Omer Nour

Structural Characterization and Biocompatible Applications of Graphene Nanosheets for Miniaturization of Potentiometric Cholesterol Biosensor

The potentiometric cholesterol biosensor based on graphene nanosheets has been successfully miniaturized. Cholesterol oxidase (ChOx) has been immobilized onto graphene nanosheets exfoliated on copp ...

Studies on Calcium Ion Selectivity of ZnO Nanowire Sensors Using Ionophore Membrane Coatings

Zinc oxide nanorods with 100nm diameter and 900nm length were grown on the surface of a silver wire (0.25mm in diameter) with the aim to produce electrochemical nanosensors. It is shown that the Zn ...

Synthesis of Co3O4 Cotton-Like Nanostructures for Cholesterol Biosensor

The use of templates to assist and possess a control over the synthesis of nanomaterials has been an attractive option to achieve this goal. Here we have used sodium dodecyl sulfate (SDS) to act as a template for the low temperature synthesis of cobalt oxide (Co3O4) nanostructures. The use of SDS has led to tune the morphology, and the product was in the form of “cotton-like” nanostructures instead of connected nanowires. Moreover, the variation of the amount of the SDS used was found to affect the charge transfer process in the Co3O4. Using Co3O4 synthesized using the SDS for sensing of cholesterol was investigated. The use of the Co3O4 synthesized using the SDS was found to yield an improved cholesterol biosensor compared to Co3O4 synthesized without the SDS. The improvement of the cholesterol sensing properties upon using the SDS as a template was manifested in increasing the sensitivity and the dynamic range of detection. The results achieved in this study indicate the potential of using template assisted synthesis of nanomaterials in improving some properties, e.g., cholesterol sensing.

Annealing Effects on Electrical and Optical Properties of N-ZnO/P-Si Heterojunction Diodes

The effects of post fabrication annealing on the electrical characteristics of n-ZnO/p-Si heterostructure are studied. The nanorods of ZnO are grown by aqueous chemical growth (ACG) technique on p-Si substrate and ohmic contacts of Al/Pt and Al are made on ZnO and Si. The devices are annealed at 400 and 600 °C in air, oxygen and nitrogen ambient. The characteristics are studied by photoluminescence (PL), current–voltage (I-V) and capacitance - voltage (C-V) measurements. PL spectra indicated higher ultraviolet (UV) to visible emission ratio with a strong peak of near band edge emission (NBE) centered from 375-380 nm and very weak broad deep-level emissions (DLE) centered from 510-580 nm. All diodes show typical non linear rectifying behavior as characterized by I-V measurements. The results indicated that annealing in air and oxygen resulted in better electrical characteristics with a decrease in the reverse current.

Zinc oxide nanostructures at the forefront of new white light- emitting technology

Zinc oxide (ZnO) nanostructures are generating significant interest due to unique characteristics that make them good candidates for UV optoelectronic applications such as biosensors and resonators. These properties are due to the wide bandgap of ZnO (3.37eV at room temperature) and to its large exciton energy (60meV), which makes it possible to employ excitonic recombination as a UV-lasing mechanism. ZnO is also a piezoelectric and biosafe material that has probably spawned the richest family of nanostructures to date. Moreover, the ferromagnetic properties of ZnO doped with rare earth metals are also of interest for the design of novel devices that store information as a particular spin orientation (spintronics). Of the techniques for growing ZnO nanostructures with controlled dimensions, we have been using two of the most common and cost-effective, namely, the catalytic vapor-liquid-solid (VLS) method and a low-temperature technique based on chemical engineering. When optimized, both approaches can be used to produce large-scale wafers and are suitable for commercial production. Figure 1 shows the schematics of the oven used in our VLS growth experiments.1 We have generated a wide family of different ZnO nanostructures, including wires (both vertically aligned and randomly oriented), ribbons, dots, flowers, branched structures, and leaves, on a variety of substrates with crystalline or amorphous surfaces.2 The room temperature photoluminescence (PL) spectra of typical ZnO nanowire samples are characterized by two main emission bands. The first is a sharp free-exciton UV band that usually centers on ∼380nm, and the second is a wider broad band observed between 420 and 700nm, historically referred to as the green luminescence or deep-level emission band. Figure 1. Fabrication of zinc oxide (ZnO) nanowires using the catalytic VLS growth method. Insert: Transmission electron microscope image of a nanowire with a gold (Au) particle at the tip. Ar: Argon.

A chip that creates micro-scale vortices in water and mimics biochemistry

An electrolyte transistor—essentially a chemical device that controls the flow of electricity—could help scientists understand and explore the chemical activity between small numbers of molecules. The device could be used in demanding areas such as the sensing of substances from the human body, applications where basic and applied scientists need smart, sensitive, and selective devices that operate in real time. In wet chemistry, for instance, our electrolyte transistor allows microand nanoscale observations of reactants forming products. In addition, the platform described here can control dynamic conditions, stirring aqueous reactants by creating microscale vortices for example. Long ago, scientists proposed and demonstrated electrolyte transistors as electrochemical sensors. These devices also proved to be biocompatible, which means that they could be used in physiological environments. Nevertheless, no practical device was demonstrated. Our prototype combines an appealing design with advanced nanolithography: the technology used to make computer chips. The prototype transistor was processed on a low-doped, n-type, oxidized-silicon substrate. Conventional electron-beam lithography was used. On the same substrate, we fabricated different cells with active linear dimensions ranging from few hundred micrometers down to few nanometers. A drop of clean-room, deionized water with a resistivity of 18.3MΩ was sprayed onto the device’s active area. Figure 1 shows a photomicrograph of the device in action, creating vortices. Our team used different cells for the three experiments described here. The first deals with microscale vortices stirring water. These experiments took place in a micro-cell (100μm × 100μm, see Figure 1. A photomicrograph of an electrolyte transistor reveals the formation of vortices (rings) at the anode. This cell is 100μm× 100μm with 3.2 volts (dc) of applied voltage. (Copyright 2005 American Institute of Physics)