Current Nanoscience - Volume 2, Issue 4, 2006

Biological protein-based entities that form nanostructures ranging from 8 to 50 nm in size represent promising candidates in the development of novel immunotherapeutics against cancer and microbial pathogens. These recombinant nanoparticles usually consist of major coat or core proteins derived from viruses like for instance papillomavirus, polyomavirus, parvovirus or hepatitis B virus that spontaneously assemble into these highly ordered, supramolecular, icosahedral structures. By genetic engineering of permissive sites or cross-linking to surface-exposed subunit domains these nanoparticles successfully serve as carrier matrix with per se adjuvant activity for the delivery of appropriate guest peptides, protein fragments and complete proteins. Using this nanobiotechnology, potent humoral and cell-mediated immunity with emphasis on CD4 and CD8 T cell responses are induced against self or non-self foreign antigens representing appropriate immunostimulatory epitopes or complete proteins of microbial pathogens or tumor-associated antigens. Breaking of T and B cell tolerance required for therapeutic interventions against cancer represents the hallmark of such an outstanding antigen delivery system. In combination with the increasing identification of validated target antigens from pathogens or tumors, and promising progress in bioprocess development, such nanostructures offer novel homologous or heterologous treatment and prevention opportunities against a variety of malignant and infectious diseases.

In search of a high resolution sensing platform with the capability of wireless operation, we identified surface acoustic wave (SAW) devices as the most promising technology. In this review we discussed the working principles of SAW devices, their applications in sensing as well as the integration of nanostructures with SAW devices for achieving enhanced sensitivity. Future research challenges and benefits of nanostructured surface acoustic wave devices for biosensing applications were also addressed.

Carbon nanotubes (CNTs) possess high electrical conductivity, high chemical stability, and extremely high mechanical strength and modulus. These special properties of both single-walled and multi-walled CNTs (SWNTs and MWNTs, respectively) have attracted much attention in electrochemistry. Functionalization of CNTs is one of the most active fields in carbon nanotube research, which provides an effective tool to broaden the spectrum of electrochemical application of CNTs. In this review, we summarize various approaches to functionalize CNTs for the development of novel electrochemical sensors. Particular emphasis is directed to the use of lipid-functionalized CNTs for sensors and biosensors and for the fabrication of photo switched-functional devices. The functionalization of the nanotubes generates a novel, interesting class of nanomaterials, which combines the properties of the nanotubes and the functional moiety, thus offering new opportunities in electrochemical sensors.

Atomic force microscopy (AFM) has developed into a powerful tool in biophysics to assess the structure and measure the inter- and intramolecular forces of biological objects. At the cutting-edge, imaging and force measurements are performed on individual membrane proteins. Here, recent achievements of high-resolution imaging and imaging in combination with controlled force measurement using AFM are reviewed. High-resolution imaging can yield topographical information to ∼ 10 Å resolution. The comparison with protein structures from X-ray crystallography shows that surface protruding loops of no more than 5 aminoacids are reliably contoured. Force measurements reveal intramolecular forces with a precision of ∼ 10 pN. Again, the comparison with atomic structures shows that forces between pairs of transmembrane helices are probed. As a major advantage, the combination of force spectroscopy measurements with high resolution imaging allow assignment of measured unfolding events with topographical changes.

High Resolution Interference Microscopy (HRIM) is a technique that allows the characterization of amplitude and phase of electromagnetic wave-fields in the far-field with a spatial accuracy that corresponds to a few nanometers in the object plane. Emphasis is put on the precise determination of topological features in the wave-field, called phase singularities or vortices, which are spatial points within the electromagnetic wave at which the amplitude is zero and the phase is hence not determined. An experimental tool working in transmission with a resolution of 20 nm in the object plane is presented and its application to the optical characterization of various single and periodic nanostructures such as trenches, gratings, microlenses and computer generated holograms is discussed. The conditions for the appearance of phase singularities are theoretically and experimentally outlined and it is shown how dislocation pairs can be used to determine unknown parameters from an object. Their corresponding applications to metrology or in optical data storage systems are analyzed. In addition, rigorous diffraction theory is used in all cases to simulate the interaction of light with the nano-optical structures to provide theoretical confirmation of the experimental results.

Exfoliated nano-clay/epoxy composites typically contain approximately 1 nm thick layers of clay dispersed in the polymer matrix. Owing to the platy morphology of the silicate layers, exfoliated clay nanocomposites can exhibit dramatically improved barrier and mechanical properties that are not available with conventional composite materials. Since epoxy applications may exist in areas of high moisture content and under mechanically induced stress, the effect of such stressing on water uptake by epoxy-clay nanocomposites is of interest. In this work, low viscosity liquid aromatic diglycidyl ether of bisphenol A (DGEBA) epoxy resin, Epon 815C, was mixed with Montmorillonite nanoclay to produce an exfoliated clay - epoxy resin system containing 0.5% nanoclay by weight. These samples were immersed in water in stressed condition (flexural stress) to assess the effect of stress on the nanocomposite epoxy system's water uptake behavior. Application of the flexural stress affected the water uptake barrier properties for the nanoclay/epoxy nanocomposites, with the stress acting to decrease the rate of absorption as well as to decrease the equilibrium moisture content in the 0.5% loaded nanocomposite. The results revealed up to 33% reduction in water uptake for the stressed samples.

Silver nanocolloids (SNC) are materials useful for wide application in chemistry and biology which are usually prepared by chemical reduction of a silver salt. Monodisperse SNC sols are relatively difficult to prepare compared to gold nanocolloids and few data are available on the optimization of the synthetic conditions as well as on the possible evolution of the nanocolloids after synthesis. To document this, we have carried out a series of chemical syntheses of SNC by the citrate and borohydride methods by varying the reductant/AgNO3 ratio. We characterized the colloids by UV-vis. spectroscopy immediately after completion of the synthetic process and during several months of storage. The spectroscopic data collected were verified for conformity with Mie theory and we retained only the data fitting to spherical nanoparticles for further analysis. Our results indicate that the SNC prepared by the citrate method contain large particles (diameters around 40 nm) which remain stable during storage. In contrast, the borohydride method generates smaller SNC. During storage, these nanoparticles were found to experience alternating nucleation and Ostwald ripening phases, which were not necessarily dependent on further silver reduction but rather on particle-particle interactions, stabilizing only after several months, depending on the synthetic conditions. We conclude that the citrate method generates stable SNC that can be safely used after synthesis, although a safe use during storage of SNC produced by borohydride reduction depends heavily on the synthetic conditions.

The development of polymeric dental composites has revolutionized the field of dentistry over the past 30 years. This development has been achieved mainly through organic monomer discovery, modifications in formulation and filler technology, advances in light curing equipment and efficient photoinitiators. Despite these developmental advances, dental composites are still limited by problems such as polymerization shrinkage and wear resistance. The post-gel polymerization shrinkage causes significant stresses in the surrounding tooth structure and composite tooth bonding leading to premature restoration failure. Other problems such as uncured organic monomers leaching from the dental composites into the surrounding gum tissue have caused cytotoxic effects. With the recent advances in nanotechnology and nanomaterials, it is postulated that mechanical properties and polymerization shrinkage of dental composites can be significantly improved. This review will focus on several recent advances of nanotechnology implementation into dental composites. The technology involved in the development of dental nanocomposites and their enhancement in mechanical properties when compared to the traditional macrofill and microfill composites will be reviewed. Some of our work in the development of low shrinking nanocomposites using functionalized Polyhedral Oligomeric Silsesquioxane (POSS) molecule will also be discussed.