Carbon dots: synthesis, properties and biomedical applications

Okra peel-derived nitrogen-doped carbon dots: Eco-friendly synthesis and multi-functional applications in heavy metal ion sensing, nitro compound detection and environmental remediation

The present study explores the kitchen waste okra peels derived synthesis of nitrogen doped carbon dots (N-CDs) via simple carbonization followed by reflux method. The synthesized N-CDs was characterized using, TEM, XPS, FTIR, XRD, Raman, UV-Visible and Fluorescence Spectroscopy. The N-CDs emits bright blue emission at 420 nm with 12 % of quantum yield as well as it follows excitation dependent emission. Further, the N-CDs were employed as a fluorescence sensor for detection of hazardous metal ions and nitro compounds. Among various metal ions and nitro compounds, the N-CDs shows fluorescence quenching response towards Cr6+, and Mn7+ metal ions as well as 4-nitroaniline (4-NA) and picric acid (PA) with significant hypsochromic and bathochromic shift for Mn7+, 4-NA and PA respectively. The developed fluorescent probe shows relatively low limit of detection (LOD) of 1.46 µg/mL, 1.05 µg/mL, 2.1 µg/mL and 2.2 µg/mL for the above analytes respectively. The N-CDs did not show any significant interference with coexisting ions and successfully applied for real water sample analysis. In addition, circular economy approach was employed for adsorption of dyes by reactivating leftover waste carbon residue which was obtained after reflux. Thus, the kitchen waste valorization and circular economy approach based N-CDs have potential applications in the field of detection of emerging pollutants, and environmental remediation.

The novel up/down-conversion dual-emission carbon dots for dual-channel ratiometric fluorescence detection of pH and Cu2

Up/down-conversion dual-emission carbon dots (U/D-CDs) are rare and have potential in analytical sensing. Herein, a kind of novel U/D-CDs was prepared successfully by a one-step solvothermal method. The prepared U/D-CDs exhibited similar dual-emission behaviors at excitation wavelengths of 300 nm and 680 nm, respectively. In addition, U/D-CDs displayed good photostability and salt-resistance. Due to the protonation-deprotonation, U/D-CDs showed strong pH dependence in the pH range of 2.0-8.0, which developed an up/down-conversion dual-channel ratiometric fluorescence (FL) probe of pH. The FL intensity of U/D-CDs can be effectively quenched by Cu2+ through the static quenching effect. Meanwhile, an obvious color change from yellow-green to blue can be observed under ultraviolet light with the increase of Cu2+ concentration. The up/down-conversion dual-channel ratiometric fluorescence sensor can be used for the visual sensing of pH and Cu2+, which also eliminates background signals and improves its accuracy and selectivity in complex samples.

Quantum dots for bone tissue engineering

In confronting the global prevalence of bone-related disorders, bone tissue engineering (BTE) has developed into a critical discipline, seeking innovative materials to revolutionize treatment paradigms. Quantum dots (QDs), nanoscale semiconductor particles with tunable optical properties, are at the cutting edge of improving bone regeneration. This comprehensive review delves into the multifaceted roles that QDs play within the realm of BTE, emphasizing their potential to not only revolutionize imaging but also to osteogenesis, drug delivery, antimicrobial strategies and phototherapy. The customizable nature of QDs, attributed to their size-dependent optical and electronic properties, has been leveraged to develop precise imaging modalities, enabling the visualization of bone growth and scaffold integration at an unprecedented resolution. Their nanoscopic scale facilitates targeted drug delivery systems, ensuring the localized release of therapeutics. QDs also possess the potential to combat infections at bone defect sites, preventing and improving bacterial infections. Additionally, they can be used in phototherapy to stimulate important bone repair processes and work well with the immune system to improve the overall healing environment. In combination with current trendy artificial intelligence (AI) technology, the development of bone organoids can also be combined with QDs. While QDs demonstrate considerable promise in BTE, the transition from laboratory research to clinical application is fraught with challenges. Concerns regarding the biocompatibility, long-term stability of QDs within the biological environment, and the cost-effectiveness of their production pose significant hurdles to their clinical adoption. This review summarizes the potential of QDs in BTE and highlights the challenges that lie ahead. By overcoming these obstacles, more effective, efficient, and personalized bone regeneration strategies will emerge, offering new hope for patients suffering from debilitating bone diseases.

Development of an accurate hand-held sensing platform for nitrite detection based on nitrogen-doped carbon dots

As is well known, excessive nitrite can seriously pollute the environment and can harm human health. Although existing methods can be used to determine nitrite content, they still have some drawbacks, such as relatively complicated operation and expensive equipment. Herein, a hand-held sensing platform (HSP) for NO2- determination was developed. First, ammonia-rich nitrogen-doped carbon dots with orange-yellow emission were designed and synthesised, which were suitable as fluorescent probes because of their good optical properties and stability. Then, the HSP based on fluorescence using photoelectric conversion technology was designed and manufactured using three-dimensional printing technology. Under optimum conditions, the voltage (V/V0) of the proposed HSP showed good linearity for NO2- detection in the range of 10-500 μM, with a detection limit of 1.95 μM. This portable sensor showed good stability, accuracy and reliability in detecting actual water and meat samples, which may ensure food safety in practical applications. Moreover, the HSP is compact, portable and easily assembled and is suitable for on-site real-time detection, which shows great application potential and prospects.

Unlocking the potential of carbon dots in agriculture using data-driven approaches

The utilization of carbon dots (CDs) in agriculture to enhance plant growth has gained significant attention, but the data remains fractionated. Systematically integrating existing data is needed to identify the factors driving the interactions between CDs and plants and strategically guide future research. Articles reporting on CDs and their effects on plants were searched based on inclusion and exclusion criteria, resulting in the collection of 71 articles comprising a total of 2564 data points. The meta-analysis reveals that the soil and foliar application of red-emitting bio-derived CDs at a low concentration (<10 ppm) leads to the most beneficial effects on plant growth. Random forest and gradient boosting algorithms revealed that the size and dose of CDs were important factors in predicting plant responses across multiple aspects (CDs properties, plant properties, environmental factors, and experimental conditions). Specifically, smaller sizes are more favorable to growth indicators (GI) below 6 nm, nutrient and quality (NuQ) at 3-6 nm, photosynthesis (PSN) below 7 nm, and antioxidant responses (AR) below 5 nm. Overall, our analysis of existing data suggests that CDs applications can significantly improve plant responses (GI, NuQ, PSN, and AR) by 10-39 %. To unlock the full potential of CDs, customized synthesis techniques should be employed to meet the specific requirements of different crops and climate condition. For example, we recommend the synthesis of small CDs (<7 nm) with emission peak values falling within the range of 405-475 and 610-670 nm to enhance plant growth. The global prediction of plant responses to CDs application in future scenarios have shown significant improvements ranging from 17 to 58 %, suggesting that CDs have widespread applicability. This novel understanding of the impact of CDs on plant response provides valuable insights for optimizing the application of these nanomaterials in agriculture.

Advances on carbon nanomaterials and their applications in medical diagnosis and drug delivery

Carbon nanomaterials are indispensable due to their unique properties of high electrical conductivity, mechanical strength and thermal stability, which makes them important nanomaterials in biomedical applications and waste management. Limitations of conventional nanomaterials, such as limited surface area, difficulty in fine tuning electrical or thermal properties and poor dispersibility, calls for the development of advanced nanomaterials to overcome such limitations. Commonly, carbon nanomaterials were synthesized by chemical vapor deposition (CVD), laser ablation or arc discharge methods. The advancement in these techniques yielded monodispersed carbon nanotubes (CNTs) and allows p-type and n-type doping to enhance its electrical and catalytic activities. The functionalized CNTs showed exceptional mechanical, electrical and thermal conductivity (3500-5000 W/mK) properties. On the other hand, carbon quantum dots (CQDs) exhibit strong photoluminescence properties with high quantum yield. Carbon nanohorns are another fascinating type of nanomaterial that exhibit a unique structure with high surface area and excellent adsorption properties. These carbon nanomaterials could improve waste management by adsorbing pollutants from water and soil, enabling precise environmental monitoring, while enhancing wastewater treatment and drug delivery systems. Herein, we have discussed the potentials of all these carbon nanomaterials in the context of innovative waste management solutions, fostering cleaner environments and healthier ecosystems for diverse biomedical applications such as biosensing, drug delivery, and environmental monitoring.

Alfalfa biomass as a green source for the synthesis of N,S-CDs via microwave treatment. Application as a nano sensor for nifuroxazide in formulations and gastric juice

BACKGROUND

Researchers have investigated different techniques for synthesis of carbon dots. These techniques include Arc discharge, laser ablation, oxidation, water/solvothermal, and chemical vapor deposition. However, these techniques suffer from some limitations like the utilization of gaseous charged particles, high current, high temperature, potent oxidizing agents, non-environmentally friendly carbon sources, and the generation of uneven particle size. Therefore, there was a significant demand for the adoption of a new technology that combines the environmentally friendly aspects of both bio-based carbon sourcing and synthesis technique.

RESULTS

Medicago sativa L (alfalfa)-derived N, S-CDs have been successfully synthesized via microwave irradiation. The N,S-CDs exhibit strong fluorescence (λex/em of 320/420 nm) with fluorescence quantum yield of 2.2 % and high-water solubility. The produced N,S-CDs were characterized using TEM, EDX, Zeta potential analysis, IR, UV-Visible, and fluorescence spectroscopy. The average diameter of the produced N, S-CDs was 4.01 ± 1.2 nm, and the Zeta potential was -24.5 ± 6.63 mv. The stability of the produced nano sensors was also confirmed over wide pH range, long time, and in presence of different ions. The synthesized N, S-CDs were employed to quantify the antibacterial drug, nifuroxazide (NFZ), by fluorescence quenching via inner filter effect mechanism. The method was linear with NFZ concentration ranging from 1.0 to 30.0 μM. LOD and LOQ were 0.16 and 0.49 μM, respectively. The method was applied to quantify NFZ in simulated gastric juice (SGJ) with % recovery 99.59 ± 1.4 in addition to pharmaceutical dosage forms with % recovery 98.75 ± 0.61 for Antinal Capsules® and 100.63 ± 1.54 for Antinal suspension®. The Method validation was performed in compliance with the criteria outlined by ICH.

SIGNIFICANCE AND NOVELTY

The suggested approach primarily centers on the first-time use of alfalfa, an ecologically sustainable source of dopped-CDs, and a cost-effective synthesis technique via microwave irradiation, which is characterized by low energy consumption, minimized reaction time, and the ability to control the size of the produced CDs. This is in line with the growing global recognition of the implementation of green analytical chemistry principles.

Enhanced pyrophosphate detection: Utilizing oPD-derived carbon dots and Fe3+ interactions in a paper strip biosensor

The development of portable, cost-effective, and straightforward DNA biosensors holds immense importance in various fields, including healthcare, environmental monitoring, and food safety. This study contributes to the objective by introducing an innovative approach for synthesizing carbon dots (Cdots) with high quantum yield (QY) and remarkable selectivity for Fe3+ ions. Utilizing o-phenylenediamine as a precursor, the study achieved a straightforward and environmentally friendly synthesis method, enabling the efficient detachment of metal ions from the Cdot surface upon introducing pyrophosphate (PPi). The presence of surface hydroxyl and amino groups facilitated specific Fe3+ recognition. Employing D-optimal response surface methodology, the study optimized Cdot synthesis parameters, identifying temperature and heating time as critical factors influencing QY. Statistical analysis confirmed the model's reliability, predicting maximum QY of 48.8 % with minimal deviation from experimental results. Characterization studies revealed the amorphous nature of Cdots through HR-TEM, XRD, and FTIR analysis. Furthermore, the proposed LAMP/PPi biosensing technique demonstrated higher sensitivity, specificity, and repeatability, with negligible interference from common anions and efficacy across varying pH levels. The limit of detection (LOD) of 0.079 (±0.01) μM and the detection range of 0.1 μM-2 mM underscore the biosensor's practical utility. This study highlights a promising direction for developing paper-based LAMP/PPi biosensors with potential diagnostics and environmental monitoring applications. Significantly, the biosensing technique is applicable to any DNA amplification method generating pyrophosphate (PPi) as a by-product.

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.

Biomass-derived carbon dots with pharmacological activity for biomedicine: Recent advances and future perspectives

Carbon dots (CDs), a type of nanoparticle with excellent optical properties, good biocompatibility, and small size, are finding increasing application across the fields of biology and biomedicine. In recent years, biomass-derived CDs with pharmacological activity (BP-CDs) derived from herbal medicines (HMs), HMs extracts and other natural products with demonstrated pharmaceutical activity have attracted particular attention. Herein, we review recent advances in the development of BP-CDs, covering the selection of biomass precursors, different methods used for the synthesis of BP-CDs from natural sources, and the purification of BP-CDs. Additionally, we summarize the many remarkable properties of BP-CDs including optical properties, biocompatibility and pharmaceutical efficacy. Moreover, the antibacterial, antiviral, anticancer, biosensing, bioimaging, and other applications of BP-CDs are reviewed. Thereafter, we discuss the advantages and disadvantages of BP-CDs and Western drug-derived CDs, highlighting the excellent performance of BP-CDs. Finally, based on the current state of research on BP-CDs, we suggest several aspects of BP-CDs that urgently need to be addressed and identify directions that should be pursued in the future. This comprehensive review on BP-CDs is expected to guide the precise design, preparation, and future development of BP-CDs, thereby advancing the application of BP-CDs in biomedicine.

Heavy atom-induced quenching of fluorescent organosilicon nanoparticles for iodide sensing and total antioxidant capacity assessment

We present a novel approach for iodide sensing based on the heavy-atom effect to quench the green fluorescent emission of organosilicon nanoparticles (OSiNPs). The fluorescence of OSiNPs was significantly quenched (up to 97.4% quenching efficiency) in the presence of iodide ions (I-) through oxidation by hydrogen peroxide. Therefore, OSiNPs can serve as a fluorescent probe to detect I- with high selectivity and sensitivity. The highly selective response is attributed to the hydrophilic surface enabling good dispersion in aqueous solutions and the lipophilic core allowing the generated liposoluble I2 to approach and quench the fluorescence of OSiNPs. The linear working range for I- was from 0 to 50 μM, with a detection limit of 0.1 μM. We successfully applied this nanosensor to determine iodine content in edible salt. Furthermore, the fluorescent OSiNPs can be utilized for the determination of total antioxidant capacity (TAC). Antioxidants reduce I2 to I-, and the extent of quenching by the remaining I2 on the OSiNPs indicates the TAC level. The responses to ascorbic acid, pyrogallic acid, and glutathione were investigated, and the detection limit for ascorbic acid was as low as 0.03 μM. It was applied to the determination of TAC in ascorbic acid tablets and fruit juices, indicating the potential application of the OSiNP-based I2 sensing technique in the field of food analysis.

Carbon Dots in Photodynamic/Photothermal Antimicrobial Therapy

Antimicrobial resistance (AMR) presents an escalating global challenge as conventional antibiotic treatments become less effective. In response, photodynamic therapy (PDT) and photothermal therapy (PTT) have emerged as promising alternatives. While rooted in ancient practices, these methods have evolved with modern innovations, particularly through the integration of lasers, refining their efficacy. PDT harnesses photosensitizers to generate reactive oxygen species (ROS), which are detrimental to microbial cells, whereas PTT relies on heat to induce cellular damage. The key to their effectiveness lies in the utilization of photosensitizers, especially when integrated into nano- or micron-scale supports, which amplify ROS production and enhance antimicrobial activity. Over the last decade, carbon dots (CDs) have emerged as a highly promising nanomaterial, attracting increasing attention owing to their distinctive properties and versatile applications, including PDT and PTT. They can not only function as photosensitizers, but also synergistically combine with other photosensitizers to enhance overall efficacy. This review explores the recent advancements in CDs, underscoring their significance and potential in reshaping advanced antimicrobial therapeutics.

Polyacrylic Acid-Coated Selenium-Doped Carbon Dots Inhibit Ferroptosis to Alleviate Chemotherapy-Associated Acute Kidney Injury

Cisplatin-associated acute kidney injury (AKI) is a severe clinical syndrome that significantly restricts the chemotherapeutic application of cisplatin in cancer patients. Ferroptosis, a newly characterized programmed cell death driven by the lethal accumulation of lipid peroxidation, is widely reported to be involved in the pathogenesis of cisplatin-associated AKI. Targeted inhibition of ferroptosis holds great promise for developing novel therapeutics to alleviate AKI. Unfortunately, current ferroptosis inhibitors possess low bioavailability or perform non-specific accumulation in the body, making them inefficient in alleviating cisplatin-associated AKI or inadvertently reducing the anti-tumor efficacy of cisplatin, thus not suitable for clinical application. In this study, a novel selenium nanomaterial, polyacrylic acid-coated selenium-doped carbon dots (SeCD), is rationally developed. SeCD exhibits high biocompatibility and specifically accumulates in the kidney. Administration of SeCD effectively scavenges broad-spectrum reactive oxygen species and significantly facilitates GPX4 expression by releasing selenium, resulting in strong mitigation of ferroptosis in renal tubular epithelial cells and substantial alleviation of cisplatin-associated AKI, without compromising the chemotherapeutic efficacy of cisplatin. This study highlights a novel and promising therapeutic approach for the clinical prevention of AKI in cancer patients undergoing cisplatin chemotherapy.

Exploring the potential of eco-friendly carbon dots in monitoring and remediation of environmental pollutants

Photoluminescent carbon dots (CDs) have garnered significant interest owing to their distinctive optical and electronic properties. In contrast to semiconductor quantum dots, which incorporated toxic elements in their composition, CDs have emerged as a promising alternative, rendering them suitable for both environmental and biological applications. CDs exhibit astonishing features, including photoluminescence, charge transfer, quantum confinement effect, and biocompatibility. Recently, CDs derived from green sources have drawn a lot of attention due to their strong photostability, reduced toxicity, better biocompatibility, enhanced fluorescence, and simplicity. These attributes have shown great promise in the areas of LED technology, bioimaging, photocatalysis, drug delivery, biosensing, and antibacterial activity. In contrast, this review offers a comprehensive overview of various green sources utilized to produce CDs and methodologies, along with their merits and demerits, with a notable emphasis on physiochemical properties. Additionally, the paper provides insight into the bibliometric analysis and recent advancements of CDs in sensing, photocatalysis, and antibacterial activity. In this field, extensive research is underway, and a total of 7,438 articles have been identified. Among these, 4242 articles are dedicated to sensing applications, while 1518 and 1678 focus on adsorption and degradation. Carbon dots demonstrate exceptional sensing capabilities within the nanomolar range with a selectivity of up to 95% for pollutants. They exhibit excellent degradation efficiency exceeding 90% within 10-130 min and possess an adsorption capacity from 100 to 800 mg/g. These fascinating qualities render them suitable for diverse applications.

Recent Advances in Nanomedicine for Ocular Fundus Neovascularization Disease Management

As an indispensable part of the human sensory system, visual acuity may be impaired and even develop into irreversible blindness due to various ocular pathologies. Among ocular diseases, fundus neovascularization diseases (FNDs) are prominent etiologies of visual impairment worldwide. Intravitreal injection of anti-vascular endothelial growth factor drugs remains the primary therapy but is hurdled by common complications and incomplete potency. To renovate the current therapeutic modalities, nanomedicine emerged as the times required, which is endowed with advanced capabilities, able to fulfill the effective ocular fundus drug delivery and achieve precise drug release control, thus further improving the therapeutic effect. This review provides a comprehensive summary of advances in nanomedicine for FND management from state-of-the-art studies. First, the current therapeutic modalities for FNDs are thoroughly introduced, focusing on the key challenges of ocular fundus drug delivery. Second, nanocarriers are comprehensively reviewed for ocular posterior drug delivery based on the nanostructures: polymer-based nanocarriers, lipid-based nanocarriers, and inorganic nanoparticles. Thirdly, the characteristics of the fundus microenvironment, their pathological changes during FNDs, and corresponding strategies for constructing smart nanocarriers are elaborated. Furthermore, the challenges and prospects of nanomedicine for FND management are thoroughly discussed.

Pulsed Laser Manufactured Heteroatom Doped Carbon Dots via Heterocyclic Aromatic Hydrocarbons for Improved Tribology Performance

Traditional laser-assisted method (top-down synthesis strategy) is applied in the preparation of carbon dots (CDs) by cutting larger carbon materials, which requires harsh conditions, and the size distribution of the CDs is seldom monodisperse. In this work, heteroatom-doped CDs, represented by N,S co-doped CDs (N,S-CDs), can be prepared successfully by pulsed laser irradiation of heterocyclic aromatic hydrocarbons-based small molecule compound solution. The friction coefficient (COF) of base oil PAO decreases from 0.650 to 0.093, and the wear volume reduces by 92.0% accompanied by 1 wt.% N,S-CDs addition, while the load-bearing capacity is improved from 100 to 950 N. The excellent lubrication performance is mainly attributed to the formation of a robust tribofilm via a tribochemical reaction between N,S-CDs and friction pairs, and the N,S-CDs can play a mending effect and polishing effect for worn surfaces. Furthermore, the lubricant containing heteroatom doped CDs are capable of being prepared in situ via pulsed laser irradiation of heterocyclic aromatic hydrocarbons in base oil, which can avoid the redispersed problem of nano-additive in base oil to maintain long-term dispersion, with COF of 0.103 and low wear volume ≈1.99 × 105 µm3 (76.9% reduction) even after standing for 9 months.

Application of Engineered Nanomaterials as Nanocatalysts in Catalytic Ozonation: A Review

Given the growing scarcity of water and the continuous increase in emerging pollutants detected in water bodies, there is an imperative need to develop new, more effective, and sustainable treatments for wastewater. Advanced oxidation processes (AOPs) are considered a competitive technology for water treatment. Specifically, ozonation has received notable attention as a promising approach for degrading organic pollutants in wastewater. However, different groups of pollutants are hardly degradable via single ozonation. With continuous development, it has been shown that using engineered nanomaterials as nanocatalysts in catalytic ozonation can increase efficiency by turning this process into a low-selective AOP for pollutant degradation. Nanocatalysts promote ozone decomposition and form active free radicals responsible for increasing the degradation and mineralization of pollutants. This work reviews the performances of different nanomaterials as homogeneous and heterogeneous nanocatalysts in catalytic ozonation. This review focuses on applying metal- and carbon-based engineered nanomaterials as nanocatalysts in catalytic ozonation and on identifying the main future directions for using this type of AOP toward wastewater treatment.

El Hamd M, Alshehri S, Helmy MI. Bioinspired Carbon Dots-Based Fluorescent Sensor for the Selective Determination of a Potent Anti-Inflammatory Drug in the Presence of Its Photodegradation Products

Herein, we synthesized biogenic carbon dots (CDs) with blue-shifted maximum excitation (λex/λem of 320/404 nm) from largely wasted tangerine seeds for the first time via a one-step hydrothermal method. The biogenic CDs exhibit a maximum excitation wavelength that overlaps with the absorption spectrum of ketorolac tromethamine (KETO) at 320 nm. The developed CDs serve as a turn-off fluorescent probe via an inner filter effect (IFE) quenching mechanism. The resulting CDs have high quantum yield (QY) (39% ± 2.89%, n = 5) and exhibited great performance toward KETO over a concentration range of 0.50-16.00 μg/mL with a limit of detection (LOD) = 0.17 μg/mL. The nanoprobe achieved a high % recovery in assaying KETO in tablet dosage form and had not been significantly affected by various interferents including co-formulated and co-administered drugs. The nanoprobe shows selectivity toward KETO, even in the presence of its photocatalytic degradation products. It can effectively investigate the elimination of KETO from aquatic systems and test its stability in pharmaceutical preparations. The developed nanoprobe underwent a comprehensive evaluation of its environmental impact using analytical eco-scale (AES), complex green analytical procedure index (Complex GAPI), and the Analytical GREEnness calculator (AGREE). The sustainability of the developed nano sensor was assessed and compared to the reported metal-based quantum dots probe for KETO using the innovative RGB 12 model, considering 12 white analytical chemistry (WAC) perspectives.

Metal-doped carbon dots for biomedical applications: From design to implementation

Carbon dots (CDs), as a new kind of fluorescent nanomaterials, show great potential for application in several fields due to their unique nano-size effect, easy surface functionalization, controllable photoluminescence, and excellent biocompatibility. Conventional preparation methods for CDs typically involve top-down and bottom-up approaches. Doping is a major step forward in CDs design methodology. Chemical doping includes both non-metal and metal doping, in which non-metal doping is an effective strategy for modulating the fluorescence properties of CDs and improving photocatalytic performance in several areas. In recent years, Metal-doped CDs have aroused the interest of academics as a promising nano-doping technique. This approach has led to improvements in the physicochemical and optical properties of CDs by altering their electron density distribution and bandgap capacity. Additionally, the issues of metal toxicity and utilization have been addressed to a large extent. In this review, we categorize metals into two major groups: transition group metals and rare-earth group metals, and an overview of recent advances in biomedical applications of these two categories, respectively. Meanwhile, the prospects and the challenges of metal-doped CDs for biomedical applications are reviewed and concluded. The aim of this paper is to break through the existing deficiencies of metal-doped CDs and fully exploit their potential. I believe that this review will broaden the insight into the synthesis and biomedical applications of metal-doped CDs.

Heteroatoms-doped carbon dots as dual probes for heavy metal detection

The utilization of l-cysteine in hydrothermal synthesis allows for the manufacture of carbon dots (CDs) that are doped with heteroatoms including oxygen, nitrogen, and sulfur (N, S, O-doped CDs). CDs have a particle size ranging from 1 to 3 nm, with an average particle size of 2.5 nm. N, S, and O-doped CDs display a blue fluorescence emission at a wavelength of 425 nm. It shows a reliance on the specific excitation wavelength between 320 and 500 nm. It has a selective quenching effect specifically with copper (Cu2+) ions when exposed to interactions with heavy metal ions, as compared to other metal ions. The assay has a limit of detection (LOD) of 2 μM and exhibits a linear correlation within the concentration range of 10-33.3 μM. The fluorescence mechanism was elucidated by employing various analytical techniques, such as transmission electron microscopy (TEM), high-resolution TEM , UV-Vis spectroscopy, zeta potential analysis, and conductometry. An analysis of the data reveals that Cu2+ ions exhibit a strong attraction to the external surface of N, S, and O-doped CDs, leading to the formation of aggregates. N, S, and O-doped CDs can be also used as probes for electrochemical investigations utilizing cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) to produce Nyquist and Bode plots. The electrochemical results offer substantiation for the interaction between Cu2+ ions and N, S, and O-doped CDs. Zero-dimensional carbon nanomaterials, i.e. CDs, can improve the detection of heavy metals using optical and electrochemical methods.

Fluorescent Nanocarbons: From Synthesis and Structure to Cancer Imaging and Therapy

Nanocarbons are emerging at the forefront of nanoscience, with diverse carbon nanoforms emerging over the past two decades. Early cancer diagnosis and therapy, driven by advanced chemistry techniques, play a pivotal role in mitigating mortality rates associated with cancer. Nanocarbons, with an attractive combination of well-defined architectures, biocompatibility, and nanoscale dimension, offer an incredibly versatile platform for cancer imaging and therapy. This paper aims to review the underlying principles regarding the controllable synthesis, fluorescence origins, cellular toxicity, and surface functionalization routes of several classes of nanocarbons: carbon nanodots, nanodiamonds, carbon nanoonions, and carbon nanohorns. This review also highlights recent breakthroughs regarding the green synthesis of different nanocarbons from renewable sources. It also presents a comprehensive and unified overview of the latest cancer-related applications of nanocarbons and how they can be designed to interface with biological systems and work as cancer diagnostics and therapeutic tools. The commercial status for large-scale manufacturing of nanocarbons is also presented. Finally, it proposes future research opportunities aimed at engendering modifiable and high-performance nanocarbons for emerging applications across medical industries. This work is envisioned as a cornerstone to guide interdisciplinary teams in crafting fluorescent nanocarbons with tailored attributes that can revolutionize cancer diagnostics and therapy.

The applications of carbon dots in oral health: A scoping review

OBJECTIVES

This scoping review aims to provide an overview of the research and potential applications of carbon dots (CDs) for oral health purposes.

DESIGN

Systematic literature searches were performed on PubMed and Web of Science databases (up to February 2023). Two co-authors selected the published works independently and extracted the data in accordance with the PRISMA statement. Studies with the application of CDs for oral health purposes were included.

RESULTS

Among 152 articles, 19 articles were finally selected. Eight studies investigated the anti-microbial effects of CDs against, for example, oral pathogens, eight studies explored the applicability of CDs in relation to oral cancer, and three studies investigated CDs in relation to cell differentiation and tissue regeneration in oral health. The studies showed the promising potential of CDs in oral health, particularly for inducing bacterial killing by increasing reactive oxygen species, killing oral cancer cells via photodynamic therapeutic effects, and inducing dental pulp and periodontal bone regeneration.

CONCLUSION

The findings show that CDs have the potential to be utilized in the future for various oral health purposes. Besides, these results underline the broad-spectrum applicability of CDs, crossing the borders of oral health.

Carbon dots as a novel photosensitizer for photodynamic therapy of cancer and bacterial infectious diseases: recent advances

Carbon dots (CDs) are novel carbon-based nanomaterials that have been used as photosensitizer-mediated photodynamic therapy (PDT) in recent years due to their good photosensitizing activity. Photosensitizers (PSs) are main components of PDT that can produce large amounts of reactive oxygen species (ROS) when stimulated by light source, which have the advantages of low drug resistance and high therapeutic efficiency. CDs can generate ROS efficiently under irradiation and therefore have been extensively studied in disease local phototherapy. In tumor therapy, CDs can be used as PSs or PS carriers to participate in PDT and play an extremely important role. In bacterial infectious diseases, CDs exhibit high bactericidal activity as CDs are effective in disrupting bacterial cell membranes leading to bacterial death upon photoactivation. We focus on recent advances in the therapy of cancer and bacteria with CDs, and also briefly summarize the mechanisms and requirements for PSs in PDT of cancer, bacteria and other diseases. We also discuss the role CDs play in combination therapy and the potential for future applications against other pathogens.

Carbon Quantum Dots: Properties, Preparation, and Applications

Carbon quantum dots are a novel form of carbon material. They offer numerous benefits including particle size adjustability, light resistance, ease of functionalization, low toxicity, excellent biocompatibility, and high-water solubility, as well as their easy accessibility of raw materials. Carbon quantum dots have been widely used in various fields. The preparation methods employed are predominantly top-down methods such as arc discharge, laser ablation, electrochemical and chemical oxidation, as well as bottom-up methods such as templates, microwave, and hydrothermal techniques. This article provides an overview of the properties, preparation methods, raw materials for preparation, and the heteroatom doping of carbon quantum dots, and it summarizes the applications in related fields, such as optoelectronics, bioimaging, drug delivery, cancer therapy, sensors, and environmental remediation. Finally, currently encountered issues of carbon quantum dots are presented. The latest research progress in synthesis and application, as well as the challenges outlined in this review, can help and encourage future research on carbon quantum dots.

CARBON DOTS: Bioimaging and Anticancer Drug Delivery

Cancer, responsible for approximately 10 million lives annually, urgently requires innovative treatments, as well as solutions to mitigate the limitations of traditional chemotherapy, such as long-term adverse side effects and multidrug resistance. This review focuses on Carbon Dots (CDs), an emergent class of nanoparticles (NPs) with remarkable physicochemical and biological properties, and their burgeoning applications in bioimaging and as nanocarriers in drug delivery systems for cancer treatment. The review initiates with an overview of NPs as nanocarriers, followed by an in-depth look into the biological barriers that could affect their distribution, from barriers to administration, to intracellular trafficking. It further explores CDs' synthesis, including both bottom-up and top-down approaches, and their notable biocompatibility, supported by a selection of in vitro, in vivo, and ex vivo studies. Special attention is given to CDs' role in bioimaging, highlighting their optical properties. The discussion extends to their emerging significance as drug carriers, particularly in the delivery of doxorubicin and other anticancer agents, underscoring recent advancements and challenges in this field. Finally, we showcase examples of other promising bioapplications of CDs, emergent owing to the NPs flexible design. As research on CDs evolves, we envisage key challenges, as well as the potential of CD-based systems in bioimaging and cancer therapy.

Separation and purification of fluorescent carbon dots - an unmet challenge

Literature reports demonstrate versatile optical applications of fluorescent carbon dots (CDs) in biological imaging, full-color solid-state lighting, optoelectronics, sensing, anticounterfeiting and so on. The fluorescence associated with CDs may originate significantly from byproducts generated during their synthesis, which need to be eliminated to achieve error-free results. The significance of purification, specifically for luminescence-based characterizations, is highly critical and imperative. Thus, there is a pressing demand to implement consistent and adequate purification strategies to reduce sample complexity and thereby realize reliable results that can provide a tactical steppingstone towards the advancement of CDs as next-generation optical materials. The article focuses on the mechanism of origin of fluorescence from CDs and further demonstrates the different purification approaches including dialysis, centrifugation, filtration, solvent extraction, chromatography, and electrophoresis that have been adopted by various researchers. Furthermore, the fundamental separation mechanism, as well as the advantages and limitations of each of these purification techniques are discussed. The article finally provides the critical challenges of these purification techniques that need to be overcome to obtain homogeneous CD fractions that demonstrate coherent and reliable optical features for suitable applications.

Photodynamic antibacterial activity of oxidase-like nanozyme based on long-lived room-temperature phosphorescent carbon dots

In this study, a novel long-lived room-temperature phosphorescent (RTP) carbon dots (P-CDs) with the properties of ultraviolet/visible (UV/Vis) light photoresponsive oxidase-like nanozyme were synthesized from diethylenetriaminepentaacetic acid and through a one-step hydrothermal method. P-CDs were used as a light-driven oxidative-like enzyme for antimicrobial studies. The results showed that under UV/Vis light irradiation, P-CDs could efficiently convert O2 into 1O2, and the strong oxidizing property of 1O2 greatly enhanced the growth inhibition of P-CDs on Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). Meanwhile, P-CDs exhibited good photodynamic antifungal properties against Botrytis cinerea (B. cinerea). Then the P-CDs were made into P-CDs/PVA films, which effectively prolonged the preservation period of fruits under photodynamic antibacterial action. The good biocompatibility and efficient photosensitive oxygen activation can make P-CDs a more practically useful oxidase-like nanozyme.

The art of simplicity: Water-soluble porphyrin-like carbon dots self-assemble into mesmerizing red glow

In this new study, we present an intriguing development in the field of theranostics: the simplistic self-assembly of red-emissive amphiphilic porphyrin-like carbon dots (P-CDs). By harnessing their exceptional photophysical properties, we have revealed a strong candidate as the ideal photosensitizer (PS) for applications, particularly in the realm of imaging. Spanning a remarkable size average between 1-4 nm, these particles exhibit both highly stable and unparalleled emission characteristics between 650 and 715 nm in water in comparison to current carbon dots (CDs) available. Lastly, these CDs were fairly non-toxic when tested against normal human cell lines as well as were found to have favorable imaging capabilities in zebrafish embryo.

Natural biomass carbon Dots-Based fluorescence sensor for high precision detection of vitamin B12 in serum

Vitamin B12(Vit B12) is an essential micronutrient for body growth, and abnormal levels of Vit B12 in the human body are closely associated with the prediction of certain diseases. Hence, a rapid, sensitive, and environment-friendly approach for Vit B12 detection was set up. Herein, the Bird's nest carbon dots (B-CDs) are synthesized by using a bird's nest and distilled water as precursors. One-step hydrothermal synthesis has created B-CDs without toxic ingredients or surface chemical modifications. The prepared B-CDs exhibited outstanding characteristics including excellent water solubility, brilliant fluorescence performance great biocompatibility, and fine stability in a broad pH range of 3.0-11.0 and high ionic strength solution. The experiment revealed that the fluorescence of the reaction system showed a regular decrease after the interaction of B-CDs with Vit B12. Additionally, there was an excellent linear relationship between the F/F0 of B-CDs and the concentration of Vit B12. The linear range was 0 ∼ 100 µM, R2 was 0.9929, and the detection limit was 0.24 µM. Finally, the proposed method successfully detected Vit B12 in human serum samples with recoveries of 96.2 %-100.3 %, showing broad clinical prospects.

Fluorescent carbon dots synthesized by waste wind turbine blade for photocatalytic degradation

Developing novel waste recycling strategies has become a feasible solution to overcome environmental pollution. In this work, a method of using waste wind turbine blade (WTB) as a carbon source to synthesize blue fluorescent carbon dots (B-CDs) by hydrothermal treatment is proposed. B-CDs are spherical and have an average particle size of 5.2 nm. The surface is rich in C-O, C=O, -CH3 , and N-H bond functional groups, containing five elements: C, O, N, Si, and Ca. The optimal emission wavelength of B-CDs is 463 nm, corresponding to an excitation wavelength of 380 nm. Notably, a relatively high quantum yield of 29.9% and a utilization rate of 40% were obtained. In addition, B-CDs can serve as a photocatalyst to degrade methylene blue dye, with a degradation efficiency of 64% under 40-min irradiation conditions. The presence of holes has a significant influence on the degradation process.

Multifunctional Carbon Dots for Biomedical Applications: Diagnosis, Therapy, and Theranostic

Designing suitable nanomaterials is an ideal strategy to enable early diagnosis and effective treatment of diseases. Carbon dots (CDs) are luminescent carbonaceous nanoparticles that have attracted considerable attention. Through facile synthesis, they process properties including tunable light emission, low toxicity, and light energy transformation, leading to diverse applications as optically functional materials in biomedical fields. Recently, their potentials have been further explored, such as enzyme-like activity and ability to promote osteogenic differentiation. Through refined synthesizing strategies carbon dots, a rich treasure trove for new discoveries, stand a chance to guide significant development in biomedical applications. In this review, the authors start with a brief introduction to CDs. By presenting mechanisms and examples, the authors focus on how they can be used in diagnosing and treating diseases, including bioimaging failure of tissues and cells, biosensing various pathogenic factors and biomarkers, tissue defect repair, anti-inflammation, antibacterial and antiviral, and novel oncology treatment. The introduction of the application of integrated diagnosis and treatment follows closely behind. Furthermore, the challenges and future directions of CDs are discussed. The authors hope this review will provide critical perspectives to inspire new discoveries on CDs and prompt their advances in biomedical applications.

A Review of Dual-Emission Carbon Dots and Their Applications

Carbon dots (CDs), as a rising star among fluorescent nanomaterials with excellent optical properties and fascinating dual-emission characteristics, have attracted increasing attention in sensing, bio-imaging, drug delivery, and so on. The synthesis of dual-emission CDs (DE-CDs) and the establishment of ratiometric fluorescence sensors can effectively diminish background interference and provide more accurate results than single-emission CDs. Although DE-CDs have generated increased attention in many fields, the review articles about DE-CDs are still insufficient. Therefore, we summarized the latest results and prepared this review. This review first provides an overview of the primary synthesis route and commonly used precursors in DE-CDs synthesis. Then, the photoluminescence mechanism behind the dual-emission phenomenon was discussed. Thirdly, the application of DE-CDs in metal cation detection, food safety analysis, biosensing, cell imaging, and optoelectronic devices has been extensively discussed. Finally, the main challenges and prospects for further development are presented. This review presents the latest research progress of DE-CDs synthesis and its application in ratiometric sensing; hopefully, it can help and encourage researchers to overcome existing challenges and broaden the area of DE-CDs research.

Nitrogen- and Sulfur-Codoped Strong Green Fluorescent Carbon Dots for the Highly Specific Quantification of Quercetin in Food Samples

Carbon dots (CDs) doped with heteroatoms have garnered significant interest due to their chemically modifiable luminescence properties. Herein, nitrogen- and sulfur-codoped carbon dots (NS-CDs) were successfully prepared using p-phenylenediamine and thioacetamide via a facile process. The as-developed NS-CDs had high photostability against photobleaching, good water dispersibility, and excitation-independent spectral emission properties due to the abundant amino and sulfur functional groups on their surface. The wine-red-colored NS-CDs exhibited strong green emission with a large Stokes shift of up to 125 nm upon the excitation wavelength of 375 nm, with a high quantum yield (QY) of 28%. The novel NS-CDs revealed excellent sensitivity for quercetin (QT) detection via the fluorescence quenching effect, with a low detection limit of 17.3 nM within the linear range of 0-29.7 μM. The fluorescence was quenched only when QT was brought near the NS-CDs. This QT-induced quenching occurred through the strong inner filter effect (IFE) and the complex bound state formed between the ground-state QT and excited-state NS-CDs. The quenching-based detection strategies also demonstrated good specificity for QT over various interferents (phenols, biomolecules, amino acids, metal ions, and flavonoids). Moreover, this approach could be effectively applied to the quantitative detection of QT (with good sensing recovery) in real food samples such as red wine and onion samples. The present work, consequently, suggests that NS-CDs may open the door to the sensitive and specific detection of QT in food samples in a cost-effective and straightforward manner.

A Ratiometric Fluorescent Sensor Based on Chelation-Enhanced Fluorescence of Carbon Dots for Zinc Ion Detection

Zinc ion, one of the most important transition metal ions in living organisms, plays a crucial role in the homeostasis of the organism. The disorder of zinc is associated with many major diseases. It is highly desirable to develop selective and sensitive methods for the real-time detection of zinc ions. In this work, double-emitting fluorescent carbon dots (CDs) are prepared by a solvothermal method using glutathione, L-aspartic acid, and formamide as the raw materials. The carbon dots specifically recognize zine ions and produce a decrease in fluorescence intensity at 684 nm and an increase at 649 nm, leading to a ratiometric fluorescent sensor for zinc detection. Through surface modification and spectral analysis, the surface groups including carboxyl, carbonyl, hydroxyl, and amino groups, and C=N in heterocycles of CDs are revealed to synergistically coordinate Zn2+, inducing the structural changes in the emission site. The CDs can afford a low limit of detection of ~5 nM for Zn2+ detection with good linearity in the range of 0.02-5 μM, showing good selectivity as well. The results from real samples including fetal bovine serum, milk powder, and zinc gluconate oral solution indicated the good applicability of the CDs in the determination of Zn2+.

A recent update on development, synthesis methods, properties and application of natural products derived carbon dots

Natural resources are practically infinitely abundant in nature, which stimulates scientists to create new materials with inventive uses and minimal environmental impact. Due to the various benefits of natural carbon dots (NCDs) from them has received a lot of attention recently. Natural products-derived carbon dots have recently emerged as a highly promising class of nanomaterials, showcasing exceptional properties and eco-friendly nature, which make them appealing for diverse applications in various fields such as biomedical, environmental sensing and monitoring, energy storage and conversion, optoelectronics and photonics, agriculture, quantum computing, nanomedicine and cancer therapy. Characterization techniques such as Photoinduced electron transfer, Aggregation-Induced-Emission (AIE), Absorbance, Fluorescence in UV-Vis and NIR Regions play crucial roles in understanding the structural and optical properties of Carbon dots (CDs). The exceptional photoluminescence properties exhibited by CDs derived from natural products have paved the way for applications in tissue engineering, cancer treatment, bioimaging, sensing, drug delivery, photocatalysis, and promising remarkable advancements in these fields. In this review, we summarized the various synthesis methods, physical and optical properties, applications, challenges, future prospects of natural products-derived carbon dots etc. In this expanding sector, the difficulties and prospects for NCD-based materials research will also be explored.

Synthesis of pH-Sensitive Nitrogen-Doped Carbon Dots with Biological Imaging Function and Their Application in Cu2+ and Fe2+ Determination by Ratiometric Fluorescent Probes

pH-sensitive nitrogen-doped carbon dots (N-CDs) were synthesized using immature seeds of elm trees as a carbon source and ethylenediamine as a coreactant through a facile one-step hydrothermal method. The N-CDs were characterized using fluorescence spectroscopy, fluorescence lifetime, ultraviolet-visible absorption, X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy, as well as transmission electron microscopy. The N-CDs displayed excellent fluorescence properties and responded to pH changes. The N-CDs exhibited low toxicity and good biocompatibility and had the potential to be used for the biological imaging of HeLa cells and mung bean sprouts. Utilizing the mechanism of fluorescence resonance energy transfer, ratiometric fluorescent probes were prepared by simple mixing of N-CDs and fluorexon in a Britton-Robinson buffer solution. The ratiometric fluorescent probe was used to detect Cu2+ and Fe2+. The linear equations were RCu = -0.0591[Q] + 3.505 (R2 = 0.992) and RFe = -0.0874[Q] + 3.61 (R2 = 0.999). The corresponding limits of detection were 0.5 and 0.31 μM, respectively. The good results had been obtained in the actual samples detection.

Inducing Circularly Polarized Luminescence by Confined Synthesis of Ultrasmall Chiral Carbon Nanodot Arrays in Pyrene-Based MOF Thin Film

Combining the features of the host-guest system and chirality is an efficient strategy to achieve circularly polarized luminescence (CPL). Herein, well-defined chiral carbon nanodot (chirCND) arrays were confined-synthesized by low-temperature calcination of a chiral amino acid loaded metal-organic framework (MOF) to induce high CPL. An achiral porous pyrene-based MOF NU-1000 thin film as the host template was prepared by a liquid-phase epitaxial layer-by-layer fashion, and chiral amino acids as the carbon sources could be confined in the porous MOF and carbonized to homogeneous and ultrasmall chirCND arrays, resulting in a chirCNDs@NU-1000 thin film (l-CNDsx@NU-1000; x = l-cysteine (cys), l-serine, l-histidine, l-glutamic acid, and l-pyroglutamic acid). The results show the pristine chirCNDs by directly carbonizing chiral amino acids hardly endow them with a CPL property. By contrast, benefiting from the arrayed confinement and coordination interaction between chirCNDs and NU-1000, the chirality transfer on the excited state of chirCNDs@NU-1000 is enabled, leading to strong CPL performance (a high luminescence dissymmetry factor glum of l-CNDscys@NU-1000 thin film reached 1.74 × 10-2). This study of chirCNDs encapsulated in fluorescent MOF thin films provides a strategy for developing uniform chiral carbon nanoarrays and offers chiral host-guest thin-film materials for optical applications.

Luminescence of carbon quantum dots and their application in biochemistry

Similar to fullerenes, carbon nanotubes and graphene, carbon dots (CDs) are causing a lot of research work in their own right. CDs are a type of surface-passivated quantum dot that contain carbon atoms. Their distinctive characteristics, such as luminescent emission that varies with size and wavelength, resistance to photobleaching, easy biological binding, lack of toxicity, and economical production without the need for intricate synthetic processes, have led to a noteworthy surge in attention within the research community. Different techniques can be utilized to create these CDs, spanning from basic candle burning to laser ablation. This review article delves into the principles of fluorescence technology, providing insights into how different synthesis methods of quantum dots impact their luminescent properties. Additionally, it highlights the latest applications of quantum dots in catalysis and biomedical fields, with special emphasis on the current status of luminescent properties in biology and chemistry. Towards the end, the article discusses the limitations of quantum dots in current practical applications, pointing out that CDs hold promising potential for future applications.

A quantum dot aptamer fluorescent sensor based on magnetic graphene oxide for the detection of zearalenone

As an estrogenic mycotoxin found in a wide range of agricultural crops, the toxicity of zearalenone (ZEN) poses a serious risk to human health. Accordingly, to achieve rapid detection of zearalenone in complex samples, an aptamer fluorescence sensor based on magnetic graphene oxide was developed. Compared with traditional methods, this technique has the virtues of simple operation, low cost, and reliable performance. Magnetic graphene oxide (MGO) was synthesized as a fluorescent bursting agent, using a chemical precipitation approach by depositing Fe3O4 on the surface of graphene oxide. As a fluorescent probe, an aptamer coupling with CdTe quantum dots and zearalenone was used. Following the specific binding of zearalenone and the aptamer, the affinity interaction between the fluorescent probe and MGO was weakened, resulting in the recovery of fluorescence and making the qualitative and quantitative analysis of zearalenone available via fluorescence intensity determination. The results indicated that the method's linear range was 5-120 μg L-1 and its detection limit was 2.9 μg L-1. In addition, the recoveries varied from 76.4 to 118.8% for crop samples, with relative standard deviations (RSDs) between 0.8 and 9.5%, which suggests an effective method for the separation and detection of mycotoxins in actual environmental samples.

Carbon Dots Strongly Immobilized onto Carbon Nanohorns as Non-Metal Heterostructure with High Electrocatalytic Activity towards Protons Reduction in Hydrogen Evolution Reaction

Highly performing, non-metal inexpensive electrocatalysts for the production of hydrogen via electrochemical water splitting are called for the replacement of current platinum-based ones. In order to speed up the electrocatalytic hydrogen evolution, abundant active sites but also efficient charge transfer is needed. In this context, 0D carbon dots (CDs) with large specific surface area, low cost, high conductivity, and rich functional groups emerge as promising non-metal electrocatalysts. Additionally, the use of conductive substrates provides an effective strategy to boost their electrocatalytic performance. Herein, the unique 3D superstructure of carbon nanohorns (CNHs), as well as without any metal content in their structure, is used to provide a conductive support of high porosity, large specific surface area, and good electrical conductivity, for the in situ growth and immobilization of CDs, via a simple hydrothermal method. The direct contact of CDs with the 3D conductive network of CNHs promotes charge transfer, accelerating hydrogen evolution. The all-carbon non-metal CDs/CNHs nanoensembleshows an onset potential close to the one of Pt/C, low charge transfer resistance, and excellent stability.

Preparation of Multicolor Fluorescent Carbon Dots Based on Catechol and o-Phthalaldehyde

As the foremost category of carbon materials, carbon dots (CDs) have been extensively applied in many domains because of their special fluorescence features and outstanding biocompatibility. However, in early studies of fluorescent CDs, as the fluorescence wavelength of most CDs was restricted to the blue or green region and was excitation dependent, the application of CDs was limited. In this study, three representative CDs, fluorescing yellow, green, and blue, were synthesized under alkaline, neutral, and acidic circumstances, respectively, while using a hydrothermal method in which catechol and phthalaldehyde acted as carbon sources and methanol functioned as the reaction solvent. The carbon nuclei of the three fluorescent CDs all had comparable graphite structures. The diversity of photoluminescence (PL) emission from these three CDs was attributed mainly to the different sizes of the sp² conjugated structures among them. Mixing synthesized CDs with epoxy resin, three colors (yellow, green, and blue) of LED using CIE coordinates (0.40, 0.44), (0.33, 0.46), and (0.21, 0.22), respectively, were successfully prepared.

Nitrogen and sulfur co-doped photoluminescent carbon dots for highly selective and sensitive detection of Ag+ and Hg2+ ions in aqueous media: Applications in bioimaging and real sample analysis

In this study, we report the synthesis of photoluminescent (PL) nitrogen (N) and sulfur (S) co-doped carbon dots (NS-CDs) from nitazoxanide and 3-mercaptopropionic acid as a precursors via a one-pot hydrothermal methods. N and S co-doped materials allows more active sites in the CDs surface resulting in an enhancement of their PL properties. NS-CDs show bright blue PL, excellent optical properties, good water solubility, and a high quantum yield (QY) of 32.1%. The as-prepared NS-CDs were confirmed by UV-Visible, photoluminescence, FTIR, XRD and TEM analysis. An optimized excitation at 345 nm, the NS-CDs exhibited strong PL emission at 423 nm with an average size of 3.53 ± 0.25 nm. Under optimized conditions, the NS-CDs PL probe shows high selectivity with Ag⁺/Hg²⁺ ions detected, while other cations no significant changes the PL signal. The PL intensity of NS-CDs linearly quenching and enhancement with Ag⁺ and Hg²⁺ ions from 0 to 50 × 10^-6 M, with the detection limit of 2.15 × 10^-6 M and 6.77 × 10^-7 M (S/N = 3). More interestingly, as-synthesized NS-CDs shows a strong binding to Ag⁺/Hg²⁺ ions with the PL quenching and enhancement to precise and quantitative detection of Ag⁺/Hg²⁺ ions in living cells. The proposed system was effectively utilized for the sensing of Ag⁺/Hg²⁺ ions in real samples resulting in high sensitivity and good recoveries (98.4-109.7%).

Carbon Dots in Treatment of Pediatric Brain Tumors: Past, Present, and Future Directions

Pediatric brain tumors remain a significant source of morbidity and mortality. Though developments have been made in treating these malignancies, the blood-brain barrier, intra- and inter-tumoral heterogeneity, and therapeutic toxicity pose challenges to improving outcomes. Varying types of nanoparticles, including metallic, organic, and micellar molecules of varying structures and compositions, have been investigated as a potential therapy to circumvent some of these inherent challenges. Carbon dots (CDs) have recently gained popularity as a novel nanoparticle with theranostic properties. This carbon-based modality is highly modifiable, allowing for conjugation to drugs, as well as tumor-specific ligands in an effort to more effectively target cancerous cells and reduce peripheral toxicity. CDs are being studied pre-clinically. The ClinicalTrials.gov site was queried using the search terms: brain tumor and nanoparticle, liposome, micelle, dendrimer, quantum dot, or carbon dot. At the time of this review, 36 studies were found, 6 of which included pediatric patients. Two of the six studies investigated nanoparticle drug formulations, whereas the other four studies were on varying liposomal nanoparticle formulations for the treatment of pediatric brain tumors. Here, we reviewed the context of CDs within the broader realm of nanoparticles, their development, promising pre-clinical potential, and proposed future translational utility.

Carbon dots with tissue engineering and regenerative medicine applications

Carbon dots (CDs) with unique physicochemical features such as exceptional biocompatibility, low cost, eco-friendliness, abundant functional groups (e.g., amino, hydroxyl, and carboxyl), high stability, and electron mobility have been broadly investigated in nano- and biomedicine. In addition, the controlled architecture, tunable fluorescence emission/excitation, light-emitting potential, high photostability, high water solubility, low cytotoxicity, and biodegradability make these carbon-based nanomaterials suitable for tissue engineering and regenerative medicine (TE-RM) purposes. However, there are still limited pre- and clinical assessments, because of some important challenges such as the scaffold inconsistency and non-biodegradability in addition to the lack of non-invasive methods to monitor tissue regeneration after implantation. In addition, the eco-friendly synthesis of CDs exhibited some important advantages such as environmentally friendly properties, low cost, and simplicity compared to the conventional synthesis techniques. Several CD-based nanosystems have been designed with stable photoluminescence, high-resolution imaging of live cells, excellent biocompatibility, fluorescence properties, and low cytotoxicity, which make them promising candidates for TE-RM purposes. Combining attractive fluorescence properties, CDs have shown great potential for cell culture and other biomedical applications. Herein, recent advancements and new discoveries of CDs in TE-RM are considered, focusing on challenges and future perspectives.

Preparations of antibacterial yellow-green-fluorescent carbon dots and carbon dots-lysozyme complex and their applications in bacterial imaging and bacteria/biofilm inhibition/clearance

The preparation of functional long-wavelength-emitting nanomaterials and the researches on their applications in antibacterial and antibiofilm fields have important significance. This paper reports the preparation of yellow-green-fluorescent and high- quantum yield carbon dots (4-ACDs) with 4-aminosalicylic acid and polyethylene imine as raw materials through one-step route, and the impacts of raw material structure and the reaction conditions upon the optical properties of the products have been investigated. 4-ACDs exhibit excellent broad-spectrum antibacterial activity, and their good biocompatibility ensures them as ideal fluorescent nano-probe for cell imaging. However, 4-ACDs could not effectively eliminate the biofilm of Staphylococcus aureus (S. aureus). CDs-LZM complex was prepared through the coupling between 4-ACDs and lysozyme (LZM) and the complex showed strong antibacterial activity against Gram-positive bacteria, particularly with MIC against S. aureus at 5 μg mL^-1. Besides, CDs-LZM showed excellent ability against the biofilm of S. aureus. At the concentration of 60 μg mL^-1, its inhibition rate against the growth of biofilm was 86 %, and elimination rate against biofilm reached 76 %. CDs-LZM exhibited obvious antibiofilm ability through removing extracellular matrix of biofilm, greatly reducing the thickness of biofilm under confocal microscopy. The application of novel long-wavelength-emitting nanomaterial in eliminating pathogenic bacteria is of great significance.

Hybrid Micelles of Carbon Quantum Dot-Doxorubicin Conjugates as Nanotheranostics for Tumor Therapy and Turn-On Fluorescence Imaging: Impact of Conjugated Structures and On-Off-On Mechanism

Carbon quantum dots (CDs) have attracted more and more attention in the field of biological imaging, while their applications are restricted due to their nonspecific fluorescence and small particle size. Herein, two pH-responsive carbon quantum dot-doxorubicin (DOX) conjugates were designed with maleic acid (MA, cis-butenedioic acid) and fumaric acid (FA, trans-butenedioic acid) as linker, respectively, which could self-assemble into unique hybrid micelles as tumor-specific carrier-free nanotheranostics. Owing to the acid-labile covalent modification with conjugated groups and the interaction with the surrounding DOX molecules, the fluorescence of CDs was completely quenched, while it could be recovered in the tumor intracellular microenvironment by acid-triggered cleavage of the fluorophore-drug conjugates, showing excellent turn-on fluorescence for effective cellular imaging. Especially, the trans conjugate with FA as linker possessed higher drug content, better drug release behavior and stronger inhibition of tumor cells than the cis one with MA as linker, demonstrating its promising potential as carrier-free nanotheranostics for future tumor treatment.

Rational Design of Nitrogen-Doped Carbon Dots for Inhibiting β-Amyloid Aggregation

The fibrillization and abnormal aggregation of β-amyloid (Aβ) peptides are commonly recognized risk factors for Alzheimer's disease (AD) brain, and require an effective strategy to inhibit the Aβ deposition and treat AD. Herein, we designed and synthesized nitrogen-doped carbon dots (N-CDs) as an Aβ-targeted probe, which exhibits the capacity of inhibiting the 1-42 Aβ (Aβ1-42) self-assembly in vitro. The N-CDs exhibited orange emission with an emission wavelength of 570 nm, which demonstrates their excellent optical properties with excitation-independent behavior. Meanwhile, the N-CDs have spherical morphologies with an average size of 2.2 nm, whose surface enriches the amino, carboxyl, and hydroxyl groups. These preparties are conducive to improving their biological water solubility and provide a large number of chemical bonds for further interaction with proteins. Contrary to this, the kinetic process, size evolutions, and morphologies changes of Aβ1-42 were inhibited in the presence of N-CDs in the determination of a thioflavin T assay, dynamic light scattering, transmission electron microscope, etc. Finally, the safety application of N-CDs on Aβ1-42-induced cytotoxicity was further demonstrated via in vitro cytotoxicity experiments. This work demonstrates the effective outcome of suppressing Aβ aggregation, which provides a new view into the high-efficiency and low-cytotoxicity strategy in AD theranostics.

Flexible and Stretchable Carbon-Based Sensors and Actuators for Soft Robots

In recent years, the emergence of low-dimensional carbon-based materials, such as carbon dots, carbon nanotubes, and graphene, together with the advances in materials science, have greatly enriched the variety of flexible and stretchable electronic devices. Compared with conventional rigid devices, these soft robotic sensors and actuators exhibit remarkable advantages in terms of their biocompatibility, portability, power efficiency, and wearability, thus creating myriad possibilities of novel wearable and implantable tactile sensors, as well as micro-/nano-soft actuation systems. Interestingly, not only are carbon-based materials ideal constituents for photodetectors, gas, thermal, triboelectric sensors due to their geometry and extraordinary sensitivity to various external stimuli, but they also provide significantly more precise manipulation of the actuators than conventional centimeter-scale pneumatic and hydraulic robotic actuators, at a molecular level. In this review, we summarize recent progress on state-of-the-art flexible and stretchable carbon-based sensors and actuators that have creatively added to the development of biomedicine, nanoscience, materials science, as well as soft robotics. In the end, we propose the future potential of carbon-based materials for biomedical and soft robotic applications.

Nanomaterial Constructs for Catalytic Applications in Biomedicine: Nanobiocatalysts and Nanozymes

Nanomaterials possess superior advantages due to their special geometries, higher surface area, and unique mechanical, optical, and physicochemical properties. Their characteristics make them great contributors to the development of many technological and industrial sectors. Therefore, novel nanomaterials have an increasing interest in many research areas including biomedicine such as chronic inflammations, disease detection, drug delivery, and infections treatment. Their relevant role is, in many cases, associated with an effective catalytic application, either as a pure catalyst (acting as a nanozyme) or as a support for catalytically active materials (forming nanobiocatalysts). In this review, we analyze the construction of nanozymes and nanobiocatalyst by different existing forms of nanomaterials including carbon-based nanomaterials, metal-based nanomaterials, and polymer-based nanocomposites. Then, we examine successful examples of such nanomaterials employed in biomedical research. The role played by nanomaterials in catalytic applications is analyzed to identify possible research directions toward the development of the field and the achievement of real practicability.

Graphical Abstract