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

Shell-Controlled Photoluminescence in CdSe/CNT Nanohybrids

A new type of nanohybrids containing carbon nanotubes (CNTs) and CdSe quantum dots (QDs) was prepared using an electrostatic self-assembly method. The CdSe QDs were capped by various mercaptocarboxylic acids, including thioglycolic acid (TGA), dihydrolipoic acid (DHLA) and mercaptoundecanoic acid (MUA), which provide shell thicknesses of ~5.2, 10.6 and 15.2 Å, respectively. The surface-modified CdSe QDs are then self-assembled onto aridine orange-modified CNTs via electrostatic interaction to give CdSe/CNT nanohybrids. The photoluminescence (PL) efficiencies of the obtained nanohybrids increase significantly with the increase of the shell thickness, which is attributed to a distance-dependent photo-induced charge-transfer mechanism. This work demonstrates a simple mean for fine tuning the PL properties of the CdSe/CNT nanohybrids and gains new insights to the photo-induced charge transfer in such nanostructures

Structural basis for the dual transport-channel functions of SLC1A transporters

The excitatory amino acid transporters (EAATs) play a vital role in the maintenance of glutamatergic neurotransmission within the synapse, involved in fundamental brain functions such as learning and memory. These secondary active transporters enable rapid glutamate reuptake into the surrounding glial cells and neurons by coupling to pre-existing electrochemical gradients of sodium ions, potassium ions and protons. In addition to this conventional transporter function, the EAATs also possess a unique ability to conduct chloride ions in a channel-like process that is thermodynamically uncoupled from substrate transport. Aberrant glutamatergic neurotransmission caused by dysfunction of the EAATs has been associated with excitotoxity-mediated cell death and the pathogenesis of multiple debilitating neurological disorders. In particular, an increased chloride conductance via an EAAT1 mutant has been directly linked to a neurological disease, episodic ataxia type 6. This thesis describes a body of work that investigates the interplay between the elevator mechanism of substrate transport and chloride permeation in the archaeal homolog and sodium-dependent aspartate transporter, GltPh, using X-ray crystallography and single particle cryo-EM. It presents crystal structures of GltPh mutants locked in the outward-facing and inward-facing states, and a novel cryo-EM structure of a GltPh protomer in the chloride conducting state, which fills in the final missing puzzle required to map the complete substrate translocation pathway. This chloride conducting state was further confirmed by a combination of computational and functional analysis, which unveiled two clusters of hydrophobic residues at either side of the membrane that gate the channel. Furthermore, this thesis also explore pathogenic mutations (P206R and L90R in GltPh) associated with episodic ataxia type 6 structurally in an attempt to explain their functional consequences. Together, this thesis enhance our mechanistic understanding of the dual functions conserved in the SLC1A transporter family, opening doors for alternative approaches to treat neurological disorders associated with transporter dysfunctions