Carbon quantum dots from carbonized walnut shells: Structural evolution, fluorescence characteristics, and intracellular bioimaging

Green synthesis of biomass-derived carbon quantum dots for photocatalytic degradation of methylene blue

Water pollution, significantly influenced by the discharge of synthetic dyes from industries, such as textiles, poses a persistent global threat to human health. Among these dyes, methylene blue, particularly prevalent in the textile sector, exacerbates this issue. This study introduces an innovative approach to mitigate water pollution through the synthesis of nanomaterials using biomass-derived carbon quantum dots (CQDs) from grape pomace and watermelon peel. Utilizing the hydrothermal method at temperatures between 80 and 160 °C over periods ranging from 1 to 24 h, CQDs were successfully synthesized. A comprehensive characterization of the CQDs was performed using UV-visible spectroscopy, Fourier-transform infrared spectroscopy, dynamic light scattering, Raman spectroscopy, and luminescence spectroscopy, confirming their high quality. The photocatalytic activity of the CQDs in degrading methylene blue was evaluated under both sunlight and incandescent light irradiation, with measurements taken at 20 min intervals over a 2 h period. The CQDs, with sizes ranging from 1-10 nm, demonstrated notable optical properties, including upconversion and down-conversion luminescence. The results revealed effective photocatalytic degradation of methylene blue under sunlight, highlighting the potential for scalable production of these cost-effective catalytic nanomaterials for synthetic dye degradation.

Synthesis of carbon quantum dots/porous aromatic frameworks (CQDs/PAF-45) composites and their enhanced photocatalytic performance

Modification and functionalization of porous aromatic framework (PAF) materials have emerged as crucial research directions in various fields. In this study, we employed a hydrothermal method to synthesize a carbon quantum dots (CQDs) solution. By loading different amounts of CQDs onto the surface of PAF-45 material through ultrasonic and hydrothermal treatments, we successfully formed CQDs/PAF-45 composite materials. The introduction of CQDs effectively transformed the hydrophobic nature of PAF-45 into a hydrophilic material, thereby overcoming the challenge of achieving efficient contact between PAF catalysts and reactants in aqueous solutions. In the photocatalytic degradation experiments of Rhodamine B (RhB), tetracycline, CQDs/PAF-45 composite materials surpassed that of the pristine PAF-45 material. Notably, the 1 wt% CQDs/PAF-45 composite material exhibited the highest photocatalytic activity, with degradation efficiencies for Rhodamine B, tetracycline, and phenol approximately 1.4 times, 1.5 times and 1.5 times higher than those of the PAF-45 material, respectively.

Carbon quantum dots in bioimaging and biomedicines

Carbon quantum dots (CQDs) are gaining a lot more attention than traditional semiconductor quantum dots owing to their intrinsic fluorescence property, chemical inertness, biocompatibility, non-toxicity, and simple and inexpensive synthetic route of preparation. These properties allow CQDs to be utilized for a broad range of applications in various fields of scientific research including biomedical sciences, particularly in bioimaging and biomedicines. CQDs are a promising choice for advanced nanomaterials research for bioimaging and biomedicines owing to their unique chemical, physical, and optical properties. CQDs doped with hetero atom, or polymer composite materials are extremely advantageous for biochemical, biological, and biomedical applications since they are easy to prepare, biocompatible, and have beneficial properties. This type of CQD is highly useful in phototherapy, gene therapy, medication delivery, and bioimaging. This review explores the applications of CQDs in bioimaging and biomedicine, highlighting recent advancements and future possibilities to increase interest in their numerous advantages for therapeutic applications.

Turning food waste into value-added carbon dots for sustainable food packaging application: A review

Carbon dots (CDs) are a recent addition to the nanocarbon family, encompassing both crystalline and amorphous phases. They have sparked significant research interest due to their unique electrical and optical properties, remarkable biocompatibility, outstanding mechanical characteristics, customizable surface chemistry, and negligible cytotoxicity. Their current applications are mainly limited to flexible photonic and biomedical devices, but they have also garnered attention for their potential use in intelligent packaging. The conversion of food waste into CDs further contributes to the concept of the circular economy. It provides a comprehensive overview of emerging green technologies, energy-saving reactions, and cost-effective starting materials involved in the synthesis of CDs. It also highlights the unique properties of biomass-derived CDs, focusing on their structural performance, cellular toxicity, and functional characteristics. The application of CDs in the food industry, including food packaging, is summarized in a concise manner. This paper sheds light on the current challenges and prospects of utilizing CDs in the packaging industry. It aims to provide researchers with a roadmap to tailor the properties of CDs to suit specific applications in the food industry, particularly in food packaging.

Assessment of biomass-derived carbon dots as highly sensitive and selective templates for the sensing of hazardous ions

Access to safe drinking water and a hygienic living environment are the basic necessities that encourage healthy living. However, the presence of various pollutants (especially toxic heavy metal ions) at high concentrations in water renders water unfit for drinking and domestic use. The presence of high concentrations of heavy-metal ions (e.g., Pb2+, Hg2+, Cr6+, Cd2+, or Cu2+) greater than their permissible limits adversely affects human health, and increases the risk of cancer of the kidneys, liver, skin, and central nervous system. Therefore, their detection in water is crucial. Due to the various benefits of "green"-synthesized carbon-dots (C-dots) over other materials, these materials are potential candidates for sensing of toxic heavy-metal ions in water sources. C-dots are very small carbon-based nanomaterials that show chemical stability, magnificent biocompatibility, excitation wavelength-dependent photoluminescence (PL), water solubility, simple preparation strategies, photoinduced electron transfer, and the opportunity for functionalization. A new family of C-dots called "carbon quantum dots" (CQDs) are fluorescent zero-dimensional carbon nanoparticles of size < 10 nm. The green synthesis of C-dots has numerous advantages over conventional chemical routes, such as utilization of inexpensive and non-poisonous materials, straightforward operations, rapid reactions, and renewable precursors. Natural sources, such as biomass and biomass wastes, are broadly accepted as green precursors for fabricating C-dots because these sources are economical, ecological, and readily/extensively accessible. Two main methods are available for C-dots production: top-down and bottom-up. Herein, this review article discusses the recent advancements in the green fabrication of C-dots: photostability; surface structure and functionalization; potential applications for the sensing of hazardous anions and toxic heavy-metal ions; binding of toxic ions with C-dots; probable mechanistic routes of PL-based sensing of toxic heavy-metal ions. The green production of C-dots and their promising applications in the sensing of hazardous ions discussed herein provides deep insights into the safety of human health and the environment. Nonetheless, this review article provides a resource for the conversion of low-value biomass and biomass waste into valuable materials (i.e., C-dots) for promising sensing applications.

Nanocellulose-Based Passivated-Carbon Quantum Dots (P-CQDs) for Antimicrobial Applications: A Practical Review

Passivated-carbon quantum dots (P-CQDs) have been attracting great interest as an antimicrobial therapy tool due to their bright fluorescence, lack of toxicity, eco-friendly nature, simple synthetic schemes, and possession of photocatalytic functions comparable to those present in traditional nanometric semiconductors. Besides synthetic precursors, CQDs can be synthesized from a plethora of natural resources including microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC). Converting MCC into NCC is performed chemically via the top-down route, while synthesizing CODs from NCC can be performed via the bottom-up route. Due to the good surface charge status with the NCC precursor, we focused in this review on synthesizing CQDs from nanocelluloses (MCC and NCC) since they could become a potential source for fabricating carbon quantum dots that are affected by pyrolysis temperature. There are several P-CQDs synthesized with a wide spectrum of featured properties, namely functionalized carbon quantum dots (F-CQDs) and passivated carbon quantum dots (P-CQDs). There are two different important P-CQDs, namely 2,2'-ethylenedioxy-bis-ethylamine (EDA-CQDs) and 3-ethoxypropylamine (EPA-CQDs), that have achieved desirable results in the antiviral therapy field. Since NoV is the most common dangerous cause of nonbacterial, acute gastroenteritis outbreaks worldwide, this review deals with NoV in detail. The surficial charge status (SCS) of the P-CQDs plays an important role in their interactions with NoVs. The EDA-CQDs were found to be more effective than EPA-CQDs in inhibiting the NoV binding. This difference may be attributed to their SCS as well as the virus surface. EDA-CQDs with surficial terminal amino (-NH₂) groups are positively charged at physiological pH (-NH³⁺), whereas EPA-CQDs with surficial terminal methyl groups (-CH₃) are not charged. Since the NoV particles are negatively charged, they are attracted to the positively charged EDA-CQDs, resulting in enhancing the P-CQDs concentration around the virus particles. The carbon nanotubes (CNTs) were found to be comparable to the P-CQDs in the non-specific binding with NoV capsid proteins, through complementary charges, π-π stacking, and/or hydrophobic interactions.

Carbon Nanodots Memristor: An Emerging Candidate toward Artificial Biosynapse and Human Sensory Perception System

In the era of big data and artificial intelligence (AI), advanced data storage and processing technologies are in urgent demand. The innovative neuromorphic algorithm and hardware based on memristor devices hold a promise to break the von Neumann bottleneck. In recent years, carbon nanodots (CDs) have emerged as a new class of nano-carbon materials, which have attracted widespread attention in the applications of chemical sensors, bioimaging, and memristors. The focus of this review is to summarize the main advances of CDs-based memristors, and their state-of-the-art applications in artificial synapses, neuromorphic computing, and human sensory perception systems. The first step is to systematically introduce the synthetic methods of CDs and their derivatives, providing instructive guidance to prepare high-quality CDs with desired properties. Then, the structure-property relationship and resistive switching mechanism of CDs-based memristors are discussed in depth. The current challenges and prospects of memristor-based artificial synapses and neuromorphic computing are also presented. Moreover, this review outlines some promising application scenarios of CDs-based memristors, including neuromorphic sensors and vision, low-energy quantum computation, and human-machine collaboration.

Facile Synthesis of Multifunctional Carbon Dots from Spent Gromwell Roots and Their Application as Coating Agents

Spent Gromwell root-based multifunctional carbon dots (g-CDs) and sulfur-functionalized g-CDs (g-SCDs) were synthesized using a hydrothermal method. The mean particle size of g-CDs was confirmed to be 9.1 nm by TEM (transmission electron microscopy) analysis. The zeta potentials of g-CDs and g-SCDs were mostly negative with a value of -12.5 mV, indicating their stability in colloidal dispersion. Antioxidant activities were 76.9 ± 1.6% and 58.9 ± 0.8% for g-CDs, and 99.0 ± 0.1% and 62.5 ± 0.5% for g-SCDs by 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging tests, respectively. In addition, the bathochromic shift of g-CDs is observed when their emission peaks appear at a higher wavelength than the excitation peaks. The prepared g-CDs and g-SCDs solutions were used as a coating agent for potato slices. The browning index of the control potato slices increased significantly from 5.0 to 33.5% during 24 to 72 h storage. However, the sample potato slices coated with g-CDs or g-SCDs suppressed the increase in the browning index. In particular, the browning index of the potato slices coated with g-SCDs ranged from 1.4 to 5.5%, whereas the potato slices coated with g-CDs had a browning index ranging from 3.5 to 26.1%. The g-SCDs were more effective in delaying oxidation or browning in foods. The g-CDs and g-SCDs also played a catalytic role in the Rhodamine B dye degradation activity. This activity will be useful in the future to break down toxins and adulterants in food commodities.

Preparation of carbon quantum dots from ionic liquid modified biomass for the detection of Fe3+ and Pd2+ in environmental water

A new type of green carbon quantum dots (ILB-CQDs) was prepared by hydrothermal method using ionic liquid as a modifier and grape skin as carbon source, and was obtained from hydrogen-bonded lattice structure ionic liquid preparation, which makes the CQDs in a ring-like stable structure with a stability period of more than 90 day. There is also the catalytic effect of the ionic liquid on cellulose, which makes the prepared CQDs show good advantages, such as uniform particle size, high quantum yield (26.7%), and very good fluorescence performance. This is a smart material for the selective detection of Fe³⁺ and Pd²⁺. It has a detection limit of 0.001 nM for Fe³⁺ and 0.23 µM for Pd²⁺ in pure water. It has a detection limit of 3.2 nmol/L for Fe³⁺ and 0.36 µmol/L for Pd²⁺ in actual water, both of which meet the requirements of WHO drinking water standards. And there is to achieve more than 90% of water restoration effect.

Current trends in carbon-based quantum dots development from solid wastes and their applications

Urbanization and a massive population boom have immensely increased the solid wastes (SWs) generation and are expected to reach 3.40 billion tons by 2050. In many developed and emerging nations, SWs are prevalent in both major and small cities. As a result, in the current context, the reusability of SWs through various applications has taken on added importance. Carbon-based quantum dots (Cb-QDs) and their many variants are synthesized from SWs in a straightforward and practical method. Cb-QDs are a new type of semiconductor that has attracted the interest of researchers due to their wide range of applications, which include everything from energy storage, chemical sensing, to drug delivery. This review is primarily focused on the conversion of SWs into useful materials, which is an essential aspect of waste management for pollution reduction. In this context, the goal of the current review is to investigate the sustainable synthesis routes of carbon quantum dots (CQDs), graphene quantum dots (GQDs), and graphene oxide quantum dots (GOQDs) from various types SWs. The applications of CQDs, GQDs, and GOQDs in the different areas are also been discussed. Finally, the challenges in implementing the existing synthesis methods and future research directions are highlighted.

Carbon Dots: Opportunities and Challenges in Cancer Therapy

Recently, carbon dots (CDs) have been actively studied and reported for their various properties. In particular, the specific characteristics of carbon dots have been considered as a possible technique for cancer diagnosis and therapy. This is also a cutting-edge technology that offers fresh ideas for treating various disorders. Though carbon dots are still in their infancy and have not yet shown their value to society, their discovery has already resulted in some noteworthy advancements. The application of CDs indicates conversion in natural imaging. Photography using CDs has demonstrated extraordinary appropriateness in bio-imaging, the discovery of novel drugs, the delivery of targeted genes, bio-sensing, photodynamic therapy, and diagnosis. This review seeks to provide a comprehensive understanding of CDs, including their benefits, characteristics, applications, and mode of action. In this overview, many CD design strategies will be highlighted. In addition, we will discuss numerous studies on cytotoxic testing to demonstrate the safety of CDs. The current study will address the production method, mechanism, ongoing research, and application of CDs in cancer diagnosis and therapy.

One-pot synthesis of N-doped carbon dots from microwave-irradiated egg white: application to raspberry ketone assay by photo-induced charge transfer fluorescence sensing

In this article, we designed one-step economic eco-harmonious microwave-assisted procedure to prepare nitrogen-doped carbon dots. We selected egg white as a cheap glycoprotein-based carbon source without the assistance of any chemicals. The synthetic process requires only 3 min during which carbonization and nitrogen doping are realized at the same time. The fabricated carbon dots were characterized for particle size, structure and photoluminescence behaviour. The nanodots were amorphous carbon-rich naturally nitrogen-doped particles with plentiful attached hydrophilic functional groups. They had average particle size 2.98 ± 1.57 nm, emitted strong blue fluorescence and showed excitation-dependant emission behaviour. What is more, the practical use of this system for raspberry ketone determination in commercially available weight loss dietary supplement product is demonstrated successfully. In ethylene glycol medium, the addition of raspberry ketone enhances the emission intensity of the synthesized carbon dots. The effect of reaction time and solvent was investigated. After optimization, the intensity enhancement was linear to the amount of raspberry ketone added to the assay solution in the concentration range of 100–1000 ng/ml, with detection and quantitation limits of 15.10 and 45.45 ng/ml, respectively. The method was validated in accordance to International Conference on Harmonization (ICH) guidelines and further applied to raspberry ketone capsules showing excellent results.

Graphical abstract

Fluorescent Carbon Dots from Food Industry By-Products for Cell Imaging

Herein, following a circular economy approach, we present the synthesis of luminescent carbon dots via the thermal treatment of chestnut and peanut shells, which are abundant carbon-rich food industry by-products. As-synthesized carbon dots have excellent water dispersibility thanks to their negative surface groups, good luminescence, and photo-stability. The excitation-emission behaviour as well as the surface functionalization of these carbon dots can be tuned by changing the carbon source (chestnuts or peanuts) and the dispersing medium (water or ammonium hydroxide solution). Preliminary in vitro biological data proved that the samples are not cytotoxic to fibroblasts and can act as luminescent probes for cellular imaging. In addition, these carbon dots have a pH-dependent luminescence and may, therefore, serve as cellular pH sensors. This work paves the way towards the development of more sustainable carbon dot production for biomedical applications.

Green Carbon Dots: Synthesis, Characterization, Properties and Biomedical Applications

Carbon dots (CDs) are a new category of crystalline, quasi-spherical fluorescence, "zero-dimensional" carbon nanomaterials with a spatial size between 1 nm to 10 nm and have gained widespread attention in recent years. Green CDs are carbon dots synthesised from renewable biomass such as agro-waste, plants or medicinal plants and other organic biomaterials. Plant-mediated synthesis of CDs is a green chemistry approach that connects nanotechnology with the green synthesis of CDs. Notably, CDs made with green technology are economical and far superior to those manufactured with physicochemical methods due to their exclusive benefits, such as being affordable, having high stability, having a simple protocol, and being safer and eco-benign. Green CDs can be synthesized by using ultrasonic strategy, chemical oxidation, carbonization, solvothermal and hydrothermal processes, and microwave irradiation using various plant-based organic resources. CDs made by green technology have diverse applications in biomedical fields such as bioimaging, biosensing and nanomedicine, which are ascribed to their unique properties, including excellent luminescence effect, strong stability and good biocompatibility. This review mainly focuses on green CDs synthesis, characterization techniques, beneficial properties of plant resource-based green CDs and their biomedical applications. This review article also looks at the research gaps and future research directions for the continuous deepening of the exploration of green CDs.

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.

Preparation, Properties, and Application of Lignocellulosic-Based Fluorescent Carbon Dots

Carbon dots (CDs) are a relatively new type of fluorescent carbon material with excellent performance and widespread application. As the most readily available and widely distributed biomass resource, lignocellulosics are a renewable bioresource with great potential. Research into the preparation of CDs with lignocellulose (LC-CDs) has become the focus of numerous researchers. Compared with other carbon sources, lignocellulose is low cost, rich in structural variety, exhibits excellent biocompatibility,^[1] and the structures of CDs prepared by lignin, cellulose, and hemicellulose are similar. This Review summarized research progress in the preparation of CDs from lignocellulosics in recent years and reviewed traditional and new preparation methods, physical and chemical properties, optical properties, and applications of LC-CDs, providing guidance for the formation and improvement of LC-CDs. In addition, the challenges of synthesizing LC-CDs were also highlighted, including the interaction of different lignocellulose components on the formation of LC-CDs and the nucleation and growth mechanism of LC-CDs; from this, current trends and opportunities of LC-CDs were examined, and some research methods for future research were put forward.

Quantum dot synthesis from waste biomass and its applications in energy and bioremediation

Quantum dots (QDs) are getting special attention due to their commendable optical properties and applications. Conventional metal-based QDs have toxicity and non-biodegradability issues, thus it becomes necessary to search for renewable precursor molecules for QDs synthesis. In recent years, biomass-based carbon rich QDs (CQDs) have been introduced which are mainly synthesised via carbonization (pyrolysis and hydrothermal treatment). These CQDs offered higher photostability, biocompatibility, low-toxicity, and easy tunability for physicochemical properties. Exceptional optical properties become a point of attraction for its multifaceted applications in various sectors like fabrication of electrodes and solar cells, conversion of solar energy to electricity, detection of pollutants, designing biosensors, etc. In recent years, a lot of work has been done in this field. This article will summarize these advancements along in a special context to biomass-based QDs and their applications in energy and the environment.

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.

Tunable fluorescent carbon dots from biowaste as fluorescence ink and imaging human normal and cancer cells

Growing global biowaste and its environmental issues challenge the need for converting biowastes into a beneficial product. Among the biowaste, here kiwi fruit (Actinidia Deliciosa) peels are considered for the preparation of carbon dots (CDs). Using a green one-pot hydrothermal-carbonization method, kiwi fruit peels were effectively converted into valuable kiwi fruit peel carbon dots (KFP-CDs). The morphology, physio-chemical and optical properties of as-synthesized KFP-CDs were analyzed using various analytical techniques such as X-ray powder diffraction, Raman spectroscopy, attenuated total reflection-Fourier transform infrared spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Ultraviolet-visible, and fluorescence spectroscopy. The KFP-CDs revealed a homogeneous spherical shape, monodispersed with an average size of 5 nm. The characterization confirms that KFP-CDs have functional groups such as -CN, -COOH, and -OH which are responsible for the easy dispersion of KFP-CDs in aqueous media. Without any preprocessing, KFP-CDs exhibit strong fluorescence upon exposure to UV light. Further, KFP-CDs displayed excitation-dependent fluorescence emission with a good quantum yield of about 18%. Thus by considering the excellent properties of KFP-CDs, KFP-CDs were used as fluorescent ink for drawing and writing without any capping/passivation agent. The pictures and words were instantaneously viewed when exposed to UV light. In addition, KFP-CDs tested for cell imaging in four human cell lines (normal and cancer cells) bestowed excellent biocompatibility and low cytotoxicity, which is important for the safe and long-term development of cellular imaging. The findings imply that KFP-CDs can be utilized as a cell labeling agent for mesenchymal stem cells, breast cancer, and thyroid cancer cells in vitro imaging. Thus, these observations revealed that investigating sustainable resource-based CDs can open up new avenues for tackling environmental issues.

Plant-Based Structures as an Opportunity to Engineer Optical Functions in Next-Generation Light Management

This review addresses the reconstruction of structural plant components (cellulose, lignin, and hemicelluloses) into materials displaying advanced optical properties. The strategies to isolate the main building blocks are discussed, and the effects of fibrillation, fibril alignment, densification, self-assembly, surface-patterning, and compositing are presented considering their role in engineering optical performance. Then, key elements that enable lignocellulosic to be translated into materials that present optical functionality, such as transparency, haze, reflectance, UV-blocking, luminescence, and structural colors, are described. Mapping the optical landscape that is accessible from lignocellulosics is shown as an essential step toward their utilization in smart devices. Advanced materials built from sustainable resources, including those obtained from industrial or agricultural side streams, demonstrate enormous promise in optoelectronics due to their potentially lower cost, while meeting or even exceeding current demands in performance. The requirements are summarized for the production and application of plant-based optically functional materials in different smart material applications and the review is concluded with a perspective about this active field of knowledge.

Natural Carbon Nanodots: Toxicity Assessment and Theranostic Biological Application

This review outlines the methods for preparing carbon dots (CDs) from various natural resources to select the process to produce CDs with the best biological application efficacy. The oxidative activity of CDs mainly involves photo-induced cell damage and the destruction of biofilm matrices through the production of reactive oxygen species (ROS), thereby causing cell auto-apoptosis. Recent research has found that CDs derived from organic carbon sources can treat cancer cells as effectively as conventional drugs without causing damage to normal cells. CDs obtained by heating a natural carbon source inherit properties similar to the carbon source from which they are derived. Importantly, these characteristics can be exploited to perform non-invasive targeted therapy on human cancers, avoiding the harm caused to the human body by conventional treatments. CDs are attractive for large-scale clinical applications. Water, herbs, plants, and probiotics are ideal carbon-containing sources that can be used to synthesize therapeutic and diagnostic CDs that have become the focus of attention due to their excellent light stability, fluorescence, good biocompatibility, and low toxicity. They can be applied as biosensors, bioimaging, diagnosis, and treatment applications. These advantages make CDs attractive for large-scale clinical application, providing new technologies and methods for disease occurrence, diagnosis, and treatment research.

Curauá-derived carbon dots: Fluorescent probes for effective Fe(III) ion detection, cellular labeling and bioimaging

This study reports the generation of curauá-derived carbon dots (C-dots) and their suitability for Fe(III) detection, bioimaging and FACS analysis. C-dots were generated from curauá (Ananas erectifolius) fibers by a facile one-step hydrothermal approach. They exhibited graphite-like structure with a mean diameter of 2.4 nm, high water solubility, high levels of carboxyl and hydroxyl functional groups, excitation-dependent multicolor fluorescence emission (in the range 450 nm - 560 nm) and superior photostability. C-dots were highly selective and effective for the detection of ferric Fe(III) ion in an aqueous medium with a detection limit of 0.77 μM in the linear range of 0-30 μM, a value much lower than the guideline limits proposed by the World Health Organization (WHO). In biological cell systems, C-dots were very well tolerated by B16F1 mouse melanoma and J774.A1 mouse macrophages cell lines, both of which effectively internalized C-dots in their cytoplasmic compartment. Finally, C-dots were effective probes for long-term live cell imaging experiments and multi-channel flow cytometry analysis. Collectively, our findings demonstrate that curauá-derived C-dots serve as versatile and effective natural products for Fe(III) ion sensing, labeling and bioimaging of various cell types. This study adds novel C-dots to the library of carbon-based probes and paves the way towards a sustainable conversion of a most abundant biomass waste into value-added products.

Advances in the Methods for the Synthesis of Carbon Dots and Their Emerging Applications

Cutting-edge technologies are making inroads into new areas and this remarkable progress has been successfully influenced by the tiny level engineering of carbon dots technology, their synthesis advancement and impressive applications in the field of allied sciences. The advances of science and its conjugation with interdisciplinary fields emerged in carbon dots making, their controlled characterization and applications into faster, cheaper as well as more reliable products in various scientific domains. Thus, a new era in nanotechnology has developed into carbon dots technology. The understanding of the generation process, control on making processes and selected applications of carbon dots such as energy storage, environmental monitoring, catalysis, contaminates detections and complex environmental forensics, drug delivery, drug targeting and other biomedical applications, etc., are among the most promising applications of carbon dots and thus it is a prominent area of research today. In this regard, various types of carbon dot nanomaterials such as oxides, their composites and conjugations, etc., have been garnering significant attention due to their remarkable potential in this prominent area of energy, the environment and technology. Thus, the present paper highlights the role and importance of carbon dots, recent advancements in their synthesis methods, properties and emerging applications.

Green Aspects in Molecularly Imprinted Polymers by Biomass Waste Utilization

Molecular Imprinting Polymer (MIP) technology is a technique to design artificial receptors with a predetermined selectivity and specificity for a given analyte, which can be used as ideal materials in various application fields. In the last decades, MIP technology has gained much attention from the scientific world as summarized in several reviews with this topic. Furthermore, green synthesis in chemistry is nowadays one of the essential aspects to be taken into consideration in the development of novel products. In accordance with this feature, the MIP community more recently devoted considerable research and development efforts on eco-friendly processes. Among other materials, biomass waste, which is a big environmental problem because most of it is discarded, can represent a potential sustainable alternative source in green synthesis, which can be addressed to the production of high-value carbon-based materials with different applications. This review aims to focus and explore in detail the recent progress in the use of biomass waste for imprinted polymers preparation. Specifically, different types of biomass waste in MIP preparation will be exploited: chitosan, cellulose, activated carbon, carbon dots, cyclodextrins, and waste extracts, describing the approaches used in the synthesis of MIPs combined with biomass waste derivatives.

Live Cell Imaging With Biocompatible Fluorescent Carbon Quantum Dots Derived From Edible Mushrooms Agaricus bisporus, Pleurotus ostreatus, and Suillus luteus

In the study, fluorescent imaging of live cells was performed using fluorescent carbon quantum dots derived from edible mushrooms species; Agaricus bisporus, Pleurotus ostreatus, and Suillus luteus as a fluorophore agent. Carbon quantum dots were synthesized through a facile and low-cost method based on microwave irradiation of dried mushroom samples in hydrogen peroxide solution under optimized conditions (microwave energy, solution type, duration of microwave treatment, amount of mushroom). Upon purification with centrifugation, microfiltration, and dialysis, the lyophilized carbon quantum dots were identified through UV-visible, fluorescence and FT-IR, X-ray photoelectron spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy, and quantum yield calculation. Cell viability assessment of the carbon quantum dots was evaluated against human epithelial cell line PNT1A using the Alamar Blue Assay. In vitro fluorescence cell imaging studies demonstrated that the carbon dots could dynamically penetrate the cell membrane and nuclear membrane and localize in both the cytoplasm and the nucleus.

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.

Protective Effects of Radix Sophorae Flavescentis Carbonisata-Based Carbon Dots Against Ethanol-Induced Acute Gastric Ulcer in Rats: Anti-Inflammatory and Antioxidant Activities

AIM

To explore the effects of Radix Sophorae Flavescentis carbonisata-based carbon dots (RSFC-CDs) on an ethanol-induced acute gastric ulcer rat model.

METHODS

The structure, optical properties, functional groups and elemental composition of RSFC-CDs synthesized by one-step pyrolysis were characterized. The gastric protective effects of RSFC-CDs were evaluated and confirmed by applying a rat model of ethanol-induced acute gastric ulcers. The underlying mechanisms were investigated through the nuclear factor-kappa B (NF-κB) signalling pathway and oxidative stress.

RESULTS

RSFC-CDs with a diameter ranging from 2-3 nm mainly showed gastric protective effects by reducing the levels of NF-κB, tumour necrosis factor-α (TNF-α), interleukin (IL)-6, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione (GSH), malondialdehyde (MDA) and inducible nitric oxide synthase (iNOS) to inhibit ethanol-induced inflammation and oxidative stress.

CONCLUSION

RSFC-CDs have anti-inflammatory and anti-oxidative effects, making them promising for application in ethanol-induced gastric injury.

Carbon Dots as Nanotherapeutics for Biomedical Application

Carbon nanodots are zero-dimensional spherical allotropes of carbon and are less than 10nm in size (ranging from 2-8nm). Based on their biocompatibility, remarkable water solubility, eco- friendliness, conductivity, desirable optical properties and low toxicity, carbon dots have revolutionized the biomedical field. In addition, they have intrinsic photo-luminesce to facilitate bio-imaging, bio-sensing and theranostics. Carbon dots are also ideal for targeted drug delivery. Through functionalization of their surfaces for attachment of receptor-specific ligands, they ultimately result in improved drug efficacy and a decrease in side-effects. This feature may be ideal for effective chemo-, gene- and antibiotic-therapy. Carbon dots also comply with green chemistry principles with regard to their safe, rapid and eco-friendly synthesis. Carbon dots thus, have significantly enhanced drug delivery and exhibit much promise for future biomedical applications. The purpose of this review is to elucidate the various applications of carbon dots in biomedical fields. In doing so, this review highlights the synthesis, surface functionalization and applicability of biodegradable polymers for the synthesis of carbon dots. It further highlights a myriad of biodegradable, biocompatible and cost-effective polymers that can be utilized for the fabrication of carbon dots. The limitations of these polymers are illustrated as well. Additionally, this review discusses the application of carbon dots in theranostics, chemo-sensing and targeted drug delivery systems. This review also serves to discuss the various properties of carbon dots which allow chemotherapy and gene therapy to be safer and more target-specific, resulting in the reduction of side effects experienced by patients and also the overall increase in patient compliance and quality of life.

A Review of Carbon Dots Produced from Biomass Wastes

The fluorescent carbon dot is a novel type of carbon nanomaterial. In comparison with semiconductor quantum dots and fluorescence organic agents, it possesses significant advantages such as excellent photostability and biocompatibility, low cytotoxicity and easy surface functionalization, which endow it a wide application prospect in fields of bioimaging, chemical sensing, environmental monitoring, disease diagnosis and photocatalysis as well. Biomass waste is a good choice for the production of carbon dots owing to its abundance, wide availability, eco-friendly nature and a source of low cost renewable raw materials such as cellulose, hemicellulose, lignin, carbohydrates and proteins, etc. This paper reviews the main sources of biomass waste, the feasibility and superiority of adopting biomass waste as a carbon source for the synthesis of carbon dots, the synthetic approaches of carbon dots from biomass waste and their applications. The advantages and deficiencies of carbon dots from biomass waste and the major influencing factors on their photoluminescence characteristics are summarized and discussed. The challenges and perspectives in the synthesis of carbon dots from biomass wastes are also briefly outlined.

Preparation of Biomass-Based Carbon Dots with Aggregation Luminescence Enhancement from Hydrogenated Rosin for Biological Imaging and Detection of Fe3

Fluorescent carbon dots (CDs) have numerous important applications, but enhancing the fluorescence emission and overcoming fluorescence quenching are still big challenges. Here, fluorescence-enhanced carbon dots (named hr-CDs) were prepared from sustainable hydrogenated rosin, using a simple hydrothermal method in a water solvent. The hr-CDs were mainly composed of graphitized carbon cores with surface functional groups. With the increase in the concentration to hr-CDs aqueous solutions, the distance between the carbon cores decreased, which resulted in the formation of J aggregates and the enhanced blue fluorescence emission. Even in the solid state, the hr-CDs show fluorescence emission because the surface functional groups could prevent π-π stacking interactions between the carbon cores. The hr-CDs show excellent resistance to photobleaching under intense ultraviolet light (200 mW/cm²). Vibrations and rotations of graphitized carbon core are restricted by low temperature and high viscosity, leading to increased radiative transition and thus increase in fluorescence intensity. The pH value in the range of 3.99-9.87 and anions have little effect on the fluorescence emission of hr-CDs. The fluorescence emission of the hr-CDs was selectively quenched by Fe³⁺ and can thus be used to detect Fe³⁺. The hr-CDs also have good biocompatibility and show the same ability in cell nuclear staining as 4',6-diamidino-2-phenylindole (DAPI).

Green synthesis of Zingiberis rhizoma-based carbon dots attenuates chemical and thermal stimulus pain in mice

Aim: To evaluate the analgesic activity of Zingiberis rhizoma-based carbon dots (ZR-CDs). Materials & methods: Novel ZR-CDs were prepared via a facile, green pyrolysis method. Microstructure, optical and functional group properties were characterized. Acetic acid writhing, hot-plate and tail-immersion tests were performed using mice to evaluate the analgesic activity of ZR-CDs, followed by a preliminary study on the analgesic mechanism. Results: ZR-CDs with a quantum yield of 5.2% had a diameter ranging from 2.23 to 3.77 nm. Remarkable analgesic effect of ZR-CDs was observed against both thermal and chemical stimulus tests, possibly mediated by an opioid-like mechanism and the regulation of 5-hydroxytryptamine levels. Conclusion: ZR-CDs have a promising potential for biomedical application in relieving pain-related diseases.

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

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

Carbon dots derived from lychee waste: Application for Fe3+ ions sensing in real water and multicolor cell imaging of skin melanoma cells

Exploit of biomass as an inexhaustible resource has accepted much more curiosity to the present research world. Herein, a simple, one-step solvothermal action has been used to synthesize an ascendable amount of fluorescent carbon dots (CDs) with an average size of~3.13 nm, from Low-reasonable and green source lychee waste. The excitation/emission maxima of CDs have 365/443 nm with high quantum yield (23.5%). The present ingredient predominantly contained carboxylic acid and hydroxyl group that acted as a passive agent for stabilizing the CDs. The structural and optical properties were evaluated through HRTEM, FTIR, UV-vis, zeta potential, XPS, fluorescence, and fluorescence lifetime experiments. We investigated the manoeuvre of our synthesized CDs as a probe for detection of Fe³⁺ ions in water bodies; This sensing approach showed impressive selectivity and sensitivity towards Fe³⁺ions with LOD 23.6 nM. The sensing mechanism took place through static quenching which was entrenched through fluorescence lifetime measurements. Fe³⁺ ions detection was basically carried out with efficacy in real water. For its lofty Photo-stability, low cytotoxicity and cell viability the probe were substantially applied for bio-imaging experiment i.e. intracellular multi-color cell imaging in skin melanoma cells (A375 cells) with and without Fe³⁺ ions exemplifying its real applications in living cells.

Bottom-up synthesis of nitrogen and oxygen co-decorated carbon quantum dots with enhanced DNA plasmid expression

In this paper, a bottom-up hydrothermal route is reported for the synthesis of oxygen and nitrogen co-decorated carbon quantum dots (CQDs) using ammonium hydrogen citrate (AHC) as a single precursor. DLS data approved the formation of 4.0 nm (average size) CQDs. XRD pattern shows the interlayer spacing (002) of 3.5 Å for CQDs, which is exactly the same as that of crystalline graphite. XPS and FTIR spectra verified the formation of oxygen and nitrogen functional groups on the CQDs surface. Co-decorated carboxyl, hydroxyl and amine groups on the CQDs surfaces make them as promising polyelectrolyte for gene delivery. Toxicity assay showed a survival rate of 70% under different incubation times and up to 500 μg/mL. The highly water-soluble, stable fluorescence and low toxic CQDs increased the gene expression of DNA plasmid in E. coli bacteria 4-fold more than the control group.

Nitrogen-doped carbon quantum dots as an antimicrobial agent against Staphylococcus for the treatment of infected wounds

Antimicrobial resistance is becoming more and more serious and has become a potential hazard to human life and health. The fabrication of some new antibacterial substances against resistant bacteria is demanded. With the wide application and research of carbon nanomaterials, nitrogen-doped carbon quantum dots (NCQDs) were synthesized by a one-step chemical route herein. The particle size of NCQDs in the range of 2-5 nm were characterized by transmission electron microscopy (TEM), atomic force microscopy, and dynamic light scattering. The functional groups and optical properties of NCQDs were investigated by UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Disk-diffusion tests showed that the NCQDs had specific antibacterial activity against Staphylococcus. TEM showed that the NCQDs could destroy the cell structure of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) but could not combat Escherichia coli. The antibacterial mechanism may be that positively charged NCQDs firstly interacted with the negatively charged bacteria, and then specifically anchored on some specific sites on the surface of Staphylococcus. The NCQDs were applied to treat wounds infected with MRSA and showed the same therapeutic effect as vancomycin. Photomicrographs of hematoxylin-eosin-stained histological sections showed that the NCQDs at concentrations effectively killing S. aureus and MRSA caused negligible toxicity to the main rat organs, including heart, liver, spleen, lung, and kidney. Thus, the NCQDs can be developed as a promising antibacterial agent for Staphylococcus. And the NCQDs are likely to treat local infections caused by Staphylococcus clinically, especially S. aureus and MRSA.