Characterization and stability of liposome-enveloped trypsin/Fe3O4 for drug delivery and drug release behavior.

Liposome encapsulating Fe3O4 (liposome complexes) has been prepared for targeting a drug to a specific organ, as well as for MRI (magnetic resonance imaging) contrast agents. The objective of the present work was to investigate the Fe3O4 properties and the effects of chitosan concentration on the characteristics of chitosan-coated liposome complexes. They were characterized by DLS, FT-IR, XRD, VSM, UV-Vis spectrometer, TEM and phase-contrast microscopy. The average liposome complex size was approximately 500 nm, with individual Fe3O4 nanoparticle sizes of 10 nm. The drug incorporation efficiency of trypsin in liposome complexes was 65-69%, the drug release was sustained and the incorporated drugs had the magnetization properties of the liposome complexes. Incorporation of chitosan into the liposome bilayer decreased trypsin release from the liposome complexes due to an increased rigidity of the liposome membrane structure. Chitosan-coated liposome complexes showed a higher stability when compared with the stability of non-coated liposome complexes.

In-situ TEM observation of repeating events of nucleation in epitaxial growth of nano CoSi2 in nanowires of Si.

The formation of CoSi and CoSi2 in Si nanowires at 700 and 800 degrees C, respectively, by point contact reactions between nanodots of Co and nanowires of Si have been investigated in situ in a ultrahigh vacuum high-resolution transmission electron microscope. The CoSi2 has undergone an axial epitaxial growth in the Si nanowire and a stepwise growth mode was found. We observed that the stepwise growth occurs repeatedly in the form of an atomic step sweeping across the CoSi2/Si interface. It appears that the growth of a new step or a new silicide layer requires an independent event of nucleation. We are able to resolve the nucleation stage and the growth stage of each layer of the epitaxial growth in video images. In the nucleation stage, the incubation period is measured, which is much longer than the period needed to grow the layer across the silicide/Si interface. So the epitaxial growth consists of a repeating nucleation and a rapid stepwise growth across the epitaxial interface. This is a general behavior of epitaxial growth in nanowires. The axial heterostructure of CoSi2/Si/CoSi2 with sharp epitaxial interfaces has been obtained. A discussion of the kinetics of supply limited and source-limited reaction in nanowire case by point contact reaction is given. The heterostructures are promising as high performance transistors based on intrinsic Si nanowires.

Synthesis and characterization of cadmium telluride nanowire.

CdTe nanowires with controlled composition were cathodically electrodeposited using track-etched polycarbonate membrane as scaffolds and their material and electrical properties were systematically investigated. As-deposited CdTe nanowires show nanocrystalline cubic phase structures with grain sizes of up to 60 nm. The dark-field images of nanowires reveal that the crystallinity of nanowires was greatly improved from nanocrystalline to a few single crystals within nanowires upon annealing at 200 °C for 6 h in a reducing environment (5% H(2)+95% N(2)). For electrical characterization, a single CdTe nanowire was assembled across microfabricated gold electrodes using the drop-casting method. In addition to an increase in grain size, the electrical resistivity of an annealed single nanowire (a few 10(5) Ω cm) was one order of magnitude greater than in an as-deposited nanowire, indicating that crystallinity of nanowires improved and defects within nanowires were reduced during annealing. By controlling the dopants levels (e.g. Te content of nanowires), the resistivity of nanowires was varied from 10(4) to 10(0) Ω cm. Current-voltage (I-V) characteristics of nanowires indicated the presence of Schottky barriers at both ends of the Au/CdTe interface. Temperature-dependent I-V measurements show that the electron transport mode was determined by a thermally activated component at T>-50 °C and a temperature-independent component below -50 °C. Under optical illumination, the single CdTe nanowire exhibited enhanced conductance.