Carbon "Quantum" Dots for Fluorescence Labeling of Cells.

The specifically synthesized and selected carbon dots of relatively high fluorescence quantum yields were evaluated in their fluorescence labeling of cells. For the cancer cell lines, the cellular uptake of the carbon dots was generally efficient, resulting in the labeling of the cells with bright fluorescence emissions for both one- and two-photon excitations from predominantly the cell membrane and cytoplasm. In the exploration on labeling the live stem cells, the cellular uptake of the carbon dots was relatively less efficient, though fluorescence emissions could still be adequately detected in the labeled cells, with the emissions again predominantly from the cell membrane and cytoplasm. This combined with the observed more efficient internalization of the same carbon dots by the fixed stem cells might suggest some significant selectivity of the stem cells toward surface functionalities of the carbon dots. The needs and possible strategies for more systematic and comparative studies on the fluorescence labeling of different cells, including especially live stem cells, by carbon dots as a new class of brightly fluorescent probes are discussed.

Carbon nanoparticles trapped in vivo-similar to carbon nanotubes in time-dependent biodistribution.

Carbon nanoparticles are in all of the carbon nanomaterials that are presently widely pursued for potential bioapplications, but their in vivo biodistribution-related properties are largely unknown. In this work, highly (13)C-enriched carbon nanoparticles were prepared to allow their quantification in biological samples by using isotope-ratio mass spectroscopy. The in vivo biodistribution results are presented and discussed, and also compared with those of the aqueous suspended carbon nanotubes reported previously. The distribution profile and time dependencies are largely similar between the nanoparticles and nanotubes, with results on both suggesting meaningful accumulation in some major organs over an extended period of time. Therefore, the surface modification of carbon nanoparticles, preferably the chemical functionalization of the nanoparticles with biocompatible molecules or species, is desirable or necessary in the pursuit of these nanomaterials for various bioapplications.

Toward structurally defined carbon dots as ultracompact fluorescent probes.

There has been much discussion on the need to develop fluorescent quantum dots (QDs) as ultracompact probes, with overall size profiles comparable to those of the genetically encoded fluorescent tags. In the use of conventional semiconductor QDs for such a purpose, the beautifully displayed dependence of fluorescence color on the particle diameter becomes a limitation. More recently, carbon dots have emerged as a new platform of QD-like fluorescent nanomaterials. The optical absorption and fluorescence emissions in carbon dots are not bandgap in origin, different from those in conventional semiconductor QDs. The absence of any theoretically defined fluorescence color-dot size relationships in carbon dots may actually be exploited as a unique advantage in the size reduction toward having carbon dots serve as ultracompact QD-like fluorescence probes. Here we report on carbon dots of less than 5 nm in the overall dot diameter with the use of 2,2'-(ethylenedioxy)bis(ethylamine) (EDA) molecules for the carbon particle surface passivation. The EDA-carbon dots were found to be brightly fluorescent, especially over the spectral range of green fluorescent protein. These aqueous soluble smaller carbon dots also enabled more quantitative characterizations, including the use of solution-phase NMR techniques, and the results suggested that the dot structures were relatively simple and better-defined. The potential for these smaller carbon dots to serve as fluorescence probes of overall sizes comparable to those of fluorescent proteins is discussed.

Formation of trans fatty acids during the frying of chicken fillet in corn oil.

To assess effects of heated edible oils on intake of trans fatty acids (TFAs); the formation of TFAs in cooking conditions was investigated by a frying system model, in which chicken fillet was fried in a commercial corn oil at 170 °C, for 12 frying cycles. The main TFAs detected in chicken fillet were trans C18:2 fatty acids (FAs) and trans C18:3 FAs, which exhibited no significant differences among the frying cycles. Besides, the content of trans C18:1 FAs were very low in all samples on different frying cycles. The intake of TFAs was estimated to be 0.06 g/100 g when chicken fillet fried in this process was consumed. These results suggest that an ordinary frying process upon a commercial corn oil has little impact on the daily TFAs intake.

Carbon "quantum" dots for optical bioimaging.

Carbon dots, generally referring to small carbon nanoparticles with various levels of surface passivation, have emerged as a new class of quantum dot-like fluorescent nanomaterials. Since the original report in 2006, carbon dots have been investigated by many research groups worldwide, with major advances already made in their syntheses, structural and mechanistic understandings, and evaluations for biocompatibilities and potential bio-applications. In this article, representative studies responsible for these advances in the development and understanding of carbon dots are reviewed, and those targeting the use of carbon dots as high-performance yet nontoxic fluorescence agents for optical bioimaging in vitro and in vivo are highlighted and discussed.

Competitive performance of carbon "quantum" dots in optical bioimaging.

Carbon-based "quantum" dots or carbon dots are surface-functionalized small carbon nanoparticles. For bright fluorescence emissions, the carbon nanoparticles may be surface-doped with an inorganic salt and then the same organic functionalization. In this study, carbon dots without and with the ZnS doping were prepared, followed by gel-column fractionation to harvest dots of 40% and 60% in fluorescence quantum yields, respectively. These highly fluorescent carbon dots were evaluated for optical imaging in mice, from which bright fluorescence images were obtained. Of particular interest was the observed competitive performance of the carbon dots in vivo to that of the well-established CdSe/ZnS QDs. The results suggest that carbon dots may be further developed into a new class of high-performance yet nontoxic contrast agents for optical bioimaging.

Carbon dots of different composition and surface functionalization: cytotoxicity issues relevant to fluorescence cell imaging.

Nanoscale carbon particles have emerged as versatile precursors for a new class of highly fluorescent nanomaterials that resemble semiconductor quantum dots. The surface-passivated fluorescent carbon nanoparticles, dubbed 'carbon dots', were already demonstrated for their potential optical bioimaging applications in vitro and in vivo. In this study, we conducted a systematic cytotoxicity evaluation on the carbon dots prepared by various combinations of precursor carbon nanoparticles and molecules for the particle surface functionalization. The results suggested that the cytotoxicity of carbon dots was dependent on the selection of surface passivation molecules. Those dots showing more significant cytotoxicity at higher concentrations were also evaluated for their effects on the fluorescence imaging of live cells. The implications of the results on the eventual use of carbon dots as cell imaging agents are discussed.

Graphene oxide: a nonspecific enhancer of cellular growth.

There have been multiple conflicting reports about the biocompatibility and antimicrobial activity of graphene oxide. To address this, we conducted a study to characterize the antimicrobial properties of graphene oxide (GO) and its biocompatibility with mammalian cells. When GO was added to a bacterial culture at 25 µg/mL, the results showed that bacteria grew faster and to a higher optical density than cultures without GO. Scanning electron microscopy indicated that bacteria formed dense biofilms in the presence of GO. This was shown by a large mass of aggregated cells and extracellular polymeric material. Bacterial growth on filters coated with 25 and 75 µg of GO grew 2 and 3 times better than on filters without GO. Closer analysis showed that bacteria were able to attach and proliferate preferentially in areas containing the highest GO levels. Graphene oxide films failed to produce growth inhibition zones around them, indicating a lack of antibacterial properties. Also, bacteria were able to grow on GO films to 9.5 × 10(9) cells from an initial inoculation of 1.0 × 10(6), indicating that it also lacks bacteriostatic activity. Thus, silver-coated GO films were able to produce clearing zones and cell death. Also, graphene oxide was shown to greatly enhance the attachment and proliferation of mammalian cells. This study conclusively demonstrates that graphene oxide does not have intrinsic antibacterial, bacteriostatic, and cytotoxic properties in both bacteria and mammalian cells. Furthermore, graphene oxide acts as a general enhancer of cellular growth by increasing cell attachment and proliferation.

Long-chain polyunsaturated fatty acids promote paclitaxel cytotoxicity via inhibition of the MDR1 gene in the human colon cancer Caco-2 cell line.

OBJECTIVE: Accumulating evidence in both humans and animal models indicates that dietary intake of long-chain polyunsaturated fatty acids (PUFAs) can improve response to chemotherapy. The intent of this study was to determine the mechanisms by which PUFAs affect the response to anticancer chemotherapy. METHODS: Human colorectal cancer cell line Caco-2 was used as a model system in this study. Caco-2 cells were treated with different concentrations of three PUFAs: eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid (AA). Real-time polymerase chain reaction was used to determine mdr1 gene (codes for P-glycoprotein [P-gp]) expression. Western blotting and calcein-acetoxymethylester efflux assay were used for P-gp expression and functional evaluation, respectively. Furthermore, apoptosis assay was conducted by adding PUFAs with paclitaxel to confirm the synergetic effect. Finally, gene expression of nuclear receptors CAR and PXR were estimated to evaluate the possible mechanisms. RESULTS: Both classes of PUFAs, omega-3 (ω-3) and omega-6 (ω-6), can cause a modest but very reproducible reduction of gene expression, protein production, and pump activity of MDR1. Incubation of cells with PUFAs greatly enhanced the cytotoxicity of the anticancer drug paclitaxel, manifested mainly through enhanced paclitaxel-induced apoptosis. Furthermore, PUFAs increased the messenger RNA (mRNA) levels of the nuclear receptors CAR and PXR, thus implicating these two transcription factors as cellular targets of PUFAs in cells but not directly affecting MDR1 regulation. CONCLUSIONS: Our results suggest that inhibition of the multidrug resistance MDR1/P-gp is one mechanism through which dietary polyunsaturated fatty acids exert a synergetic effect on the response of tumor cells to anticancer drugs.

Inhibitory effects of muscadine anthocyanins on α-glucosidase and pancreatic lipase activities.

Inhibitory effects of the Noble muscadine grape extracts and the representative phytochemicals for anthocyanins (i.e., cyanidin and cyanidin-3,5-diglucoside) on two enzymes, that is, α-glucosidase and pancreatic lipase, were investigated regarding their antidiabetic activities. The study demonstrated that the anthocyanin extracts and the selected chemicals obeyed the competitive mode against the enzymes. The methanolic extracts of whole fruit and skin of the muscadine showed inhibitory activities against the α-glucosidase with their IC(50) values at 1.50 and 2.73 mg/mL, and those against the lipase at 16.90 and 11.15 mg/mL, respectively, which indicated that the muscadine extracts possessed strong antidiabetic activities. Particularly, the ethyl acetate (EtoAc) extract and the butanol (BuOH) extract exhibited much higher inhibitory activities against both enzymes than the CHCl(3) and water extracts, while the majority of anthocyanins existed in the BuOH fractions. Moreover, cyanidin exhibited a much stronger antidiabetic activity than cyanidin-3,5-diglucoside, suggesting that anthocyanins may have higher inhibitory activities after being digested. Further chromatographic analysis by high-performance liquid chromatography-mass spectrometry identified five individual anthocyanins, including cyanidin, delphinidin, petunidin, peonidin, and malvidin glycosides.

Fullerene-conjugated doxorubicin in cells.

The conjugation of fullerene with well-established drug molecules has been a representative strategy to impart fullerene-specific properties for improved formulation. However, conjugates involving fullerenes or other nanomaterials often differ significantly from the free drug molecules in cellular uptake and distributions. For the highly effective anticancer drug doxorubicin (DOX), its strong absorption and fluorescence in the visible spectral region enable the tracking of DOX-containing conjugates by optical techniques. In this work, a stoimetrically and structurally well-defined fullerene-DOX conjugate was studied in terms of fluorescence microscopy, including the fluorescence imaging with two-photon excitation, to examine the uptake and distribution in human breast cancer cells. The results suggested that the conjugate was distributed mostly in the cytoplasm, significantly different from free DOX molecules (predominantly in the cell nucleus, as already reported in the literature). Mechanistic implications of the results are discussed. Also discussed are potentials of conjugated DOX species as self-labeled fluorescent probes in bioimaging and other mechanistic investigations on drug delivery.

Selective interactions of sugar-functionalized single-walled carbon nanotubes with Bacillus spores.

It was reported previously that monosaccharide-functionalized single-walled carbon nanotubes (SWNTs) could interact with Bacillus anthracis (Sterne) spores with the mediation of a divalent cation such as Ca(2+) to result in significant spore aggregation and reduction in colony forming units. In this work a more systematic investigation was performed on interactions of the SWNTs functionalized with individual mannose and galactose moieties and their various dendritic configurations with B. anthracis and B. subtilis spores in the presence and absence of a divalent cation. Significant differences and selectivity between the Bacillus spores and between different sugars and their configurations were observed. The relevant results are presented, and their mechanistic implications are discussed.

Carbon dots for optical imaging in vivo.

It was found and recently reported that small carbon nanoparticles can be surface-passivated by organic or biomolecules to become strongly fluorescent. These fluorescent carbon nanoparticles, dubbed "carbon dots", can be successfully used for in vitro cell imaging with both one- and two-photon excitations, as already demonstrated in the literature. Here we report the first study using carbon dots for optical imaging in live mice. The results suggest that the carbon dots remain strongly fluorescent in vivo, which, coupled with their biocompatibility and nontoxic characteristics, might offer great potential for imaging and related biomedical applications.

Aqueous Compatible Fullerene-Doxorubicin Conjugates.

Covalent conjugates of fullerene C(60) and the highly effective anticancer drug doxorubicin (DOX) were prepared and studied. The conjugation was through the amide linkage to preserve the intrinsic properties of DOX and fullerene cage. As designed, the conjugates with hydrophilic ethylene glycol spacers exhibited much improved aqueous compatibility, with significant solubility in water-DMSO mixtures. The anti-neoplastic activities of DOX were apparently unaffected in the conjugates according to evaluations in vitro with a human breast cancer cell line.

Carbon Dots as Nontoxic and High-Performance Fluorescence Imaging Agents.

Fluorescent carbon dots (small carbon nanoparticles with the surface passivated by oligomeric PEG molecules) were evaluated for their cytotoxicity and in vivo toxicity and also for their optical imaging performance in reference to that of the commercially supplied CdSe/ZnS quantum dots. The results suggested that the carbon dots were biocompatible, and their performance as fluorescence imaging agents was competitive. The implication to the use of carbon dots for in vitro and in vivo applications is discussed.

Single-walled carbon nanotube as a unique scaffold for the multivalent display of sugars.

Single-walled carbon nanotube (SWNT) is a pseudo-one-dimensional nanostructure capable of carrying/displaying a large number of bioactive molecules and species in aqueous solution. In this work, a series of dendritic beta-D-galactopyranosides and alpha-D-mannopyranosides with a terminal amino group were synthesized and used for the functionalization of SWNTs, which targeted the defect-derived carboxylic acid moieties on the nanotube surface. The higher-order sugar dendrons were more effective in the solubilization of SWNTs, with the corresponding functionalized nanotube samples of improved aqueous solubility characteristics. Through the functionalization, the nanotube apparently serves as a unique scaffold for displaying multiple copies of the sugar molecules in pairs or quartets. Results on the synthesis and characterization of these sugar-functionalized SWNTs and their biological evaluations in binding assays with pathogenic Escherichia coli and with Bacillus subtilis (a nonvirulent simulant for Bacillus anthracis or anthrax) spores are presented and discussed.

Doped Carbon Nanoparticles as a New Platform for Highly Photoluminescent Dots.

There have been rapid advances in the development and applications of semiconductor quantum dots (QDs) represented by CdSe/ZnS. However, a serious limitation of these QDs is the necessary use of toxic heavy metals. It is reported here that small carbon nanoparticles doped with inorganic salts serve as a highly promising new platform for brightly photoluminescent dots. The photoluminescent carbon dots with the carbon core doped with ZnO (C(ZnO)-Dots) or ZnS (C(ZnS)-Dots) in aqueous solutions are competitive to the commercially available CdSe/ZnS QDs in luminescence brightness.