L. Monica Veca

Metallic single-walled carbon nanotubes for conductive nanocomposites.

This article reports an unambiguous demonstration that bulk-separated metallic single-walled carbon nanotubes offer superior performance (consistently and substantially better than the as-produced nanotube sample) in conductive composites with poly(3-hexylthiophene) and also in transparent conductive coatings based on PEDOT:PSS. The results serve as a validation on the widely held view that the carbon nanotubes are competitive in various technologies currently dominated by conductive inorganic materials (such as indium tin oxide).

Reversible Accumulation of PEGylated Single-Walled Carbon Nanotubes in the Mammalian Nucleus

Carbon nanotubes (CNTs) have been shown to cross cell membranes and can mediate the internalization of macromolecules. These characteristics have constituted CNTs as an exciting new tool for drug delivery and biological sensing. While CNTs exhibit great potential in biomedical and pharmaceutical applications, neither the cell penetration mechanism of CNTs nor the intracellular fate of the internalized CNTs are fully understood. In this study, time-lapse fluorescence microscopy was used to investigate the intracellular distribution of FITC labeled PEGylated single-walled CNTs (FITC-PEG-SWCNTs) in living cells and shown that PEGylated SWCNTs entered the nucleus of several mammalian cell lines in an energy-dependent process. The presence of FITC-PEG-SWCNTs in the cell nucleus did not cause discernible changes in the nuclear organization and had no effect on the growth kinetics and cell cycle distribution for up to 5 days. Remarkably, upon removal of the FITC-PEG-SWCNTs from the culture medium, the internalized FITC-PEG-SWCNTs rapidly moved out of the nucleus and were released from the cells. Thus, the intracellular PEGylated SWCNTs were highly dynamic and the cell penetration of PEGylated SWCNTs appeared as bidirectional. These observations suggest SWCNTs may be used as an ideal nanovector in biomedical and pharmaceutical applications.

Acute and long-term effects after single loading of functionalized multi-walled carbon nanotubes into zebrafish (Danio rerio)

Carbon nanotubes (CNTs) are widely explored for biomedical applications, but there is very limited information regarding their in vivo biodistribution and biocompatibility. Here, we report the in vivo biodistribution and long-term effects of functionalized multi-walled carbon nanotubes (MWCNTs) in developing zebrafish. The fluorescent-labeled MWCNTs were introduced into zebrafish embryos at 1-cell stage and at 72 h post fertilization through microinjection. After single injection, both acute and long-term interactions between zebrafish and functionalized MWCNTs were studied. The injected FITC-BSA-MWCNTs (at 1-cell stage) were allocated to all blastoderm cells of the embryos through proliferation, and were distinctively excluded from the yolk cell. When introduced into the circulation system, FITC-BSA-MWCNTs moved easily in the compartments and finally were cleaned out by the body at 96 h after the loading. At early stages, the treated zebrafish embryos generated immune response by accumulating circulating white blood cells at the trunk region. Under transmission electron microscope, many lysosome-like vesicles were observed in the blastoderm cells of the treated embryos. The zebrafish loaded with MWCNTs had normal primordial germ cells at early stage and produced second generation later on. However, the larvae of the second generation had obviously lower survival rates as compared to the untreated groups, suggesting a negative effect on the reproduction potential. These results suggest that extensive purification and functionalization processes can help improve the biocompatibility of CNTs. This study also indicates that purified CNTs may have long-term toxicity effects when they were delivered into the body.

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.

Polymer/carbon nanocomposites for enhanced thermal transport properties - carbon nanotubes versus graphene sheets as nanoscale fillers

Light-weight composite materials of superior thermal transport properties are important to thermal management and other applications. Carbon nanomaterials with their high thermal conductivities have been widely pursued for such a purpose. Specifically, carbon nanotubes have been shown both theoretically and experimentally to possess extraordinarily high thermal conductivities at the individual nanotube level, and thus are logically considered as ideal fillers for highly thermally conductive polymeric nanocomposites. However, the predicted dramatically enhanced thermal transport in polymers upon the incorporation of carbon nanotubes has not yet materialized. Recently, graphene research has brought new opportunities to the development of polymer/carbon nanocomposites of high thermal conductivities, with already some successful uses of exfoliated graphite sheets as nanoscale fillers. In this work poly(vinyl alcohol) (PVA) was selected as the polymer matrix for the dispersion of single-walled carbon nanotubes (seamlessly with PVA functionalization and solubilization) vs. few-layer graphene sheets as nanoscale carbon fillers for a more direct comparison on the thermal transport performance in the resulting nanocomposites. The effect of aligning the nanotubes embedded in the nanocomposite films via mechanical stretching was also evaluated. Implications of the comparison between the nanotubes and nanosheets with respect to their potentials in thermally conductive polymeric nanocomposites are discussed.

Covalent conjugation of carbon dots with Rhodamine B and assessment of their photophysical properties

The unique photoluminescent properties of carbon dots (CDs) continue to encourage a great interest in their development for a wide range of applications in energy conversion, optoelectronics or sensing. Engaging carbon dots in resonance energy transfer processes with organic dyes could enable the design of functional materials to greatly enhance the performance of solar cells and other optoelectronic devices, or to create new types of sensors. In this work, CDs were functionalized with Rhodamine B (RhB) isothiocyanate, (CD–PEG1500N–Rh) via a simple procedure after surface modification of bare carbon nanoparticles with poly(ethylene glycol) bis(3-aminopropyl) (PEG1500N). The morphology of CD–PEG1500N was ascertained using HR-TEM while the covalent linkage of Rhodamine B at the surface of PEG1500N capped CDs was proved by spectroscopic analysis. The overlap between the emission spectra of CDs and the absorption spectrum of RhB molecules favoured fluorescent (Forster) resonance energy transfer (FRET) from the CDs to the dye molecules. The FRET mechanism was firstly demonstrated by steady-state fluorescence measurements and its efficiency was estimated by photoluminescence lifetime measurements, using the time correlated single photon counting (TCSPC) method with the excitation of picosecond pulse lasers. The synthetic accessibility and the transfer efficiency of these conjugates make them reliable candidates for fluorescent materials to be later used in FRET based sensing platforms and photovoltaic devices.

Light-weight nanocomposite materials with enhanced thermal transport properties

Abstract Polymeric nanocomposite materials that are highly thermally conductive are important to a variety of applications, with examples ranging from flexible radiators in space to high-performance aircrafts and vehicles and to cutting-edge electronics. Among widely used nanoscale fillers in the development of these materials are carbon nanotubes and graphene sheets. As concluded in previous reviews, the performance of carbon nanotubes for imparting high thermal conductivity into polymeric matrices was generally poor. Here recent results associated with the effort on significant performance improvements are reviewed as an update. By contrast, graphene sheets have emerged as effective nanoscale fillers for polymeric nanocomposites of excellent thermal transport performance, reaching levels that are competitive to those achieved by metals. The significant recent results on thermally conductive polymeric nanocomposites with graphene sheets are highlighted, and their potential applications and issues on their further performance improvements are discussed.

Micro-Raman spectroscopy of graphene transferred by wet chemical methods

A comparative study regarding single layer graphene (GR) transfer from copper to oxidized silicon substrate using Soak and Peel delamination, Contact printing, Electrochemical delamination is presented. Structural modifications of GR were determined by Raman spectroscopy, while optical and atomic force microscopy emphases the size and area of the transferred GR films.

Photoluminescent Carbon Nanomaterials: Properties and Potential Applications

Carbon nanoparticles and nanotubes upon surface passivation or modification via chemical functionalization exhibit strong photoluminescence in the visible and into the near-IR. In this Chapter, the general features and related optical characteristics of the photoluminescence are highlighted, mechanistic issues discussed, and their potential material and biomedical applications explored. For single-walled carbon nanotubes, the similarities and differences between the defect-derived emission and the band-gap fluorescence (emission from individualized single-walled carbon nanotubes) are also discussed.