Sheng-Tao Yang

Bandgap‐Like Strong Fluorescence in Functionalized Carbon Nanoparticles

Semiconductor quantum dots (QDs), especially the highly fluorescent CdSe-based core-shell nanostructures, have generated much excitement for their variety of potential applications in optical bioimaging and beyond.[1,2] These QDs are widely considered as being more advantageous over conventional organic dyes as well as genetically engineered fluorescent proteins in terms of optical brightness and photostability.[1,3–5] However, a serious disadvantage with these popular QDs is their containing heavy metals such as cadmium, whose significant toxicity and environmental hazard are well-documented.[6–9] Alternative benign (nontoxic) QD-like fluorescent nanomaterials have therefore been pursued, including the recent finding of fluorescent carbon nanoparticles (dubbed “carbon dots”).[10,11]

Removal of methylene blue from aqueous solution by graphene oxide.

Graphene oxide (GO) is a highly effective absorbent of methylene blue (MB) and can be used to remove MB from aqueous solution. A huge absorption capacity of 714 mg/g is observed. At initial MB concentrations lower than 250 mg/L, the removal efficiency is higher than 99% and the solution can be decolorized to nearly colorless. The removal process is fast and more efficient at lower temperatures and higher pH values. The increase of ionic strength and the presence of dissolved organic matter would further enhance the removal process when MB concentration is high. The results indicate that GO can be applied in treating industrial effluent and contaminated natural water. The implications to graphene-based environmental technologies are discussed.

Folding/aggregation of graphene oxide and its application in Cu2+ removal.

Graphene oxide (GO) can be aggregated by Cu(2+) in aqueous solution with a huge Cu(2+) absorption capacity. The Cu(2+) causes GO sheets to be folded and also to form large aggregates that were characterized by confocal microscopy and atomic force microscopy. The folding/aggregation is most likely triggered by the coordination between GO and Cu(2+). The equilibrium Cu(2+) concentrations and equilibrium absorption capacity of GO were measured to estimate the maximum absorption capacity of GO for Cu(2+) and the absorption model. GO has a huge absorption capacity for Cu(2+), which is around 10 times of that of active carbon. Representative results are presented and the implication to Cu(2+) removal is discussed.

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.

Long-term accumulation and low toxicity of single-walled carbon nanotubes in intravenously exposed mice

The biomedical application of single-walled carbon nanotubes (SWCNTs), such as drug delivery and cancer treatment, requires a clear understanding of their fate and toxicological profile after intravenous administration. In this study, the long-term accumulation and toxicity of intravenously injected SWCNTs in the main organs (such as liver, lung and spleen) in mice were carefully studied. Although SWCNTs stayed in mice over 3 months, they showed low toxicity to mice. The long-term accumulation of SWCNTs in the main organs was evidenced by using Raman spectroscopy and TEM technique. Statistically significant changes in organ indices and serum biochemical parameters (LDH, ALT and AST) were observed. The histological observations demonstrate that slight inflammation and inflammatory cell infiltration occurred in lung, but the serum immunological indicators (CH 50 level and TNF-alpha level) remained unchanged. No apoptosis was induced in the main organs. The decreasing glutathione (GSH) level and increasing malondialdehyde (MDA) level suggest that the toxicity of SWCNTs might be due to the oxidative stress.

Carbon-based quantum dots for fluorescence imaging of cells and tissues

Carbon dots (or carbon quantum dots in some literature reports), generally small carbon nanoparticles with various surface passivation effects, have attracted widespread attention in recent years, with a rapidly increasing number of research publications. The reported studies covered many aspects of carbon dots, from the development of many new synthetic methodologies to an improved mechanistic elucidation and to the exploration of application opportunities, especially for those in the fluorescence imaging of cells and tissues. There have also been significant advances in the establishment of a shared mechanistic framework for carbon dots and other carbon-based quantum dots, graphene quantum dots in particular. In this article, representative recent studies for more efficient syntheses of better-performing carbon dots are highlighted along with results from explorations of their various bioimaging applications in vitro and in vivo. Similar fluorescence properties and potential imaging uses of some graphene quantum dots are also discussed, toward a more consistent and uniform understanding of phenomenologically different carbon-based quantum dots.

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.

Effect of size and dose on the biodistribution of graphene oxide in mice

AIM Graphene oxide (GO) has promising applications in bioimaging, diagnostics and therapeutics. This work studied the effects of size and injection dose on the biodistribution of GO to accelerate the development of a GO-based drug. METHODS GO samples were intravenously injected into mice. The content of GO in organs/tissues at different time points was measured using an (125)I-labeling technique. GO in the liver and lungs was further confirmed by both Raman spectroscopic and TEM observations. The dispersion state of GO in serum was evaluated by flow cytometry. RESULTS Regardless of size, GO was cleared from the blood quickly and accumulated mainly in the liver and lungs. The uptake of GO in lungs increased with increasing injection dose and size. The dispersion state (i.e., size of the GO-protein complex in blood) dominated the biodistribution. CONCLUSION The size and dose of GO affected its fate in vivo. For medical applications, small-sized GO with suitable funtionalization is recommended.

Pharmacokinetics, metabolism and toxicity of carbon nanotubes for biomedical purposes.

Carbon nanotubes (CNTs) have attracted great interest of the nano community and beyond. However, the biomedical applications of CNTs arouse serious concerns for their unknown in vivo consequence, in which the information of pharmacokinetics, metabolism and toxicity of CNTs is essential. In this review, we summarize the updated data of CNTs from the biomedical view. The information shows that surface chemistry is crucial in regulating the in vivo behaviors of CNTs. Among the functionalization methods, PEGylation is the most efficient one to improve the pharmacokinetics and biocompatibility of CNTs. The guiding effects of the pharmacokinetics, metabolism and toxicity information on the biomedical applications of CNTs are discussed.

A generally adoptable radiotracing method for tracking carbon nanotubes in animals

Carbon nanotube (CNT) mediated drug delivery systems have currently aroused a great deal of interest. Such delivery systems for drugs, proteins and genes have been preliminarily studied using cellular and animal models. For the further study of the pharmacokinetics and related biological behaviours of CNTs in vivo, a fast and convenient tracing method is particularly demanded. In this paper, we developed a generally adoptable tracing method for the biodistribution study of functionalized CNTs in vivo. Taurine covalently functionalized multi-walled carbon nanotubes (tau-MWNTs) and Tween-80 wrapped MWNTs (Tween-MWNTs) were labelled with (125)I, and then their distribution in mice was determined. It is interesting that Tween-80 can reduce the RES uptake of MWNTs remarkably. The resulting distribution of (125)I-tau-MWNTs was very consistent with that using (14)C-taurine-MWNTs as the CNTs tracer, which means the easy (125)I labelling method is reliable and effective.