Nanocomposites of colloidal gold particles and fatty acids formed by the high-affinity biotin-avidin interaction

The formation of thin nanocomposite films comprising colloidal gold particles in a fatty acid matrix by a simple solution based diffusion process is described. A simple two-step process accomplishes the formation of the composite films. In the first stage, avidin molecules are incorporated into thermally evaporated arachidic acid (AA) films by simple immersion of the lipid films in an aqueous solution of the protein. The diffusion of the avidin molecules is driven by attractive electrostatic interaction between charged side chains of the protein and the carboxylate ions of the AA matrix. Thereafter, biotinylated colloidal gold particles are incorporated into the protein-containing AA matrix by a similar immersion procedure. The high-affinity biotin-avidin interaction drives the diffusion of the biotinylated gold particles into the matrix and a colloidal nanocomposite results. The kinetics of protein incorporation as well as colloidal particle diffusion in the fatty acid matrix were characterized using quartz crystal microgravimetry (QCM) and ultraviolet-visible spectroscopy and analyzed in terms of a one-dimensional diffusion model. The nanocomposite films were further characterized by Fourier transform infrared (FTIR) spectroscopy which, together with the QCM and UV-vis spectroscopy measurements of the biotin-avidin recognition driven gold particle diffusion, indicates that the protein molecules are encapsulated in the fatty acid matrix without significant perturbation to their biological activity

Preparation of Surface Adsorbed and Impregnated Multi-walled Carbon Nanotube/Nylon-6 Nanofiber Composites and Investigation of their Gas Sensing Ability

We have prepared electrospun Nylon-6 nanofibers via electrospinning, and adsorbed multi-walled carbon nanotubes (MWCNTs) onto the surface of Nylon-6 fibers using Triton® X-100 to form a MWCNTs/Nylon-6 nanofiber composite. The dispersed MWCNTs have been found to be stable in hexafluoroisopropanol for several months without precipitation. A MWCNTs/Nylon-6 nanofiber composite based chemical sensor has demonstrated its responsiveness towards a wide range of solvent vapours at room temperature and only mg quantities of MWCNTs were expended. The large surface area and porous nature of the electrospun Nylon-6/MWCNT nanofibers facilitates greater analyte permeability. The experimental analysis has indicated that the dipole moment, functional group and vapour pressure of the analytes determine the magnitude of the responsiveness

Vanadium pentoxide nanotubes by eelectrospinning

Nanofibers of vanadium pentoxide (V2O5) were synthesized by electrospinning a polymeric solution containing vanadium ion and with subsequent sintering. Conventionally, electrospun TNFs were produced by using a co-axial spinneret; however, TNFs in the present study were obtained by manipulating the concentration ratio of the precursor solution, distance, humidity and flow rate during electrospinning using a single spinneret and sintering with time and temperature change. On the basis of this hypothesis, nanofibers could be altered from elongated 1-D nanofibers to nanowires, nanotubes, spheres and flakes respectively. The surface morphology, structure, roughness and the crystal structure were analyzed using Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), and X-ray diffraction (XRD). The current work has demonstrated a case study for energy storage where V2O5 nanotubes when tested shows the capacitance of 190 Fg−1 in 2M KCl electrolyte indicating an example for the energy storage which may be applicable for other electrochemical devices such as Li-ion batteries, fuel cells, hydrogen storage etc

Biotinylation of colloidal gold particles using interdigitated bilayers: a UV-visible spectroscopy and TEM study of the biotin-avidin molecular recognition process

The surface modification of colloidal gold particles with biotin groups using a technique based on interdigitated bilayers is described. The biotinylation of the colloidal particles is accomplished by a two-step process. The first step involves the self-assembly of a close-packed primary monolayer of octadecanethiol (ODT) molecules on the colloidal particle surface. Thereafter, a secondary monolayer of alkylbiotin molecules is self-assembled on the ODT-capped gold colloidal particles by interdigitation of the alkyl groups of the biotin molecules with the hydrocarbon chains of the primary monolayer. The resulting biotinylation of the colloidal particles is checked by the high-affinity biotin-avidin interaction, which leads to cross-linking of the colloidal particles and an easily measurable change in the optical properties of the sol. This approach may be important for the incorporation of molecules with functional groups that become inactive due to modification of the molecule with colloidal particle surface-anchoring groups such as thiol groups and thus shows scope for development

Optical absorption study of the biotin-avidin interaction on colloidal silver and gold particles

The biotin-avidin reaction is well studied and is often used as a prototypical interaction in the development of immunoassays. In this paper, this reaction is studied on the surface of colloidal silver and gold particles as a first step in the development of a sol-based assay. More specifically, silver and gold colloidal particles were biotinylated by self-assembly of a biotin disulfide molecule, and the reaction of the surface-modified colloidal particles with avidin molecules was followed using optical absorption spectroscopy. The specific interaction of avidin, a tetrameric protein, with biotin leads to cross-linking of the colloidal particles ("flocculation") and a consequent growth of a long wavelength absorption peak. The degree of flocculation was quantified using a semiempirical flocculation parameter, and the dependence of this parameter on the extent of biotinylation of the colloidal particle surface as well as the concentration of avidin in solution was studied to determine the optimum working conditions of the sol. The silver sol required electrostatic stabilization of the biotin-capped particles through the simultaneous incorporation of a charged bifunctional molecule, 4-carboxythiophenol, in the capping monolayer while the gold sol was stable with biotin capping. Both biotinylated silver and gold sols showed a visible color change on addition of avidin. However, changes in the optical absorption spectra were more marked for the silver sol

Patterned assembly of Yarrowia lipolytica yeast cells onto thermally evaporated octadecylamine films

Thermally evaporated patterned films of the lipid, octadecylamine (ODA), have been used in the immobilization of the hydrocarbon-degrading cells, Yarrowia lipolytica. The immobilization of the yeast cells occurs on hydrophobic surfaces presented by the lipid film elements in the patterned structure, the attachment of the cells to the lipid film occurring possibly through hydrophobic interactions between the hydrocarbon chains of the fatty amine film and the cell wall of the yeasts. It is observed that the cell immobilization is extremely faithful to the underlying lipid template indicating potential use in tissue engineering as well as materials applications involving specific enzyme-based biotransformations