Current Nanoscience - Volume 3, Issue 4, 2007

Quantum dots (QDs) have rapidly emerged as an attractive alternative to conventional organic fluorophores in a variety of biological imaging applications. Their improved photostability allows for long-term dynamic imaging of cellular processes and their narrow, size-tunable emission permits unprecedented multiplexing capabilities. Additionally, the inherent brightness of core/shell QDs, with quantum yields capable of exceeding 85%, provides increased sensitivity for both diagnostic screening and single molecule tracking applications. To date, the primary focus of research in this field has been directed towards modifying the surface chemistries of the QDs to introduce biological specificity while, at the same time, limiting nonspecific cellular interactions. As such, biomolecules such as antibodies, peptides, streptavidin and biotin have all been conjugated to QDs and been used to demonstrate specific labeling of cellular targets. Additionally, polyethylene glycol (PEG) modification of the QD surface has been shown to limit nonspecific interactions. The use of small molecule QD-conjugates has also been demonstrated as an effective means for targeted labeling of membrane associated receptors. This approach introduces specificity via ligand-receptor interactions, resulting in a highly modular system which is easily modified to interrogate a wide variety of cellular targets. This article provides a comprehensive review of the current status of QD imaging applications in biological systems with a particular emphasis on the design and application of small molecule nanoconjugates.

Development of renewable energy resources in the near future is an urgent issue. One attractive strategy is the development of dye-sensitized solar cells (DSSCs); they are extremely promising, because they are made of low-cost materials and do not need elaborate apparatus to manufacture. Titania is the most promising material for the electrode of DSSCs, and then morphological control and carrier transport optimization are the key properties needed in titanium oxide materials for DSSCs. We review the formation procedures and characteristics of titanium oxide nanocrystalline products, which exhibit various morphological shapes in nanometer scale, i. e., nanotubes, nanorods, nanowires and nanosheets, and their arrays. We also present new findings in our laboratory on the formation of titania nanorods and network structures of single-crystal-like titania nanowires as well as their application for DSSCs. In order to evaluate the electrical properties of DSSCs with electrodes composed of various nanoscale titania materials, measurement procedures for electron transport processes in DSSCs are also reviewed, together with our results in electrochemical impedance spectroscopy to determine various parameters concerning about electron transport.

Photonic crystals offer unprecedented opportunities for the realization of all-optical integrated circuits and optical computation. Colloidal self-assembly provides a much cheaper and simpler alternative to complex nanolithography in creating three-dimensional photonic crystals operating at visible and telecommunication wavelengths. The self-organized colloidal arrays can also be used as templates in fabricating nanostructured materials that have important technological applications ranging from biosensors to plasmonic devices. The present paper reviews recent advances in the assembly of colloidal photonic crystals, mainly focuses on the spin-coating technological platform that is compatible with standard microfabrication, enabling mass-fabrication of wafer-scale colloidal photonic crystals. Various templating approaches based on the spin-coating platform for making periodic nanomaterials and their potential applications are also addressed.

The improvement of materials performance and their respective processing routes ever has been the driving force for material science and engineering. For the preparation of non-metallic inorganic materials the synthesis from chemical precursors is a field of steadily increasing scientific and industrial importance: Products in a broad variety of compositions can be obtained by sol-gel techniques. The shaping of intermediates allows the specific preparation of many microarchitectural configurations such as powders, fibers, thin films and aerogels. For purely inorganic products the sintering temperatures are low compared to conventional mixed-oxide ceramic processing which enables e.g. the coating of glasses and metals. Hybrid inorganic-organic compositions combine some advantages of polymers and ceramics. Nature has found amazing alternative ways to produce high-performance inorganic-organic composites at ambient temperatures under physiological conditions: Teeth, bone and nacre are self-evident examples for the capability of biomineralization processes. Even though many aspects of the related mechanisms in vivo are not yet fully understood, the utilization of the basic strategies of natural biomineralization has become a challenge to material scientist in an interdisciplinary approach. In this paper the strong points of sol-gel processing are highlighted, its limitations are discussed and related to the unique characteristics of natural biomineralization. Subsequently biomimetic and biologically-inspired material syntheses routes are reviewed which try to compensate the shortcomings of sol-gel techniques.

Drug delivery systems largely contribute to cancer therapy in terms of tumor targeting and controlled release of cargo molecules. While targeting of tumor “tissue” has been achieved using nanocarriers, delivery of cargo molecules into tumor cells is still challenging. Intracellular delivery of nanocarriers is an essential process to overcome multi-drug resistance and for the delivery of cargo molecules for both therapy and vaccine applications. Nanocarriers may gain access to the interior of target cells either non-specifically, as in adsorptive endocytosis, or specifically, as in receptor-mediated endocytosis. Once internalized, they must subsequently break free of their endosomal compartments in order to deliver their cargo into either the cytosol or nucleus. If the nucleus is the target, as in DNA delivery, the nanocarrier must then traffick to the perinuclear region and deliver the cargo into the nucleus, either by physically transporting DNA through the nuclear pore complex (NPC), or by releasing DNA at the door of the NPC, allowing free DNA to gain access. This review article includes both principles and mechanisms of intracellular delivery of nanocarriers, and gives a few examples of their application.

Absorption of carbamazepine (CBZ) from gastrointestinal tract is slow and erratic. In order to improve oral absorption of CBZ, 1-O-alkylglycerol/lecithin stabilized o/w nanoemulsions incorporating CBZ in oil phase were prepared and characterized. Nanoemulsions had a size around 200 nm. Their oral bioavailability in rabbits and in situ intestinal absorption in rats were evaluated. In in situ studies, the test and control systems were charged into intestine and instead of lumenal samples, blood samples from tail vein were analyzed for CBZ content. These results indicated faster rate and higher extent of absorption for nanoemulsions than control (a micron sized aqueous CBZ suspension). The high rate of release from and adherence of nano-oil particles to mucosa seems to have enhanced absorption of CBZ in this model. Among nanoemulsions 1-O-decylglycerol/lecithin stabilized system showed faster rate of absorption, higher Cmax and area under the curve (AUC). Improvement in oral absorption of CBZ from nanoemulsions was also evident from the bioavailability study conducted on rabbits. Peak serum concentration (Cmax) and AUC were higher for nanoemulsions than control. This study indicated increase in absorption and decrease in disposition of CBZ when administered as nanoemulsions. Broadly the globule size and permeabilization effect due to 1-O-alkylglycerols seem to be the factors responsible for enhanced absorption due to nanoemulsions in in situ and in vivo experiments. However the permeability effect of 1-O-alkylglycerol was prominent only in in situ experiments.

When diagnosing human bone as Osteoporotic, the quantity of bone, assessed by measurement of the bone mineral density (BMD), is often used in the estimate of fracture resistance. However, bone quantity is only one of the factors that determine the ability of bone to resist fracture. Bone quality describes the remaining characteristics and traits that determine the fracture resistance of bone. Bone is a composite material, consisting of minerals embedded in an organic matrix. The mechanical properties of a composite material are determined by the structural interactions of the individual constituents, which is different from the sum of mechanical properties of the individual constituents. The size of the building blocks of bone is in the nanometer range, the diameter of collagen is 100 nanometers and mineral plates range from the typical diameter of 10-20 nanometers to 200 nanometers. To understand the ability of bone to resist fracture, and its quality as a tissue, it is important to appreciate the intricate interplay between these building blocks. This review focuses on the parameters that contribute to bone quality, including recent evidence for the roles of factors such as collagen cross-linking, microcracking and bone remodelling.