C. H. Voon

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.

Effect of temperature of oxalic acid on the fabrication of porous anodic alumina from Al-Mn alloys

The influence of temperature of oxalic acid on the formation of well-ordered porous anodic alumina on Al-0.5 wt% Mn alloys was studied. Porous anodic alumina has been produced on Al-0.5 wt%Mn substrate by single-step anodising at 50Vin 0.5Moxalic acid at temperature ranged from 5°C to 25°C for 60 minutes. The steady-state current density increased accordingly with the temperature of oxalic acid. Hexagonal pore arrangement was formed on porous anodic alumina that was formed in oxalic acid of 5, 10 and 15°C while disordered porous anodic alumina was formed in oxalic acid of 20 and 25°C. The temperature of oxalic acid did not affect the pore diameter and interpore distance of porous anodic alumina. Both rate of increase of thickness and oxide mass increased steadily with increasing temperature of oxalic acid, but the current efficiency decreased as the temperature of oxalic acid increased due to enhanced oxide dissolution from pore wall.

Effect of manganese content on the fabrication of porous anodic alumina

The influence ofmanganese content on the formation of well-ordered porous anodic alumina was studied. Porous anodic alumina has been produced on aluminium substrate of different manganese content by single-step anodizing at 50V in 0.3M oxalic acid at 15°C for 60 minutes. The well-ordered pore and cell structure was revealed by subjecting the porous anodic alumina to oxide dissolution treatment in a mixture of chromic acid and phosphoric acid. It was found that the manganese content above 1wt% impaired the regularity of the cell and pore structure significantly, which can be attributed to the presence of secondary phases in the starting material with manganese content above 1wt%. The pore diameter and interpore distance decreased with the addition of manganese into the substrates. The time variation of current density and the thickness of porous anodic alumina also decreased as a function of the manganese content in the substrates.

Cell-targeting aptamers act as intracellular delivery vehicles

Aptamers are single-stranded nucleic acids or peptides identified from a randomized combinatorial library through specific interaction with the target of interest. Targets can be of any size, from small molecules to whole cells, attesting to the versatility of aptamers for binding a wide range of targets. Aptamers show drug properties that are analogous to antibodies, with high specificity and affinity to their target molecules. Aptamers can penetrate disease-causing microbial and mammalian cells. Generated aptamers that target surface biomarkers act as cell-targeting agents and intracellular delivery vehicles. Within this context, the “cell-internalizing aptamers” are widely investigated via the process of cell uptake with selective binding during in vivo systematic evolution of ligands by exponential enrichment (SELEX) or by cell-internalization SELEX, which targets cell surface antigens to be receptors. These internalizing aptamers are highly preferable for the localization and functional analyses of multiple targets. In this overview, we discuss the ways by which internalizing aptamers are generated and their successful applications. Furthermore, theranostic approaches featuring cell-internalized aptamers are discussed with the purpose of analyzing and diagnosing disease-causing pathogens.

Highly sensitive Escherichia coli shear horizontal surface acoustic wave biosensor with silicon dioxide nanostructures

Surface acoustic wave mediated transductions have been widely used in the sensors and actuators applications. In this study, a shear horizontal surface acoustic wave (SHSAW) was used for the detection of food pathogenic Escherichia coli O157:H7 (E.coli O157:H7), a dangerous strain among 225 E. coli unique serotypes. A few cells of this bacterium are able to cause young children to be most vulnerable to serious complications. Presence of higher than 1cfu E.coli O157:H7 in 25g of food has been considered as a dangerous level. The SHSAW biosensor was fabricated on 64° YX LiNbO3 substrate. Its sensitivity was enhanced by depositing 130.5nm thin layer of SiO2 nanostructures with particle size lesser than 70nm. The nanostructures act both as a waveguide as well as a physical surface modification of the sensor prior to biomolecular immobilization. A specific DNA sequence from E. coli O157:H7 having 22 mers as an amine-terminated probe ssDNA was immobilized on the thin film sensing area through chemical functionalization [(CHO-(CH2)3-CHO) and APTES; NH2-(CH2)3-Si(OC2H5)3]. The high-performance of sensor was shown with the specific oligonucleotide target and attained the sensitivity of 0.6439nM/0.1kHz and detection limit was down to 1.8femto-molar (1.8×10-15M). Further evidence was provided by specificity analysis using single mismatched and complementary oligonucleotide sequences.

Rheological and Thermal Study of Chitosan Filled Thermoplastic Elastomer Composites

The chitosan filled thermoplastic elastomer (TPE) composites with different filler loading was prepared by melt mixing at 180 °C. The effect of 3-aminopropyltriethoxysilane (3-APE) as coupling agent on the rheological and thermal properties of composites were investigated. The melt flow indexer was used to characterize the melt flow index (MFI) of TPE/Chitosan composites at temperature of 180 to 210 °C. It was found that addition of chitosan into composites had reduced the MFI values. Besides that, the MFI values of composites were found to increase linearly with temperature. The treated composites demonstrated lower MFI values, indicated that better interfacial bonding was established between chitosan and TPE and the flowability of the composite melts was hindered. The TGA results reported that the treated composites had better thermal stability and lower total weight loss as compared to untreated composites at similar filler loading.

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.

Effect of Electrolyte Concentration on the Growth of Porous Anodic Aluminium Oxide (AAO) on Al-Mn Alloys

In this study, the effect concentration of electrolyte on pore nucleation process during anodizing was investigated. It was found that the concentration of oxalic acid influenced the morphologies and regularities of porous AAO formed on aluminum-manganese substrate. When the concentration of oxalic acid is 0.1 M, the porous AAO exhibited a disordered pores arrangement and no long range order was observed. However, when the concentration was increased to 0.3 M and 0.5 M, hexagonal pores arrangement and long range order were obtained. Although the hexagonal pore arrangement was still retained, further increasing the concentration of oxalic acid to 0.7 M render the long range order disappeared. The rate of increase of oxide mass of porous AAO increased with the concentration of oxalic acid.

Biotechnological Processes in Microbial Amylase Production

Amylase is an important and indispensable enzyme that plays a pivotal role in the field of biotechnology. It is produced mainly from microbial sources and is used in many industries. Industrial sectors with top-down and bottom-up approaches are currently focusing on improving microbial amylase production levels by implementing bioengineering technologies. The further support of energy consumption studies, such as those on thermodynamics, pinch technology, and environment-friendly technologies, has hastened the large-scale production of the enzyme. Herein, the importance of microbial (bacteria and fungi) amylase is discussed along with its production methods from the laboratory to industrial scales.