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Nanosized materials may produce adverse physiological effects or potential health risks due to their unique physical and chemical properties. Herein, the universal presence of fluorescent carbon dots (CDs) in commercial beers was confirmed through a systematic survey. The beer CDs were roughly spherically shaped in appearance and emitted bright blue fluorescence under ultraviolet light with quantum yields (QYs) ranging from 1.42% to 3.92%. Furthermore, digestion, biodistribution, and cytotoxicity assessments of CDs from Snow beer were conducted as an example. The CDs were significantly quenched during in vitro digestion. The dynamic distribution of CDs in mice showed that they easily accumulated in the intestine and liver, and more importantly, the beer CDs were found in the brain, which indicated that they were able to cross the blood–brain barrier. Acute toxicity of the beer CDs was evaluated using BALB/c mice, and the results revealed that the biochemical parameters of mice after administration of a single dose of 2 g kg−1 body weight were almost same as those of the control groups. Histological analysis showed no obvious organ damage in the tested mice. The in vitro results indicated that CDs dispersed onto both the cell membrane and the cytoplasm of MC3T3-E1 cells, alter the cell cycle progression, and caused cell apoptosis at high doses. This work reports the potential risk of CDs in beer and provides valuable information regarding CDs in food. [ABSTRACT FROM AUTHOR]

Carbon dots with both one- and two-photon fluorescence have drawn great attention for biomedical imaging. Herein, nitrogen-doped carbon dots were facilely developed by one-pot hydrothermal method using bovine serum albumin and formic acid as carbon sources. They are highly water-soluble with strong fluorescence when excited with ultraviolet or near infrared light. The carbon dots have a diameter of ∼8.32 nm and can emit strong two-photon induced fluorescence upon excitation at 750 nm with a femtosecond laser. X-ray photoelectron spectrometer analysis revealed that the carbon dots contained three components, C, N and O, corresponding to the peak at 285, 398 and 532 eV, respectively. The Fourier-transform infrared spectroscopy analysis revealed that there are carboxyl and carboxylic groups on the surface, which allowed further linking of functional molecules. pH stability study demonstrated that the carbon dots are able to be used in a wide range of pH values. The fluorescence mechanism is also discussed in this study. Importantly, these carbon dots are biocompatible and highly photostable, which can be directly applied for both one- and two-photon living cell imaging. After proper surface functionalization with TAT peptide, they can be used as fluorescent probes for live cell nuclear-targeted imaging. [ABSTRACT FROM AUTHOR]

Abstract: Carbon dots (C-dots) are a class of novel fluorescent nanomaterials, which have drawn great attention for their potential applications in bio-nanotechnology. Multicolor C-dots have been synthesized by chemical nitric acid oxidation using the reproducible plant soot as raw material. TEM analysis reveals that the prepared C-dots have an average size of 3.1nm. The C-dots are well dispersed in aqueous solution and are strongly fluorescent under the irradiation of ultra-violet light. X-ray photoelectron spectroscopy characterization demonstrates that the O/C atomic ratio for C-dots change to from 0.207 to 0.436 due to the chemical oxidation process. The photo bleaching experiment reveals that the C-dots show excellent photostability as compared with the conventional organic dyes, fluorescein and rhodamine B. The fluorescence intensity of the C-dots did not change significantly in the pH range of 3–10. To further enhance the fluorescence quantum yield, the C-dots were surface modified with four types of passivation ligands, 4,7,10-trioxa-1,13-tridecanediamine (TTDDA), poly-L-lysine (PLL), cysteine and chitosan and the fluorescence quantum yields of the TTDDA, PLL, cysteine and chitosan passivated C-dots were improved 1.53-, 5.94-, 2.00- and 3.68-fold, respectively. Fourier-transform infrared (FTIR) spectra were employed to characterize the surface groups of the C-dots. The bio-application of the C-dots as fluorescent bio-probes was evaluated in cell imaging and ex vivo fish imaging, which suggests that the C-dots may have potential applications in biolabeling and bioimaging. [Copyright &y& Elsevier]

• N-doped fluorescent carbon dots (CDs) were prepared from roast duck breasts. • The synthesis of CDs from roast duck is facile and regenerative. • The absolute fluorescence quantum yield of CDs can up to be 38.05%. • The CDs were successfully employed as probes for cellular and C. elegans imaging. Biocompatible fluorescent carbon dots (CDs) were prepared via a simple and green route using duck breasts as a natural carbon source. The CDs from duck breasts were well dispersed, and their mean particle size decreased from 2.59 to 1.95 nm when the roasting temperature increased from 200 to 300 °C. Abundant functional groups such as OH, COOH, and NH 2 were observed on the surface of the CDs, providing the CDs with good water solubility. These CDs emitted strong fluorescence under ultraviolet light irradiation and exhibited superior photostability. The absolute fluorescence quantum yield of CDs rose from 10.53% to 38.05% when the relative nitrogen content of CDs increased from 7.18% to 12.73%. The CDs showed low toxicity to PC12 cells for prolonged exposure. Therefore, the duck CDs were successfully developed as fluorescent probes for in vitro PC12 cells and in vivo Caenorhabditis elegans imaging. These results indicated that the CDs derived from roast duck were biocompatible and can potentially be used as probes in bio-imaging. [ABSTRACT FROM AUTHOR]

• Fluorescent carbon dots (C-dots) were prepared from human urine in a facile method. • The human urine C-dots have a fluorescence quantum yield (QY) of 4.8%. • After hydrothermal treatment of urine, the fluorescence QY increased to 17.8%. • The C-dots were successfully used in Hela cells, Caenorhabditis elegans, onion epidermal cells and bean sprouts imaging. • The urine C-dots have good biocompatibility and have potential for bio-imaging. This study aims to obtain water-soluble fluorescent carbon dots (C-dots) from low-value metabolites through a simple, economical, one-step synthetic route. The urine C-dots (UCDs) and hydrothermally treated urine C-dots (HUCDs) were obtained, respectively, using straightforward Sephadex filtration method from human adults and hydrothermal reaction method. The UCDs and HUCDs emit fluorescence upon being excited with ultraviolet light with a quantum yield of 4.8% and 17.8%, respectively. TEM analysis revealed that UCDs and HUCDs had an average size of 2.5 nm and 5.5 nm, respectively. X-ray photoelectron spectroscopy (XPS) analysis showed the UCDs and HUCDs were mainly composed of carbon, oxygen and nitrogen. Fourier-transform infrared (FTIR) spectroscopy demonstrated the presence of functional groups, such as amino, hydroxyl, carboxylate and carbonyl groups onto the C-dots. The UCDs and HUCDs can be directly used for in vivo and in vitro imaging in Hela cells, Caenorhabditis elegans, onion epidermal cells and bean sprouts. The cytotoxicity study revealed that the UCDs and HUCDs were not toxic to normal rat kidney (NKR) cells with good biocompatibility. The results revealed that the C-dots derived from urine have good biocompatibility, strong fluorescence and may have potential to be a safe fluorescent probe for bio-imaging. [ABSTRACT FROM AUTHOR]

Ascorbic acid (AA) is an essential vitamin and plays an irreplaceable role in humans' daily life. Therefore, it is of profound significance to develop effective strategies for AA sensing. Herein, a novel bi-functional sensing strategy was developed by using carbon dots (CDs) and MnO 2 nanosheet as the fluorometric/magnetic signal source. When AA was absence, the fluorescence of CDs was quenched by MnO 2 nanosheet due to the inner filter effect. Neither the fluorescence nor magnetic signal of the nanoprobe can be detected. In the presence of AA, a redox reaction occurred between MnO 2 nanosheet and AA resulting in the generation of magnetic resonance imaging (MRI) response Mn2+ and decomposing of MnO 2 nanosheet structure, thus leading to the recovery of CDs fluorescence. The detection limit of the AA was determined to be 2.89 μM with a linear range of 0–80 μM in fluorescence mode, and detection limit of 0.776 μM with a linear range of 0–80 μM in MRI mode when used transverse relaxation rate as signal. Furthermore, the developed fluorometric/magnetic bi-functional nanoprobe showed good biocompatibility, high response rate, high selectivity towards AA and could be used to analyses AA in real samples. Moreover, in vivo imaging of AA in mice was achieved in magnetic mode. The fluorometric/magnetic bi-function sensor for AA detection was introduced, which provided a novel strategy for sensor design based on CDs. Image 1 • A novel bi-functional sensing strategy was designed based on inner filter effect. • Fluorometric/magnetic signals were activated by redox reaction between AA and MnO 2. • Both in vitro and in vivo AA detection were achieved. [ABSTRACT FROM AUTHOR]

• Carbon dots (CDs) with fluorescence quantum yield of 58% were prepared by hydrothermal method. • Tryptophan was selected as CDs precursor after screening from seventeen amino acids. • The CDs can be used for both one- and two-photon fluorescence cellular imaging. • The CDs conjugating with TAT peptide showed good capability in nuclear-targeted imaging. Carbon dots (CDs) with both one- and two-photon fluorescence have attracted much attention in the field of bioimaging. In this study, we reported a strategy for the design of peptide-conjugated CDs for cellular nuclear-targeted imaging. The CDs were prepared from amino acid and formic acid via an one-step hydrothermal synthesis method, and then modified with trans-activator of transcription (TAT) peptide for both one- and two- photon nuclear-targeted fluorescence imaging. The CDs derived from tryptophan (Trp) and formic acid showed the highest fluorescence quantum yield of 58.4% with an average size about 1.7 nm in diameter. The maximum excitation and emission wavelengths of the Trp/formic acid CDs were 360 and 442 nm, respectively. The Trp/formic acid CDs were successfully conjugated with TAT peptide through the reaction between the amino group of the peptide and carboxylic group of the CDs. Upon grafting with TAT peptide, the resulted TAT-Trp/formic acid CDs could be used as nuclear-targeted fluorescent probes for both one- and two-photon live cell fluorescence imaging. [ABSTRACT FROM AUTHOR]

Highlights • Properties of carbon dots from baked lamb were dependent on heating temperature. • Carbon dots from baked lamb could alter the cell cycle progression slightly. • Carbon dots from baked lamb could scavenge free radicals both in vitro and in vivo. Abstract The formation and properties of nanostructures during food processing have attracted much attention in recent years. Herein, the formation and physicochemical properties of fluorescence carbon dots (CDs) from baked lamb at different baking temperatures (200, 300, and 350 °C) were investigated. The morphology, surface functional groups and fluorescent quantum yield of the CDs were found to be highly dependent on the heating temperature. Biocompatibility of CDs investigation indicated that they were able to disperse onto both the cell membrane and the cytoplasm of HepG2 cells, and alter the cell cycle progression slightly. Moreover, the CDs from baked lamb of 350 °C showed the maximum scavenging capability to free radicals and could protect the cell from oxidative damage in vitro. This contribution represents the first report regarding the properties and formation process of CDs in baked lamb, providing valuable insights into baking temperature influence on physicochemical properties of the CDs. [ABSTRACT FROM AUTHOR]

Abstract: The presence of the carbon dots (C-dots) in food is a hotly debated topic and our knowledge about the presence and the use of carbon dots (C-dots) in food is still in its infancy. We report the finding of the presence of photoluminescent (PL) C-dots in commercial Nescafe instant coffee. TEM analysis reveals that the extracted C-dots have an average size of 4.4nm. They were well-dispersed in water and strongly photoluminescent under the excitation of ultra-violet light with a quantum yield (QY) about 5.5%, which were also found to possess clear upconversion PL properties. X-ray photoelectron spectroscopy characterization demonstrates that the C-dots contain C, O and N three elements with the relative contents ca. 30.1, 62.2 and 7.8%. The X-ray diffraction (XRD) analysis indicates that the C-dots are amorphous. Fourier-transform infrared (FTIR) spectra were employed to characterize the surface groups of the C-dots. The C-dots show a pH independent behavior by varying the pH value from 2 to 11. The cytotoxicity study revealed that the C-dots did not cause any toxicity to cells at a concentration as high as 20mg/mL. The C-dots have been directly applied in cells and fish imaging, which suggested that the C-dots present in commercial coffee may have more potential biological applications. [Copyright &y& Elsevier]

• The properties of carbon dots (CDs) from baked lamb were baking time-dependent. • The cytotoxicity of CDs from baked lamb increased with extension of baking time. • The CDs from baked lamb strengthened reactive oxygen species production. • The CDs disrupted glycolysis, tricarboxylic acid cycle, 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. [ABSTRACT FROM AUTHOR]