Edible coating using carbon quantum dots for fresh produce preservation: A review of safety perspectives

Fresh produce deteriorates and spoils after harvest due to its perishable nature. Deterioration in quality over time has become a major problem for the food industry, placing an undue burden on the economy and agriculture. Food scientists have developed various methods and technologies to prevent spoilage of fruits and vegetables during storage and logistics. Utilizing carbon quantum dots (CQDs) in the form of active packaging and coatings has been a popular strategy recently. CQDs have recently attracted attention as sustainable and functional nanomaterials. CQDs are popular among food scientists due to their easy and economical synthesis, sustainability, non-toxicity, biocompatibility, edibility, UV protection, and antibacterial and antioxidant activities. Although many studies have been conducted and reviewed on the utilization of CQDs in the manufacture of flexible active packaging materials, relatively few studies have investigated the use of CQDs in edible coating formulations for fresh produce. The main reasons for this are concerns about the potential toxicity and edibility of CQDs if they are coated directly on fresh produce. Therefore, this review aims to address these issues by investigating the dose-dependent non-toxicity and biocompatibility of sustainable CQDs along with other important properties from a food packaging perspective. Additionally, this review focuses on the studies performed so far on the direct coating of CQD-based formulations on fresh and fresh-cut fruits and vegetables and discusses the important impact of CQDs on the quality of coated agricultural products. This review is intended to provide food packaging researchers with confidence and prospects for utilizing sustainable CQDs in direct coating formulations for food.

Carbon nitride dots do not impair the growth, development, and telomere length of tadpoles

Carbon nanoparticles, or carbon dots, can have many beneficial uses. However, we must consider whether they may have any potential negative side effects on wildlife or the ecosystem when these particles end up in wastewater. Early development stages of amphibians are particularly sensitive to contaminants, and exposure to carbon dots could disrupt their development and cause morbidity or death. Past studies have investigated short-term exposure to certain types of nanoparticles, but if these particles get into wastewater exposure may not be short term. Therefore, we tested whether chronic exposure to different concentrations of carbon dots affects the growth, metamorphosis, and telomere length of Cuban tree frog (Osteopilus septentrionalis) tadpoles. We exposed 12 groups of five tadpoles each to different concentrations of carbon dots and a control for three months and tracked survival, growth and metamorphosis. We used carbon nitride dots approximately 2 nm in size at concentrations of 0.01 mg/ml and 0.02 mg/ml, known to interrupt development in zebrafish embryos. After three months, we measured telomere length from tissue samples. We found no difference in tadpole survivorship, growth, development rate, or telomere length among any of the groups, suggesting that carbon dots at these concentrations do not disrupt tadpole development.

Understanding the Interaction between Nanomaterials Originated from High-Temperature Processed Starch/Myristic Acid and Human Monocyte Cells

High-temperature cooking approaches trigger many metabolically undesirable molecule formations, which pose health risks. As a result, nanomaterial formation has been observed while cooking and reported recently. At high temperatures, starch and myristic acid interact and lead to the creation of nanomaterials (cMS-NMs). We used a non-polar solvent chloroform to separate the nanomaterials using a liquid-liquid extraction technique. The physico-chemical characterization was carried out using dynamic light scattering (DLS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR). To determine the biological impact of these nanomaterials using different in vitro assays, including a cell viability assay, microscopic staining, and gene expression analysis, we adopted the THP-1 cell line as an in vitro monocyte model in our study. The TEM images revealed that fabricated cMS nanomaterials are smaller than 100 nm in diameter. There were significant concerns found in the cytotoxicity assay and gene expression analysis. At concentrations of 100-250 µg/mL, the cMS-NMs caused up to 95% cell death. We found both necrosis and apoptosis in cMS-NMs treated THP-1 cells. In cMS-NMs-treated THP-1 cells, we found decreased expression levels in IL1B and NFKB1A genes and significant upregulation in MIF genes, suggesting a negative immune response. These findings strongly suggest that cMS-NMs originated from high-temperature food processing can cause adverse effects on biological systems. Therefore, charred materials in processed foods should be avoided in order to minimize the risk of health complications.

Cationic fluorescent carbon dots with solution ultra-stability and its rapid/on-site sensing application for HClO

Carbon dots (CDs) as a remarkable fluorescent nanomaterial have the advantages of easy preparation, good photostability and high sensitivity. However, the poor aqueous solution stability of carbon dots largely limited their practical application due to the characteristic of easily forming precipitation for long time storage. Here, a kind of cationic fluorescent carbon dots CDs-P(Ph)3 was designed by introducing a cationic compound, (4-carboxybutyl) triphenyl phosphonium bromide, to construct an electrostatic shell outside the dots. Such electrostatic shell could highly improve carbon dots stability in an aqueous solution to make CDs-P(Ph)3 stable for long-term storage with negligible aggregation. Meanwhile, the sensitivity of CDs-P(Ph)3 for hypochlorous acid (HClO) was also enhanced on the basis of the electron-withdrawing effect of cationic substituents on the surface of carbon dots. The limit of detection of CDs-P(Ph)3 for HClO was as low as ∼0.32 μM. Additionally, the fluorescence of CDs-P(Ph)3 could be rapid quenched by HClO with a quenching efficiency of more than 80% within 30 s. The excellent stability of CDs-P(Ph)3 in an aqueous solution made it suitable for on-site detecting HClO in real samples, such as tap, well and lake water. Such designed fluorescent nanomaterial would provide a practical application pathway for optical sensing detection in environmental samples.

An overview on animal/human biomass-derived carbon dots for optical sensing and bioimaging applications

Over the past decade, carbon dots (CDs) have emerged as some of the extremely popular carbon nanostructures for diverse applications. The advantages of sustainable CDs, characterized by their exceptional photoluminescence (PL), high water solubility/dispersibility, non-toxicity, and biocompatibility, substantiate their potential for a wide range of applications in sensing and biology. Moreover, nature offers plant- and animal-derived precursors for the sustainable synthesis of CDs and their doped variants. These sources are not only readily accessible, inexpensive, and renewable but are also environmentally benign green biomass. This review article presents in detail the production of sustainable CDs from various animal and human biomass through bottom-up synthetic methods, including hydrothermal, microwave, microwave-hydrothermal, and pyrolysis methods. The resulting CDs exhibit a uniform size distribution, possibility of heteroatom doping, surface passivation, and remarkable excitation wavelength-dependent/independent emission and up-conversion PL characteristics. Consequently, these CDs have been successfully utilized in multiple applications, such as bioimaging and the detection of various analytes, including heavy metal ions. Finally, a comprehensive assessment is presented, highlighting the prospects and challenges associated with animal/human biomass-derived CDs for multifaceted applications.

An Overview of the Potential of Food-Based Carbon Dots for Biomedical Applications

Food-based carbon dots (CDs) hold significant importance across various fields, ranging from biomedical applications to environmental and food industries. These CDs offer unique advantages over traditional carbon nanomaterials, including affordability, biodegradability, ease of operation, and multiple bioactivities. This work aims to provide a comprehensive overview of recent developments in food-based CDs, focusing on their characteristics, properties, therapeutic applications in biomedicine, and safety assessment methods. The review highlights the potential of food-based CDs in biomedical applications, including antibacterial, antifungal, antivirus, anticancer, and anti-immune hyperactivity. Furthermore, current strategies employed for evaluating the safety of food-based CDs have also been reported. In conclusion, this review offers valuable insights into their potential across diverse sectors and underscores the significance of safety assessment measures to facilitate their continued advancement and application.

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.

Fluorescent Carbon Dots Derived From Soy Sauce for Picric Acid Detection and Cell Imaging

Picric acid (PA) is a powerful nitro-aromatic explosive that harms the environment and human health. Developing non-toxic and low-cost sensors for the rapid detection of PA is essential. An environment-friendly fluorescent probe for PA detection is designed based on carbon dots (CDs) directly separated from edible soy sauce by silica gel column chromatography. Neither organic reagents nor heating process was needed to prepare CDs. The obtained CDs exhibit bright blue fluorescence, good water solubility, and photostability. The fluorescent probe for PA was developed according to the CD's fluorescence can be significantly quenched via the inner filter effect between CDs and PA. The linear range was 0.2-24 µM with a limit of detection of 70 nM. This proposed method was successfully employed to detect PA in the real water samples with satisfactory recoveries between 98.0-104.0%. Moreover, the CDs were suitable for fluorescence imaging of HeLa cells owing to their low toxicity and good biocompatibility.

Carbon Quantum Dots from Roasted Coffee Beans: Their Degree and Mechanism of Cytotoxicity and Their Rapid Removal Using a Pulsed Electric Field

Carbon quantum dots (CQDs) from heat-treated foods show toxicity, but the mechanisms of toxicity and removal of CQDs have not been elucidated. In this study, CQDs were purified from roasted coffee beans through a process of concentration, dialysis and lyophilization. The physical properties of CQDs, the degree and mechanism of toxicity and the removal method were studied. Our results showed that the size of CQDs roasted for 5 min, 10 min and 20 min were about 5.69 ± 1.10 nm, 2.44 ± 1.08 nm and 1.58 ± 0.48 nm, respectively. The rate of apoptosis increased with increasing roasting time and concentration of CQDs. The longer the roasting time of coffee beans, the greater the toxicity of CQDs. However, the caspase inhibitor Z-VAD-FMK was not able to inhibit CQDs-induced apoptosis. Moreover, CQDs affected the pH value of lysosomes, causing the accumulation of RIPK1 and RIPK3 in lysosomes. Treatment of coffee beans with a pulsed electric field (PEF) significantly reduced the yield of CQDs. This indicates that CQDs induced lysosomal-dependent cell death and increased the rate of cell death through necroptosis. PEF is an effective way to remove CQDs from roasted coffee beans.

Structure-Activity Relationship of Carbon Nitride Dots in Inhibiting Tau Aggregation

Due to the numerous failed clinical trials of anti-amyloid drugs, microtubule associated protein tau (MAPT) now stands out as one of the most promising targets for AD therapy. In this study, we report for the first time the structure-dependent MAPT aggregation inhibition of carbon nitride dots (CNDs). CNDs have exhibited great promise as a potential treatment of Alzheimer's disease (AD) by inhibiting the aggregation of MAPT. In order to elucidate its structure-activity relationship, CNDs were separated via column chromatography and five fractions with different structures were obtained that were characterized by multiple spectroscopy methods. The increase of surface hydrophilic functional groups is consistent with the increase of polarity from fraction 1 to 5. Particle sizes (1-2 nm) and zeta potentials (~-20 mV) are similar among five fractions. With the increase of polarity from fraction 1 to 5, their MAPT aggregation inhibition capacity was weakened. This suggests hydrophobic interactions between CNDs and MAPT, validated via molecular dynamics simulations. With a zebrafish blood-brain barrier (BBB) model, CNDs were observed to cross the BBB through passive diffusion. CNDs were also found to inhibit the generation of multiple reactive oxygen species, which is an important contributor to AD pathogenesis.

Facile preparation of aqueous-soluble fluorescent polyethylene glycol functionalized carbon dots from palm waste by one-pot hydrothermal carbonization for colon cancer nanotheranostics

Carbon dots (CDs) are categorized as an emerging class of zero-dimension nanomaterials having high biocompatibility, photoluminescence, tunable surface, and hydrophilic property. CDs, therefore, are currently of interest for bio-imaging and nano-medicine applications. In this work, polyethylene glycol functionalized CDs (CD-PEG) were prepared from oil palm empty fruit bunch by a one-pot hydrothermal technique. PEG was chosen as a passivating agent for the enhancement of functionality and photoluminescence properties of CDs. To prepare the CDs-PEG, the effects of temperature, time, and concentration of PEG were investigated on the properties of CDs. The as-prepared CDs-PEG were characterized by several techniques including dynamic light scattering, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, fluorescence spectroscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy and Thermogravimetric analysis. The as-prepared CDs under hydrothermal condition at 220 °C for 6 h had spherical morphology with an average diameter of 4.47 nm. Upon modification, CDs-PEG were photo-responsive with excellent photoluminescence property. The CDs-PEG was subsequently used as a drug carrier for doxorubicin [DOX] delivery to CaCo-2, colon cancer cells in vitro. DOX was successfully loaded onto CDs-PEG surface confirmed by FT-IR and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometer (MALDI-TOF/MS) patterns. The selective treatment of CDs-PEG-DOX against the colorectal cancer cells, , relative to normal human fibroblast cells was succesfully demonstrated.

A Novel Vaccaria Semen Carbonisatum Carbon Nanocomposites and Their Protective Effects on Alcohol-Induced Liver Injury in Mice

Objective: To discover the efficacy of Vaccariae Semen Carbonisatum nano-components (VSC-NCs) on alcoholic liver injury in mice. Methods: VSC was calcined at high temperature in a muffle furnace, and VSC-NCs were extracted and isolated. Mouse model of alcoholic liver injury was used and alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), total bile acid (TBA), oxidative stress and histopathological assessments were done. Results: Characterization and analysis showed that VSC-NCs were spherical, with a particle size distribution of 1.0 to 5.5 nm. The results of animal experiments showed that VSC-NCs could significantly reduce the content of ALT, AST, TBA and ALP in mice with alcohol-induced liver injury, and at the same time significantly increase the level of SOD and reduce the level of malondialdehyde. These results indicated that VSC-NCs could improve the scavenging of reactive oxygen species (ROS) in the body. The ability to reduce the production of lipid peroxides, so as to achieve hepatoprotective effect. Conclusion: VSC-NCs were prepared for the first time, and was confirmed that it has a significant protective effect on liver injury caused by alcohol. In addition, VSC-NCs can be used as a potential drug for the treatment of alcohol-induced liver injury.

"Off-on" fluorescence probe based on green emissive carbon dots for the determination of Cu2+ ions and glyphosate and development of a smart sensing film for vegetable packaging

An ultra-sensitive glyphosate nanosensor, based on carbon dots (CDs), was successfully developed with excellent long-wavelength emission (530 nm), a high quantum yield (41.3%), and an impressive detection limit (0.8 ng·mL-1). This is the lowest value for glyphosate detection achieved by CD-based fluorescence analysis. The sensor was derived from a separate precursor, 1,4-dihydroxyanthraquinone, and was based on the "off-on" fluorescence analysis, where Cu2+ acts as a dynamic quencher and glyphosate as a fluorescence restorer (excitation wavelength 460 nm). Trace detection of glyphosate is possible with a wide detection range of 50-1300 ng·mL-1 and spiked recoveries between 93.3 and 110.0%. Exploration in depth confirmed that (1) the fluorescence of CDs was derived from the carbon core, (2) the large sp2 conjugated domain consisting of graphitic carbon and nitrogen contributed to the long-wavelength emission, and (3) CDs had an impressive binding interaction with Cu2+, which endow high sensitivity to glyphosate detection. The nanosensor has also be used as a dual-mode visual sensor and a smart sensing membrane that can identify glyphosate on the surface of vegetables, thus showing good practical applicability. Synthetic methods of G-CDs and its detection mechanisms for glyphosate.

Change of Cell Toxicity of Food-Borne Nanoparticles after Forming Protein Coronas with Human Serum Albumin

Nanoparticles (NPs) can form protein coronas with plasma proteins after entering the biological environment due to their surface adsorption ability. In this study, the effects of protein coronas of roast squid food-borne nanoparticles (FNPs) with human serum albumin (HSA) on the HepG-2 and normal rat kidney (NRK) cells were investigated. The hydrodynamic diameters of the HSA and HSA-FNPs were 8 and 13 nm, respectively. The cytotoxicity and cell membrane damage of FNPs to HepG-2 cells increased with the increase of roasting temperature. The presence of 4.78 × 10^-3 mol/L FNPs increased the numbers of cellular necrosis and prolonged the G₂ phase of the cell cycle. The formation of protein coronas of squid FNPs mitigated the autophagy phenomenon by FNPs on HepG-2 cells. Moreover, protein coronas reduced the mitochondrial membrane potential in the HepG-2 and NRK cells and the production of reactive oxygen species caused by FNPs. The abnormal contents of oxidative stress indicators such as glutathione, superoxide dismutase, malondialdehyde, and catalase in HepG-2 and NRK cells induced by FNPs were alleviated due to the presence of HSA. These results suggested that the protein coronas formed by HSA on FNPs mitigated the cytotoxicity compared with the bare FNPs, thus providing insights into the interaction of squid FNPs with HSA.

Food-Borne Nanocarriers for Calcium Delivery: A New Choice for Nutrient Supplements

Calcium is considered as an important nutrient element for the maintenance of human health, and food-borne nanoparticles (FNs) produced during food processing may have potential as nanocarriers for calcium ion delivery. Beef is an important source of animal protein that has high protein and low fat content and is rich in a variety of amino acids; thus, beef may be a suitable material for the development of calcium nanocarriers. In this paper, FNs were synthesized from beef by one-step hydrothermal synthesis. The FNs had a spherical shape with a size of about 3.0 nm and emitted a bright blue fluorescence under 365 nm ultraviolet irradiation. The amino nitrogen atom and carboxyl oxygen atom of the functional groups on the surface of the FNs were the main binding sites for the chelation of Ca(II). The size of the FNs-Ca(II) complex was about 4.75 nm, and the specific signal peak of calcium at 3.7 keV was observed in its energy dispersive X-ray spectroscopy spectrum. The viability of cells treated with FNs-Ca(II) was more than 65%, while viability was only 60% after treatment with CaCl₂. The results showed that the FNs from beef have great potential in calcium delivery for the development of a calcium supplement.

Microwave-assisted synthesis of nitrogen-doped carbon dots using prickly pear as the carbon source and its application as a highly selective sensor for Cr(VI) and as a patterning agent

Preparation of water-dispersible carbon dots from inexpensive natural carbon precursors and its application for purposes such as sensing, bio-imaging and patterning agents is showing growing interest in recent years. In this study, we have reported the preparation of nitrogen-doped carbon dots (N-CDs) using prickly pear as the carbon source and m-xylylenediamine as the nitrogen source using a one-step microwave-assisted synthetic process. The N-CDs prepared were characterized on the basis of elemental analysis, XPS, powder-XRD, FT-IR, Raman, TEM, UV-vis and fluorescence spectroscopy. Doping of nitrogen in the N-CDs made them highly fluorescent and the study on their ion-recognition property revealed that they detect highly toxic Cr(VI) with high selectivity and sensitivity (LOD, 0.04 μM) and without interference from the other ions used in this study. By immobilizing these N-CDs onto filter paper, sensor strips were prepared for on-site monitoring/field applications and they were successfully used for the detection of Cr(VI) in water. Detailed spectral analysis revealed that the mechanism of Cr(VI) sensing involved a phenomenon called the "inner filter effect" and analysis of the fluorescence lifetime data suggested the "static quenching" of fluorescence intensity. These N-CDs were used to prepare fluorescent carbon ink and were successfully used as patterning agents.

Protective Effects of Carbon Dots Derived from Armeniacae Semen Amarum Carbonisata Against Acute Lung Injury Induced by Lipopolysaccharides in Rats

Introduction

The charcoal processed product of Armeniacae Semen Amarum (ASA), ASA Carbonisata (ASAC), has long been used for its anti-inflammatory effects. However, the material basis and mechanism of action of ASAC remain unclear.

Aim

To explore the anti-inflammatory effects of Armeniacae Semen Amarum Carbonisata-derived carbon dots (ASAC-CDs).

Methods

The physicochemical properties of ASAC-CDs including morphology, optical properties, functional groups were characterized by a series of methods, mainly including electron microscopy, optical technology and X-ray photoelectron spectroscopy. The anti-inflammatory effect of ASAC-CDs was evaluated and confirmed using acute lung injury (ALI) induced by lipopolysaccharides (LPS) in rats.

Results

The ASAC-CDs ranged from 1.5 to 5.5 nm in diameter, with a quantum yield of 3.17%. ASAC-CDs alleviated LPS-induced inflammation, as demonstrated by reducing the levels of IL-6, IL-1β and TNF-α and increasing the contents of IL-10 in rat serum. More interestingly, ASAC-CDs reduce the content of MDA and MPO and increase the activity of SOD and the content of GSH, indicating the antioxidant activity of ASAC-CDs.

Conclusion

These results demonstrate the remarkable anti-inflammatory effects of ASAC-CDs against ALI induced by LPS, which provide an important basis for the application of ASAC-CDs in clinical anti-pneumonia, and lay an experimental foundation for the research and development of novel nano-drugs.

Carbon dots synthesized from microorganisms and food by-products: active and smart food packaging applications

Nanotechnology is rapidly becoming a commercial reality for application in food packaging. In particular, the incorporation of nanoparticles into packaging materials is being used to increase the shelf life and safety of foods. Carbon dots (C-dots) have a diverse range of potential applications in food packaging. They can be synthesized from environmentally friendly sources such as microorganisms, food by-products, and waste streams, or they may be generated in foods during normal processing operations, such as cooking. These processes often produce nitrogen- and sulfur-rich heteroatom-doped C-dots, which are beneficial for certain applications. The incorporation of C-dots into food packaging materials can improve their mechanical, barrier, and preservative properties. Indeed, C-dots have been used as antioxidant, antimicrobial, photoluminescent, and UV-light blocker additives in food packaging materials to reduce the chemical deterioration and inhibit the growth of pathogenic and spoilage microorganisms in foods. This article reviews recent progress on the synthesis of C-dots from microorganisms and food by-products of animal origin. It then highlights their potential application for the development of active and intelligent food packaging materials. Finally, a discussion of current challenges and future trends is given.

Effects of adding sodium nitrite and tea polyphenols on the characterizations and cytotoxicity of carbon nanoparticles from fried pork

Carbon nanoparticles (CNPs) extensively present in thermal-processed foods. Sodium nitrite (NaNO₂) and tea polyphenols (TP) are commonly used in meat processing, while the properties and cytotoxicity of CNPs existed in fried pork added NaNO₂ and TP remain unknown. The results showed that compared with no addition (NA, 4.008 ± 0.43 nm) in soaked pork, the smaller diameters of CNPs (0.968 ± 0.44 nm) were found in CNPs-NaNO₂-20 group (addition 20 mg/kg NaNO₂), the larger (155.8 ± 7.30 nm) in CNPs-TP-100 group (addition 100 mg/kg TP). The diameter of CNPs was positively correlated with the added concentration. CNPs decreased the viability of HL-7702 cells. Compared with NA group, cell viability in CNPs-NaNO₂-80 group was obviously (p < 0.05) decreased by 3.17%, while the CNPs-TP-200 group was 13.84% higher. CNPs could block cells growth by arresting cells in S-phase and increasing cellular ROS levels. CNPs generated in fired pork added 200 mg/kg TP in soaking showed less cytotoxicity.

Gel-like carbon dots: A high-performance future photocatalyst

To protect water resources, halt waterborne diseases, and prevent future water crises, photocatalytic degradation of water pollutants arouse worldwide interest. However, considering the low degradation efficiency and risk of secondary pollution displayed by most metal-based photocatalysts, highly efficient and environmentally friendly photocatalysts with appropriate band gap, such as carbon dots (CDs), are in urgent demand. In this study, the photocatalytic activity of gel-like CDs (G-CDs) was studied using diverse water pollution models for photocatalytic degradation. The degradation rate constants demonstrated a remarkably enhanced photocatalytic activity of G-CDs compared with most known CD species and comparability to graphitic carbon nitride (g-C₃N₄). In addition, the rate constant was further improved by 1.4 times through the embedment of g-C₃N₄ in G-CDs to obtain CD-C₃N₄. Significantly, the rate constant was also higher than that of g-C₃N₄ alone, revealing a synergistic effect. Moreover, the use of diverse radical scavengers suggested that the main contributors to the photocatalytic degradation with G-CDs alone were superoxide radicals (O₂^-) and holes that were, however, substituted by O₂^- and hydroxyl radicals (OH) due to the addition of g-C₃N₄. Furthermore, the photocatalytic stabilities of G-CDs and CD-C₃N₄ turned out to be excellent after four cycles of dye degradation were performed continuously. Eventually, the nontoxicity and environmental friendliness of G-CDs and CD-C₃N₄ were displayed with sea urchin cytotoxicity tests. Hence, through various characterizations, photocatalytic degradation and cytotoxicity tests, G-CDs proved to be an environmentally friendly and highly efficient future photocatalyst.

The effects of carbon dots produced by the Maillard reaction on the HepG2 cell substance and energy metabolism

Endogenous nanoparticles produced during food processing have received considerable attention due to their unique physicochemical properties and potential safety risks. However, the bio-impact of endogenous nanoparticles on cell metabolism has not been fully studied. In this work, the effects of carbon dots (CDs) derived from the Maillard reaction of glucose and lysine on the cellular substance and energy metabolism were assessed using HepG2 cells as a model. When the HepG2 cells were incubated with 10.0 mg mL-1 of CDs, the mitochondrial membrane potential decreased significantly and the mitochondrial function was affected. The extracellular acidification rate and oxygen consumption rate were decreased in comparison to normal cells without CDs. The CDs blocked the glycolysis pathway by reducing the activities of key enzymes including phosphofructokinase and pyruvate kinase. The energy supply pathway of HepG2 cells changed from glycolysis to TCA cycle, but the increase of the TCA cycle flux could not meet the requirements for restoring cell proliferation. The increase of the compensatory flux in the TCA cycle may be the result of up-regulation of the metabolism of glucogenic amino acids and ketogenic amino acids, while lipid metabolism did not seem to be affected in this process.

Green Phellodendri Chinensis Cortex-based carbon dots for ameliorating imiquimod-induced psoriasis-like inflammation in mice

Background

Carbon dots (CDs) with multifaceted advantages have provided hope for development brand-new nanodrug for treating thorny diseases. This study developed a green and simple calcination method to prepare novel CDs as promising drug for psoriasis treatment. The as-prepared CDs using Phellodendri Chinensis Cortex (PCC) as sole precursor were characterized by a series of methods, mainly including electron microscopy, optical technology and X-ray photoelectron spectroscopy (XPS).

Results

Results displayed that fluorescence (Quantum yield = 5.63%) and nontoxic PCC-based CDs (PCC-CDs) with abundant chemical groups exhibited solubility and tiny sizes at average of (1.93 ± 0.53) nm, which may be beneficial for its inherent biological activity. Moreover, by using the typical imiquimod (IMQ)-induced psoriasis-like skin mouse model, we firstly demonstrated the pronounced anti-psoriasis activity of as-prepared PCC-CDs on ameliorating the appearance, psoriasis area and severity index (PASI) scores as well as histopathological morphology of both back skin tissues and right ears in IMQ-induced mouse. Further potential mechanisms behind the anti-psoriasis activities may be related to suppress M1 polarization and relatively promote M2 polarization of macrophage both in vitro and in vivo.

Conclusion

These results suggested that PCC-CDs have potential to be an anti-psoriasis candidate for clinical applications to treat psoriasis, which not only provided an evidence for further broadening the biological application of CDs, but also provided a potential hope for application nanodrugs to treat thorny diseases.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00847-y.

Fluorescence nanoparticles from instant coffee accumulated in lysosome and induced lysosome-dependent cell death via necroptosis-like pathway

Fluorescence nanoparticles (FNs) are a type of nano-dots generated during baking process, and their safety on organism is unclear and little is known to their cytotoxicity. In this study, the FNs from instant coffee were purified and characterized. The FNs with an average size about 2.08 nm emitted bright blue fluorescence with lifetime about 2.74 ns. The element and functional groups were analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, respectively. The results indicated that these FNs were internalized in lysosomes and induced apoptosis of normal rat kidney (NRK) and Caco-2 cells. While, the pan-caspase inhibitor, Z-VAD-FMK didn't decrease the rate of apoptosis and cell death of the FNs-treated NRK and Caco-2 cells. These internalized FNs enlarged lysosomes, decreased lysosomal enzyme degradation activity and increased lysosomal pH value. Partial co-localization of receptor-interacting serine-threonine kinase 3 (RIPK3) to lysosomes in FNs-treated cells was observed, and the amount of RIPK1 and RIPK3 increased after treatment with FNs. The results demonstrated that the FNs from instant coffee induced lysosomal membrane permeabilization and initiated necroptosis.

Comparison of the effects of synthesis methods of B, N, S, and P-doped carbon dots with high photoluminescence properties on HeLa tumor cells

Although heteroatom doping is widely used to promote the optical properties of carbon dots for biological applications, the synthesis process still has problems such as multi-step process, complicating the setting of instrument along with uncontrolled products. In the present study, some elements such as boron, nitrogen, sulfur, and phosphor were intentionally doped into citric acid-based carbon dots by furnace- and microwave-assisted direct and simple carbonization processes. The process produced nanoparticles with an average diameter of 5-9 nm with heteroatoms (B, N, S, and P) placed on the core and surface of carbon dots. Among the doped carbon dots prepared, boron-doped carbon dots obtained by the microwave-assisted (B-CDs2) process showed the highest photoluminescence intensity with a quantum yield (QY) of about 32.96%. All obtained carbon dots exhibit good stability (at pH 6-12 and high ionic strength concentrations up to 0.5 M), whereas cytotoxicity analysis showed that all doped carbon dots are low-toxic with an average cell viability percentage above 80% up to 500 μg mL-1. It can be observed from the CLSM image of all doped carbon dots that the doping process not only increases the QY percentage, but also might accelerate the HeLa uptake on it and produce strong carbon dot emission at the cytoplasm of the cell. Thus, the proposed synthesis process is promising for high-potency bioimaging of HeLa cancer cells.

Molecular interaction of fluorescent carbon dots from mature vinegar with human hemoglobin: Insights from spectroscopy, thermodynamics and AFM

Foodborne nanoparticles have attracted considerable interest due to their distinctive fluorescence and physicochemical properties. The discovery of vinegar carbon dots (VCDs) has drawn our attention to study their effect on human plasma protein. Herein, spectral, constructional, morphological, and enzymatic activity assessments were carried out to investigate the interaction of VCDs with human hemoglobin (HHb). The intrinsic fluorescence of HHb was quenched significantly by the VCDs through a static quenching process. Furthermore, binding constants and important thermodynamic parameters were calculated, the negative enthalpy and entropy changes were accompanied by a negative Gibbs energy, which proposed the binding between VCDs with HHb was spontaneous. Moreover, negative enthalpy and entropy change corroborated the involvement of van der Waals force and hydrogen bonds in the binding process. Results from FTIR, atomic force microscopy and circular dichroism revealed change of HHB after binding with VCDs although their essential morphological features were unaffected. The esterase activity of HHb decreased after VCDs treatment in a dose-dependent manner, which further confirmed the effect of VCDs on HHb. The results offered detailed information about the interaction between VCDs and HHb.

Effects of fluorescent carbon dots from the baked lamb on energy and lipid metabolism

Food-borne carbon dots (CDs) may cause health risks due to their unique properties. However, previous efforts were mainly focused on the characterization of their physicochemical properties, their effects on cellular metabolism are not entirely revealed. Herein, the features and potential toxicity of CDs from lamb baked for 15, 30, and 45 min were evaluated, their cytotoxicity increased with the extension of baking time. Furthermore, the metabolic responses of PC12 cells after exposure to CDs from lamb baked for 45 min were investigated. The CDs perturbed purine metabolism, causing reactive oxygen species accumulation. Meanwhile, the CDs down-regulated glycolysis and TCA cycle, led to a significant decrease in ATP. Additionally, the CDs induced triglyceride accumulation, mainly through enhanced fatty acid biosynthesis. The adverse effects of CDs from baked lamb involved the perturbation of energy production, purine metabolism, and triglyceride biosynthesis, which provided additional information about the risks of CDs from food items.

Sandalwood-derived carbon quantum dots as bioimaging tools to investigate the toxicological effects of malachite green in model organisms

Malachite green is an N-methylated diaminophenylmethane dye that has generated much concern over its suggestive carcinogenic nature. After its excessive use in aquaculture industry as an effective ectoparasitide, much debate was raised over its toxicological effects leading to scientific studies conducted on animal models. Even after several bans, malachite green is still easily available in many parts of the world and unscrupulously even used to give green vegetables a fresher look. This study aims to address this concern by systematically studying the toxicological effects of malachite green through bioimaging in plant and animal cell and tissue. Sandalwood-derived carbon quantum dots have been used as a bioimaging tool since they are non-cytotoxic and show excellent fluorescence properties. Onion tissues demonstrate the translocation of the dye inside cells having high affinity for the nuclei and cell walls. Toxicological effects on the growth of Vigna radiata (mung beans) have been studied methodically. Bioimaging of the transverse cross-section of the dye-treated plant root shows a significant difference from the control. In animal cells, dose-dependent decrease in cell viability of MG-63 cells was observed with MG. CQD showed good fluorescence in both cytoplasm and nucleus of MG63 cells. In addition, CQDs were employed as a great tool for bioimaging of the histopathologically adverse effects of MG in Golden hamster animal model. This study showed CQDs could be used as an alternative non-site specific fluorescent probe for cell and tissue imaging for better visualization of cell and tissue architectural changes.

Endogenous Fluorescence Carbon Dots Derived from Food Items

Background

Fluorescent carbon dots (CDs) are a novel class of carbon-based nanomaterials that were discovered in 2004. However, nobody knew that CDs existed in food items naturally until 2012. Properties of nanosize materials are distinct from those of their bulk materials due to the particle size and accordingly alter their bioavailability and/or biocompatibility. Therefore, the potential health risk of nanoparticles in food has drawn massive attention. Currently, almost all studies regarding the biosafety of nanoparticles in food have mainly focused on engineered nanoparticles used as food additives and have excluded the endogenous nanoparticles in food. Therefore, investigation of the properties of food-borne fluorescent CDs and their potential health risk to humans is of great significance.

Scope and approach

This review summarizes the existing literature on fluorescent carbon dots (CDs) in food, with particular attention to their properties, formation process, and the potential health risks posed to consumers. The knowledge gap between food-borne nanoparticles and their potential risks is identified, and future research is proposed.

Key findings and conclusions

The presence of fluorescent CDs in food produced during food processing has been summarized. Fluorescent CDs less than 10 nm in size mainly contain carbon, oxygen, hydrogen, and/or nitrogen. The presence of CDs in food items was first demonstrated in 2012, and their formation was attributed to heating of the starting material. The properties of CDs in food are different from the engineered nanoparticles used as food as additives and represent a novel kind of nanostructure in food. Further studies should focus on the chronic effects of CDs, although their toxicity is low, because investigations both in vivo and in vitro are limited.

Fluorescent nanoparticles in the popular pizza: properties, biodistribution and cytotoxicity

Food-borne nanoparticles that are generated during the thermal processing of various consumed foods are of great concern due to their unique properties. In this study, the presence of fluorescent nanoparticles (FNPs) in pizza, their biodistribution and cytotoxicity were investigated. The spherical FNPs have a diameter of about 3.33 nm. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analysis revealed that they contained 68.21% C, 27.44% O, 2.75% N and 1.60% S, and the functional groups on their surface included -OH, -COOH, C[double bond, length as m-dash]C, -NH2 and C[double bond, length as m-dash]O. In vitro and in vivo biodistribution of pizza FNPs was evaluated using normal rat kidney (NRK) cells, onion epidermal cells, Caenorhabditis elegans and mice. The fluorescence microscopy images clearly indicate that the pizza FNPs appear to be localized within the cytoplasm. However, the FNPs remained restricted to the extracellular space of the onion epithelium and did not enter the onion cell cytoplasm because of the cell wall. The FNPs were swallowed by the Caenorhabditis elegans worms when exposed to food OP50 and distributed within the pharynx, intestine and anus. Obvious fluorescence of the FNPs in the stomach, intestine, liver, lung and kidney was observed for the FNPs in mouse organs, but not the brain, heart, and spleen. Furthermore, the produced FNPs were found to cause cell cycle arrest at the G0/G1 phase in NRK cells, and resulted in cell apoptosis at high doses. The outcome of this research offers an important insight into the nature of thermal processing-induced nanoparticles and their in vivo and in vitro biological effects.

Hydrophilic Food-Borne Nanoparticles from Beef Broth as Novel Nanocarriers for Zinc

Food-borne nanoparticles (FNs) may be used as nanocarriers for metal ion chelation in micronutrient supplements. In this paper, the preparation and characterization of hydrophilic FNs were reported from beef broth cooked with a pressure cooker at 117 °C for different periods (30, 50, and 70 min) and their potential application as nanocarriers for zinc was investigated. The broth FNs are quasi-spherical with good water solubility and ultrasmall size, which can emit a strong sapphire color under 365 nm ultraviolet irradiation. X-ray photoelectron spectroscopy (XPS) analysis showed that there are carboxyl, amino, and hydroxyl groups on the FNs, which are useful for Zn(II) chelation. The vibration band of C═O at 1688 cm^-1 in the infrared spectrum of FNs shifted to 1718 cm^-1 after binding with Zn(II) ions, suggesting the participation of the carbonyl group in Zn(II) ion chelation. The appearance of Zn_2p XPS peaks, at 1021.6 and 1045 eV for Zn(II)-FNs, clearly demonstrated the formation of Zn-O between the FNs and zinc ions. Biodistribution of FNs and the Zn(II)-FN complex in normal rat kidney cells demonstrated that they could easily enter normal rat kidney cells. A downfield was found for the signals of Zn(II)-FNs in ¹H nuclear magnetic resonance spectroscopy and strongly suggested the binding of Zn(II) ions to FNs through carboxylic acid, hydroxyl, and amine groups. In addition, no obvious cytotoxicity was found for Zn(II)-FNs compared to zinc (ZnSO₄) and commercial zinc gluconate. The results revealed that the FNs from beef broth may have a potential as nanocarriers for zinc chelation.

Interactions of carbon quantum dots from roasted fish with digestive protease and dopamine

The carbon quantum dots from roasted fish interacted with digestive protease and dopamine.

Insights into melanoidin conversion into fluorescent nanoparticles in the Maillard reaction

Melanoidins are not the final product of the Maillard reaction, and they can be further converted to fluorescent nanoparticles after hydrothermal treatment.

Food-borne nanocarriers from roast beef patties for iron delivery

Fluorescent nanoparticles (FNs) from roast beef patties were characterized and used as nanocarriers for ferrous ions.

Characterization of Endogenous Nanoparticles from Roasted Chicken Breasts

Emergence of endogenous nanoparticles in thermally processed food has aroused much attention due to their unique properties and potential biological impact. The aim of this study was to investigate the presence of fluorescence nanoparticles in roasted chicken breasts, elemental composition, physicochemical properties, and their molecular interaction with human serum albumin (HSA). Transmission electron microscopy analysis revealed that the foodborne nanoparticles from roasted chicken were nearly spherical with an average particle size of 1.7 ± 0.4 nm. The elemental analysis of X-ray photoelectron spectroscopy showed the composition of nanoparticles as 47.4% C, 25.8% O, and 26.1% N. The fluorescence of HSA was quenched by the nanoparticles following a static mode, and the molecular interaction of nanoparticles with HSA was spontaneous (Δ G⁰ < 0), where hydrogen bonding and van der Waals forces played an important role during HSA-nanoparticles complex stabilization through thermodynamic analysis by isothermal titration calorimetry. The principal location of the nanoparticles binding site on HSA was primarily in site I as determined by site-specific marker competition. The conformational of HSA was also changed and α-helical structure decreased in the presence of nanoparticles. Our studies revealed that fluorescent nanoparticles were produced after roasting of chicken breast at 230 °C for 30 min for the first time. The obtained nanoparticles can interact with HSA in a spontaneous manner, thus providing valuable insight into foodborne NPs as well as their effects to human albumin protein.

Fluorescent Carbon Dots Derived from Maillard Reaction Products: Their Properties, Biodistribution, Cytotoxicity, and Antioxidant Activity

Food-borne nanoparticles have received great attention because of their unique physicochemical properties and potential health risk. In this study, carbon dots (CDs) formed during one of the most important chemical reactions in the food processing field, the Maillard reaction from the model system including glucose and lysine, were investigated. The CDs purified from Maillard reaction products emitted a strong blue fluorescence under ultraviolet light with a fluorescent quantum yield of 16.30%. In addition, they were roughly spherical, with sizes of around 4.3 nm, and mainly composed of carbon, oxygen, hydrogen, and nitrogen. Their surface groups such as hydroxyl, amino, and carboxyl groups were found to possibly enable CDs to scavenge DPPH and hydroxyl radicals. Furthermore, the cytotoxicity assessment of CDs showed that they could readily enter HepG2 cells while causing negligible cell death at low concentration. However, high CDs concentrations were highly cytotoxic and led to cell death via interference of the glycolytic pathway.

Bio-distribution and interaction with dopamine of fluorescent nanodots from roasted chicken

The formation of a new type of food-borne FNDs with varying particle sizes and different fluorescence properties in chicken roasted at different temperatures, and theirin vitrointeraction with dopamine are reported.

Ultrasmall fluorescent nanoparticles derived from roast duck: their physicochemical characteristics and interaction with human serum albumin

Fluorescent nanoparticles (FNPs) produced from roast meat have drawn widespread attention due to their potential hazards to human health.

A facile and green approach to prepare carbon dots with pH-dependent fluorescence for patterning and bioimaging

Carbon dots prepared with the adoption of ubiquitous natural fruit juices as precursors have good applications in pH sensing, patterning and bioimaging.

Fluorescent nanoparticles from mature vinegar: their properties and interaction with dopamine

In this paper we report the discovery of fluorescent nanoparticles (FNs) in Chinese mature vinegar.