An efficient edge-functionalization method to tune the photoluminescence of graphene quantum dots

Oxidation of Hydrogen Sulfide to Polysulfide and Thiosulfate by a Carbon Nanozyme: Therapeutic Implications with an Emphasis on Down Syndrome

Hydrogen sulfide (H2 S) is a noxious, potentially poisonous, but necessary gas produced from sulfur metabolism in humans. In Down Syndrome (DS), the production of H2 S is elevated and associated with degraded mitochondrial function. Therefore, removing H2 S from the body as a stable oxide could be an approach to reducing the deleterious effects of H2 S in DS. In this report we describe the catalytic oxidation of hydrogen sulfide (H2 S) to polysulfides (HS2+n - ) and thiosulfate (S2 O3 2- ) by poly(ethylene glycol) hydrophilic carbon clusters (PEG-HCCs) and poly(ethylene glycol) oxidized activated charcoal (PEG-OACs), examples of oxidized carbon nanozymes (OCNs). We show that OCNs oxidize H2 S to polysulfides and S2 O3 2- in a dose-dependent manner. The reaction is dependent on O2 and the presence of quinone groups on the OCNs. In DS donor lymphocytes we found that OCNs increased polysulfide production, proliferation, and afforded protection against additional toxic levels of H2 S compared to untreated DS lymphocytes. Finally, in Dp16 and Ts65DN murine models of DS, we found that OCNs restored osteoclast differentiation. This new action suggests potential facile translation into the clinic for conditions involving excess H2 S exemplified by DS.

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

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

Unraveling fluorescent mechanism of biomass-sourced carbon dots based on three major components: Cellulose, lignin, and protein

The complexity of biomass components leads to significant variations in the performance of biomass-based carbon dots (CDs). To shed light on this matter, this study presents a comparative analysis of the fluorescence properties of CDs using pure cellulose, lignin, and protein as models. Three CDs showed different fluorescent properties, resulting from the structure difference and carbonization behavior in the hydrothermal. The relatively gentle thermal degradation of proteins allows the macromolecular structure of amino acids to be preserved. This preservation results in a more regular lattice structure, a larger sp2 domain size, and N-doping, which contribute to the highest quantum yield (QY) of 8.7% of the CDs. In contrast, cellulose undergoes more severe thermal degradation with large amounts of small molecules generated, resulting in the CDs with fewer surface defects, more irregular lattice structures, and lower QY. These results provide a guideline for the design of carbon dots from different biomass.

Carboxyl groups on carbon nanodots as co-reactant sites for anodic electrochemiluminescence of tris(2,2-bipyridine)ruthenium(II)

Carbon nanodots (C-dots) with good biocompatibility have been extensively utilized as co-reactants for electrochemiluminescence (ECL) of the tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+) system. However, the ECL intensity of this system is still relatively low and the mechanism of C-dots as co-reactants remains unclear, which greatly limits its further application in bio-analysis. In this work, we revealed that the carboxyl groups on C-dots are co-reactant sites for Ru(bpy)32+ ECL by systematically investigating the contribution of carboxyl, hydroxyl and carbonyl groups on the surface of C-dots to the ECL intensity. Further treatment with hydrogen peroxide to increase the carboxyl-group content on C-dots resulted in a 10-fold increase in ECL intensity over the original Ru(bpy)32+/C-dots system. This work provides new insights for the rational design of ECL systems with C-dots as co-reactants and offers new chances for further applications of C-dots in the field of ECL.

Bismuth, Nitrogen-Codoped Carbon Dots as a Dual-Read Optical Sensing Platform for Highly Sensitive, Ultrarapid, Ratiometric Detection of Doxorubicin

Doxorubicin (DOX) is a potent anticancer drug, but it has side effects on normal tissues, particularly myocardial cells. Therefore, it is crucial to detect the DOX concentration in body fluids for effective clinical treatment. In this work, N,Bi-codoped CDs (Bi,N-CDs) were synthesized through a one-step hydrothermal method to carbonize the raw materials of 2,4-dinitroaniline and bismuth nitrate. The resulting Bi,N-CDs showed a reduced emission at 490 nm and an enhanced emission at 590 nm in the presence of DOX. The ratio of fluorescence (FL) intensity (F590/F490) was found to be a reliable indicator of DOX concentration, ranging from 0.05 to 30 μM and 40-200 μM, with detection limits (LOD) of 34 and 24 nM, respectively. A ratiometric fluorescence nanoprobe was established for highly selective and sensitive detection of DOX using a specific electrostatic interaction and inner filter effect between Bi,N-CDs and DOX. Meanwhile, Bi,N-CDs exhibited a distinct color change ranging from yellow to orange-red when exposed to DOX, allowing for a colorimetric method to measure DOX levels in the range of 0.05-30 μM, with a detection limit of 169 nM. The probe was triumphantly used to monitor DOX in actual samples via a dual-mode optical sensing strategy. This study contributes to the development of heteroatom-doped CDs and expands their potential applications for detecting biological samples.

Molecularly or atomically precise nanostructures for bio-applications: how far have we come?

A huge variety of nanostructures are promising for biomedical applications, but only a few have been practically applied. Among the various reasons, the limited structural preciseness is a critical one, as it increases the difficulty in product quality control, accurate dosing, and ensuring the repeatability of material performance. Constructing nanoparticles with molecule-like preciseness is becoming a new research field. In this review, we focus on the artificial nanomaterials that can currently be molecularly or atomically precise, including DNA nanostructures, some metallic nanoclusters, dendrimer nanoparticles and carbon nanostructures, describing their syntheses, bio-applications and limitations, in view of up-to-date studies. A perspective on their potential for clinical translation is also given. This review is expected to provide a particular rationale for the future design of nanomedicines.

The detection of the captured circulating tumor cells on the core-shell nanofibrous membrane using hyaluronic acid-functionalized graphene quantum dots

In recent years, cancerous cases have increased remarkably worldwide, and metastasis is the leading cause of death. Therefore, research on the early detection of cancer and metastasis has expanded to aid successful cancer treatment. Here in this paper, at the first step, an electrospun nanofibrous membrane (NFM) with a core-shell structure was fabricated from PCL and HA to achieve cancer cell capturing (about 75% of cells). On the other hand, hyaluronic acid (HA)-functionalized graphene quantum dots (GQDs) were used to detect captured cancer cells on NFM through the changes in photoluminescence intensity. Therefore, CD44 receptor-HA interaction is the main principle used for both entrapment and detection of cancer cells. Results demonstrated the GQD-HA fluorescent intensity of solution decreased through the increase of the captured cancer cell numbers on NFM, which is related to the more adsorption of GQD nanocomposites to the CD44 receptors. In contrast, this intensity for noncancerous cells was steady with any cell concentrations. This difference shows the system's remarkable selectivity and specificity, which can be crucial in fluorescent imaging for accurate cancer diagnosis.

SNAP@CQD as a promising therapeutic vehicle against HCoVs: an overview

This report discusses potential therapies for treating human coronaviruses (HCoVs) and their economic impact. Specifically, we explore therapeutics that can support the body's immune response, including immunoglobulin (Ig)A, IgG and T-cell responses, to inhibit the viral replication cycle and improve respiratory function. We hypothesize that carbon quantum dots conjugated with S-nitroso-N-acetylpenicillamine (SNAP) could be a synergistic alternative cure for treating respiratory injuries caused by HCoV infections. To achieve this, we propose developing aerosol sprays containing SNAP moieties that release nitric oxide and are conjugated onto promising nanostructured materials. These sprays could combat HCoVs by inhibiting viral replication and improving respiratory function. Furthermore, they could potentially provide other benefits, such as providing novel possibilities for nasal vaccines in the future. Teaser: Synergistic effect of carbon quantum dots and S-nitroso-N-acetylpenicillamine (SNAP) could be suggested as an alternative treatment for the respiratory damage caused by HCoV infections that further open possibilities of developing novel nasal vaccines.

Integration of Nanographenes and Organic Chemistry - Toward Nanographene-based Two-Dimensional Materials

Graphene and its relatives have received considerable attention from the fields of physics and chemistry since the isolation of pristine graphene sheets. Nanographenes (NGs) are graphene fragments that are a few to tens of nanometers in diameter. Compared to graphene and its relatives, such as graphene oxides, NGs can be handled more easily, and their large π surface and oxygen functional groups on the edge allow postsynthetic modifications. The study of NGs is gradually shifting from the development of synthetic procedures to postsynthetic modification. From the structural point of view, NGs can be regarded as two-dimensional carbon polymers. Their unique structures and affinity for organic molecules make NGs excellent scaffolds for two-dimensional materials, which are now an important topic in organic and polymer chemistry. In this conceptual article, we introduce the position of NGs from the perspective of two-dimensional substances and briefly summarize both the structural features of NGs and the effects of functionalization on their physical properties. These are valuable when producing reasonable strategies for their postsynthetic modifications.

Hit Multiple Targets with One Arrow: Pb2+ and ClO- Detection by Edge Functionalized Graphene Quantum Dots and Their Applications in Living Cells

Recently, multimodal detection of analytes through a single nanoprobe has become an eminent approach for researchers. Herein a fluorescent nanoprobe, functionalized-GQD (F-GQD), has been designed through edge functionalization of graphene quantum dots (GQDs) by 2,6-diaminopyridine molecules. The fluorescence of F-GQD is quite sensitive to medium pH, making it a suitable pH sensor within the pH range 2-6. Interestingly, F-GQD shows dual sensing of Pb²⁺ and ClO^- by entirely different pathways; Pb²⁺ exhibits fluorescence turn-on performance while ClO^- triggers turn-off fluorescence quenching. The fluorescence enhancement may originate from the Pb²⁺-induced aggregation of the nanodots. The limit of detection (LOD) was also impressive, 1.2 μM and 12.6 nM for Pb²⁺ and ClO^-, respectively. The detailed mechanistic investigations reveal that both dynamic and static quenching effects operate together in the F-GQD-ClO^- system. The dynamic quenching was attributed to the energy migration from F-GQD to ClO^- through hydrogen bonding interaction (static quenching) between the amine group at the F-GQD surface and ClO^-. The F-GQD nanodot reveals excellent sensitivity toward the detection of ClO^- in real samples. Moreover, the F-GQDs also serve as multicolor fluorescent probes for cell imaging; the probe can easily penetrate the cell membrane and successfully detect intracellular ClO^-.

Physical Surface Modification of Carbon-Nanotube/Polydimethylsiloxane Composite Electrodes for High-Sensitivity DNA Detection

The chemical modification of electrode surfaces has attracted significant attention for lowering the limit of detection or for improving the recognition of biomolecules; however, the chemical processes are complex, dangerous, and difficult to control. Therefore, instead of the chemical process, we physically modified the surface of carbon-nanotube/polydimethylsiloxane composite electrodes by dip coating them with functionalized multi-walled carbon nanotubes (F-MWCNTs). These electrodes are used as working electrodes in electrochemistry, where they act as a recognition layer for sequence-specific DNA sensing through π-π interactions. The F-MWCNT-modified electrodes showed a limit of detection of 19.9 fM, which was 1250 times lower than that of pristine carbon/polydimethylsiloxane electrodes in a previous study, with a broad linear range of 1-1000 pM. The physically modified electrode was very stable during the electrode regeneration process after DNA detection. Our method paves the way for utilizing physical modification to significantly lower the limit of detection of a biosensor system as an alternative to chemical processes.

Edge-Functionalized Nanographenes

Nanographenes (NGs) have recently emerged as new carbon materials. Their nanoscale size results in a size-dependent quantum confinement effect, opening the band gap by a few eV. This energy gap allows NGs to be applied as optical materials. This property has attracted researchers across multiple scientific fields. The photophysical properties of NGs can be manipulated by introducing organic groups onto their basal planes and/or into their edges. In addition, the integration of organic functional groups into NGs results in NG-based hybrid materials. These features make the post-synthetic modification of NGs an active research area. As obtainable information on chemically functionalized NGs is limited owing to their nonstoichiometry and structural uncertainty, their structural characterization requires a combination of multiple spectroscopic methods. Therefore, information on the characterization procedures of recently published chemically functionalized NGs is of value for advancing the field of NG-based hybrid materials. The present review focuses on the structural characterization of chemically functionalized NGs. It is hoped that this review will help to advance this field.

Eco-Friendly 1,3-Dipolar Cycloaddition Reactions on Graphene Quantum Dots in Natural Deep Eutectic Solvent

Due to their outstanding physicochemical properties, the next generation of the graphene family-graphene quantum dots (GQDs)-are at the cutting edge of nanotechnology development. GQDs generally possess many hydrophilic functionalities which allow their dispersibility in water but, on the other hand, could interfere with reactions that are mainly performed in organic solvents, as for cycloaddition reactions. We investigated the 1,3-dipolar cycloaddition (1,3-DCA) reactions of the C-ethoxycarbonyl N-methyl nitrone 1a and the newly synthesized C-diethoxyphosphorylpropilidene N-benzyl nitrone 1b with the surface of GQDs, affording the isoxazolidine cycloadducts isox-GQDs 2a and isox-GQDs 2b. Reactions were performed in mild and eco-friendly conditions, through the use of a natural deep eutectic solvent (NADES), free of chloride or any metal ions in its composition, and formed by the zwitterionic trimethylglycine as the -bond acceptor, and glycolic acid as the hydrogen-bond donor. The results reported in this study have for the first time proved the possibility of performing cycloaddition reactions directly to the p-cloud of the GQDs surface. The use of DES for the cycloaddition reactions on GQDs, other than to improve the solubility of reactants, has been shown to bring additional advantages because of the great affinity of these green solvents with aromatic systems.

Graphene Quantum Dots as Flourishing Nanomaterials for Bio-Imaging, Therapy Development, and Micro-Supercapacitors

Graphene quantum dots (GQDs) are considerably a new member of the carbon family and shine amongst other members, thanks to their superior electrochemical, optical, and structural properties as well as biocompatibility features that enable us to engage them in various bioengineering purposes. Especially, the quantum confinement and edge effects are giving GQDs their tremendous character, while their heteroatom doping attributes enable us to specifically and meritoriously tune their prospective characteristics for innumerable operations. Considering the substantial role offered by GQDs in the area of biomedicine and nanoscience, through this review paper, we primarily focus on their applications in bio-imaging, micro-supercapacitors, as well as in therapy development. The size-dependent aspects, functionalization, and particular utilization of the GQDs are discussed in detail with respect to their distinct nano-bio-technological applications.

Chemically Functionalized Two-Dimensional Carbon Materials

Nanographenes (NGs), also known as graphene quantum dots, have recently been developed as nanoscale graphene fragments. These nanocarbon species can be excited with UV light and emit light from the UV-to-visible region. This photoemission has received great attraction across multiple scientific fields. NGs can be produced by cutting off carbon sources or fusing small organic molecules to grow graphitic structures. Furthermore, the organic synthesis of NGs has been intensely studied. Recently, the number of research papers on postsynthetic modification of NGs has gradually increased. Installed organic groups can tune the properties of NGs and provide new functionalities, opening the door for the development of sophisticated carbon-based functional materials. This review sheds light on recent progress in the postsynthetic modification of NGs and provides a brief summary of their production methods.

A co-crystallization induced surface modification strategy with cyanuric acid modulates the bandgap emission of carbon dots

Along the line of offering surface modification strategies to tune emission properties of carbon dots (CDs), a co-crystallization strategy with cyanuric acid (CA) was developed to modulate the bandgap emissions of CDs and produce highly emissive solid composite CD-based materials. The original blue emission of the CDs changed to a green emission of the CDs@CA crystals, which showed a high photoluminescence quantum yield of 62% and room temperature phosphorescence. The CA molecules firmly bonded to the surface of the CDs and cannot be disrupted by polar solvents or temperature stimuli under ambient conditions, which influenced electron transitions of CDs leading to improved luminescence with excellent thermal stability both in solution and solid states.

An easy synthesis of nitrogen and phosphorus co-doped carbon dots as a probe for chloramphenicol

Heteroatom doping in carbon dots (CDs) was found to be an efficient way to regulate the structure of electronic energy levels and enhance the fluorescence characteristics of CDs. Nevertheless, most reported fabrication processes of heteroatom-doped CDs are rigorous and complex. Herein, a facile and novel strategy was developed to rapidly prepare nitrogen and phosphorus co-doped CDs (N,P-CDs) using acetic acid as the carbon source, and arginine, 1,2-ethylenediamine (EDA) and diphosphorus pentoxide as the dopants, respectively. The optical, morphological and structural characterizations of the synthesized N,P-CDs were investigated via UV and photoluminescence spectroscopy, X-ray photoelectron spectroscopy, TEM, and FT-IR spectroscopy. The N,P-CDs display outstanding fluorescence stability under high ionic strength (1.6 M KCl), and long time UV irradiation, indicating that they can be used as favorable candidates for fluorescent probes. The fluorescence of N,P-CDs was selectively quenched by chloramphenicol (CAP) with a short response time. The linear range of the response to CAP was from 0.8 to 70 μM with a limit of detection of 0.36 μM (S/N = 3). Notably, the fabricated N,P-CDs were employed for the highly selective and sensitive detection of CAP in milk samples, indicating their potential applications in biologically related areas.

The spontaneous synthesis of nitrogen and phosphorus co-doped carbon dots was reported, and they were used as a probe for chloramphenicol.

Surface Sensitive Photoluminescence of Carbon Nanodots: Coupling between the Carbonyl Group and π-Electron System

The functional groups and π-electron system of carbon dots (C-dots) were carefully controlled by several innovative chemical methods, without any changes in size, to unravel the relationship between the surface structure and photoluminescence (PL). The results of experiments and theoretical calculations reveal that the PL of C-dots is related to the surface state. The energy gap is determined by the coupling of the π-electron system and carbonyl group, and the quantum yield (QY) is dependent on the carbonyl group. The carbonyl group is the main factor increasing the ratio of nonradiation to radiation recombination, thereby leading to the low QY of C-dots. This work provides a strategy for effectively tuning the structure of C-dots, giving rise to the tunable PL emission wavelength and highly desirable QY, which enables us to further unravel the PL mechanism.

Catalytic oxidation and reduction reactions of hydrophilic carbon clusters with NADH and cytochrome C: features of an electron transport nanozyme

Previously, our group reported on the promising efficacy of poly(ethylene glycol)-hydrophilic carbon clusters (PEG-HCCs) to work as broadly active and high capacity antioxidants in brain ischemia and injury models including stroke and traumatic brain injury coupled with hemorrhagic shock. PEG-HCCs are a carbon nanomaterial derived from harsh oxidation of single wall carbon nanotubes and covalently modified with poly(ethylene glycol). They retain no tubular remnants and are composed of a highly oxidized carbon core functionalized with epoxy, peroxyl, quinone, ketone, carboxylate, and hydroxyl groups. HCCs are the redox active carbon core of PEG-HCCs, which have a broad reduction potential range starting at +200 mV and extending to -2 V. Here we describe a new property of these materials: the ability to catalytically transfer electrons between key surrogates and proteins of the mitochondrial electron transport complex in a catalytic fashion consistent with the concept of a nanozyme. The estimated reduction potential of PEG-HCCs is similar to that of ubiquinone and they enabled the catalytic transfer of electrons from low reduction potential species to higher reduction electron transport complex constituents. PEG-HCCs accelerated the reduction of resazurin (a test indicator of mitochondrial viability) and cytochrome c by NADH and ascorbic acid in solution. Kinetic experiments suggested a transient tertiary complex. Electron paramagnetic resonance demonstrated NADH increased the magnitude of PEG-HCCs' intrinsic radical, which then reduced upon subsequent addition of cytochrome c or resazurin. Deconvolution microscopy identified PEG-HCCs in close proximity to mitochondria after brief incubation with cultured SHSY-5Y human neuroblastoma cells. Compared to methylene blue (MB), considered a prototypical small molecule electron transport shuttle, PEG-HCCs were more protective against toxic effects of hydrogen peroxide in vitro and did not demonstrate impaired cell viability as did MB. PEG-HCCs were protective in vitro when cells were exposed to sodium cyanide, a mitochondrial complex IV poison. Because mitochondria are a major source of free radicals in pathology, we suggest that this newly described nanozyme action helps explain their in vivo efficacy in a range of injury models. These findings may also extend their use to mitochondrial disorders.

White light emitting lanthanide based carbon quantum dots as toxic Cr (VI) and pH sensor

Although, great attention is paid to synthesize fluorescent carbon quantum dots (CQDs) for versatile applications, the field remains still attractive to achieve white light using these nano materials. In the present work, CQDs are synthesized from citric acid and lanthanide ions viz. Europium (Eu) and Terbium (Tb) are doped in CQD moiety to explore superior optical response for multifunctional applications. By proper tuning of excitation wavelength, perfect white light with Commission Internationale de l'Elcairage (CIE) index (0.345, 0.344) is obtained using these Europium Terbium co-doped CQDs (Eu-Tb-CQD). The observed photoluminescence of white light emitting lanthanide based CQD is pH dependent and will be used as a visual pH sensor. These luminescent Eu and Tb co-doped CQDs are also very useful to detect toxic Cr (VI) with excellent selectivity and sensitivity as compared to pure CQDs. It shows high quenching efficiency (∼95%) in presence of only 160 µM Cr(VI). The selectivity and lower detection limit are also obtained as ∼80% and 0.175 µM respectively.

Recent Advances on Graphene Quantum Dots: From Chemistry and Physics to Applications

Graphene quantum dots (GQDs) that are flat 0D nanomaterials have attracted increasing interest because of their exceptional chemicophysical properties and novel applications in energy conversion and storage, electro/photo/chemical catalysis, flexible devices, sensing, display, imaging, and theranostics. The significant advances in the recent years are summarized with comparative and balanced discussion. The differences between GQDs and other nanomaterials, including their nanocarbon cousins, are emphasized, and the unique advantages of GQDs for specific applications are highlighted. The current challenges and outlook of this growing field are also discussed.

Ultrasensitive fluorometric determination of iron(iii) and inositol hexaphosphate in cancerous and bacterial cells by using carbon dots with bright yellow fluorescence

An ON–OFF–ON dual-function fluorescent nanoprobe is described for the trace detection of ferric ions and inositol hexaphosphate (IP6) in living cells.

Dramatic photoluminescence quenching in carbon dots induced by cyclic voltammetry

We disclose an electrochemically activated quenching mechanism that is dominant in certain types of C-dots.

Synthesis of white-light-emitting graphene quantum dots via a one-step reduction and their interfacial characteristics-dependent luminescence properties

Graphene quantum dots (GQDs) have attracted great attention because of their possible applications in various fields.

Insight into the multiple quasi-molecular states in ethylenediamine reduced graphene nanodots

Three cases of quasi-molecular fluorescence of graphene nanodots are examined by EDA reduction and converting blue light into white light through phosphor-based light-emitting diodes.

Modifying the Size of Ultrasound-Induced Liquid-Phase Exfoliated Graphene: From Nanosheets to Nanodots

Ultrasound-induced liquid-phase exfoliation (UILPE) is an established method to produce single- (SLG) and few-layer (FLG) graphene nanosheets starting from graphite as a precursor. In this paper we investigate the effect of the ultrasonication power in the UILPE process carried out in either N-methyl-2-pyrrolidone (NMP) or ortho-dichlorobenzene (o-DCB). Our experimental results reveal that while the SLGs/FLGs concentration of the NMP dispersions is independent of the power of the ultrasonic bath during the UILPE process, in o-DCB it decreases as the ultrasonication power increases. Moreover, the ultrasonication power has a strong influence on the lateral size of the exfoliated SLGs/FLGs nanosheets in o-DCB. In particular, when UILPE is carried out at ∼600 W, we obtain dispersions composed of graphene nanosheets with a lateral size of 180 nm, whereas at higher power (∼1000 W) we produce graphene nanodots (GNDs) with an average diameter of ∼17 nm. The latter nanostructures exhibit a strong and almost excitation-independent photoluminescence emission in the UV/deep-blue region of the electromagnetic spectrum arising from the GNDs' intrinsic states and a less intense (and strongly excitation wavelength dependent) emission in the green/red region attributed to defect states. Notably, we also observe visible emission with near-infrared excitation at 850 and 900 nm, a fingerprint of the presence of up-conversion processes. Overall, our results highlight the crucial importance of the solvent choice for the UILPE process, which under controlled experimental conditions allows the fine-tuning of the morphological properties, such as lateral size and thickness, of the graphene nanosheets toward the realization of luminescent GNDs.

Electrochemical Methods to Study Photoluminescent Carbon Nanodots: Preparation, Photoluminescence Mechanism and Sensing

With unique and tunable photoluminescence (PL) properties, carbon nanodots (CNDs) as a new class of optical tags have been extensively studied. Because of their merits of controllability and sensitivity to the surface of nanomaterials, electrochemical methods have already been adopted to study the intrinsic electronic structures of CNDs. In this review, we mainly deal with the electrochemical researches of CNDs, including preparation, PL mechanism, and biosensing.

Facile labelling of graphene oxide for superior capacitive energy storage and fluorescence applications

The majority of supercapacitor research studies on graphene materials today have been based upon developing electrochemical double-layer capacitors (EDLCs) using reduced graphenes. In contrast, graphene oxide (GO) is often neglected as a supercapacitor candidate due to its low electrical conductivity and surface area. Nonetheless, we present herein a fast (1 h) labelling of GO with o-phenylenediamine (PD) to produce PD-GO, exploiting inherent oxygen groups in creating new functionalities that exhibit capacitive enhancement from pseudo-capacitance. A high specific capacitance of 191 F g(-1) was obtained (at 0.2 A g(-1)), comparable to recent binder-free graphene supercapacitors. The large surface-normalized capacitance of up to 628 μF cm(-2) is also many times greater than the intrinsic capacitance of single-layer graphene (21 μF cm(-2)) as a result of additional pseudo-capacitance. A high capacity retention of ∼85% with each 10-fold increase in current density further indicates excellent rate performance. Hence, this approach in enhancing GO pseudo-capacitance may be similarly feasible as graphene EDLCs. Additionally, PD-GO was also found to exhibit a bright green fluorescence with a 540 nm maximum. The strongest fluorescence intensities arose from the smallest PD-GO fragments, and we attribute the origin to localised sp(2) domains and newly formed phenazine edge groups. The dual enhancement of dissimilar properties such as capacitance and fluorescence emphasizes the continued significance of covalent functionalisation towards tuning of properties in graphene-type materials.

Fluorescence-Converging Carbon Nanodots-Hybridized Silica Nanosphere

Ultrabright carbon nanodots-hybridized silica nanospheres (CSNs) are synthesized through the Stöber process of silane functionalized C-dots. The fluorescence of carbon nanodots is converged intensely. A CSN is about 3800 times brighter than a single-carbon nanodot. Along with their high brightness and low cytotoxicity, CSNs also indicate their potential application in cellular labeling.

Tuning photoluminescence and surface properties of carbon nanodots for chemical sensing

Obtaining tunable photoluminescence (PL) with improved emission properties is crucial for successfully implementing fluorescent carbon nanodots (fCDs) in all practical applications such as multicolour imaging and multiplexed detection by a single excitation wavelength. In this study, we report a facile hydrothermal approach to adjust the PL peaks of fCDs from blue, green to orange by controlling the surface passivation reaction during the synthesis. This is achieved by tuning the passivating reagents in a step-by-step manner. The as-prepared fCDs with narrow size distribution show improved PL properties with different emission wavelengths. Detailed characterization of fCDs using elemental analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy suggested that the surface chemical composition results in this tunable PL emission. Surface passivation significantly alters the surface status, resulting in fCDs with either stronger surface oxidation or N element doping that ultimately determine their PL properties. Further experiments suggested that the as-prepared orange luminescent fCDs (O-fCDs) were sensitive and specific nanosensing platforms towards Fe(3+) determination in a complex biological environment, emphasizing their potential practical applications in clinical and biological fields.

Graphene quantum dots modified ZnO + Cu heterostructure photocatalysts with enhanced photocatalytic performance

GQDs surface modified ZnO + Cu heterostructure photocatalysts was prepared via a simple spin-coating and annealing process, which exhibits enhanced photocatalytic performance.

Tailoring of ammonia reduced graphene oxide into amine functionalized graphene quantum dots through a Hofmann rearrangement

A Hofmann rearrangement tailored and exfoliated multi-layered ammonia reduced graphene oxide into amine functionalized graphene quantum dots.

Origin of tunable photoluminescence from graphene quantum dots synthesized via pulsed laser ablation

A one-step synthesis of graphene quantum dots (GQDs) has been implemented using pulsed laser ablation (PLA) with carboxyl-functionalized multiwalled carbon nanotubes (MWCNTs).

Bright-Yellow-Emissive N-Doped Carbon Dots: Preparation, Cellular Imaging, and Bifunctional Sensing

Fluorescent carbon dots (CDs) have attracted much attention in recent years because of their superior optical and chemical properties, thus demonstrating many potential applications. However, the previously reported CDs mostly show strong emission only in the blue-light region, and the long-wavelength (i.e., yellow- to red-light) emissions are usually very weak. Such a drawback restricts their further applications, particularly in the biology-relevant fields. Herein, a rare example of N-doped CDs that emit bright-yellow fluorescence (i.e., y-CDs) is reported using 1,2,4-triaminobenzene as carbon precursor. The as-prepared y-CDs exhibit not only respectable emission quantum yield and highly optical stabilities but superior biocompatibility and biolabeling potentials. In addition, the y-CDs are found to show an interesting "ON-OFF-ON" three-state emission with the stepwise addition of Ag(+) and cysteine (Cys), indicating potential applications as a bifunctional sensing platform. Thanks to the highly intense emission of y-CDs, the gradual quenching and restoration of their fluorescence with the addition of Ag(+) and further Cys could also be observed with the naked eye. More importantly, the ensemble of the y-CDs and Ag(+) demonstrates practicability for the highly selective and sensitive detection of Cys in human plasma samples with satisfactory results.