Intrinsic and selective activity of functionalized carbon nanotube/nanocellulose platforms against colon cancer cells.

Given their large surface area and versatile chemical reactivity, single-walled carbon nanotubes (SWCNTs) are regarded as the basis of new pharmacological complexes. In this study, SWCNTs are chemically functionalized with fluorescein, folic acid, and capecitabine, a drug that is commonly used against colorectal cancer. These functionalized SWCNTs are dispersed in water by taking advantage of their synergistic interaction with type-II nanocrystalline cellulose (II-NCC), and the resulting colloidal system is tested in vitro on both normal (differentiated) and cancerous (proliferative) human colon cells (Caco-2). The functionalized SWCNT/II-NCC hybrids show a higher activity than the reference (capecitabine) against the Caco-2 cancer cell line. However, this effect appears to be intrinsically associated with the SWCNT/II-NCC complex, particularly boosted by fluorescein, as the presence of capecitabine is not required. In addition, confocal microscopy fluorescence imaging using cell cultures highlights the enormous potential of this nanohybrid platform for colon cancer theranostics.

The viscosity of dilute carbon nanotube (1D) and graphene oxide (2D) nanofluids.

Controlling the physicochemical properties of nanoparticles in fluids directly impacts on their liquid phase processing and applications in nanofluidics, thermal engineering, biomedicine and printed electronics. In this work, the temperature dependent viscosity of various aqueous nanofluids containing carbon nanotubes (CNTs) or graphene oxide (GO), i.e. 1D and 2D nanoparticles with extreme aspect ratios, is analyzed by empirical and predictive physical models. The focus is to understand how the nanoparticle shape, concentration, motion degrees and surface chemistry affect the viscosity of diluted dispersions. To this end, experimental results from capillary viscosimeters are first examined in terms of the energy of viscous flow and the maximum packing fraction applying the Maron-Pierce model. Next, a comparison of the experimental data with predictive physical models is carried out in terms of nanoparticle characteristics that affect the viscosity of the fluid, mostly their aspect ratio. The analysis of intrinsic viscosity data leads to a general understanding of motion modes for carbon nanoparticles, including those with extreme aspect ratios, in a flowing liquid. The resulting universal curve might be extended to the prediction of the viscosity for any kind of 1D and 2D nanoparticles in dilute suspensions.

Differential properties and effects of fluorescent carbon nanoparticles towards intestinal theranostics.

Given the potential applications of fluorescent carbon nanoparticles in biomedicine, the relationship between their chemical structure, optical properties and biocompatibility has to be investigated in detail. In this work, different types of fluorescent carbon nanoparticles are synthesized by acid treatment, sonochemical treatment, electrochemical cleavage and polycondensation. The particle size ranges from 1 to 6 nm, depending on the synthesis method. Nanoparticles that were prepared by acid or sonochemical treatments from graphite keep a crystalline core and can be classified as graphene quantum dots. The electrochemically produced nanoparticles do not clearly show the graphene core, but it is made of heterogeneous aromatic structures with limited size. The polycondensation nanoparticles do not have CC double bonds. The type of functional groups on the carbon backbone and the optical properties, both absorbance and photoluminescence, strongly depend on the nanoparticle origin. The selected types of nanoparticles are compatible with human intestinal cells, while three of them also show activity against colon cancer cells. The widely different properties of the nanoparticle types need to be considered for their use as diagnosis markers and therapeutic vehicles, specifically in the digestive system.

Production and stability of mechanochemically exfoliated graphene in water and culture media.

The preparation of graphene suspensions in water, without detergents or any other additives is achieved using freeze-dried graphene powders, produced by mechanochemical exfoliation of graphite. These powders of graphene can be safely stored or shipped, and promptly dissolved in aqueous media. The suspensions are relatively stable in terms of time, with a maximum loss of ∼25% of the initial concentration at 2 h. This work provides an easy and general access to aqueous graphene suspensions of chemically non-modified graphene samples, an otherwise (almost) impossible task to achieve by other means. A detailed study of the stability of the relative dispersions is also reported.

Peptide-based biomaterials. Linking l-tyrosine and poly l-tyrosine to graphene oxide nanoribbons.

Peptide-based biomaterials are being studied actively in a variety of applications in materials science and biointerface engineering. Likewise, there has been ongoing exploration over the last few decades into the potential biological applications of carbon nanomaterials, motivated by their size, shape, structure and their unique physical and chemical properties. In recent years, the functionalization of carbon nanotubes and graphene has led to the preparation of bioactive carbon nanomaterials that are being used in biomedicine as structural elements and in gene therapy and biosensing. The present study proposes different strategies for the bonding of l-tyrosine and the homopolypeptide poly-l-tyrosine to graphene oxide nanoribbons (GONRs). The covalent attachment of l-tyrosine was undertaken by amidation of the α-amine group of tyrosine with the existing carboxylic groups in GONR and by means of esterification through phenol nucleophiles contained in their side chains. In both cases use was made of protective groups to address the functionalization with the desired reactive groups. The linking of GONRs to the PTyr was attempted according to two different strategies: either by ester bonding of commercial PTyr through its phenol side groups or by in situ ring-opening polymerization of an N-carboxyanhydride tyrosine derivative (NCA-Tyr) with Tyr-functionalized GONRs. These biofunctionalized nanomaterials were characterized by Raman and infrared spectroscopies, X-ray photoelectron spectroscopy, thermogravimetric analysis, transmission electron microscopy, fluorescence and electrochemical techniques. On the basis of their properties, prospects for the potential utilization of the prepared hybrid nanomaterials in different applications are also given.

Tailored SWCNT functionalization optimized for compatibility with epoxy matrices.

We have modified single walled carbon nanotubes (SWCNTs) with well defined matrix-based architectures to improve interface interaction in SWCNT/epoxy composites. The hardener and two pre-synthesized oligomers containing epoxy and hardener moieties were covalently attached to the SWCNT walls by in situ diazonium or carboxylic coupling reactions. In this way, SWCNTs bearing amine or epoxide-terminated fragments of different molecular weights, which resemble the chemical structure of the cured resin, were synthesized. A combination of characterization techniques such as Raman and infrared absorption (FTIR) spectroscopy, elemental analysis and coupled thermogravimetry-FTIR spectroscopy were used to identify both the functional groups and degree of functionalization of SWCNTs synthesized by the laser ablation and arc-discharge methods. Depending on the type of reaction employed for the chemical functionalization and the molecular weight of the attached fragment, it was possible to control the degree of functionalization and the electronic properties of the functionalized SWCNTs. Improved dispersion of SWCNTs in the epoxy matrix was achieved by direct integration without using solvents, as observed from optical microscopy and rheology measurements of the SWCNT/epoxy mixtures. Composite materials using these fillers are expected to exhibit improved properties while preserving the thermosetting architecture.

Block copolymer assisted dispersion of single walled carbon nanotubes and integration into a trifunctional epoxy.

Arc discharge single walled carbon nanotubes were processed by acid treatment, dispersion in a Pluronic F68 block copolymer aqueous solution and centrifugation. The as-prepared material was characterized by transmission electron microscopy, X-ray diffraction and Raman spectroscopy, showing an important degree of debundling as well as the removal of most of the graphitic and metallic impurities from pristine nanotubes. The nanotube-Pluronic material was integrated into an advanced trifunctional epoxy resin, triglycidyl p-aminophenol, using 4,4'-diaminodiphenylsulfone as the curing agent. The material was incorporated into the epoxy system (0.1, 0.25, 0.50, 1.0, 2.0 wt%) throughout hot magnetic stirring and ultrasonication. Curing kinetics was studied using differential scanning calorimetry, applying the Vyazovkin's isoconversional method. In the early stages of curing, the kinetic study revealed a decrease in the activation energy for samples containing Pluronic, suggesting that Pluronic induced an improvement in the mobility of reactants. The cured composites were characterized by Raman spectroscopy, thermogravimetric analysis and scanning electron microscopy. Micrographs revealed successful integration and homogeneous distribution of the nanotube-Pluronic material in the epoxy matrix, while direct integration of bare nanotubes originated aggregates and inhomogeneity.

The influence of a compatibilizer on the thermal and dynamic mechanical properties of PEEK/carbon nanotube composites.

The effect of polyetherimide (PEI) as a compatibilizing agent on the morphology, thermal, electrical and dynamic mechanical properties of poly(ether ether ketone) (PEEK)/single-walled carbon nanotube (SWCNT) nanocomposites, has been investigated for different CNT loadings. After a pre-processing step based on ball milling and pre-mixing under mechanical treatment in ethanol, the samples were prepared by melt extrusion. A more homogeneous distribution of the CNTs throughout the matrix is found for composites containing PEI, as revealed by scanning electron microscopy. Thermogravimetric analysis demonstrates an increase in the matrix degradation temperatures under dry air and nitrogen atmospheres with the addition of SWCNTs; the level of thermal stability of these nanocomposites is maintained when PEI is incorporated. Both differential scanning calorimetry and synchrotron x-ray scattering studies indicate a slight decrease in the crystallization temperatures of the compatibilized samples, and suggest the existence of reorganization phenomena during the heating, which are favoured in the composites incorporating the compatibilizer, due to their smaller crystal size. Dynamic mechanical studies show an increase in the glass transition temperature of the nanocomposites upon the addition of PEI. Furthermore, the presence of PEI causes an enhancement in the storage modulus, and hence in the rigidity of these systems, attributed to an improved interfacial adhesion between the reinforcement and the matrix. The electrical and thermal conductivities of these composites decrease with the incorporation of PEI. Overall, the compatibilized samples exhibit improved properties and are promising for their use in industrial applications.