Current Nanoscience - Volume 6, Issue 3, 2010

High levels of covalently functionalised single walled carbon nanotubes (SWCNT) have been produced using a rapid atmospheric pressure microwave reflux in a 1:1 mix of concentrated nitric and sulphuric acids. The resulting product shows high solubility (0.74 mg/ml at pH 11) and also displays a maximum solubility dependency based on the pH of the solution. The presence of sulphone and sulphonate functional groups has been shown using EDXA, TGA and IR analysis. The structural and electronic characteristics of the nanotubes were monitored using Raman spectroscopy and SEM imaging. Spray coating was used to form transparent conducting thin films from the functionalised nanotubes. The films demonstrated sheet resistances from 300 Ω / and a 25-85% optical transmission at 800 nm. This method provides a fast and effective route to the formation of conductive nanotube thin-films without the need for surfactant stabilisation of the solution. In addition the functionalisation was shown to be a fully reversible process sensitive to thermal treatment. Film formation removed the nanotube functionalisation and restored the pristine nanotube structure.

Silica nanotubes were synthesized via sol-gel process using poly(ethylene glycol) functionalized multi-walled carbon nanotubes (MWNT-PEG) as the dual templates. Through the hydrolysis of tetraethoxysilane (TEOS), a continuous coating of silica was deposited over the MWNT surfaces to form core-shell structures. Hollow silica nanotubes were finally obtained by removal of core carbon components through calcination. The as-prepared hollow silica structures were characterized by electron microscopy, energy dispersive X-ray spectrometry and infrared spectroscopy. The synthesized silica nanotubes might find potential applications in many fields such as encapsulation, catalysis, biological separation, and sensing.

An electrostatic experiment, performed inside a Field-Emission Scanning Electron Microscope equipped with two electrical probes, is used for the accurate determination of the Young's modulus of as-grown nanowires. One electrode being in contact with the substrate and the other one at close distance to the nanowire's tip, an electrical bias was slowly ramped up to attract and eventually bring the nanowire into contact with the attracting probe. While the SEM was shut down during this procedure to avoid electrical perturbation, the threshold bias that results in the eventual contact was determined from an I-V curve recorded simultaneously. Despite the impossibility of visualizing the nanowire's motion during this operation, a direct relationship can be established between that threshold bias, the corresponding deflection and the nanowire's Young's modulus. This technique, consisting essentially of two SEM images and one I-V curve, was applied to multi-walled carbon nanotubes of various lengths and orientations and resulted in an accurate Young’s modulus of 0.92 +/- 0.28 TPa.

The objective of this work is to discuss the microstructural effect of TiO2 nanotubes on formation mechanism and morphology of apatite layer. An anodization method was employed to prepare self-organized TiO2 nanotubes on the surface of pure titanium, followed by these substrates being soaked in simulated body fluid (SBF) to form a bioactive layer. By manipulating the anodization time between 0.5 h and 3 h, nanotubes could be grown of any desired length ranging from 662 ± 5 nm to 1291 ± 5 nm. The diameter of rod-like apatite layer grown on the nanotubes decreased yet subsequently increased with the variation of nanotubular surface morphology and length. In addition, the nanotube length dependence of apatite formation can be ascribed to the different dissolution rate of nanotubes during the deposition of calcium phosphate (Ca-P) coatings, as well as the different penetration rate of Ca and P ions toward nanotube layer.

The self-assembly of anatase TiO2 nanorods into 1D (ribbon), 2D (smectic, domino, honeycomb) and 3D (lamellar) liquidcrystalline ordered superlattices is a process that depends on the collaboration between evaporation dynamics and directional interactions. Herein, the roles of entropic depletion attractions and energetic dipole-dipole couplings between TiO2 nanorods in self-assembly process are particularly emphasized. Excess oleic acid surfactants act as depletion agents to induce the inter-rod depletion effect, and the origin of electric dipole moment along the longitudinal axes of TiO2 rods is theoretically authenticated by applying the Accelrys Materials Studio as a new strategy combined with Tasker's theory. These nanorod superlattices provided here may have great importance for tailoring new promising structures for photovoltaic application or exploring new inorganic liquid crystal materials.

Highly crystallized titania nanorods were prepared by a hydrothermal method, and their formation processes were investigated by characterizing reaction products in a series of desired time intervals by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), and scanning electron microscopy (SEM). A complex electrode of dye-sensitized solar cells was then fabricated using the high-crystalline nanorods thus prepared. In the initial reaction stage (0.5—3.5 h), film-like products with amorphous or amorphous-like structure were observed. In the film with amorphous phase, very tiny two-dimensional anatase crystals were formed as nuclei, and the number and size of the nuclei increased with time. The nuclei were identified to have plane-like shape with the intensity ratio (004)/(200)—signifying growth in the c-axis— being almost zero. When the intensity ratio reached around 0.4, indicating slight growth in the c-axis, a drastic change in the shape and crystalline structure was observed to take place. This change was found to occur in a very short period (3.5-4 h), resulting from the phase transition from film with amorphous-like structure to titania nanorods with anatase crystalline structure. It was at 6 h or later that the HRTEM images showed titanium atoms aligning perfectly in titania anatase structure. This series of findings evidenced the formation of highly crystallized titania with various shapes and encouraged the fabrication of high-efficiency dye-sensitized solar cells; high electronic conductivity of the highly crystallized nanorods was found to contribute to achieving a conversion efficiency as high as 8.52 %.

Curcumin is a natural compound with biological activities and potent anticancer effects that has the drawback of poor water solubility which leads to low bioavailability. In this work curcumin was formulated in new physicochemically characterized micellar carriers composed of new synthetic block copolymers. The study of the in vitro release rate of curcumin from the formulas, as well as the in vitro activity of free curcumin and of curcumin-loaded into micelles, against a panel of colorectal cancer cell lines was also part of this study. New β—lactam functionalized poly(isoprene-b-ethylene oxide) amphiphilic block copolymers, were synthesized by the combination of anionic polymerization and selective postpolymerization functionalization of the polyisoprene block with chlorosulfonylisocyanate. Micelles composed of the synthetic copolymers were formulated in order to incorporate curcumin. As the results revealed, increase in the percentage of the lipophilic block of micelles, led to higher encapsulation efficiency and loading capacity while the size was found to be smaller and the in vitro release rate slower. In vitro cytotoxicity results showed similar or slightly higher activity for curcuminloaded into micelles than free curcumin, a fact that could be attributed to the similar in vitro cellular uptake profiles of curcumin and of curcumin-loaded into micelles.

A novel molecular computing model based on circular DNA was developed to solve a 3-coloring graph problem. This computing model uses circular DNA and works as to dial a number. The method of selecting true solutions is similar to dialing on a telephone. Moreover, the key methods in this model were circularization of single single-strand DNA (ssDNA) molecules and a backtracking deletion algorithm. In the course of computing, the structure of the DNA molecule was transformed into linear double-strand DNA (dsDNA), linear ssDNA, and circular ssDNA. For a 3-coloring graph problem with n vertices, the algorithm time complexity and the space complexity are both O(n2) at most. The computing achievement by this model indicates that circular DNA has extensive applications in molecular computing research.

The present study was designed to examine the uptake, localization, and the cytotoxic effects of well-dispersed fluorescent porous silica nanoparticles (FITC-SiO2 NPs) in mouse neural stem cells (C 17.2, NSCs). NSCs were exposed to various concentrations of FITC-SiO2 NPs for different times and then the uptake and toxicity were assessed. Apoptotic cells were observed and analyzed by confocal microscopy and flow cytometry. Results of confocal microscopy examination revealed that silica nanoparticles were taken up into the cells. Cell viability decreased significantly as a function of both nanoparticle dosage (12- 240 μg/ml) and exposure time (12 h, 24 h 72 h). FITC-SiO2 NPs show marked toxicity at high concentration (240 μg/mL) after co-incubation for 72 h. There were clear dose- and timedependent silica-induced cytotoxicity and genotoxicity within the range of experimental concentrations. Interestingly, we have caught the whole process of NSCs apoptosis induced by FITC-SiO2 NPs. The understanding of such a mechanism may provide a scientific basis for the possible application of porous silica in drug delivery and controlled release.

Cholesterol-modified pullulan (CHSP) conjugate with succinyl linkages was synthesized and characterized by fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H NMR) and X-ray diffraction (XRD). The degree of substitution (DS) of cholesterol moiety determined by 1H NMR ranged from 3.87 to 5.70 cholesterol groups per hundred glucose units. CHSP self-aggregated nanoparticles were prepared by probe sonication in aqueous media and analyzed by dynamic laser light-scattering (DLS), zeta potential, transmission electron microscopy (TEM) and the fluorescence probe technologies. These novel nanoparticles were almost spherical in shape, and their size, ranging from 73.0 to 51.8 nm, could be controlled by DS. The zeta potentials of CHSP self-aggregated nanoparticles were near zero in aqueous media. The value of critical aggregation concentration (cac) was dependent on the DS of cholesterol moiety. Mitoxantrone (MTO), as a model anticancer drug, was loaded into the CHSP nanoparticles by dialysis method. MTO-loaded CHSP self-aggregated nanoparticles were almost spherical in shape and their size increased from 153.1 to 174.2 nm with the MTO-loading capacity increasing from 4.35% to 14.29%. The encapsulation efficiency (EE) of the process and loading capacity (LC) of the nanoparticles increased with increasing cholesterol DS. XRD powder patterns showed that crystal peaks of MTO disappeared when MTO was entrapped into CHSP nanoparticles. The release behavior of MTO from CHSP self-aggregated nanoparticles was studied in vitro. The results showed that the release behavior of MTO from CHSP nanoparticles exhibited a sustained release, and MTO release rate decreased with increasing the pH value of media.

We present a general route to the facile and spontaneous synthesis of gold (Au) and silver (Ag) nanoparticles (NPs) through the use of hydroxylated poly(amidoamine) (PAMAM) dendrimers as both stabilizers and reducing agents. The formation of Au NPs can be achieved by simply mixing the generation 4 (G4) and 5 (G5) glycidol-modified PAMAM dendrimers with HAuCl4 in either methanol or water at room temperature. The size of the formed Au NPs can be varied through the change of dendrimer generations and reaction solvents. We also show that 1,2-epoxyhexane-modified G4 PAMAM dendrimers can be used as both stabilizers and reducing agents to form Au NPs, providing a useful approach to tuning the surface hydrophilicity of Au NPs. Furthermore, using the same strategy of spontaneous formation of Au NPs, Ag NPs can be readily formed through the use of glycidol hydroxyl-terminated G5 PAMAM dendrimers as both stabilizers and reducing agents. The facile synthesis of Au and Ag NPs using hydroxylated PAMAM dendrimers may offer many opportunities for their uses in a variety of applications.

The infrared radiation from Nd:YAG laser (1604 nm, 8ns, 125mJ, 15.6MW) is focused by IR lens (20cm) to irradiate Cu (99.99%) target in air. The angular distribution and arrival of ions are collected by Faraday Cups (FC). For anisotropic investigation, the cups are arranged at different positions (5cm and 10cm) from the target at different angles (5°, 30°, 45°, 60° and 90°) with respect to the normal on target surface. Faraday Cups are biased at -100V and the ion current signals are obtained on Tektronix TDS 3054B Digital Storage oscilloscope (500 MHz) through integrated circuit. The debris that deposited on FC is also characterized by SEM and EDX analysis. Metallurgical analysis of exposed FC provides evidences of Cu material on Faraday's cup. Mass removal rate for copper target is also calculated. Maximum arrival rate of ions is observed at angle 5° and minimum ions flux is at angle 90° to normal on the target surface. The results show the plume is peaked strongly in forward direction. The laser matter interaction is good for the laser based ion sources generation, which can produce a collimated beam of ions because of forward peaking.

Introduction: Intranasal drug administration is a non-invasive method of bypassing the blood—brain barrier (BBB) to deliver therapeutic agents to the brain and spinal cord. This method also delivers those drugs that do not cross the BBB to the central nervous system (CNS) thus eliminating the need for systemic delivery, and subsequently reducing the unwanted systemic side effects. Delivery from the nose- to-brain occurs within minutes along both the olfactory and trigeminal neural pathways. Materials and Methods: Rat model was developed to determine existence of neural and non neural pathways after nasal delivery in rats. For the study mucoadhesive nanoparticles were prepared by ionic crosslinking method and the study was investigated using intranasal administration of Tc99m labeled chitosan nanoparticulate formulation in dead and alive rats. Result: The result showed a significant increase of 4.4 times radiolabeled drug concentration in the brain of live rats as compared to the radiolabeled drug concentration in the dead rats (p < 0.01). Conclusion This experimental rat model provides a proof for existence of neural and non-neural pathway for nose to brain using a novel formulation for crossing BBB which is of importance in finding a solution for neurodegenerative disorders.

The increasing use of ultraviolet (UV) light in medicine, industrial environments, for cosmetic use, and even in consumer products necessitates that greater attention be paid to the potential hazards of this type of electromagnetic radiation. To avoid any adverse effects of exposure to this type of radiation, suitable protection filters were produced to block UV bands. Nanostructure composite and thin film of titanium dioxide coatings on glass have been prepared by the sol—gel method. TiO2 sol suspension was prepared by first adding titanium tetra isopropoxide (Ti(OPr)4 or TTP) to a mixture of ethanol and HCl (molar ratio TTP:HCl:EtOH:H2O = 1:1.1:10:10) and then adding a 2 wt.% solution of hydroxyl ethyl cellulose (HEC) as dispersant followed by of stirring. Precalcined TiO2 nanopowder was mixed with a sol and heat treated. Thin and composite films were deposited on the glass substrate (microscope glass slide) by spincoating them at ambient conditions. After drying, samples were heated to 500 °C. The resulting films were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). The purpose of our study was to determine if thin and composite TiO2 films with ultraviolet light have any effect on the growth of Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Bacillus species (Bacillus sp.) We have seen unusual results in which TiO2 thin and composite films protect E. coli, S. aureus and Bacillus sp from UV light. The survival of E. coli with UV alone was 3.2 % while with UV and TiO2 composite film was 91%. The UVabsorbing coatings are transparent, colorless, and exhibit high optical quality. The UV-protective coatings offer an easy method to protect the living organisms against UV.