Theses & Dissertations

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

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Now showing 1 - 5 of 34
  • 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
    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
    Synthesis of silicone carbide nanowhiskers by microwave irradiation method
    ( 2018)
    Suhaimi Mat Kahar
    This work described the synthesis of silicon carbide nanowhiskers (SiCNWs) by using the microwave heating.. The main objective of this project is to study the feasibility of synthesis of SiCNWs from expanded graphite (EG) and silica using microwaves heating. Several parameters were studied such as the effect of ratio of graphite and silica, heating temperature, heating duration and types of graphite on the formation of SiCNWs in term of morphology, compositions, optical properties and purity. In this study, SiCNWs was synthesized by microwave heating mixture of EG and silica and the effect of processing parameters on the synthesis were studied. For effect of ratio of EG and silica, the mixture of EG and silica with the ratio 1:3 was found to be suitable for the synthesis of SiCNWs because the formation of high purity β-SiC nanowhiskers. Mixture of silica and EG with the ratios 1:5 and 1:7 had the traces of unreacted graphite. Study of effect of heating temperature revealed a temperature at 1400 ºC is suitable for the synthesis of SiCNWs. β-SiC appeared as the only phase in the XRD pattern of SiCNWs formed at 1400˚C. FESEM imaging confirmed the presence of only a negligible amount of graphite or silica in SiCNWs synthesized at 1400˚C. Meanwhile, PL spectrum indicated the presence of single phase β-SiC peak at 440 nm which is associated with band gap of 2.8 eV. Single absorption bands of Si-C bond were detected at 803.5 cm-1 in FTIR analysis. SiCNWs produced in this study at 1400˚C has good thermal stability with 6% of weight loss. Effect of heating duration was also studied and 40 minutes was found to be the most ideal heating duration for the synthesis of SiCNWs. β-SiC appeared as the only phase in the XRD pattern for SiCNWs formed by using 40 and 60 minutes of heating duration with no traces of unreacted silica and graphite. FESEM imaging confirmed that no trace of graphite or silica was present in SiCNWs synthesized at heating duration of 40 and 60 minutes. SiCNWs produced by heating at 40 and 60 minutes have high thermal stability with weight loss lower than 6%. It was found that SiC nanowhiskers (SiCNWs) were formed when EG was used as the starting material, while SiC nanoparticles (SiCNPs) were formed when FG was used. β-SiC appeared as the only phase in the x-ray diffraction pattern for SiCNMs formed by FG and EG. FESEM confirmed that no trace of graphite or silica was present in both SiCNWs and SiCNPs. Meanwhile, photoluminescence spectra show the presence of β-SiC peak at 440 nm and associated with band gap of 2.8 eV for both SiCNWs and SiCNPs. Absorption bands of Si-C bond were detected at 803.4 cm-1 for SiCNPs and 802.5 cm-1 for SiCNWs in the FTIR spectra. SiCNWs and SiCNPs have high thermal stability with weight loss less than 6 %. In conclusion, SiCNWs and SiCNPs have been successfully synthesized through the microwave heating of a mixture of silica/EG and silica/FG in an argon atmosphere.
      3  14
  • 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 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