R. M. Ayub

High-performance integrated field-effect transistor-based sensors.

Field-effect transistors (FETs) have succeeded in modern electronics in an era of computers and hand-held applications. Currently, considerable attention has been paid to direct electrical measurements, which work by monitoring changes in intrinsic electrical properties. Further, FET-based sensing systems drastically reduce cost, are compatible with CMOS technology, and ease down-stream applications. Current technologies for sensing applications rely on time-consuming strategies and processes and can only be performed under recommended conditions. To overcome these obstacles, an overview is presented here in which we specifically focus on high-performance FET-based sensor integration with nano-sized materials, which requires understanding the interaction of surface materials with the surrounding environment. Therefore, we present strategies, material depositions, device structures and other characteristics involved in FET-based devices. Special attention was given to silicon and polyaniline nanowires and graphene, which have attracted much interest due to their remarkable properties in sensing applications.

HIV-1 Tat biosensor: Current development and trends for early detection strategies.

Human immunodeficiency virus (HIV) has infected almost 35 million people worldwide. Various tests have been developed to detect the presence of HIV during the early stages of the disease in order to reduce the risk of transmission to other humans. The HIV-1 Tat protein is one of the proteins present in HIV that are released abundantly approximately 2-4 weeks after infection. In this review, we have outlined various strategies for detecting the Tat protein, which helps transcribe the virus and enhances replication. Detection strategies presented include immunoassays, biosensors and gene expression, which utilize antibodies or aptamers as common probes to sense the presence of Tat. Alternatively, measuring the levels of gene transcription is a direct method of analysing the HIV gene to confirm the presence of Tat. By detection of the Tat protein, virus transmission can be detected in high-risk individuals in the early stages of the disease to reduce the risk of an HIV pandemic.

Studying Effect Dimensions of Design and Simulation Silicon Nanowire Filed Effect Biosensor

We investigated into report a study biosensor based on silicon into an effect on the dimensions of conductance design and simulation nanowire surface with molecular DNA for sensitivity. In the design nanowire of A biosensor with 3 layers starting with polyisilicon nanowire of radius 8 NM surrounded by a 50-nm electrode layer, and the substrate by a 300nm. COMSOL Multiphysics software used to provide interaction with molecules such as DNA and the distribution of the electrostatic potential in the narrower due to the dimensions, surface nanowire charge was computed using Poisson equation with Boltzmann statistics. In the result of the effect geometry was also studied and the different dimension yield different space charge and the surface charge at interactive site were also investigated and the study demonstrate steps wise identification of all critical parameters for (DNA) attachment with surface nanowires.

Deposition and characterization of ZnO thin film for FET with back gate biasing-based biosensors application

This paper presents the preparation and characterization of zinc oxide (ZnO) thin film prior deposition on the channel of field-effect transistor with back gate biasing (FET-BG) for biosensing application. Sol-Gel technique is a chosen method for the preparation of the ZnO seed solution, followed by the deposition process through spin coating technique on the silicon dioxide (SiO2). Prior to that, the SiO2 layer is grown on a silicon die. The ZnO seed solution is deposited at various numbers of coating layer (1, 3, and 5 coating layers), baked, and annealed prior to characterization of its surface morphological, structural, crystalline phase, and electrical characterization. The results obtained give a significant evidences for the future deposition process of the ZnO thin films as the FET-BG biosensor device on the silicon-on-insulator (SOI) wafer.

Characteristics of TiO2 thin film with back-gate biasing for FET-based biosensors application

Biosensors become a main attraction nowadays due to its importance towards human health. Its allow rapid and label-free detection that provides low cost clinical sampling. A FET device was fabricated from silicon-on-insulator (SOI) type of wafer with titanium dioxide (TiO2) thin film as a sensing medium. TiO2 was deposited by using sol-gel solution, spin coated on the device, patterned and anneal. The physical characterization by using AFM and XRD was conducted to confirm the thin film was a TiO2 and electrical characterization was to determine the electrical properties, stability and sensitivity of the devices. From the result AFM and XRD confirm the thin layer was a TiO2 layer with grain boundaries and several peaks of TiO2 anatase crystal structure. The current-voltage (I-V and Vbg-Id) show that the TiO2 thin film has a good electrical properties and sensitivity that very suitable in sensing application especially detecting biomolecules for disease detection.

pH Measurement Using Titanium Dioxide Nanoparticles Thin Film Based Sensors

Optimization gap size and integration of TiO2 nanoparticles thin film produce a sensitive sensor device. Sol-gel spin coated TiO2 nanoparticles thin film is coated on a conventional fabricated IDEs with gap sizes of 7 μm, 10 μm, 14 μm and 17 μm which is then validated through electrical characterization. I-V characteristics of without and with TiO2 thin film of various gap sizes are subjected to pH test are then plotted to describe the resistance of the devices and correlate with the sensitivity measurement. Sensing devices show that devices with larger spacing and greater pH values have higher current. On the other hand, integration of TiO2 thin film reduced the resistance of devices. Among the four gap sizes, 7 μm gap sized device is the most sensitive one due to the tremendous difference after small amount of pH dropped on surface, thus lowering the detection limit.

The impact of minority carrier lifetime and carrier concentration on the efficiency of CIGS solar cell

This paper deals with minority carrier lifetime and carrier concentration of Cu(In, Ga)Se2 (CIGS)-based thin film solar cells with a ZnS(n)/CIGS(p) heterojunction structure. The structure is simulated in commercial numerical simulation and the impact of minority carrier lifetime in the CIGS absorber layer on the open circuit voltage, short circuit current density, fill factor and efficiency of the CIGS solar cell are investigated. The increase of minority carrier lifetime has also increased the CIGS solar cell performance. Similar effects are also observed at different carrier concentrations of CIGS layer. All these simulated results give a helpful indication for a practical fabrication process.

Oxidation functionalization of multiwalled carbon nanotube by mild acid sonication

Multiwalled carbon nanotube (MWCNT) has excellent properties in thermal and electrical conductivities, high tensile strength and surface area and low mass over volume. However, the usage is still limited due to its inert characteristic. MWCNT surface is hydrophobic and not miscible in most solvents. This work emphasize on simple and practical method of functionalization by sonication in mild acid condition. 6M of Nitric acid and Sulfuric acid mixture (Method I) and 6M of Nitric acid (Method II) were demonstrated as an oxidizing agent to introduce carboxyl functional group on MWCNTs surface. Both type of functionalization has demonstrated carboxyl formation but functionalization in acid mixture was chosen to be used for further study for aptamer immobilization. FTIR and SEM have been used to investigate the binding properties and surface morphology respectively. The functionalization time has also been studied by using dispersability test which resulted in good dispersion after 1 hour of functionalization.

Functionalization of Multi Wall Carbon Nanotubes Using Nitric Acid Oxidation

Functionalized of Multi Wall Carbon Nanotubes (MWCNTs) were demonstrated using the nitric acid (HNO3) oxidation technique in order to get opened caps, removing carbonaceous and metal particles impurities for carboxylic groups (-COOH). The surface morphology and the existence of the carboxyl-group on the MWCNTs were examined using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM), respectively. The carboxylic groups were observed at the peak of 1640.40cm-1 via FTIR and indicate the absorbance intensity of the functionalized MWCNTs is 2.22 A which is higher than raw material. Furthermore, SEM image shows the bundle of structure on the raw MWCNTs signified the Van der Waals interaction between MWCNTs while after functionalized a groovy CNTs wall were observed due to presence of carboxyl group at the defect sites.

Preparation and characterization of MWCNT dispersed in various solutions

In modern technology of biomedical applications, the potential of carbon nanotubes based materials has been widely used in recent years. In this paper, the preparation of the multi wall carbon nanotube (MWCNT) with biocompatibility of these composite are investigated, although many aspects have been studied separately by researchers. We have chosen three different solvents; namely chitosan, Sodium Dodecyl Sulfate (SDS), and isopropyl alcohol (IPA) to mix with MWCNT respectively. This functionalized CNT with carboxylic (COOH) groups were prepared in three different liquid forms and further will be dropped on fabricated Interdigitated electrodes (IDEs) as devices. Scanning electron microscopy (SEM) was used to identify the structures effect of synthesized MWCNT in different solvents. The conductivities show the ability of chitosan and SDS to be used as a solvent in order to synthesis MWCNTs and further will be used as a biosensor.