Polymers in Carbon Dots: A Review

Orientational Assembly of Carbon Dots-Enabled Electrochemiluminescence Sensors for Ultrasensitive Detection of Halogenated Phenols

Developing simple, sensitive, and miniaturized sensors is crucial for the prevention and control of halogenated phenolic pollutants exposed to the environment. In this work, oriented carbon dot assemblies are developed for the electrochemiluminescence (ECL) sensing of halogenated phenolic pollutants for the first time. Leveraging liquid-liquid phase separation during ternary solution evaporation, carbon dots (C-dots) self-organize into mesoporous structures (o-Cdots) and granular structures (r-Cdots) on the hydrophobic glass carbon surface, enabling immobilized C-dot ECL sensors. Their superior ECL performances are displayed upon cathodic potential scan in 0.1 mol/L pH 7.4 PBS with the coreactant S2O82-. Compared to hydrophilic o-Cdots, hydrophobic r-Cdots exhibit robust ECL. Physical adsorption of halogenated phenols onto the hydrophobic r-Cdot surface significantly elevates the resistance of interfacial charge transfer and disrupts the recombination of intermediate C-dot•- and SO4•- within the r-Cdot ECL, endowing a novel and broad-spectrum sensor development. The r-Cdot-based ECL sensor enables the detection of several typical halogenated phenolic compounds in a wide concentration range from 5 × 10-11 to 5 × 10-7 mol/L. Remarkably, the detection limit for 2-chlorophenol can even reach 10-14 mol/L. The developed ECL sensor also demonstrates outstanding stability and resistance to interference from common ions and natural metabolites in the environment. These peculiarities enable its superior performance in detecting halogenated phenols in lake water and tap water with ideal recoveries at different spike levels. This work offers significant insights into the relationship between C-dot assembly structures and their ECL behaviors, paving the way for the rational design of portable C-dot-based sensors for pollutant detections.

Bioactive Carbon Dots from Clove Residue: Synthesis, Characterization, and Osteogenic Properties

Background/Objectives: Bone regeneration using nanomaterial-based approaches shows promise for treating critical bone defects. However, developing sustainable and cost-effective therapeutic materials remains challenging. This study investigates the osteogenic potential of clove-derived carbon dots (C-CDs) for bone regeneration applications. Methods: C-CDs were synthesized using a green hydrothermal method. The osteogenic potential was evaluated in human bone marrow-derived mesenchymal stem cells (hBM-MSCs) and validated using ectopic bone formation and calvarial defect models. Results: C-CDs demonstrated uniform morphology (~10 nm) with efficient cellular uptake. In vitro studies showed successful osteogenic differentiation through the upregulation of RUNX2, ALP, COL1A1, and BMP-2 mediated by Wnt/β-catenin/GSK3β and BMP signaling pathways. In vivo models have also demonstrated that C-CDs are effective in promoting bone regeneration. Conclusions: These findings establish C-CDs as promising candidates for bone regeneration therapy, offering a sustainable alternative to current treatments. While optimization is needed, their demonstrated osteogenic properties warrant further development for regenerative medicine applications.

Reliability of Multi-Emissive Carbon Quantum Dots for Multiplexing; Assessing the Figures of Merit

Incredible properties of quantum dots (QDs) have once again been acclaimed with this year's (2023) Nobel prize in chemistry. On the other hand, the invention of multicolour molecular imaging of cell surface receptors for tumour diagnosis by Koyama and group has opened up a new era in diagnostics. Among them carbon quantum dots (CQDs) are interesting class of fluorescent nanomaterials, superior in terms of low toxicity, high solubility and biocompatibility along with simple and cost-effective synthesis processes unlike the traditional metal chalcogenide or perovskite quantum dots. Multi emissive fluorescence property of these carbon quantum dots are very useful in multiplex sensing. Their excellent biocompatibility and low toxicity have attracted researchers to use them extensively for biosensing and imaging of multiple analytes at a time. Core state emission from π-domains and surface state emissions of functional groups surrounding CQDs play a major role in achieving the multicolour emissions and this review discusses the various strategies used to achieve desired multi colour emissions, yet preserving their stability, non-interactive emissive states and quantum yields. Their fine tuning via variation in temperature, pH, time, and heteroatom doping has been comprehensively discussed. A thorough history compared to a list of characteristics for creating effective multicolour CQDs will point us in the proper route. This minireview also assesses the electronic band structure of these multicolour CQDs, their stability with respect to multi emissions, photoluminescence quantum yields, approaches employed for tunability of their optical band gaps, and also enhancement of carrier lifetimes, to arrive at conclusions on the reliability of these materials for multiplexing. The mechanisms namely chemical coupling, FRET, On-Off, Ab-antigen interactions involved in sensing mechanisms involving these materials are analysed in depth. Ultimately, the present obstacles and future directions for the use of these CQDs in sensing applications are discussed.

Exploring Carbon Dots: Green Nanomaterials for Unconventional Lasing

In recent years, the progress toward lighting miniaturization is focused on luminescent nanomaterials. Among them, fluorescent carbon dots (CDs) are receiving increasing attention thanks to their astonishing optical properties complemented by their intrinsic biocompatibility and low toxicity. The CDs can be easily dispersed in water, organic solvents or incorporated in polymeric matrices, preserving their emission properties. However, the relationship between their structural and optical properties is still not fully elucidated, motivating a consistent research effort for the comprehension of their features. Nevertheless, CDs demonstrate to be efficient gain materials for lasing, thanks to their high quantum yield (QY), emission tunability in the visible and near infrared (NIR) range, short lifetimes, and high absorption cross section, even if the synthetic reproducibility, the low reaction yield and the spectral width of the emission may limit their effective exploitation. This review summarizes the latest advancements in the investigation of the characteristic properties of CDs that make laser action possible, illustrating optical geometries for lasing and random lasing, both in solution and solid state, and the few currently demonstrated breakthroughs. While the journey toward their effective application is still long, the potential of CD-based laser sources is promising in various technological fields and futuristic perspectives will be discussed.

The Mechanism and Latest Research Progress of Blood-Brain Barrier Breakthrough

The bloodstream and the central nervous system (CNS) are separated by the blood-brain barrier (BBB), an intricate network of blood vessels. Its main role is to regulate the environment within the brain. The primary obstacle for drugs to enter the CNS is the low permeability of the BBB, presenting a significant hurdle in treating brain disorders. In recent years, significant advancements have been made in researching methods to breach the BBB. However, understanding how to penetrate the BBB is essential for researching drug delivery techniques. Therefore, this article reviews the methods and mechanisms for breaking through the BBB, as well as the current research progress on this mechanism.

Jamun Seed-Derived Nitrogen-Doped Carbon Dots: A Novel Microwave-Assisted Synthesis for Ultra-Bright Fluorescence and Mn7+ Detection

For the synthesis of heteroatom-doped carbon nanostructures, biomass is considered as a promising option. Utilizing the microwave-assisted method, we have demonstrated an easy and straightforward one-pot synthesis of nitrogen-doped luminous carbon dots (NCDs) from jamun seed powder and guanidine hydrochloride. Structural and morphological analyses were performed using various analytical techniques. Under ultraviolet light of 315 nm, NCDs emit a bright blue fluorescence, possess a high quantum yield of 26.90%, exhibit strong water dispersion, and demonstrated excellent stability. The average particle size of the NCDs was found to be 7.5±1.2 nm, with a spherical shape. NCDs exhibit high selectivity and sensitivity in fluorescence quenching when exposed to Mn7+ ions. Over a concentration range of 2-30 µM, the fluorescence response (F0/F) shows a linear relationship with Mn7+ concentration, with a detection limit of 0.81 µM. The probe exhibited negligible interference and proved to be effective in accurately quantifying Mn7+ in spiked real-water samples.

Emergence of Quantum Dots as Innovative Tools for Early Diagnosis and Advanced Treatment of Breast Cancer

Quantum dots (QDs) semiconducting nanomaterials, have garnered attention due to their distinctive properties, including small size, high luminescence, and biocompatibility. In the context of triple-negative breast cancer (TNBC), notorious for its resistance to conventional treatments, QDs exhibit promising potential for enhancing diagnostic imaging and providing targeted therapies. This review underscores recent advancements in the utilization of QDs in imaging techniques, such as fluorescence tomography and magnetic resonance imaging, aiming at the early and precise detection of tumors. Emphasis is placed on the significance of QD design, synthesis and functionalization processes as well as their use in innovative strategies for targeted drug delivery, capitalizing on their ability to selectively deliver therapeutic agents to cancer cells. As the research in this field advances rapidly, this review covers a classification of QDs according to their composition, the characterization techniques than can be used to determine their properties and, subsequently, emphasizes recent findings in the field of TNBC-targeting, highlighting the imperative need to address challenges, like potential toxicity or methodologies standardization. Collectively, the findings explored thus far suggest that QDs could pave the way for early diagnosis and effective therapy of TNBC, representing a significant stride toward precise and personalized strategies in treating TNBC.

Efficient chiral hydrogel template based on supramolecular self-assembly driven by chiral carbon dots for circularly polarized luminescence

Since the chiral emission of excited states is observed on carbon dots (CDs), exploration towards the design and synthesis of chiral CDs nanomaterials with circularly polarized luminescence (CPL) properties has been at a brisk pace. In this regard, the "host and guest" co-assembly strategy based on the combination of CDs and chiral templates has been of unique interest recently for its convenient operation, multicolor tunable CPL, and wide application of prepared CDs-composited materials in optoelectronic devices and information encryption. However, the existing chiral templates that match perfectly with chiral CDs exhibiting optical activity both in ground and excited states are rather scarce. In this work, we synthesize the chiral CDs that could induce the spontaneous supramolecular self-assembly of N-(9-fluorenylmethox-ycarbonyl) (Fmoc)-protected glutamic acid to form chiral hydrogels with helical nanostructure. The co-assembled hydrogels show powerful chiral template function, which not only enable chiral CDs with a luminescence dissymmetry factor (glum) up to 10-2, but also have universal chiral transfer to inserted dye molecules, realizing full-color CPL and Förster resonance energy transfer (FRET) CPL as well as the distinction between left and right circularly polarized light. This CPL-active template based on chiral CDs enriches the design scenario of chiral functionalized nanomaterials.

Non-toxic orange carbon dots stimulate photosynthesis and CO2 assimilation in hydroponically cultivated green beans (Phaseolus vulgaris)

Continuous increasing leaf photosynthesis may enhance plant yield. As an evolutionary property, plants use less photosynthetic capacity than is theoretically possible. Plant nanobionics is a bioengineering field that improves plant functions using nanoparticles. We applied orange carbon dots (o-CDs) onto the foliage of green beans (Phaseolus vulgaris ) grown in hydroponics to improve their photosynthetic performance and CO2 assimilation. Photosynthesis parameters, photosynthetic pigments content, total phenolic content (TPC) and antioxidative activity (TAA) were measured. Results show that photosynthetic pigments remained unchanged, while photosynthesis was improved. Both o-CDs concentrations decreased TPC and TAA. The light response curve showed higher CO2 assimilation at both o-CDs concentrations, particularly at lower light intensity. Correlation analysis confirmed increased CO2 binding and assimilation at 1mg L-1 . This study demonstrated the potential of using o-CDs as a safe biostimulator through photosynthesis increase and CO2 assimilation without toxic effects on plants. This may stimulate yield increase that paves the way for their agricultural application.

Carbon Dot Based Carbon Nanoparticles as Potent Antimicrobial, Antiviral, and Anticancer Agents

Antimicrobial and anticancer drugs are widely used due to increasing widespread infectious diseases caused by microorganisms such as bacterial, fungal, viral agents, or cancer cells, which are one of the major causes of mortality globally. Nevertheless, several microorganisms developed resistance to antibiotics as a result of genetic changes that have occurred over an extended period. Carbon-based materials, particularly carbon dots (C-dots), are potential candidates for antibacterial and anticancer nanomaterials due to their low toxicity, ease of synthesis and functionalization, high dispersibility in aqueous conditions, and promising biocompatibility. In this Review, the content is divided into four sections. The first section concentrates on C-dot structures, surface functionalization, and morphology. Following that, we summarize C-dot classifications and preparation methods such as arc discharge, laser ablation, electrochemical oxidation, and so on. The antimicrobial applications of C-dots as antibacterial, antifungal, and antiviral agents both in vivo and in vitro are discussed. Finally, we thoroughly examined the anticancer activity displayed by C-dots.

pH-Dependent Non-Covalent Release of Chemotherapy from Carriers

Although Warburg discovered pH discrepancies between tumor and normal tissues nearly 100 years ago, developing therapies to take advantage of this concept was relatively slow for the first 70 years. During the last 30 years, there has been an exponential increase in the use of pH-dependent strategies for both low molecular weight drugs and nanoparticles. Two frequently discussed approaches are the chemotherapy's release from pH-sensitive covalent linkages of macromolecules or from pH-dependent disruption of charged polymeric nanoparticles. In contrast, pH-dependent non-covalent bonds between the chemotherapy agent and macromolecules have rarely been discussed, yet this underappreciated strategy has great potential. These non-covalent interactions are primarily ionic or hydrogen bonds with supporting roles from hydrophobic bonds. In addition to the facile coupling of the drug with the carrier, these non-covalent interactions may show marked pH dependence. Consistent with pH dependence, many of these drug-loaded carriers showed significant in vitro and, in some cases, striking in vivo activity. In this review, we will focus on pH-sensitive non-covalent bonds, highlighting the release of drugs from diverse carriers such as tetrahedron DNA structures, cyclodextrin, polymeric carriers, and carbon-based quantum particles.

Histamine Recognition by Carbon Dots from Plastic Waste and Development of Cellular Imaging: Experimental and Theoretical Studies

The present work highlights the sustainable approach for the transformation of plastic waste into fluorescent carbon dots (CDs) through carbonization and then they were functionalized with L-cysteine and o-phenylenediamine. CDs which were characterized by different analytical techniques such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are employed to recognize Cu2+, Fe2+, and Hg2+ ions. The results show that the fluorescence emission was considerably quenched, and it is consistent with the interference and Jobs plots. The detection limit was found to be 0.35µM for Cu(II), 1.38 µM for Hg(II), and 0.51µM Fe(III). The interaction of CDs with metal ions enhances the fluorescence intensity detecting histamine successfully. It shows that plastic waste-based CDs can be applied clinically to detect toxic metals and biomolecules. Moreover, the system was employed to develop the cellular images using Saccharomyces cerevisiae cells with the support of a confocal microscope. Furthermore, theoretical studies were performed for the naphthalene layer (AR) as a model for C-dots, then optimized its structure and analyzed by using the molecular orbital. The obtained TD-DFT spectra coincided with experimental spectra for CDs/M2+/histamine systems.

Surficial amino groups coupling induced concentration-dependent fluorescence and fluorescence quantum yield of nitrogen-dopped carbon quantum dots via efficient charge transfer

Modification of surficial functional groups among carbon quantum dots (CQDs) has been considered an efficient approach to regulate the fluorescence emission of CQDs. However, the mechanism of how surficial functional groups affect fluorescence is vague which fundamentally limits the further applications of CQDs. Here we report the concentration-dependent fluorescence and fluorescence quantum yield of nitrogen-dopped carbon quantum dots (N-CQDs). At high concentrations (≥0.188 g/L), fluorescence redshift occurs accompanied with decrease in fluorescence quantum yield. Fluorescence excitation spectra and HOMO-LUMO energy gaps calculations show that energy levels of excited states of N-CQDs are relocated via the coupling of surficial amino groups among N-CQDs. Furthermore, electron density difference maps and broadened fluorescence spectra obtained from both experimental measurement and theoretical calculation further confirm that the coupling of surficial amino groups dominates the fluorescence property and verify the formation of charge-transfer state of N-CQDs complex at high concentrations which provides pathways for efficient charge transfer. Given that charge-transfer state induced fluorescence loss and fluorescence spectra broadening are the typical characteristics of organic molecules, CQDs exhibit the optical properties of both quantum dots and organic molecules.

An Overview on Carbon Quantum Dots Optical and Chemical Features

Carbon quantum dots are the materials of a new era with astonishing properties such as high photoluminescence, chemical tuneability and high biocompatibility. Since their discovery, carbon quantum dots have been described as nanometric high-fluorescent carbon nanoparticles, but this definition has become weaker year after year. Nowadays, the classification and the physical explanation of carbon quantum dots optical properties and their chemical structure remain matter of debate. In this review, we provide a clear discussion on these points, providing a starting point for the rationalization of their classification and a comprehensive view on the optical and chemical features of carbon quantum dots.

High performance carbon dots based prodrug Platform: Image-Guided photodynamic and chemotherapy with On-Demand drug release upon laser irradiation

The design of therapeutic nanoplatforms based on fluorescent carbon dots (CDs) has become a viable strategy because of their aqueous solubility, biocompatibility, and ease of further functionalization. By doping various heteroatoms into pristine CDs structures, we synthesized N-, Cl-, and S-doped CDs (NClS/CDs), as well as Se-, N-, and Cl-doped CDs (NClSe/CDs) with superior optoelectronic properties using rapid and straightforward microwave heating. The quantum efficiencies of these NClS/CDs and NClSe/CDs were enhanced to 30.7 % and 42.9 %, respectively, compared to those of undoped CDs (0.66 %). Owing to their better light absorption properties, NClS/CDs efficiently produced reactive oxygen species (ROS) under 532 nm laser irradiation for photodynamic therapy (PDT). Considering the ROS generation and surface carrier abilities of NClS/CDs, we designed the loading of camptothecin (CPT) drug via a thioketal linker (TL), resulting in h/CDs@CPT nanovesicles (NVs) with a drug-loading efficiency of 46.5 %. Under laser irradiation in an acidic environment, ROS-triggered CPT release was observed, with 50.2 % of CPT released following the breakdown of the ROS-sensitive TL. In vitro cellular studies revealed that h/CDs@CPT NVs possessed minimal cytotoxicity toward HeLa and 4 T1 cancer cells, despite the high clinical efficacy of PDT and ROS-induced chemotherapeutic response under laser treatment. Confocal microscopy of HeLa and 4 T1 cells revealed that h/CDs@CPT NVs produced red-emissive photographs for potential cancer cell detection. Therefore, our study presents an image-guided PDT and chemotherapeutic platform based on h/CDs@CPT NVs, which will be an attractive candidate for future cancer treatment.

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.

Carbon Quantum Dots: Synthesis, Structure, Properties, and Catalytic Applications for Organic Synthesis

Carbon quantum dots (CQDs), also known as carbon dots (CDs), are novel zero-dimensional fluorescent carbon-based nanomaterials. CQDs have attracted enormous attention around the world because of their excellent optical properties as well as water solubility, biocompatibility, low toxicity, eco-friendliness, and simple synthesis routes. CQDs have numerous applications in bioimaging, biosensing, chemical sensing, nanomedicine, solar cells, drug delivery, and light-emitting diodes. In this review paper, the structure of CQDs, their physical and chemical properties, their synthesis approach, and their application as a catalyst in the synthesis of multisubstituted 4H pyran, in azide-alkyne cycloadditions, in the degradation of levofloxacin, in the selective oxidation of alcohols to aldehydes, in the removal of Rhodamine B, as H-bond catalysis in Aldol condensations, in cyclohexane oxidation, in intrinsic peroxidase-mimetic enzyme activity, in the selective oxidation of amines and alcohols, and in the ring opening of epoxides are discussed. Finally, we also discuss the future challenges in this research field. We hope this review paper will open a new channel for the application of CQDs as a catalyst in organic synthesis.

One-Pot Synthesis of Dual Color-Emitting CDs: Numerical and Experimental Optimization towards White LEDs

Carbon Dots (CDs) are fluorescent carbon-based nanoparticles that have attracted increasing attention in recent years as environment-friendly and cost-effective fluorophores. An application that can benefit from CDs in a relatively short-term perspective is the fabrication of color-converting materials in phosphor-converted white LEDs (WLEDs). In this work we present a one-pot solvothermal synthesis of polymer-passivated CDs that show a dual emission band (in the green and in the red regions) upon blue light excitation. A purposely designed numerical approach enables evaluating how the spectroscopic properties of such CDs can be profitable for application in WLEDs emulating daylight characteristics. Subsequently, we fabricate nanocomposite coatings based on the dual color-emitting CDs via solution-based strategies, and we compare their color-converting properties with those of the simulated ones to finally accomplish white light emission. The combined numerical and experimental approach can find a general use to reduce the number of experimental trial-and-error steps required for optimization of CD optical properties for lighting application.

Structure-Property-Activity Relationships in Carbon Dots

Carbon dots (CDs) are one of the most versatile nanomaterials discovered in the 21st century. They possess many properties and thus hold potentials in diverse applications. While an increasing amount of attention has been given to these novel nanoparticles, the broad scientific community is actively engaged in exploring their limits. Recent studies on the fractionalization and assembly of CDs further push the limits beyond just CDs and demonstrate that CDs are both a mixture of heterogeneous fractions and promising building blocks for assembly of large carbon-based materials. With CDs moving forward toward both microscopic and macroscopic levels, a good understanding of the structure-property-activity relationships is essential to forecasting the future of CDs. Hence, in this Perspective, structure-property-activity relationships are highlighted based on the repeatedly verified findings in CDs. In addition, studies on CD fractionalization and assembly are briefly summarized in this Perspective. Eventually, these structure-property-activity relationships and controllability are essential for the development of CDs with desired properties for various applications especially in photochemistry, electrochemistry, nanomedicine, and surface chemistry. In summary, in our opinion, since 2004 until the present, history has witnessed a great development of CDs although there is still some room for more studies. Also, considering many attractive properties, structure-property-activity relationships, and the building block nature of CDs, a variety of carbon-based materials of interest can be constructed from CDs with control. They can help reduce blind trials in the development of carbon-based materials, which is of great significance in materials science, chemistry, and any fields related to the applications.

Applications of Carbon Dots for the Treatment of Alzheimer's Disease

There are currently approximately 50 million victims of Alzheimer's disease (AD) worldwide. The exact cause of the disease is unknown at this time, but amyloid plaques and neurofibrillary tangles in the brain are hallmarks of the disease. Current drug treatments for AD may slow the progression of the disease and improve the quality of life of patients, but they are often only minimally effective and are not cures. A major obstacle to developing and delivering more effective drug therapies is the presence of the blood-brain barrier (BBB), which prevents many compounds with therapeutic potential from reaching the central nervous system. Nanotechnology may provide a solution to this problem. Among the medical nanomaterials currently being studied, carbon dots (CDs) have attracted widespread attention because of their ability to cross the BBB, non-toxicity, and potential for drug/gene delivery.

An insight into embryogenesis interruption by carbon nitride dots: can they be nucleobase analogs?

The carbon nitride dot (CND) is an emerging carbon-based nanomaterial. It possesses rich surface functional moieties and a carbon nitride core. Spectroscopic data have demonstrated the analogy between CNDs and cytosine/uracil. Recently, it was found that CNDs could interrupt the normal embryogenesis of zebrafish. Modifying CNDs with various nucleobases, especially cytosine, further decreased embryo viability and increased deformities. Physicochemical property characterization demonstrated that adenine- and cytosine-incorporated CNDs are similar but different from guanine-, thymine- and uracil-incorporated CNDs in many properties, morphology, and structure. To investigate the embryogenesis interruption at the cellular level, bare and different nucleobase-incorporated CNDs were applied to normal and cancerous cell lines. A dose-dependent decline was observed in the viability of normal and cancerous cells incubated with cytosine-incorporated CNDs, which matched results from the zebrafish embryogenesis experiment. In addition, nucleobase-incorporated CNDs were observed to enter cell nuclei, demonstrating a possibility of CND-DNA interactions. CNDs modified by complementary nucleobases could bind each other via hydrogen bonds, which suggests nucleobase-incorporated CNDs can potentially bind the complementary nucleobases in a DNA double helix. Nonetheless, neither bare nor nucleobase-incorporated CNDs were observed to intervene in the amplification of the zebrafish polymerase-alpha 1 gene in quantitative polymerase chain reactions. Thus, in conclusion, the embryogenesis interruption by bare and nucleobase-incorporated CNDs might not be a consequence of CND-DNA interactions during DNA replication. Instead, CND-Ca²⁺ interactions offer a plausible mechanism that hindered cell proliferation and zebrafish embryogenesis originating from disturbed Ca²⁺ homeostasis by CNDs. Eventually, the hypothesis that raw or nucleobase-incorporated CNDs can be nucleobase analogs proved to be invalid.

Potential Development of N-Doped Carbon Dots and Metal-Oxide Carbon Dot Composites for Chemical and Biosensing

Among carbon-based nanomaterials, carbon dots (CDs) have received a surge of interest in recent years due to their attractive features such as tunable photoluminescence, cost effectiveness, nontoxic renewable resources, quick and direct reactions, chemical and superior water solubility, good cell-membrane permeability, and simple operation. CDs and their composites have a large potential for sensing contaminants present in physical systems such as water resources as well as biological systems. Tuning the properties of CDs is a very important subject. This review discusses in detail heteroatom doping (N-doped CDs, N-CDs) and the formation of metal-based CD nanocomposites using a combination of matrices, such as metals and metal oxides. The properties of N-CDs and metal-based CDs nanocomposites, their syntheses, and applications in both chemical sensing and biosensing are reviewed.

Self-assembly of carbon nanodots induced by liquid-liquid phase separation in a surface microdroplet

Evaporating a sessile drop of ternary solutions containing one hydrotrope (such as ethanol) and two immiscible fluids exhibiting fascinating phase separation behaviours, has opened up a new pathway for controlled nanomaterial assembly. In this work, we studied the influence of liquid-liquid phase separation (LLPS) on the assembly of carbon nanodots (C-dots), 2 nm fluorescent carbon-based nanomaterials with high water solubility. Through self-evaporation of a micro-sized droplet containing ethanol, C-dot-water solution and different oils on a hydrophobic surface, C-dots rearranged into film, porous and granular structures by controlling the properties of oil component in the tenary droplet. Vapour pressure, solubility, surface tension and compositions of the oil components were investigated systematically for their impacts on the evaporation process of C-dot-laden droplets. By using confocal microscopy, we clearly revealed that C-dot assembly was triggered by LLPS in these four oil-water-ethanol ternary systems. The corresponding evaporation and assembly processes were unravelled to be determined by how the ternary solutions pass through the liquid-liquid equilibrium curves in the phase diagrams during evaporation. Our findings deepen the understanding of phase-separation behaviours for nanomaterial assembly as well as provide a novel, simple, and well-controlled approach for depositing different C-dot based nanostructures onto surfaces, which will benefit a wide range of practical applications in the fields of energy, environment and health.

Spontaneously sp2-Carbonized Fluorescent Polyamides as a Probe Material for Bioimaging

Spontaneously sp²-carbonized polyamides (PA1, PA2) were prepared via Knoevenagel-type side reactions of malonyl moieties under mild conditions in the polycondensation of dicarbonyl chloride and diamine. Both polymers were soluble in water and emissive in the visible region, and the fluorescence (FL) intensity and the maximum wavelength were highly dependent on the excitation wavelength and the pH. Their chemical structures and FL origin were clarified by performing various spectroscopic analyses. π*-π transition was assumed to be allowed in an enol form based on the conjugated structure formed by the side reaction; this was responsible for its pH dependency and high FL quantum efficiency. In particular, PA2, which comprises the tertiary amide linkage, showed quick endocytosis, low cytotoxicity, excellent biocompatibility, and exclusively stained lysosomes with the lowest intracellular pH. These results will help in understanding the origin of the FL emission of carbonized nanomaterials and exploring more advanced functions in the field of bioimaging.

Polymer Composites with Quantum Dots as Potential Electrode Materials for Supercapacitors Application: A Review

Owing to the nanometer size range, Quantum Dots (QDs) have exhibited unique physical and chemical properties which are favourable for different applications. Especially, due to their quantum confinement effect, excellent optoelectronic characteristics is been observed. This considerable progress has not only uplifted the singular usage of QDs, but also encouraged to prepare various hybrid materials to achieve superior efficiency by eliminating certain shortcomings. Such issues can be overcome by compositing QDs with polymers. Via employing polymer composite with QDs (PQDs) for supercapacitor applications, adequate conductivity, stability, excellent energy density, and better specific capacitance is been achieved which we have elaborately discussed in this review. Researchers have already explored various types of polymer nanocomposite with different QDs such as carbonaceous QDs, transition metal oxide/sulphide QDs etc. as electrode material for supercapacitor application. Synthesis, application outcome, benefits, and drawbacks of these are explained to portray a better understanding. From the existing studies it is clearly confirmed that with using PQDs electrical conductivity, electrochemical reactivity, and the charge accumulation on the surface have prominently been improved which effected the fabricated supercapacitor device performance. More comprehensive fundamentals and observations are explained in the current review which indicates their promising scopes in upcoming times.

Carbon dot composites for bioapplications: a review

Carbon dots (CDs) have received extensive attention in the last decade for their excellent optical, chemical and biological properties. In recent years, CD composites have also received significant attention due to their ability to improve the intrinsic properties and expand the application scope of CDs. In this article, the synthesis processes of four types of CD composites (metal-CD, nonmetallic inorganics-CD, and organics-CD as well as multi-components-CD composites) are systematically summarized first. Then the recent advancements in the bioapplications (bioimaging, drug delivery and biosensing) of these composites are also highlighted and discussed. Last, the current challenges and future trends of CD composites in biomedical fields are discussed.

Green synthesis of fluorescent carbon dots with antibacterial activity and their application in Atlantic mackerel (Scomber scombrus) storage

Antimicrobial materials prepared from natural products could provide new ways to preserve seafood and extend the shelf life. Herein, four kinds of fluorescent carbon dots were prepared using onion, ginger, garlic, and fish through one-step hydrothermal synthesis. The four prepared carbon dots were nearly spherical and nanosized, with amorphous structure, neutral charge and good water dispersibility. The onion and garlic carbon dots contained more sulfur elements than the ginger and fish carbon dots. Interestingly, the onion carbon dots exhibited the best antibacterial activity against Pseudomonas fragi with good stability over a wide pH range. In addition, the onion carbon dots also exhibited antimicrobial activity against representative Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. The minimum inhibitory concentration (MIC) and the minimal bactericidal concentration (MBC) of onion carbon dots against Pseudomonas fragi were 2 mg mL^-1 and 4 mg mL^-1, respectively. The integrity of the cell wall and the cell membrane were damaged for Pseudomonas fragi, and the extracellular alkaline phosphatase (AKP) and ATP activity also increased after exposure to the onion carbon dots, thus leading to a decrease in the cell viability and alteration of the cellular morphology for Pseudomonas fragi. Furthermore, the preservation effect of onion carbon dots on Atlantic mackerel evaluated by storage at 4 °C revealed that the onion carbon dots significantly reduced drip loss, total volatile basic nitrogen (TVB-N) value and total viable counts (TVC) value, and extended the shelf life of Atlantic mackerel by 2 days. This finding suggests that onion carbon dots have potential to be applied as a bacteriostatic agent for aquatic products.

Intrinsic Blue Fluorescence of 2.0G PAMAM-DCM Polymer Dots and Its Applications for Fe3+ Sensing

A typical and environment-friendly fluorescent polyamine-amine (PAMAM) features good compatibility and unique surface modification, while it is restricted by a low fluorescence property performance and an unclear fluorescence mechanism. In this work, we prepared blue fluorescent PAMAM polymer dots (PDs) via a simple hydrothermal method based on dichloromethane (DCM) and 2.0G PAMAM. The quantum yield achieved was 32.1%, which was 25 times stronger than that of 2.0G PAMAM due to the lone-pair electron leap of the amine groups, the aggregation of carbonyl groups, as well as the crosslinking induced by DCM inside the PAMAM. In addition, the fluorescent 2.0G PAMAM-DCM PDs show a great Fe3+ sensing property with the detection limit of 56.6 nM, which is much lower than the safety limits (5.36 μM) in drinking water, indicating its great potential for Fe3+ detection in aqueous media.

Preparation of carbon quantum dots/polyaniline nanocomposite: Towards highly sensitive detection of picric acid

Carbon quantum dots/polyaniline (CQDs/PANI) nanocomposite was successfully prepared by in-situ polymerization of aniline. CQDs were synthesized hydrothermally from gelatin with a diameter size of 4.2 nm and a 17% quantum yield. FTIR, UV-vis absorption, fluorescence spectrophotometer, XRD, TEM, XPS and lifetime decay were used to characterize the obtained nanocomposite. The formation of PANI revealed a high quenching effect on CQDs where the TEM images showed that the formed CQDs were greatly embedded in PANI matrix. In this study, CQDs/PANI nanocomposite was used for the detection of picric acid (PA) in the range 0.37-1.42 μM with a low detection limit (LOD) of 0.056 μM. The prepared sensor showed good enhancement and sensitivity towards PA in comparison to pristine CQDs and other nanostructured materials. The mechanism of PA detection has been studied where it was observed that PA is electrostatically interacted to the nanocomposite through - OH group of PA and the protonated PANI salt formed in CQDs/PANI nanocomposite by fluorescence resonance energy transfer applications. The proposed CQDs/PANI sensor was then utilized in real water samples and successfully determined the different amounts of PA spiked into tap water.

Carbon Dot/Polymer Composites with Various Precursors and Their Sensing Applications: A Review

Carbon dots (CDs) have generated much interest because of their significant fluorescence (FL) properties, extraordinary photophysical attributes, and long-term colloidal stability. CDs have been regarded as a prospective carbon nanomaterial for various sensing applications because of their low toxicity, strong and broad optical absorption, high chemical stability, rapid transfer properties, and easy modification. To improve their functionality, CD/polymer composites have been developed by integrating polymers into CDs. CD/polymer composites have diversified because of their easy preparation and applications in sensing, optoelectronics, semiconductors, molecular delivery, and various commercial fields. Many review articles are available regarding the preparation and applications of CDs. Some review articles describing the production and multiple applications of the composites are available. However, no such article has focused on the types of precursors, optical properties, coating characteristics, and specific sensing applications of CD/polymer composites. This review aimed to highlight and summarize the current progress of CD/polymer composites in the last five years (2017–2021). First, we overview the precursors used for deriving CDs and CD/polymer composites, synthesis methods for preparing CDs and CD/polymer composites, and the optical properties (absorbance, FL, emission color, and quantum yield) and coating characteristics of the composites. Most carbon and polymer precursors were dominated by synthetic precursors, with citric acid and polyvinyl alcohol widely utilized as carbon and polymer precursors, respectively. Hydrothermal treatment for CDs and interfacial polymerization for CDs/polymers were frequently performed. The optical properties of CDs and CD/polymer composites were almost identical, denoting that the optical characters of CDs were well-maintained in the composites. Then, the chemical, biological, and physical sensing applications of CD/polymer composites are categorized and discussed. The CD/polymer composites showed good performance as chemical, biological, and physical sensors for numerous targets based on FL quenching efficiency. Finally, remaining challenges and future perspectives for CD/polymer composites are provided.

Molecular dynamics insight into viscosity reduction of hydrolysed polyacrylamide by using carbon quantum dots

Hydrolysed polyacrylamide (HPAM) is widely used in many industrial fields where its rheological properties play a leading role. Recent discovery of the reduction of HPAM's viscosity by adding carbon quantum dots (CQDs), however, is controversial to the established theories. By using all atom molecular dynamics simulation with an OPLS-AA force field, this study aims to provide detailed molecular insight into such an uncommon phenomenon. The dynamic structures of the HPAM chain in the presence or absence of CQDs were clearly captured from the molecular aspect. The results reveal that the adsorption of CQD reduces the gyration radius of the HPAM chain, and it is the corresponding hydration effect that leads to the reduction of the viscosity. The amide rather than the carboxylate group along the HPAM chain is dominant in terms of the interaction with the CQDs, and the driven atoms depend on the surface where the polymer is adsorbed.

Photosynthesis Enhancement in Maize via Nontoxic Orange Carbon Dots

The sustained increase in leaf photosynthesis may increase crop yield. Due to many limitations, plants use much less photosynthetic capacity than is theoretically possible. Plant nanobionics investigates nanoparticle application in living plants, which improves certain plant functions. We synthesized and tested nontoxic orange carbon dots (o-CDs) for the photosynthetic efficiency increase in maize (Zea mays L.). We applied o-CDs foliarly or by adding to the growth solution. The photosynthetic parameters and content of photosynthetic pigments were recorded. The total phenolic content (TPC) and total antioxidant activity (TAA) were measured to monitor the plant antioxidant response to o-CDs. The photosynthetic parameters' values were higher for foliar than for solution application. The 1 mg/L o-CDs applied foliarly and 5 mg/L in solution increased photosynthetic parameters in leaves. The o-CDs raised photosynthetic pigments. The TAA and TPC results indicate reduced antioxidant activity in the plant organs more exposed to o-CDs, depending on the way of application.

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.

Recent Developments in Carbon Quantum Dots: Properties, Fabrication Techniques, and Bio-Applications

Carbon dots have gained tremendous interest attributable to their unique features. Two approaches are involved in the fabrication of quantum dots (Top-down and Bottom-up). Most of the synthesis methods are usually multistep, required harsh conditions, and costly carbon sources that may have a toxic effect, therefore green synthesis is more preferable. Herein, the current review presents the green synthesis of carbon quantum dots (CQDs) and graphene quantum dots (GQDs) that having a wide range of potential applications in bio-sensing, cellular imaging, and drug delivery. However, some drawbacks and limitations are still unclear. Other biomedical and biotechnological applications are also highlighted.

Polymerization-Driven Photoluminescence in Alkanolamine-Based C-Dots

Carbonized polymer dots (CPDs), a peculiar type of carbon dots, show extremely high quantum yields, making them very attractive nanostructures for application in optics and biophotonics. The origin of the strong photoluminescence of CPDs resides in a complicated interplay of several radiative mechanisms. To understand the correlation between CPD processing and properties, the early stage formation of carbonized polymer dots has been studied. In the synthesis, citric acid monohydrate and 2-amino-2-(hydroxymethyl)propane-1,3-diol have been thermally degraded at 180 °C. The use of an oil bath instead of a more traditional hydrothermal reactor has allowed the CPD properties to be monitored at different reactions times. Transmission electron microscopy, time-resolved photoluminescence, nuclear magnetic resonance, infrared, and Raman spectroscopy have revealed the formation of polymeric species with amide and ester bonds. Quantum chemistry calculations have been employed to investigate the origin of CPD electronic transitions. At short reaction times, amorphous C-dots with 80 % quantum yield, have been obtained.

Recent advances in the modification of carbon-based quantum dots for biomedical applications

Carbon-based quantum dots (CDs) are mainly divided into two sub-groups; carbon quantum dots (CQDs) and graphene quantum dots (GQDs), which exhibit outstanding photoluminescence (PL) properties, low toxicity, superior biocompatibility and facile functionalization. Regarding these features, they have been promising candidates for biomedical science and engineering applications. In this work, we reviewed the efforts made to modify these zero-dimensional nano-materials to obtain the best properties for bio-imaging, drug and gene delivery, cancer therapy, and bio-sensor applications. Five main surface modification techniques with outstanding results are investigated, including doping, surface functionalization, polymer capping, nano-composite and core-shell structures, and the drawbacks and challenges in each of these methods are discussed.

Lignin-derived red-emitting carbon dots for colorimetric and sensitive fluorometric detection of water in organic solvents

Water contained in organic solvents or products in chemical industries, as contaminants, poses an adverse risk in chemical reaction, life or environmental safety. However, conventional fluorescent water sensing suffers from drawbacks, including limited organic solvents, narrow linear range, lack of visual detection, single detection strategy, and others. Herein, a novel type of red-emitting carbon dots (RCDs) has been created via one-step solvothermal synthesis based on biomass (e.g., lignin) as the carbon source and p-phenylenediamine (PPD) as the nitrogen source. Colorimetric and fluorometric detection of water in organic solvents has been demonstrated. The RCDs showed excitation-independent photoluminescence (PL) in different solvents and solvatochromic behavior, red in water, orange in ethanol, yellow in N,N-dimethyl formamide (DMF), and green in acetone. Remarkably, detection of water content in six organic solvents, including polar solvents (ethanol, acetone, dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), and DMF) and apolar solvent (ether), was performed. With increasing water content in solvents, emission colors changed from green to red, or yellow to red, offering qualitative sensing of water. Furthermore, a broad linear detection range (10-90%), low limits of detection (LOD) (e.g., 0.36% for ethanol and 0.082% for acetone), and good generality for various organic solvent systems were realized. Particularly, dual sensing strategies, including PL quenching and shift with water in various solvents, were achieved simultaneously, showing great potential for the development of advanced optical sensors with high performance.

Sonochemical synthesis of carbon dots, mechanism, effect of parameters, and catalytic, energy, biomedical and tissue engineering applications

Carbon-based nanomaterials are gaining more and more interest because of their wide range of applications. Carbon dots (CDs) have shown exclusive interest due to unique and novel physicochemical, optical, electrical, and biological properties. Since their discovery, CDs became a promising material for wide range of research applications from energy to biomedical and tissue engineering applications. At same time several new methods have been developed for the synthesis of CDs. Compared to many of these methods, the sonochemical preparation is a green method with advantages such as facile, mild experimental conditions, green energy sources, and feasibility to formulate CDs and doped CDs with controlled physicochemical properties and lower toxicity. In the last five years, the sonochemically synthesized CDs were extensively studied in a wide range of applications. In this review, we discussed the sonochemical assisted synthesis of CDs, doped CDs and their nanocomposites. In addition to the synthetic route, we will discuss the effect of various experimental parameters on the physicochemical properties of CDs; and their applications in different research areas such as bioimaging, drug delivery, catalysis, antibacterial, polymerization, neural tissue engineering, dye absorption, ointments, electronic devices, lithium ion batteries, and supercapacitors. This review concludes with further research directions to be explored for the applications of sonochemical synthesized CDs.