Theses & Dissertations

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https://hdl.handle.net/20.500.14170/2003

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  • Publication
    A computational analysis of interaction between inorganic semiconductor nanowire and molecular partial charge for DNA sensor application
    ( 2015)
    Abdulmohaimen W Fagri
    This research aimed to investigate the effects of partial charge due to DNA hybridization on the conductance of the silicon nanowire through finite element calculations. A biosensor was designed with the silicon nanowire of 15 nm radius at the core and surrounded by a silicon dioxide (2 SiO) layer of 2 nm thickness. The oxide layer was surrounded by a 5 nm thick functional bio-interface layer incorporating probe ssDNA and this whole system was immersed in an electrolyte of 80 nm radius. For the purpose of modeling and simulation, each of this layers was treated as a continuum medium characterized by the corresponding dielectric constant. In order to determine the effects of hybridization on nanowire conductance, the distribution of the electrostatic potential in the nanowire and other layers were first computed using Poisson equation with Boltzmann statistics without adding target DNA in the electrolyte layer. The conductance of the nanowire in this condition was computed by integrating the effect of the potential charge carriers within the nanowire and partial charge due to probe ssDNA. Then, the potential distribution was again calculated with the target DNA in the electrolyte and the conductance of the nanowire was re-calculated. Partial charge due to hybridization between probe and target DNAs was first computed using molecular dynamics simulation and integrated into the finite element calculation. The Finite element calculations showed that the nanowire conductance depended nonlinearly on the external charge (partial charge) of the bio-interface due to the hybridization of the target DNA with probe DNA in the functional layer.
      13  6
  • Publication
    Characrerization, analysis and optical studies of cadmium sulfide nanostructures deposited on different substrates for optoelectroninc applications
    ( 2014)
    Abdul Wahab Salem Z. Lahewil
    Recently the research on nanotechnology has become increasingly popular due to their unique physical, chemical, optical and catalytic properties compared to their bulk counterparts. Nanotechnology revolutionizes many technology and industry sectors such as energy, environmental science, safety, medical sciences, medical instrumentation and many others. An II-VI semiconductor material, CdS nanostructure with a band gap of about 2.45 eV, has attracted great attention among the researches due to the peculiar properties. The objective of this research is to synthesize CdS nanostructure thin films deposited on different type of substrates glass, quartz, n-type and p-type silicon using sol-gel spin coating technique for optoelectronic applications. The CdS nanostructure thin films was synthesized and characterized using XRD, AFM, SEM, UV-VIS, PL, FTIR, TGA, DTA, DSC and Keithley 2400 Source Meter. Silver electrodes were thermally evaporated on the surface of CdS nanostructure thin films using stainless steel shadow mask. For CdS nanostructure thin films deposited on glass substrates, the results have indicated that the CdS has hexagonal structure. The thickness of CdS nanostructure thin films as measured by AFM is found to be in the range of 150 nm and 10 nm at 1000 rpm and 5000 rpm spin coating speeds respectively. For CdS nanostructure thin films deposited onto quartz substrates and annealed at 800 ºC with different spin coating speeds 1000, 3000 and 5000 rpm, the structural, morphological and analytical studies were investigated and found that the grain size of CdS nanostructure thin films found to be in the range 1.81 nm to 4.35 nm. The band gap was measured with an indication of transmission within the visible range. It is found that the band gap changed due to small grain size of CdS nanostructure thin films. The morphology of CdS nanostructure thin films are found to be continuous, dense and well adhered. The films surface is much smoother and the particles are well distributed. For CdS nanostructure thin films deposited into n-type and p-type silicon substrates at different annealing temperatures in the range from 200 oC to 600 oC. The effects of annealing temperatures were investigated on the structural, morphological, optical and electrical properties to improve the CdS nanostructure thin films. The XRD analysis shows that the crystalline quality of CdS nanostructures can be improved by increasing the temperature to 400 oC, but further increase to 600 oC leads to degradation of the crystalline quality. The bulk modulus was calculated and showed good agreement with experimental and theoretical results for different substrates to be found in the range 27.6 to 281.3 GPa. The optical properties of absorption namely; reflection, transmission, extinction coefficient and the energy band gap were obtained by PL and UV-VIS spectroscopies. The calculated refractive index and optical dielectric constant, the results are in agreement with experimental data. The best results for CdS nanostructure thin films are found using p-type silicon substrates annealed at 400 oC. The thermal properties of CdS nanostructures also investigated and found to be evident that a good thermal treatment can largely decrease the film strain and improve its crystallinity.
      2  13
  • Publication
    Characterization of immunosensor for early detection of Cucumber Mosaic Virus (CMV) detection in chili
    ( 2017)
    Shahrul Aizzam Ariffin
    Cucumber Mosaic Virus (CMV) is one of the major constraints towards cucurbit crops such as cucumbers, zucchinis, pumpkins, papayas and watermelons production, while for non-cucurbit crops such as chilies, tomatoes, spinach, lettuces, celeries, beans, tobaccos and weeds production in South and Southeast Asia. Based on previous studies approximately 5-10 % annual losses of chili yield in Asia was caused by CMV, which accounts for nearly RM 6.05 billion annual loss in chili production worldwide. This loss has given a huge impact especially to the farmers if there are no serious actions taken. Most farmers are using common approach which is visual observation to detect the CMV on their crops despite the visual observation is difficult to identify a symptom caused by the CMV since the visual of symptom depends on the concentration of virus itself and because of that reason, this method is not reliable to eradicate this virus from scratch. Therefore, a portable electrochemical immunosensor based cucumber mosaic virus detection like screen-printed carbon electrode was developed and it can be employed whether in laboratory and field that is essential. In addition, study on the CMV disease and antibody activity was demonstrated to making sensor actively recognize only the CMV molecules by using specify antibody. The CMV purification is used to eliminate the impurities and then, optimization of the purified CMV was performed using sandwich immunoassay format. The purification of antibody was demonstrated to eliminate salt and other proteins and the purified antibody was optimized using sandwich immunoassay format and direct immunoassay format. The initial results showed the both purified substance possess high binding strength. Subsequently, a purified antibody was conjugated with gold nanoparticles and the conjugated solution was used for the immunosensor surface modification to change the immunosensor surface properties. The electrical signal produced from the sensor validation process was measured using chronoamperometric (CM) technique. By using the same technique, the set voltage potential was spotted at 0.2 V and the LOD of immunosensor was at 0.1 mg mL-1. After that, the immunosensor was tested with other pathogens to verify the immunosensor selectivity. The initial study shows the immunosensor fully identifies the purified CMV and did not react to other purified pathogens whereby gives the lowest cross-reactivity. In the CMV screening the same cross-reactivity method was executed and the crude chili leaves that taken around MARDI plantation were used to detect CMV in the chili trees. The results of the CMV screening show the presence of CMV in some samples. Thus, this research provides a sensitive and selective detection tool to the farmers that allow an early detection on their chili plantations.
      19  2
  • Publication
    Deposition of Graphene-like carbon on copper foil using Methane
    ( 2017)
    Lee Hon Cheun
    Graphene, a two-dimensional carbon allotrope that is made up of single-layer sp2 hybridized carbon atoms arranged in a hexagonal configuration. Since graphene was discovered in year 2004, graphene research has surged exponentially owing to its unique and remarkable properties. A variety of methods have been proposed to synthesize graphene layer of which the most promising method is using chemical vapour deposition (CVD). However, there still lie a lot of issues about effects of reaction parameters and growth mechanism in the catalytic growth using CVD method. For example, is the separation of the graphene from the substrate and uniformity of graphene layer on the substrate. In this study, catalytic decomposition of methane was employed for producing graphene layer on copper foil. The reaction parameters in CVD process including reaction times, reaction temperatures and methane flow rates were varied to study the impact of these parameters on the graphene samples. Various characterization tests including Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were carried out on the graphene samples produced. The agglomerations of carbon were observed at the grain boundaries of the copper substrate. The carbon content on the graphene sample increased when the reaction time, reaction temperature or methane flow rate were increased. This indicated that more and more carbon atoms were deposited on the copper foil when the reaction time, reaction temperature and methane flow rate were increased. On the other hand, the weight percentage of carbon agglomeration at the grain boundaries was higher than that of the centre of grains in all samples. Besides, XRD diffraction peak for the copper oxide and small graphite peak at 2θ=26.5° were seen which signified very low quantity of graphene-like carbon structures were formed under high reaction times (90 and 300 seconds), high reaction temperature (1050°C) and methane flow rates (200-600mlpm). In addition, XPS results confirmed the presence of the C1s spectrum at 284.8eV which ascribed to the existence of sp2-hybridized carbon on the samples. With this sp2-hybridized carbon, it is confirmed again very low amount of graphene-like carbon materials were synthesized and distributed randomly on the surface of our samples. However, no Raman peak at D(1350cm-1), G(1580cm-1) and 2D(2700cm- 1) were shown to represent the graphene on the sample but only the Raman peaks of copper oxide were detected. From above results, the produced samples contain very small amount of graphene layer due to two limitations: no hydrogen gas and high methane flow rate were used. Furthermore, the presence of oxygen species in the CVD furnace even further hinders the formation of graphene layer and eventually, the graphene layer was less likely to be formed on the copper substrate.
      8  3
  • Publication
    Design and fabrication of n-ISFET using Si₃N₄/SiO₂ structure for pH measurement
    ( 2013)
    Nur Syuhada Md. Desa
    The design and fabrication of n-ISFET using Si₃N₄/SiO₂ structure for pH measurement has been carried out. In general Ion Sensitive Field Effect Transistor (ISFET) is a potentiometric pH sensor which widely used in chemical, biochemical and biomedical applications due to its advantages such as small size, low power consumption, robustness, and fast response time over the ion-selective electrode (ISE). In this study, the ISFET was designed and fabricated in-house in Micro Fabrication Cleanroom Laboratory using a standard Complementary Metal Oxide Semiconductor (CMOS) processes fabrication except the gate area was replaced by reference electrode, sensing membrane and electrolyte under test. The main objective of this study is to present a concept, the design, fabrication and testing appropriate to process flow in fabricating the n-ISFFET on silicon wafer, which will finally be characterized using a suitable test methodology. Hence, fabrication on p- type <100> 4 inch silicon wafer by photolithography, wet chemical etching, thermal oxidation, diffusion and metallization with focus on a pH measurement has been executed.The n-ISFET was operated when the surface absorption of the charges in the electrolyte under test simultaneously interact with both reference electrode and surface sensing membrane. Overall process has 5 mask levels consist of source mask and drains mask, gate mask, contact mask and metallization mask. The fifth mask was used to find the best thickness of silicon nitride for sensing membrane layer and 50 nm was selected. For sensing material, SiO2 insulator layer was used and later deposited on top with Si3N4 insulator layer by Plasma Enhanced Chemical Vapor Deposition (PECVD). The latter layer serves as a pH sensitive membrane. The electrical tests were performed using buffer solutions with varying pH values, indicated that the transistor can be employed to measure the pH of solutions at room temperature. The interaction between these methods will modulate a threshold voltage and simultaneously will extracted the output (IdVd) and transfer (IdVg) characteristic curves at three differences channel length; 250μm, 300 μm and 500 μm respectively.The best pH sensitivity achieved at the channel length 500 μm with the measurement value equal to 54.43 milivolt per pH (mV/pH).
      4  37
  • Publication
    Design and fabrication of SWNT-FET based biosensor
    ( 2012)
    Mohd Syamsul Nasyriq Samsol Baharin
    Nanotubes have generated intense research activities from scientists of various disciplines because they represent a new class of materials for the study of one-dimensional physics. Single-walled carbon nanotubes (SWNTs) have many other magnificent properties and it has impressive properties in three aspects, mechanical, electrical, and biological due to ability of single-walled carbon nanotubes (SWNTs) to exhibit self-assemble monolayer (SAM0. The main objective of this project is to design and fabricate carbon nanotube based biosendor for future application medical diagnostics. The electrical transport of semiconducting single-walled carbon nanotubes with the diameter of ~1.5 nm and length of 2 μm to 6 μm for its applications as biomolecules detection was investigated. Single-walled carbon nanotubes field effect transistors (SWNT-FET) were fabricated in house using three masks designed. Initially backgated field effect transistor (FET) was formed and followed with the growth of oxide as insulation layer. Multilayer metal of platinum,Pt and gold,Au were grown on top of oxide layer and finalized with the integration of single-walled carbon nanotubes (SWNTs). The oxide thickness achieved is ~18nm and multilayer metal of platinum,Pt and gold,Au thickness is ~10nm and ~90nm respectively. The integration of single-walled carbon nanotubes (SWNTs) with field effect transistor (FET) was performed using AC dielectrophoresis nanomanipulation technique resulting promising results of integration proven via Scanning Electron Microscope (SEM). Fabricated device resulting conductance of G ~ 0.03 x 4e2/h and hole mobility of μp ~ 3060 cm2/V.s in saturation mode. This device also shows resemblances with conventional p-type metal-oxide-semiconductor FETs (MOSFETs) through IDS-VDS curve and appears to be gate voltage dependence through conductance-gate voltage curve. Thus, these results prove that fabricated device functioned as p-type metal-oxide-semiconductor FETs (MOSFETs) and can be used for the application of biomolecules detection such as protein by monitoring the device changes of IDS-VDS characteristics.
      2  36
  • Publication
    Development and fabrication of carbon nanotube (CNT) based pH sensor
    ( 2013)
    Low Foo Wah
    The development, fabrication and characterization of single-walled carbon nanotubes (SWCNTs) based pH sensor using aligned SWCNT were reported. The SWCNT alignment is defined by a single carbon nanotube aligned between the fabricated electrodes. This research involves the study of SWCNTs dispersion, alignment of SWCNT between microgap electrodes and characterization on the effect of change in the pH level on the impedance, conductance and capacitance of the aligned SWCNT. In the SWCNT dispersion study, the SWCNTs were dispersed in Isopropyl Alcohol (IPA), Dichloromethane (DCM), Acetone and Triton-X 100. It was found that SWCNT disperse best in the IPA solution because the dispersed SWCNTs have remained dispersed which can be observed from the clear solution even after 14 days as compared to DCM, acetone and Triton-X 100. On the other hand, the SWCNTs in DCM, acetone and Triton-X 100 have shown a thick mass of coagulated SWCNT after 14 days of dispersion. A chrome mask which consists of 6 groups with different gap measurement was designed. Each group has 5 different designs to facilitate the SWCNT alignment. After that, the devices were fabricated using gold material as electrode to increase the electrical conductivity and permittivity of the device. The SWCNT was then aligned on the fabricated devices using AC dielectrophoresis method. The AC dielectrophoresis method involved control in the voltage and frequency to increase the chance of SWCNT alignment between the microgap. The devices were brought to electrical characterization before and after SWCNT alignment to compare the effect on the device capacitance. It was found that the capacitance before SWCNT alignment is higher than after SWCNT alignment of the device. Before SWCNT alignment, the dielectric of the capacitive device is air which is a better insulator than SWCNT that is a semiconductor material. This phenomenon is due to the fact that dielectric decrease electric field and capacitance is inversely proportional to electric field. On the other hand, the device was tested for its impedance using pH buffer solutions. As pH value was decreased, impedance has also decreased. The hydrogen ions were found to bind to the carboxyl group of the SWCNT creating positive holes in the SWCNT hence increasing its conductivity. As a conclusion, this research successfully demonstrated the process to design, fabricate and characterize the SWCNT based sensor.
      30  3
  • Publication
    Development and fabrication of Ion-sensitive Field Effect Transistor (ISFET) for pH detection, DNA immobilization and hybridization
    ( 2013)
    Chong Soon Weng
    The fabrication of ion sensitive field-effect transistor (ISFET) using silicon nitride (Si3N4) as the sensing membrane is reported. The operation of ISFET is based on the surface charge adsorption of the membrane-solution interface. This thesis describes the design, fabrication and characterization of ISFET for pH detection, DNA immobilization and hybridization. Four photomasks were utilized in the fabrication process to create the ISFET device. The fabricated ISFET device was first brought to morphological characterization before proceeding with the electrical characterization. For the analysis of ISFET in test solution, the Ag/AgCl electrode was used as the reference electrode immersed in different values pH buffer. The results were generated by LabTracer 2.0 measurement system which shows that IV characteristic of ISFET devices gives linear response. The acidic pH buffers contains H+ ions which attract more electron into the conduction channel lowering the channel resistance giving higher value of current flow. While the alkaline pH buffers contains OH- ions which pushed away the electrons from the conduction channel generating more positive holes increasing the channel resistance, thus giving a lower value of current flow. When tested with phosphate buffer solution (PBS), the curves show a decreasing trend of drain current with decreasing concentration of the PBS. It was found that the device has a sensitivity of 43.13 mV/pH. The ISFET device has undergo DNA processes after the electrical characterization with pH and PBS. The DNA immobilization and hybridization processes were detected through a drop in the drain current of the device. Prior to DNA immobilization, the silicon nitride surface was chemically modified to enable the ISFET sensing membrane for DNA probes coupling. It was also observed that with decreasing concentration of DNA complimentary targets in the hybridization process has contributed to the decreasing drain current detected. As a conclusion, the silicon nitride ISFET is a flexible device which can be used to detect pH as well as to perform DNA immobilization and hybridization.
      4  20
  • Publication
    Development of multiwalled carbon nanotube integrated field eEffect transistor for highly sensitive HIV-1 tat protein biosensor
    ( 2019)
    Fatin Nabilah Mohd Faudzi
    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 to 4 weeks after infection. Early stage detection of the disease can be achieved by detecting Tat protein in high risk individuals. This mitigates the risk of a HIV pandemic. A back gated field effect transistor (BGFET) has been developed to be a biosensor for the early detection of HIV. Tat protein has been used as the target while split RNA aptamer has been chosen as the detection probe. The binding interactions between split RNA aptamer and HIV-1 Tat protein on a biosensor device was validated using colorimetric assay. The assay successfully demonstrated the interaction occurred between split RNA aptamer and HIV-1 Tat indicated by the changes of gold nanoparticles color from pink to purple. BGFET was made biocompatible by using carbon nanomaterials like multiwalled carbon nanotube (MWCNT) as biomolecules immobilization site. Acid oxidation treatment was conducted to functionalize MWCNT with carboxyl functional groups and subsequently characterized through field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) analysis had profound ~2.91% increment in overall oxygen group and ~1% increment was noticed with a specific carboxyl content owing to C=O and O–C=O bonding. The binding interaction between split RNA aptamer and HIV-1 Tat protein was characterized by Fourier transform infrared (FTIR) binding analysis and electrical quantification of current signal (Ids) over a gate voltage (Vgs). The attainment of sensitivity with aptamer and HIV-1 Tat interaction on the fabricated device was 600 pM. To ensure the genuine interaction of aptamer with HIV-1 Tat, other HIV-1 proteins, Nef and p24 were interacted with aptamer and they displayed the negligible interferences with gate voltage shift of 3.5 mV and 5.7 mV, which shows 4 and 2.5 folds lesser than HIV-1 Tat interaction, respectively.
      9  28
  • Publication
    Development of nanoparticle sensors for the detection and quantification of swine DNA in mixed biological and commercial samples for halal authentication
    ( 2011)
    Md. Eaqub Ali
    Verification of declared components in meats and meat products is essential to ensure transparency in food labeling and to safeguard consumers’ trusts, religious faiths, health, and hard earned fortunes. The annual turnover of the global Halal food market has reached USD 661billion in 2011 and will be proliferating in the coming years. To coup up in highly competitive market and to make an excessive profit, fraudulent labeling of Halal brand is frequently occurring. As pork and pork-derivatives are easily available at cheaper prices, replacement of higher priced Halal meats in commercial meat products with lower valued pork has become quite prevalent. However, the mixing of pork and pork-derived materials in the Halal and Kosher foods is a serious matter as they are not allowed to be consumed by the followers of Islam and Judaism by respective religious laws. Thus, sensitive, dependable, and easy performable analytical tools have long been desired to detect and quantify the minute level of adulterated pork in Halal and Kosher foods. Conventional methods based on polymerase chain reaction (PCR)-based DNA analysis has reached a ceiling stage and has limitations in detecting shorter-length DNA markers which are proven to be survived in the harsh conditions of food processing. Further, PCR-based methods are not only expensive but also needs product authentication to eliminate ambiguity in certain instances. DNA detection using gold nanoparticles (GNPs) is very promising because it does not need any complex and expensive instrumentations and allows rapid and reliable detection of very short-length (15-30 bp) DNA sequences. In this report, we have developed two types of GNP-based sensors. The first one is the colorimetric sensor that allowed visual detection of PCR amplified and non-amplified swine DNA markers (27 and 25 nucleotides) within 10 min without any instrumental aids in a mixed background of processed and unprocessed meat products. It also permitted the verification of the visually determined results by the distinct features of the absorption spectra of the aggregated and non-aggregated GNPs. The detection limit (DL) of this method varied between 4-6 ng μL-1 of porcine genomic DNA. The second one was the hybrid nanobioprobe that covalently integrated a fluorophore labeled 27-nucleotide AluI-fragment of swine mitochondrial cytochrome b (mt-cytb) gene. It allowed simultaneous detection and quantification of porcine muticopy mt-DNA targets within 60 min with the help of a cost-effective fluorescent spectroscopy. The DL of this method was 0.42 ng μL-1 of contaminated pork in severely autoclaved pork-beef binary mixture in which longer-size PCR template were broken down to smaller fragments leading to detection failure by the PCR- methodology. The shorter-lengths DNA markers (15-30 bp) suitable for biosensor application were developed by in-silico digestion of swine mt-genome with AluI restriction enzymes. Prior to biosensor applications, the swine specificity of the developed mt-DNA markers was tested by developing a very short (109 bp) PCR-restriction fragment length polymorphism (RFLP) assay as well as a TaqMan probe quantitative real-time PCR (qPCR) assay containing appropriate AluI-sites within the amplicon. Both the PCR-RFLP and qPCR assays were effective to detect as low as 0.0001 ng of pure swine-genomic DNA and 0.001 ng of pork contamination in readyto- eat commercial meat products.
      5  18
  • Publication
    Development of shear horizontal surface acoustic wave with silicon dioxide nanoparticles waveguide sendor for Escherichia Coli O157: H7 detection
    ( 2017)
    Ten Seng Teik
    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. The presence of higher than 1 cfu E .coli O157:H7 in 25 g of food has been considered as a dangerous level. Thus, highly sensitive sensor is needed for this. The aim of this research work is to develop nanostructure waveguide shear horizontal surface acoustic wave (SHSAW) sensor for the detection of E.coli O157:H7. The interdigital transducer (IDT) is the heart of SHSAW sensor. It deterrmines the resonant frequency and the sensitivity of the sensor. In generally, the higher the resonant frequency, the higher sensitive the sensor will be, the width of IDT has to fabricated to sub micrometer. These involve more expensive cost and complicated methods. However, few reports mentioned IDT design parameters such number of transmission and receiving electrode fingers, electrode length or acoustic aperture and length of delay line or propagation path, can increase the SHSAW sensor sensitivity. Herein, COMSOL Multiphysics simulations were implemented for this investigation, the delay line length and aperture sizes are found that can increase the mass loading sensitivity. The research was continued by the development and evaluation of fabrication SHSAW device by using the improved conventional lithography process was conducted. The results show that the dimension of devices were precisely(less than 1%, relative standard deviation (RSD)) and accurately (less than 4% error from theoretical calculation) fabricated in laboratory for experimentally study on the effects of IDT parameters toward mass loading sensitivity. From the response surface methodology, 12 μm pitch sizes IDT with 0.72 mm aperture size, 2.1 mm delay line length and 385.1607 MHz average resonant frequency were identified as the most optimum parameters to achieve highest sensitive of devices.
      11  2
  • Publication
    Development of silicon nanowire lab-on-chip microfluidics integrated biosensor for low concentration bio-molecules detection
    ( 2015)
    Tijjani Adam
    Lab-on-chip fabricated with one-dimensional nanowires offer excellent electrical properties where bio molecular analysis at very low concentrations is becoming increasingly relevant for medical and research communities. Good number of techniques and promising results has been established for detecting small concentrations; however, for high-throughput measurements and label-free detection are still area of fresh investigation. Many research groups have reported high level of bio recognition by using semiconductor nanowire. The semiconductors silicon nanowire biosensor utilizes a Nano wire between two conducting materials. The nanowire has its atoms concentrated on its surface. Thus, any small changes in the charges present on the nanowire will cause a change in the flow of current. In this thesis, a simulation study coupled with experimental approach to explain the change in wire surface behavior as function of the surface charge. The linear behavior of the conductivity to increase the sensitivity of a semiconducting nanowire biosensor is ascertained. The silicon wire should be between 5 to 20nm to allow mean distance between atoms, the oxide should be as thin as possible for optimum surface integrity, and the functional layer should be thin and have a high dielectric constant. The ionic concentration of the electrolyte should be kept low in order to have a large Debye screening length. To confirm these theoretical results, Silicon nanowire of ≈ 15nm was fabricated using conventional photolithography coupled with dry etching process. To determine the capability of the device, it subjected to various pH values and to achieve this, the device is being operated based on the principle of Field Effect Transistor (FET). The surface of the device is hole dominated (p-type material).
      6  11
  • Publication
    Development of silicon on insulator based nanogap sensor for Escherichia Coli O157:H7 detection
    ( 2018)
    Nur Humaira Md Salleh
    Breakthrough in nanotechnology provides a great extent in biosensor development and application. Previous studies showed that nanogap sensor device provides excellent electrical behavior in sensing biomolecules samples. Nanogap sensor is a device having a pair of electrodes facing each other, which a molecule trapped in between its will be identified by observing the electrical characterization. Conventional development process requires prolonged and tedious compulsory additional method. Thus this research project focus on developing various size of uniform nanogap structure in nanometre scales which are capable of sensing Escherichia coli O157:H7 (E. coli O157:H7) at a low concentration level. The development of the device was divided into nanogap structure and gold pad structure process using electron beam lithography (EBL) method and conventional photolithography method respectively. Silicon on insulator (SOI) substrate was used to fabricate the nanogap structure and gold was used as a gold pad for a probing purpose. The developed nanogap devices was physically characterized by Field Emission Scanning Electron Microscopy and Scanning Electron Microscope. Meanwhile, the performance of the devices was tested by evaluating the capacitance and impedance reading by sweeping a frequency from 1M Hz to 0.1 Hz at room temperature with 1.0 mV input using Dielectric Analyzer. The devices were tested with de-ionized water and different pH level to optimize the sensor sensitivity that related to the nanogap size. Prior to the detection of E. coli deoxyribonucleic acid (DNA), the device was surface modified with NH2-Amine functionalized silane group using 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde for DNA to be covalently bonded with the APTES modified surface. The principle of the E. coli detection is based on charge density changes of the DNA probe immobilization and DNA target hybridization on the modified surface. The morphological testing results shows that the developed devices were observed with 40, 80 and 100 nm nanogap size. It was found that, the device with smallest gap size, 40 nm shows the highest sensitivity and stability compared to the device with bigger gap size, 80 and 100 nm. In this project 40 nm size nanogap device was successfully developed as biosensor for E. coli O157: H7 detection with capability to distinguish the impedance value between complementary, non-complementary and single mismatch DNA sequences. In addition, the device was able to detect E. coli O157: H7 DNA target at concentration limit from 10 nM to 1 pM with linear regression equation is 𝐶 (𝜇𝐹) = 3 × 10−7𝑥 + 5 × 10−9 and the correlation coefficient is 0.98.
      3  7
  • Publication
    Development of surface acoustic wave sensor for female aedes mosquito detection
    ( 2016)
    Zaid T. Salim
    The cases of dengue fever (DF) and dengue hemorrhagic fever have been increasing worldwide in the last decade. These conditions lead to large economic losses and health complications. To date, a direct cure for DF and an efficient device to control or detect Aedes mosquitoes causing DF are unavailable. Therefore, the fabrication of a device to prevent dengue virus infection is necessary. In this study, the design and the fabrication of a surface acoustic wave (SAW) sensor for female Aedes mosquito detection are presented. This study is the first to report the detection of female Aedes mosquitoes in human habitations using a SAW sensor. SAW technology can be applied to create highly sensitive sensors because of its extreme sensitivity to surface perturbation. A layered SAW device based on the ZnO/interdigital transducer (IDT)/128° YX lithium niobate (LiNbO3) structure was designed, fabricated, and characterized in this thesis study. First, the device was characterized theoretically using the finite element method in COMSOL Multiphysics 4.3b. The frequency response, SAW propagation mode(s), SAW displacement efficiency, and electromechanical coupling coefficient were theoretically investigated. Various ZnO layer thicknesses were used to obtain the ideal conditions. Numerical results were verified with a fabricated device. A good correlation was obtained between the simulation and experimental results.
      15  7
  • Publication
    Electrical label-free sensing of cardiac troponin biomarker: FET-based integration with substrate-gate coupling
    ( 2017)
    Mohamad Faris Mohamad Fathil
    Acute myocardial infarction (AMI) is a leading cause of death worldwide despite the existence of therapy’s advances. Therefore, an early diagnosis method by using cardiac biomarkers is essential to enable correct countermeasures. Cardiac Troponin I (cTnI) is one of the cardiac biomarkers for early diagnosis of AMI and considered as ‘gold standard’ for cardiac muscle injury determination. The detection of cTnI through an electrical-based biosensor allows label-free detection by converting biomolecular binding event into a significant electrical signal via a semiconductor transducer. It utilizes conductivity to specify the existence of biomolecules. One of the electrical-based biosensors known as field-effect transistor (FET)-based biosensor has drawn much attention for owning the concept of charge transduction; thus, allows early, high sensitivity, high selectivity, and rapid diagnosis of the specific cardiac biomarker at low concentrations. In this work, the zinc oxide (ZnO)-FET biosensor coupled with substrategate has been designed and fabricated for the detection of cTnI biomarker. ZnO thin film, as n-type biocompatible semiconductor material, and also as transducer was deposited via sol-gel and spin coating techniques between p-type source and drain terminal on SOI substrate, forming a p-n-p junction, a device capable of bio-sensing application. The surface morphology of the thin film was characterized by using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). The thin film, which demonstrated hexagonal wurtzite phase as shown by X-ray diffraction (XRD) analysis appropriate for biomolecules interaction. The surface of the ZnO thin film was immobilized with cTnI monoclonal antibody (MAb-cTnI) as biological receptor via covalent binding technique for capturing cTnI biomarker. The process was validated by Fourier transform-infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The device structure was simulated in Silvaco Atlas 2D-simulator, to elucidate its electrical characteristic, by means of hole and electron concentration in the channel and buried oxide/substrate interface, respectively. The device demonstrated a new strategy via electrical characterization with the introduction of substrate-gate coupling that enhanced the formation of hole conduction layer at the channel between drain and source region. Finally, the biosensor shown significant increment in relative changes of drain current level in a linear range of 6.2 to 16.5 % with the increase of positively charge cTnI biomarker concentrations from 1 ng/ml to 10 μg/ml. The device sensitivity of the detection is at 2.51 %·(g/ml)-1 with limit of detection (LOD) down to 3.24 pg/ml.
      11  5
  • Publication
    Fabrication and characterization of silicon and polysilicon nanogaps electrodes using size reduction technique for chemical and biomolecules detection
    ( 2012)
    Thakra. S. Dhahi
    Nanogap electrodes may be defined as a pair of electrodes separated by nano-scale spacing. Two important studies enabled the non-scientists to envision the development of nanogap-based electrical and electronic sensors and devices for the ultrasensitive detection of DNA. In the first study DNA can transport charges and can bridge the electrodes separated by a nanoscale gap whereas for second study, charge transport is interrupted when the molecule undergo denaturation from double-stranded to single-stranded conformation. The aim of this research work is to design, fabricate, characterize, and test nanogap-electrode based device for biochemical detection and DNA immobilization and hybridization detection. However, the focus of this research is to investigate electrically and chemically the effect of different materials and gap sizes on the nanogap electrodes design. Fabrication and characterization of less than 10 nm gap for both silicon and polysilicon nanogap electrodes structures being the main target in this research. Two masks were designed for the fabrication of nanogap and electrodes pad on silicon (Si) and silicon-on-insulator (SOI) wafers as a starting substrate to fabricate polysilicon and silicon nanogap devices respectively. Nanogap electrodes devices were fabricated using a size reduction technique which involves sequential and repeated thermal oxidation and wet etching processes. A thick layer of silicon and polysilicon materials were used to provide device stability throughout the fabrication process. The surface morphology of the fabricated nanogap structure was characterized using SEM and FESEM. The observed results showed the gap size of a 6-nm and 5-nm for silicon and polysilicon electrodes structure respectively. Gold pad electrodes were then fabricated on the silicon and polysilicon nanogap structures to increase the electrical conductivity and permittivity of the devices especially during bio-molecules detection. Capacitance, permittivity and conductivity are measured electrically to characterize the fabricated nanogap structures using a dielectric analyzer. However, sourcemeter equipment was first used to measure the current and characterize the resistivity of the nanogap structures as a function of applied voltage. It was found that the resistivity decreases with the reduction in gap sizes to aid the passage of current flow between the electrodes. Furthermore, the devices were chemically tested for the measurement of pH and yeast concentrations. It was found that the capacitance, permittivity and conductivity increased with pH and decreased with yeast concentrations. Finally, the devices were used as a DNA sensor for nucleic acid hybridization detection which is a key step in molecular diagnostics, gene profiling and environmental monitoring. Amine functionalized group from APTES were used to modify the silicon and polysilicon electrodes surface. Amine- groups (NH2) were labeled with gold nanoparticles to tag a thiol-modified DNA probe onto the nanogap surfaces. The developed biosensors clearly differentiated complementary, noncomplementary and single mismatched DNA targets through the measurements of capacitance, conductance and permittivity. The detection limit of the sensors was 5 nmol/L of target DNA. As a conclusion, this research successfully demonstrated the process to design, fabricate, characterize and test nanogap based biosensor using size reduction technique for DNA hybridization detection.
      2  11
  • Publication
    Fabrication and characterization of ZnO nanostructures for DNA detection
    ( 2013)
    Foo Kai Loong
    Zinc oxide (ZnO), a representative of group II-IV metal-oxide semiconductor material is widely studied in the current research community. ZnO with its wide direct band-gap (3.37eV) and high exciton binding energy (60meV) providing the advantages of their electrical and optical properties. Due to these unique properties and easiness to grow using bottom-up approach combines with high isoelectric point, toxic-free, high surface-area-to-volume ratio, biosafe, and biocompatible, ZnO nanostructures have great interest in the application of biosensor. The aim of this research work is to synthesis, fabricate, and characterize ZnO nanostructures based sensor for DNA immobilization and hybridization detection. Two types of ZnO nanostructures were studied, namely thin films and nanorods (NRs). Highly transparent ZnO thin films were successfully synthesized using ease and low-cost sol-gel spin-coating method. ZnO NRs with nanoscale possessed high crystalline structure was further grown from the asprepared thin films through low-temperature hydrothermal growth. In this thesis, we studied the influence of different solvents on the structure, optical and electrical properties of the ZnO nanostructures. Four types of solvents namely methanol, ethanol, isopropanol, and 2-methoxyethanol had been chosen for ZnO seed solution preparation. The observed results using FESEM indicated that the nanoparticles and nanorods with the size less than 40 nanometer and 60 nanometer, respectively were successfully synthesized. The investigation on optical properties using UV-Vis-NIR spectrophotometer confirmed ZnO is classified as a wide band gap semiconductor material. In order to fabricate a biosensor with high sensitivity and selectivity, a gold nanoparticles (GNPs) were selected for the surface modification of ZnO nanostructures which later formed gold-thiolate conjugation with thiol-modified ssDNA probes. Two approaches were used for the immobilization and hybridization of DNA detection, which were dielectric analysis and electrochemical analysis. DNA detection using dielectric analyzer was done on interdigitated electrodes gold modified ZnO thin films. The developed sensor clearly differentiated complementary and non-complementary of target DNA through the measurement of capacitance, permittivity, and impedance. DNA detection using electrochemical analysis with cyclic voltammetry confirmed surface ZnO NRs modified with (3-Aminopropyl)triethoxysilane (APTES) and gold nanoparticles provided better detection of target DNA in comparison with those only contained gold nanoparticles.
      9  4
  • Publication
    Gold nanoparticles enhanced DNA biosensor based on Silica interdigitated electrodes for detection of Human Papillomavirus
    ( 2018)
    Nor Azizah Parmin
    The increment in cervical cancer cases caused by the genital Human Papillomavirus (HPV) is a major worldwide problem for the women healthcare. In Malaysia, more than 5,000 cervical cancer patients, die from the delay in detecting cancer cells that are spreading to the final stage in 2015. The National Cancer Society of Malaysia (NCSM) reports that more than 11,000 women have been diagnosed with cervical cancer every year, especially young women in the late 30s. Rapid detection methods for the prevention and identification are required to solve the health and safety problems related to this pathogenic virus. Current detection methods require extensive specimen sample preparation and prolonged assay procedures. Thus, this research has focused on developing rapid detection methods, which are capable of sensing these viruses at a higher sensitivity. HPV 16 was used as the standard reference strain for the development of rapid methods. Nanoscaled interdigitated electrodes (IDEs) has been developed for the identification and miniaturizing the size of sensor but have higher performance for the biomedical engineering usage by detecting deoxyribonucleic acid (DNA) of HPV caused cervical cancer. With the conventional lithography (CL) for device fabrication, an electrical biosensor based on gold nanoparticle (GNP) IDE wasconstructed before the addition of 3-aminopropyltriethoxysilane (APTES). The optimized IDE was then employed for the detection of HPV DNA by the introduced two-steps mechanism after the surface modification by APTES. APTES is linking the modified HPV DNA probe with carboxyl group (-COOH) immobilization by covalent binding via amine (-NH2) coupling APTES on the sensing surface based IDE, and DNA hybridization. Surface structure analysis with scanning electron microscopy (SEM) was used to characterize the changes in the surface appearance. Fourier transform infrared (FTIR) spectroscopy analysis was used to assess the attachment procedures. The detection principle works by detecting the changes in the electrical current of IDE, which bridges the source and drain terminal to sense the immobilization of HPV DNA probe and hybridization with target DNA. It was found that the sensor showed the selectivity for HPV DNA target in a linear range with the concentrations ranges from 1 pM to 1 µM. With this analysis, the sensitivity limit of detection (LOD) was approximately 1 pM and it is comparable with the currently available sensors.In addition, the developed biosensor device was able to discriminate among complementary synthetic target, single mismatch, and non-complementary DNA sequences. A commercial, HCII Hybrid capture based Enzyme-Linked Immunosorbent Assay (ELISA) method for 13 types of high-risk HPV including HPV 16 and 18 wasused as a validation technique for confirming the effectiveness of GNP based IDE electrical biosensor in real samples. The advantage of this sensor is fast detection without labeling application and is useful in identifying the strength of HPV DNA probe binding to HPV target. This electrical biosensor system will be useful for the development of devices with on-site analysis.
      18  7
  • Publication
    Integration of substrate-gate couple p-type anatase TiO₂ for field-effect transistor based biosensors
    ( 2017)
    Adzhri Rahmat
    The term “biosensor” is a short form for “biological sensor”. A biosensor is generally defined as an analytical device, which converts the biochemical responses into quantifiable electronic signal. The device is made up of a transducer and biological receptor. The transducer surface needs to be functionalized with biological receptors such as an antibody, an enzyme or a nucleic acid. The biological receptor is employed to identify the specific target (i.e. DNA or antigen) molecule and the transducer to transform the specific interaction of the biomolecule into electronic signal. This method allows high sensitivity, rapid response and label-free detection. In this work, the integration of substrate-gate coupling of field-effect transistor (FET) based sensor with p-type anatase TiO₂ as a transducer material for detection of cardiac troponin I biomarker is presented. The work is initiated with fabrication of substrate-gated FET based biosensor on p-type silicon-on-insulator (SOI) wafer. Photolithography process with three different masks are used; 1) to create 10 μm channel in between the source and drain area, 2) to expose substrate-gate electrode through the top-silicon and buried oxide (SiO₂) layer, and 3) Al metal contact deposition for source, drain and substrate gate electrodes. Next, TiO₂ that acts as a transducer material is deposited on top of the channel by using sol-gel technique, creating a thin film TiO₂ on the surface. Several characterization methods have been used to determine the TiO₂ properties such as surface morphology (AFM, SEM), material crystallinity (XRD), surface functionalization (FTIR, XPS), and electrical characteristics (SPA). The deposited TiO₂ thin film possess p-type anatase structure due to titanium vacant defect, with average grain size of 65 nm. The fabricated device with TiO₂ thin film (before functionalization and detection of biomolecule), shows that there is electrical flow with the presence of TiO₂ connecting between source and drain, and it can be modulated with substrate-gate bias. Subsequently, the TiO₂ surface is functionalized with APTES and Glutaraldehyde prior to be subjected into antibody-antigen interaction, characterized by using XPS and FTIR. It shows, the changes or the presence of peaks at each surface functionalization proved that the chemical bonding have occurred. To demonstrate the functionality and performance of for biomolecule detection, the device is demonstrated to detection of cardiac troponin biomarker (cTnI) with concentration from 1ng/ml until 10 μg/ml. cTnI is a gold standard for diagnosis of cardiovascular disease. With the presence of substrate-gate biasing (Vbg = - 3 V), the device demonstrated significant amplification signal with LOD of 0.238 ng/ml can be achieved. This bring to a confirmation that the p-type anatase TiO2 offers excellent interaction with cTnI biomolecule. Coupled with substrate-gated FET, enhance sensitivity of bio-sensing can be achieved due modulation of electrical conductivity along the channel.
      2  29
  • Publication
    Junctionless transistors: parametric study with conventional doping in MOSFETS
    ( 2016)
    Nurul Huda Abdul Rahman
    The advancement of today technologies has been aggressively developed as the needs of current technology that becoming competitive and demanding to accommodate human lifestyle. The electronic gadgets drive the market with the requirements to provide efficient chip functionality at higher speed and extra functionality. This has become more challenging as the transistor density and performance are aggressively increasing. Thus, continuous downscaling of the conventional transistor will lead to severe short-channel effect (SCE), and one of the solutions is a ultra-shallow junction. Ultra-shallow junction is very challenging as it increases in fabrication cost and difficulty in the fabrication process. In this study, the channel, drain, and source have the same type of doping where the ultra-shallow junction has been eliminated. Hence, it is called junctionless. There will be no diffusion will take place where it will remove the high cost for ultrafast annealing techniques. Besides that, it allows the transistor to be fabricated with a shorter channel if the gradient of the doping concentration is zero between drain and channel or source and channel. This operation principle of the junctionless transistor is investigated through numerical simulations using technology computer aided design (TCAD) simulation tools. Firstly, the device performance of 3-Dimensional (3D) silicon-on-insulator (SOI) junctionless transistor (JLT) with 100 and 10 nm gate lengths, have been compared to the 3D SOI junction transistor (JT) with the same gate length. In order to achieve full depletion, the parameters such as metal gate workfunction, doping concentration, drain bias, and dimension are considered in the simulation process. The digital figure-of-merits characteristics such as threshold voltage (VTH), on-current, subthreshold slope, and draininduced- barrier-lowering are the main parameters that have been investigated. Following next is the characterization on the analog and radio frequency (RF) figures-of-merit. Based on the simulations, 1) the designated JLT device is more suitable to the higher gate workfunction of more than 5.0 eV whereas the designated JT device is more suitable with mid-gap values of gate workfunction of 4.6 eV. 2) the JLT transistor requires high gate work-function to have control over the channel. 3) the JT device is less sensitive to the variation of silicon body thickness (TSi) and width (WSi) compared to JLT. Lastly, the device performance on analog and RF figures of merit shows that no significant different between JLT and JT with the latter case shows slightly better performance, related to lower gate-to-gate capacitance (Cgg).
      16  2