an optional solution to develop various multi-functional platforms for disease diagnosis and corresponding clinical treatment.

Applications of natural product-derived carbon dots in cancer biology

Natural products have contributed conspicuously to the development of innovative nanomedicines. Hence, the interface between nanomaterial science and plant natural products may bestow comprehensive diagnostic and therapeutic strategies for tackling diseases such as cancer and neurological disorders. Natural product-derived carbon dots (NPdCDs) have revealed noteworthy attributes in the fields of cancer theranostics, microbial imaging, drug sensing and drug delivery. As plants consist of a cocktail of bioactive phytomolecules, the NPdCDs can be anticipated to have medicinal properties, biocompatibility, photo-stability and easy functionalization. NPdCDs have wide-ranging applications. The primary objective of this review is to comment on recent developments in the use of NPdCDs, with special reference to their application in cancer biology. The future of the use of NPdCDs has also been considered.

Hybridized Graphene for Supercapacitors: Beyond the Limitation of Pure Graphene

Graphene-based supercapacitors have been attracting growing attention due to the predicted intrinsic high surface area, high electron mobility, and many other excellent properties of pristine graphene. However, experimentally, the state-of-the-art graphene electrodes face limitations such as low surface area, low electrical conductivity, and low capacitance, which greatly limit their electrochemical performances for supercapacitor applications. To tackle these issues, hybridizing graphene with other species (e.g., atom, cluster, nanostructure, etc.) to enlarge the surface area, enhance the electrical conductivity, and improve capacitance behaviors are strongly desired. In this review, different hybridization principles (spacers hybridization, conductors hybridization, heteroatoms doping, and pseudocapacitance hybridization) are discussed to provide fundamental guidance for hybridization approaches to solve these challenges. Recent progress in hybridized graphene for supercapacitors guided by the above principles are thereafter summarized, pushing the performance of hybridized graphene electrodes beyond the limitation of pure graphene materials. In addition, the current challenges of energy storage using hybridized graphene and their future directions are discussed.

Engineered two-dimensional nanomaterials: an emerging paradigm for water purification and monitoring

Water scarcity has become an increasingly complex challenge with the growth of the global population, economic expansion, and climate change, highlighting the demand for advanced water treatment technologies that can provide clean water in a scalable, reliable, affordable, and sustainable manner. Recent advancements on 2D nanomaterials (2DM) open a new pathway for addressing the grand challenge of water treatment owing to their unique structures and superior properties. Emerging 2D nanostructures such as graphene, MoS₂, MXene, h-BN, g-C₃N₄, and black phosphorus have demonstrated an unprecedented surface-to-volume ratio, which promises ultralow material use, ultrafast processing time, and ultrahigh treatment efficiency for water cleaning/monitoring. In this review, we provide a state-of-the-art account on engineered 2D nanomaterials and their applications in emerging water technologies, involving separation, adsorption, photocatalysis, and pollutant detection. The fundamental design strategies of 2DM are discussed with emphasis on their physicochemical properties, underlying mechanism and targeted applications in different scenarios. This review concludes with a perspective on the pressing challenges and emerging opportunities in 2DM-enabled wastewater treatment and water-quality monitoring. This review can help to elaborate the structure-processing-property relationship of 2DM, and aims to guide the design of next-generation 2DM systems for the development of selective, multifunctional, programmable, and even intelligent water technologies. The global significance of clean water for future generations sheds new light and much inspiration in this rising field to enhance the efficiency and affordability of water treatment and secure a global water supply in a growing portion of the world.

Carbon Nanomaterials Embedded in Conductive Polymers: A State of the Art

Carbon nanomaterials are at the forefront of the newest technologies of the third millennium, and together with conductive polymers, represent a vast area of indispensable knowledge for developing the devices of tomorrow. This review focusses on the most recent advances in the field of conductive nanotechnology, which combines the properties of carbon nanomaterials with conjugated polymers. Hybrid materials resulting from the embedding of carbon nanotubes, carbon dots and graphene derivatives are taken into consideration and fully explored, with discussion of the most recent literature. An introduction into the three most widely used conductive polymers and a final section about the most recent biological results obtained using carbon nanotube hybrids will complete this overview of these innovative and beyond belief materials.

Ultrasonic Generation of Thiyl Radicals: A General Method of Rapidly Connecting Molecules to a Range of Electrodes for Electrochemical and Molecular Electronics Applications

Herein, we report ultrasonic generation of thiyl radicals as a general method for functionalizing a range of surfaces with organic molecules. The method is simple, rapid, can be utilized at ambient conditions and involves sonicating a solution of disulfide molecules, homolytically cleaving S-S bonds and generating thiyl radicals that react with the surfaces by forming covalently bound monolayers. Full molecular coverages on conducting oxides (ITO), semiconductors (Si-H), and carbon (GC) electrode surfaces can be achieved within a time scale of 15-90 min. The suitability of this method to connect the same molecule to different electrodes enabled comparing the conductivity of single molecules and the electrochemical electron transfer kinetics of redox active monolayers as a function of the molecule-electrode contact. We demonstrate, using STM break-junction technique, single-molecule heterojunction comprising Au-molecule-ITO and Au-molecule-carbon circuits. We found that despite using the same molecule, the single-molecule conductivity of Au-molecule-carbon circuits is about an order of magnitude higher than that of Au-molecule-ITO circuits. The same trend was observed for electron transfer kinetics, measured using electrochemical impedance spectroscopy for ferrocene-terminated monolayers on carbon and ITO. This suggests that the interfacial bond between different electrodes and the same molecule can be used to tune the conductivity of single-molecule devices and to control the rate of charge transport in redox active monolayers, opening prospects for relating various types of interfacial charge-transfer rate processes.

A cationic quantum dot-based ratiometric fluorescent probe to visually detect berberine hydrochloride in human blood serums

Berberine hydrochloride (BH) is an isoquinoline alkaloid normally used as drug to treat diseases. Compared with the traditional detection methods, the carbon quantum dots (CQDs) have better selectivity, high sensitivity, easy operation, and is inexpensive which could be widely utilized as fluorescent nanoprobes to detect various compounds quantificationally. And ratiometric fluorescent sensors conspicuously increase sensitivity and precision detection and improve quantification. In this work, we use water-soluble and fluorescent cationic carbon dots cetylpyridinium chloride monohydrate (CPC)-CQDs to connect with pinacyanol chloride (PC) and sodium tetraphenylborate (ST) as the ratiometric fluorescent probe to detect BH. The ratiometric fluorescent probe has high sensitivity towards alkaloids and metal ions, photochemical stability (60 min), and pH stability (from 6.0 to 8.0), with the detection range from 0 to 200 μM, and limit was as low as 57.35 nM. The accuracy of the method was verified by spiked recovery experiment in different human blood serums which were drawn from healthy adult volunteers to explore the practicability. The recoveries were in the range 94.34 to 105.48% with relative standard deviations (RSD) of 0.80 to 2.92%. In addition, we could observe that the fluorescence was gradually darkened, and the color turned yellow to realize the visual detection. It is expected that this work would open up a new strategy for detecting BH in the environment and human blood serums.

Dual-color graphene quantum dots and carbon nanoparticles biosensing platform combined with Exonuclease III-assisted signal amplification for simultaneous detection of multiple DNA targets

Sensitive and simultaneous detection of multiple biomarkers such as target DNA or proteins using biocompatible materials with good analysis performance remains an important challenge. Herein, we successfully developed a signal "off-on" highly sensitive multiplex detection platform based on the combination of dual-color graphene quantum dots (blue GQDs and green GQDs) modified DNA probes with carbon nanoparticles (CNPs), which is a cheap, effective nonfluorescent quencher to simultaneously quench the fluorescence of both GQDs-DNA probes. The Exo III-assisted sequence-independent target recycling and signal amplification strategy was integrated into this sensing platform, which endows it with high sensitivity towards the multiplex detection of targets DNA. The detection limits of 6.6 pM for HIV and 9.5 pM for HBV were achieved respectively, which is about 60-fold lower than that of traditional unamplified homogeneous fluorescent assay methods. Our proposed multiplex detecting platform is advantageous in both respective and simultaneous detection of multiple targets and can also discriminate perfectly matched targets from mismatched targets in both PBS buffer and 1% human serum samples, demonstrating its potential to be a reliable strategy for highly sensitive simultaneous detection of multiple target genes in practical diagnosis applications.

Metformin derived carbon dots: Highly biocompatible fluorescent nanomaterials as mitochondrial targeting and blood-brain barrier penetrating biomarkers

Carbon dots (CDs) have been intensively studied since their discovery in 2004 because of their unique properties such as low toxicity, excellent biocompatibility, high photoluminescence (PL) and good water dispersibility. In this study metformin derived carbon dots (Met-CDs) were synthesized using a microwave assisted method. Met-CDs were meticulously characterized using ultra-violet spectroscopy (UV-vis), photoluminescence (PL), Fourier Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force (AFM) and transmission electron (TEM) microscopies. According to results of cytotoxicity studies, Met-CDs possess low-toxicity and excellent biocompatibility towards both non-tumor and tumor cell lines indicating that Met-CDs are outstanding candidates for living cell bioimaging studies. Furthermore, bioimaging studies have displayed that Met-CDs can penetrate the cell membrane and disperse throughout the cell structure including the nucleus and mitochondria. More specifically, Met-CDs tend to start localizing selectively inside the mitochondria of cancer cells, but not of non-tumor cells after 1 h of incubation. Finally, a zebrafish study confirmed that Met-CDs cross the blood-brain barrier (BBB) without the need of any other ligands. In summary, this study presents synthesis of Met-CDs which feature abilities such as mitochondrial and nucleus localizations along with BBB penetration.

Present trends in the encapsulation of anticancer drugs

Different nanomedicine devices that were developed during the recent years can be suitable candidates for their application in the treatment of various deadly diseases such as cancer. From all the explored devices, the nanoencapsulation of several anticancer medicines is a very promising approach to overcome some drawbacks of traditional medicines: administered dose of the drugs, drug toxicity, low solubility of drugs, uncontrolled drug delivery, resistance offered by the physiological barriers in the body to drugs, among others. In this chapter, the most important and recent progress in the encapsulation of anticancer medicines is examined: methods of preparation of distinct nanoparticles (inorganic nanoparticles, dendrimers, biopolymeric nanoparticles, polymeric micelles, liposomes, polymersomes, carbon nanotubes, quantum dots, and hybrid nanoparticles), drug loading and drug release mechanisms. Furthermore, the possible applications in cancer prevention, diagnosis, and cancer therapy of some of these nanoparticles have been highlighted.

Size-focusing results in highly photoluminescent sulfur quantum dots with a stable emission wavelength

Sulfur quantum dots (SQDs) are a new kind of functional nanomaterial, but several challenges still exist in relation to their synthesis and application, such as low-yield and time-consuming synthetic methods, low photoluminescence quantum yields (PLQYs), and the non-selectivity of their detection mechanisms. Herein, we report the drastic enhancement of the fluorescence performance of water-soluble SQDs via the one-pot synthesis of size-focusing QDs using ultrasound microwave radiation. The synthetic period has been greatly shortened to 2 h via the present process. Notably, the proposed SQDs exhibit a highly stable emission wavelength with a record high PLQY of 58.6%. The mechanistic study indicates that size-focusing is a key factor relating to the proposed high-performance SQDs. As they also have robust stability, the proposed SQDs show a wide range of potential applications. Inspired by the characteristic properties of the SQDs and specific analytes, a simple SQD-based fluorescence sensing platform, via a redox-reaction-mediated mechanism, has been successfully developed for the rapid and selective detection of Ce(iv). In addition, this system has been effectively applied to some Ce(iv)-related biological assays, such as ascorbic acid (AA) analysis. This work is an important breakthrough in the SQD field, opening up avenues for solving the challenging problems relating to SQD-based probes, enriching the fundamental understanding of them, and greatly extending their applications, especially in biomedicine.

Insights into graphene oxide interaction with human serum albumin in isolated state and in blood plasma

The interactions of graphene oxide (GO), a 2-dimensional nanomaterial with hydrophilic edges, hydrophobic basal plane and large flat surfaces, with biological macromolecules, are of key importance for the development of novel nanomaterials for biomedical applications. To gain more insight into the interaction of GO flakes with human serum albumin (HSA), we examined GO binding to HSA in its isolated state and in blood plasma. Calorimetric data reveal that GO strongly stabilizes free isolated HSA against a thermal challenge at low ionic strength, indicating strong binding interactions, confirmed by the drop in ζ-potential of the HSA/GO assemblies compared to bare GO flakes. However, calorimetry also revealed that the HSA-GO molecular interaction is hampered in blood plasma, the ionic strength being particularly important for the interactions. Molecular modelling calculations are in full concert with these experimental findings, indicating a considerably higher binding affinity for HSA to GO in its partially unfolded state, characteristic to low-ionic-strength environment, than for the native protein conformation, observed under physiological conditions. Therefore, for the first time we demonstrate an impeded interaction between HSA and GO nanoflakes in blood plasma, and suggest that the protein is protected from the plausible toxic effects of GO under native conditions.