Michelle T.T. Tan

Sensitivity enhancement of graphene/zinc oxide nanocomposite-based electrochemical impedance genosensor for single stranded RNA detection

An efficient electrochemical impedance genosensing platform has been constructed based on graphene/zinc oxide nanocomposite produced via a facile and green approach. Highly pristine graphene was synthesised from graphite through liquid phase sonication and then mixed with zinc acetate hexahydrate for the synthesis of graphene/zinc oxide nanocomposite by solvothermal growth. The as-synthesised graphene/zinc oxide nanocomposite was characterised with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray diffractometry (XRD) to evaluate its morphology, crystallinity, composition and purity. An amino-modified single stranded DNA oligonucleotide probe synthesised based on complementary Coconut Cadang-Cadang Viroid (CCCVd) RNA sequence, was covalently bonded onto the surface of graphene/zinc oxide nanocomposite by the bio-linker 1-pyrenebutyric acid N-hydroxysuccinimide ester. The hybridisation events were monitored by electrochemical impedance spectroscopy (EIS). Under optimised sensing conditions, the single stranded CCCVd RNA oligonucleotide target could be quantified in a wide range of 1.0×10-11M to 1.0×10-6 with good linearity (R =0.9927), high sensitivity with low detection limit of 4.3×10-12M. Differential pulse voltammetry (DPV) was also performed for the estimation of nucleic acid density on the graphene/zinc oxide nanocomposite-modified sensing platform. The current work demonstrates an important advancement towards the development of a sensitive detection assay for various diseases involving RNA agents such as CCCVd in the future.

Enhancing Electroconductivity of Yytria-Stabilised Zirconia Ceramic Using Graphene Platlets

A simple method to produce graphene-Yytria stabilised zirconia (YSZ) ceramic composite with significant improvement in electrical properties is reported here. The material was consolidated by annealing in presence of Argon gas that allowed densification of the ceramics. A detailed x-ray diffraction (XRD) analysis was used to study the phases and crystallinity of graphene-YSZ ceramic composite. XRD patterns of the sintered composite showed that graphene diffraction peaks were detected at 2θ≈27°. Furthermore, experimental results indicate that electrical conductivity of YSZ composites drastically increased with the addition of graphene platelets, and it reached a value of 2.8 S/cm at 2 wt.%.

One-step green hydrothermal synthesis of biocompatible graphene/TiO2 nanocomposites for non-enzymatic H2O2 detection and their cytotoxicity effects on human keratinocyte and lung fibroblast cells

Highly sensitive and selective immunosensors that can detect disease biomarkers at ultra-low levels in early stages are urgently needed to reduce mortality risks. A facile and efficient approach using sonochemical-assisted solvent graphene exfoliation and a hydrothermal synthesis method has been used to prepare graphene/titanium dioxide (G/TiO2) nanocomposites. Nanocomposites containing different ratios of graphene and TiO2 precursors were prepared to determine the optimum composition of G/TiO2 that has the highest conductivity and electrocatalytic properties. Characterisation methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and high resolution TEM (HRTEM) were used to study the crystallinity, surface characteristics, elemental composition, and morphology of the synthesised nanocomposites. The synthesised materials were also confirmed via Raman spectroscopy. Using ferricyanide as the redox active probe, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analyses indicated that 1 : 8 ratio of G/TiO2 exhibited the best current response and the lowest charge transfer resistance (Rct) of 1525 Ω. The potential of G/TiO2 for electrochemical sensing application was investigated using hydrogen peroxide (H2O2), a by-product of most enzymatic processes, as the analyte of interest. The sensitivity of the sensor towards H2O2 was 0.557 μA mM-1, with a limit of detection (LOD) at 56.89 μM. An in vitro cell proliferation assay was carried out to investigate the biocompatibility of the nanocomposites. The half-maximal inhibitory concentration (IC50) values obtained were >500 μg ml-1 for human lung fibroblasts (MRC5) and 5-25 μg ml-1 for human skin cells (HaCat).

Recent developments in ceramic microthrusters and the potential applications with green propellants: a review

Conventional chemical propellants such as hydrazine and ammonium perchlorate have been used within the realm of contemporary space propulsion devices and are well established owing to their rich heritage. However, their limitations such as toxicity, difficulty in operational handling and environmental impacts have raised concerns. In view of these limitations, the significance of green propellants such as hydroxylammonium nitrate, hydrogen peroxide (H2O2) and ammonium dinitramide has become more pronounced. In this paper, recent developments in ceramic microthrusters and the associated ceramic microfabrication techniques are reviewed. The characteristics of green propellants are examined, followed by the evaluation of previous attempts to incorporate green propellants into ceramic microthrusters. This has further unveiled the possibilities of green and clean space missions in the future.

Study of ternary metal oxides as supercapacitor electrodes

Supercapacitors are energy storage devices that make use of ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudocapacitors). They complement batteries in electrical energy storage. Recent advances in charge storage mechanisms and the development of advanced nanostructured materials has yielded notable improvement in the performance of supercapacitors. The structural and electrochemical properties of the mixed metallic oxides AlₓCuyCozFe₂O₄ (where x + y + z = 1) nanomaterials, which crystallise in a cubic spinel AFe₂O₄ structure are investigated systematically with a gradual substitution of Al by transition metals. The crystal structure information studied by X-ray diffraction (XRD) depicts the formation of single phase spinel structure, while electron-dispersive X-ray spectroscopy (EDX) reveals the stoichiometric relations of Al, Cu and Co.

Study on Mechanical Properties of Zirconia-Alumina Based Ceramics

This paper describes the characterisations of ceramic composites consisting of different compositions of alumina and zirconia. The material characterisations were performed from the aspects of densification, hardness and fracture toughness. The surface morphology and elemental composition of the composite were studied using SEM and EDX respectively. As for physical properties, the highest attainable hardness and fracture toughness were 11.35 GPa and 3.41 MPa m0.5 respectively for ceramic composite consisted of 80 wt % Zr and 20 wt% Al. Sintering at 1150oC assisted in the densification of ceramics.