Current Nanoscience - Volume 4, Issue 2, 2008

Nanomaterials are typically considered as solid physical structures that comprise grain boundaries at the resolution of less than 100 nanometers, whereby nanotechnologies are depicted as dealing with the design of various applications based on employing the former. Some of the essential features of nanomaterials and the scientific approaches to their investigation are discussed in the course of this work. The real reason for the current scientific and technological interest in the physical effects at nanoscale is linked with the historic trend of refinement of human knowledge and of the corresponding ability to manipulate with the structural patterns of the Universe. Interesting novel properties of nanomaterials are presented as resulting from the interplay between the surface properties and quantum effects at nanoscale. Examples of peculiar combination properties that materials can exhibit with the transition to nanosized form are mentioned, with a particular emphasis on the nanoscopic aggregates of water molecules. Specific challenges tied with the further growth of the field, including the prospectives of functional superstructuring, biomimicry, green chemistry, and the interdisciplinary approach to research, are eventually outlined.

Polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) were prepared via the electrospinning process. Silver (Ag) modifications of these CNFs were carried out using in-situ Ag reaction as well as Ag coating methods. Ag modified CNFs from both methods yielded higher electrical conductivity than the neat CNFs due to the synergetic effect from the Ag nanoparticles. The effects of fiber diameter, fiber aspect ratio and the interconnecting network nature of the non-woven fiber mat on the electrical and thermal decompositional properties of as-prepared fibers were also investigated. The structural characterizations of as-prepared fibers were performed using SEM, Raman spectroscopy, WAXD, and TGA methods.

Silver nanoparticles have been prepared under microwave irradiation from a solution of silver nitrate. Different morphologies of silver colloids with charming colors could be obtained using two different reducing agents namely sodium citrate (SC) and N1, N2- diphenylbenzamidine (DPBA) or simply amidine. The structures of silver colloids were determined by TEM. UV-Vis spectroscopy was used to follow the reaction process and to characterize the optical properties of the resultant silver colloids. The influence of two different mild conventional and unconventional reducing agents on the morphology of silver was investigated.

We report extracellular mycosynthesis of silver nanoparticles by Fusarium acuminatum Ell. and Ev. (USM-3793) isolated from infected ginger (Zingiber officinale). An aqueous silver nitrate solution was reduced to metallic silver when exposed to F. acuminatum cell extract leading to the appearance of a brown color within 15-20 minutes. The color is due to the formation of silver nanoparticles and the excitation of surface plasmons. The optical spectrum showed the plasmon resonance at 420 nm and analysis by transmission electron microscopy confirmed the presence of silver nanoparticles. The nanoparticles produced were spherical with a broad size distribution in the range of 5-40 nm with average diameter of 13 nm. The reduction of the silver ions occurs probably by a nitrate-dependent reductase enzyme, which we found to be present in the extra-cellular medium. We tested the silver particles for their broad-band antibacterial activity on different human pathogens. We observed efficient antibacterial activity against multidrug resistant and highly pathogenic bacteria, including multidrug resistant Staphylococcus aureus, Salmonella typhi, Staphylococcus epidermidis, and Escherichia coli. The synthesis of silver nanoparticles by the fungus F. acuminatum may therefore serve as a simple, cheap, eco-friendly, reliable and safe method to produce an antimicrobial material.

This paper presents a hydrothermal method for the synthesis and stabilization of gold nanodisks with a preferential growth direction along the (111) plane inside environmentally-besign sodium alginate sol by a one-step strategy without additional reducing agent. This is carried out by transferring a sodium alginate/HAuCl4 aqueous solution into a stainless steel autoclave with a Teflon liner and heating in an oven at 100°C for 30 h. Field emission scanning electron microscopy observation indicates that the gold nanodisks are predominantly hexagonal shape with micrometer-scale in diameter. Transmission electron microscope, selected area electron diffraction, and Xray diffraction analyses show that the gold nanodisks grow preferentially along the Au (111) plane. Some influential factors on the growth of gold nanodisks are discussed. The results suggest that the reactants' concentrations and reaction time are crucial to the formation of gold nanodisks and their growth mechanism is tentatively explained.

TiO2 nanocrystalline powders were synthesized in the anatase phase by a modified sol-gel method. The effect of calcination temperature was also studied; XRD pattern of the sample dried at 100°C showed a significant amount of amorphous content, and crystallinity enhanced by increasing the calcination temperature. AFM images demonstrate submicron agglomerate particles. FT-IR spectra represent the formation of Ti-O-Ti bond for the as-prepared powder. Following the trend of increasing the temperature Ti-O bond was intensified. The pure anatase structure with no undesirable impurity phase was resulted at 500°C. N2 adsorption and desorption isotherms pointed out a mesoporous powder and the specific surface area using BET method was measured 50 m2/g, which is corresponding to about 30 nm particle size. This is in agreement with TEM and XRD results of particle average diameter. Photocatalytic activity of the sample calcined at 500°C was examined using methyl orange, which is comparable with commercial TiO2 (P-25). This method of nanopowder synthesis is presentable, since well-crystallized nanoparticles with good surface area and photocatalytic activity can be achieved.

In order to obtain oriented nanostructured materials for nanoelectronic/microelectronic applications, a simple sol-gel method to form ZnO nano-structures under different heat treatment conditions was investigated. The results indicated that ZnO nanobelts could be obtained by the presence of small amount of triethanolamine, which acted as soft template. The orientation degree of the ZnO nanobelts was improved significantly by optimizing preparation condition. Via adjusting the pH of hydrothermal treatment, large-scale highly oriented ZnO belt arrays were obtained. The XRD result agreed well with that of the standard XRD results of ZnO. The photocurrent of the oriented ZnO belt array increased about 2 orders of magnitude after light exposure.

The Wiener index of a graph G is defined as W(G) =1/2&b.Sigma;{x,y}⊆V(G)d(x,y), where V(G) is the set of all vertices of G and for x,y &b.epsis; V(G), d(x,y) denotes the length of a minimal path between x and y. In this paper an algorithm for computing the Wiener matrix of a TUC4C8(R) nanotube T = T[p,q] is given. Using this matrix, an exact expression is given, for the Wiener index of T.

Water condensation is shown to have a major influence on electric charge transport and nanostructure formation in polymer-, and semiconductor-thin-film surfaces in the proximity of a biased Atomic Force Microscope (AFM) tip. The water forms a meniscus bridge between the AFM tip and the surface to form a three-component system comprised of the AFM tip, water meniscus, and the surface. The associated electric field in the meniscus is spatially non-uniform and has a magnitude of the order of 108-1010 Vm-1. An intensive experimental analysis of the input and output electric currents in the AFM tip/water meniscus/surface system, performed at various relative humidity levels between 10 and 60%, indicates that the magnitude of the output current, drained from surface, reaches values as large as several μA which exceeds the input current, injected via the AFM tip (0.01-10 nA), by at least an order of magnitude. This effect is particularly evident when the relative humidity is greater than 20-25%, suggesting that the water meniscus is ionized by the strong electric field to produce electrons. Since the method described here for nanopatterning is applicable for materials with significantly different physical, electronic, and optical properties, and is dependent largely on the ambient humidity level and the strength of the electric field, it is suggested that the method may be extended to a variety of other materials.

A central composite experimental design was applied to investigate the effect of five preparative variables on the size and cisplatin encapsulation efficiency of poly(lactide-co-glycolide)-methoxy poly(ethylene glycol) (PLGA-mPEG) nanoparticles. The nanoparticles were prepared by a nano-precipitation process and were characterized with regard to their morphology by scanning electron microscopy, their size by photon correlation spectroscopy and their drug content by atomic absorption spectroscopy respectively. The preparative variables investigated were: solids concentration, aqueous to organic phase volume ratio, temperature, rate of organic phase addition in aqueous phase and agitation. The nanoparticles prepared in this study appeared to be spherical and rather homogeneous in size under the scanning electron microscope. The size and the drug encapsulation of the prepared nanoparticles ranged between 90-180 nm and 0%-40%, respectively. The fitted model could adequately describe the experimental data. The statistical analysis showed that all preparative variables studied, except temperature, affected significantly both the size and the drug loading of nanoparticles. The size was most affected by the agitation whereas the loading was most affected by the phase ratio. Significant interactions between the preparative variables were also observed. The “desirability function” approach was applied to simultaneously optimize the nanoparticles with regard to their size and cisplatin encapsulation. The predictive power of the applied model was more satisfactory in the case of nanoparticles size than with cisplatin encapsulation efficiency. It appears to be feasible to select optimum conditions for the preparation of PLGA-mPEG nanoparticles of cisplatin based on a central composite design and the “desirability function” optimization approach.

An extension of the classical thermodynamics to nanometer scale has been conducted to elucidate information regarding size dependence of phase transition functions and binary phase diagrams. The theoretical basis of the extension is Lindemann's criterion for solid melting, Mott's expression for vibrational melting entropy, and Shi's model for size dependent melting temperature. These models are combined into a unified one without adjustable parameters for melting temperatures of nanocrystals. It is shown that the melting temperature of nanocrystals may drop or rise depending on interface conditions and dimensions. The model has been applied to size dependences of melting enthalpy and atomic cohesive energy, critical temperatures for glass transition, ferromagnetic transition, ferroelectric transition, superconductor transition and ferromagnetic-antiferromagnetic transition. Moreover, the above modeling has been utilized to determine the size-dependent continuous binary solution phase diagrams, bi-layer transition diagrams of metallic multilayers, and solid transition phase diagrams after modeling the transition entropy and atomic interaction energy functions of nanocrystals. Moreover, the model has been used to predict size dependence of diffusion activation energy and diffusion coefficient. These thermodynamic approachs have extended the capability of the classical thermodynamics to the thermodynamic phenomena in the nanometer regime.

Self- assembly of biological molecules forms the basic principle in the formation of complex biological structures. Numerous proteins and peptides have been emerging as nanobiomaterials due to their ability to self-assemble into nanoscale structures like nanotubes, nanovesicles, helical ribbons and three dimensional fibrous scaffolds. This mini review discusses the basic principle underlying molecular self-assembly of proteins and peptides towards designing novel biomimetic nanomaterials and their potential applications in electronics, biotechnology, nanotechnology and biomedicine.

Molecular organization has an important influence on the performance of organic materials, i.e. solar cells, light emitting diodes or sensors. 4,4'-Dimethyl-2,2'-bipyridines have been identified as a promising candidate for such applications. Therefore, high resolution STM investigations at the solid-liquid interface have been conducted, to study the intermolecular interaction of the bipyridine moieties. The results provide inside in the self-organization behavior of 4,4'-dimethyl-2,2'-bipyridines and the conclusions might help to understand the molecular arrangement of this class of molecules and might serve, on the long term, as a key to optimize their interaction with respect to improved optoelectronic properties.

The aim of this paper is to develop highly magnetized, biodegradable and biocompatible, polymeric nanoparticles for drug delivery in cell therapy. Alginate magnetic nanoparticles are realized by an emulsion/reticulation technique, after the dispersion of magnetite in an alginate solution. Such nanoparticles are characterized in terms of external morphology (FIB imaging), microstructure (TEM imaging), size distribution, zeta potential, magnetic properties (SQUID analysis) and drug release behaviour. Magnetization curves show the typical trend of superparamagnetic materials. Important parameters, such as magnetic permeability and magnetic momentum, are derived by employing Langevin theory. Experimental results reveal that a bi-exponential model fully describes the drug release. Finally, in vitro experiments on NIH/3T3 cells are carried out and demonstrate that our magnetic alginate nanoparticles can effectively drive the drug delivery towards an external magnetic field source.

The use of three dimensional scaffolds in tissue engineering is well reported, as is the exploitation of nanotopography to influence cell response. To date, due to fabrication limitations, the combination of these two has experienced limited research. This paper reports on the use of polymer demixing, a rapid and cheap nanofabrication method, to create a defined nanotopography in 0.5mm diameter nylon tubes. Results indicate that the resultant nano-island topography reduced endothelial cell adhesion and spreading, strongly influenced cell morphology, and appeared to increase endocytic activity. The use of such constructs that boast topographical cues have great potential in tissue and cell engineering studies for future clinical use, in particular with respect to conduits and stents.