K. L. Foo

‘Spotted Nanoflowers’: Gold-seeded Zinc Oxide Nanohybrid for Selective Bio-capture

Hybrid gold nanostructures seeded into nanotextured zinc oxide (ZnO) nanoflowers (NFs) were created for novel biosensing applications. The selected ‘spotted NFs’ had a 30-nm-thick gold nanoparticle (AuNP) layer, chosen from a range of AuNP thicknesses, sputtered onto the surface. The generated nanohybrids, characterized by morphological, physical and structural analyses, were uniformly AuNP-seeded onto the ZnO NFs with an average length of 2–3 μm. Selective capture of molecular probes onto the seeded AuNPs was evidence for the specific interaction with DNA from pathogenic Leptospirosis-causing strains via hybridization and mis-match analyses. The attained detection limit was 100 fM as determined via impedance spectroscopy. High levels of stability, reproducibility and regeneration of the sensor were obtained. Selective DNA immobilization and hybridization were confirmed by nitrogen and phosphorus peaks in an X-ray photoelectron spectroscopy analysis. The created nanostructure hybrids illuminate the mechanism of generating multiple-target, high-performance detection on a single NF platform, which opens a new avenue for array-based medical diagnostics.

Nanobioprobe for the determination of pork adulteration in burger formulations

We report the development of a swine-specific hybrid nanobioprobe through a covalent integration of a fluorophore-labeled 27- nucleotide AluI-fragment of swine cytochrome b gene to a 3 nm gold nanoparticle for the determination of pork adulteration in processed meat products. We tested the probe to estimate adulterated pork in ready-to-eat pork-spiked beef burgers. The probe quantitatively detected 1-100% spiked pork in burger formulations with ≥90% accuracy. A plot of observed fluorescence against the known concentration of AluI-digested pork DNA targets generated a concave curve, demonstrating a power relationship (y = 2.956x0.509) with a regression coefficient (R2) of 0.986. No cross-species detection was found in a standard set of pork, beef, chicken, mutton, and chevon burgers. The method is suitable for the determination of very short-length nucleic acid targets which cannot be estimated by conventional and real-time PCR but are essential for the determination of microRNA in biodiagnostics and degraded DNA in forensic testing and food analysis.

Low Temperature Annealed Zinc Oxide Nanostructured Thin Film-Based Transducers: Characterization for Sensing Applications.

The performance of sensing surfaces highly relies on nanostructures to enhance their sensitivity and specificity. Herein, nanostructured zinc oxide (ZnO) thin films of various thicknesses were coated on glass and p-type silicon substrates using a sol-gel spin-coating technique. The deposited films were characterized for morphological, structural, and optoelectronic properties by high-resolution measurements. X-ray diffraction analyses revealed that the deposited films have a c-axis orientation and display peaks that refer to ZnO, which exhibits a hexagonal structure with a preferable plane orientation (002). The thicknesses of ZnO thin films prepared using 1, 3, 5, and 7 cycles were measured to be 40, 60, 100, and 200 nm, respectively. The increment in grain size of the thin film from 21 to 52 nm was noticed, when its thickness was increased from 40 to 200 nm, whereas the band gap value decreased from 3.282 to 3.268 eV. Band gap value of ZnO thin film with thickness of 200 nm at pH ranging from 2 to 10 reduces from 3.263eV to 3.200 eV. Furthermore, to evaluate the transducing capacity of the ZnO nanostructure, the refractive index, optoelectric constant, and bulk modulus were analyzed and correlated. The highest thickness (200 nm) of ZnO film, embedded with an interdigitated electrode that behaves as a pH-sensing electrode, could sense pH variations in the range of 2-10. It showed a highly sensitive response of 444 μAmM-1cm-2 with a linear regression of R2 =0.9304. The measured sensitivity of the developed device for pH per unit is 3.72μA/pH.

Morphological, Structural, and Electrical Characterization of Sol-Gel-Synthesized ZnO Nanorods

ZnO nanorods were grown on thermally oxidized p-type silicon substrate using sol-gel method. The SEM image revealed high-density, well-aligned, and perpendicular ZnO nanorods on the oxidized silicon substrate. The XRD profile confirmed the c-axis orientation of the nanorods. PL measurements showed the synthesized ZnO nanorods have strong ultraviolet (UV) emission. The electrical characterization was performed using interdigitated silver electrodes to investigate the stability in the current flow of the fabricated device under different ultraviolet (UV) exposure times. It was notified that a stable current flow was observed after 60 min of UV exposure. The determination of stable current flow after UV exposure is necessary for UV-based gas sensing and optoelectronic devices.

Fabrication and characterization of ZnO thin films by sol-gel spin coating method for the determination of phosphate buffer saline concentration

The fabrication, characterization and application of nanostructured zinc oxide (ZnO) thin films on interdigitated silver elec- trodes were described for the determination of phosphate buffer saline (PBS) concentration. The ZnO thin films were synthesized on a silicon dioxide wafer using a sol-gel spin coating technique. Two different seed solutions were prepared by dissolving Zn-acetate dihy- drate in methanol and isopropanol in presence of a stabilizer, monoethanolamine. The field emission scanning electron microscope, atomic force microscope, X-ray diffractometer and Fourier transform infrared characterization revealed the presence of hexagonal ZnO nano-crystals in all thin films. However, the smaller sized and homogeneous ZnO nano-crystals were observed in isopropanol derived thin films. These thin films were used to discriminate the concentrations of different PBS solutions and the discriminatory signals were captured using a low-cost dielectric analyzer and a source meter. The frequency-capacitance curve reflected 2.85 fold increase in capaci- tance values when the sensor was exposed to 1000-fold diluted PBS in deionized water. A change in PBS concentration from 1000 fold to 10 fold increased the current flow from 6uF to 122uF. Thus the capacitance and current flow demonstrated a proportional relationship with the concentration of PBS, suggesting the application of the fabricated sensor in the determination and discrimination of chemical- species concentration in various solutions.

Study of Zinc Oxide Films on SiO2/Si Substrate by Sol–Gel Spin Coating Method for pH Measurement

This In this work, zinc oxide film was deposited onto the SiO2/Si substrate with low-cost sol-gel spin coating method. Zinc oxide thin film was deposited on the silver interdigit elctrodes for the pH measurement. The surface morphology and microstructures of the deposited zinc oxide films were analyzed by field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). Whereas the crystallinity and structure of the zinc oxide films were determined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The measurement at various pH values, which were ±1 above and below of the neutral pH had been conducted with a real time dielectric analyzer measurement. It was observed that the increase in pH would decrease the capacitance of the device.

Fabrication and Characterization of IDE Based Sensor through Conventional Lithography Method

This paper mainly illustrate regarding the fabrication process of IDE based sensor for bio-molecular detection process. Material that is utilized in this process is zinc oxide due to bio-compability and elevated electrical characteristic. IDE mask is designed by using auto-cad software which tailors for detection of bio substance which is extremely small scale in size. Zinc Oxide material is also used due to presented of nanostructure that can be synthesized through hydrothermal route. Zinc oxide solution is prepared by series of sol-gel process and is coated on the SiO substrate which acts as insulator layer during the lithography process. IDE mask is patterned transfer on sample by using conventional lithography process which the parameters are critically adjusted to ensure that the pattern transfer process occur with minimal defects. The fabricated sensor will be further validated through electrical and morphological characteristic. Capacitance test and impedance test is taken with various pH solution to observe the response of the sensor with different pH values. Keywords: IDE sensor, bio-compability, Zinc Oxide, auto-cad software, sol-gel, SiO substrate, hydrothermal route

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.

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.

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.