Theses & Dissertations

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

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Browsing Theses & Dissertations by Subject "Biosensors"
  • 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.
      2  19
  • 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.
      3  19
  • Publication
    Development of back-gated silicon nanowire field-effect transistor biosensor for Dengue virus type 2 (DENV-2) detection
    (Universiti Malaysia Perlis (UniMAP), 2021)
    Wan 'Amirah Basyarah Zainol Abidin
    Dengue fever (DF) is an infectious disease spread by mosquitoes with a significantly rising rate of death over decades worldwide. Presently, the label-based ELISA method in detecting dengue virus (DENV) is time-consuming and laborious. Thus, label-free biosensor has been shown to be useful and capable to overcome the limitations by ELISA. In this thesis, the detection of dengue virus type-2 (DENV-2) deoxyribonucleic acid (DNA) using a field-effect transistor (FET) biosensor is introduced and demonstrated. Among various types of established field-effect transistor based biosensing technologies, silicon nanowire (SiNW) FET-based biosensor has proved to be a versatile class of potentiometric nano biosensor, are notable for their attractive characteristics, such as real-time, highly sensitive and label-free detection of a wide range of biomolecules. Therefore, this research aims to develop a label-free biosensor device with high sensitivity through accurate measurement to detect DENV-2 DNA using SiNW act as a transducer and creates electrical potential variations to control the conductivity of the source and the drain. The SiNW had been fabricated between the source and drain of the FET based on p-type Silicon-on-insulator (SOI) substrate, with the presence of back gate biasing, through top-down fabrication methods such as lithography and inductively coupled plasma reactive ion etching (ICP-RIE) technology. The surface morphological of the SiNW had been characterized via the nano-characterization technique, which is field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). Simultaneously, the element composition of the transducer was analyzed via Energy Dispersive X-ray (EDX). The surface modification was then performed by immobilizing the single-stranded DNA (ssDNA) dengue probes layer on a transducer surface through covalent binding, recognizing its complementary DNA target form immobilized double-stranded DNA (dsDNA). A complete device fabrication process with the smallest nanowire width obtained is 159 nm with a height of 11 nm. Electrical characterization is disclosed, starting with device validation using three different pH values of pH12, pH7 and pH4, and then testing with various target concentrations and analyzing selectivity. Through electrical measurement, the device gives a good response in current-voltage characteristic by coupling with a back gate in enhancing the accumulation of the hole conduction layer on the channel surface. The SiNW is validated as a transducer by testing with different pH where the fabricated device's sensitivity is 0.599 nA/pH. Meanwhile, the detection of DNA hybridization is shown for target concentration as small as 10 fM with the device sensitivity of 3.3 nAM-1. Hence, it shows that this device as a promising diagnostic platform for point-of-care testing (POCT) and have significant implications in medical healthcare.
      6  17
  • 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 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).
      2  18
  • 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
    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.
      5  11
  • 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.
      2  11
  • Publication
    Impedimetric-based biosensor for Cardiac Troponin 1 detection: sensing strategy aided by Hybrid rGO and Gold Interdigitated Electrode
    (Universiti Malaysia Perlis (UniMAP), 2021)
    Steven Taniselass
    Cardiovascular diseases (CVD) are the number one cause of death among the noncommunicable diseases globally. CVD are referred to diseases that associated with the abnormalities of blood flow in heart and often related with ‘heart attack’ condition or in clinical term as an acute myocardial infarction (AMI). Cardiac Troponin I (cTnI) biomarker is widely accepted as gold standard for AMI recognition due to its high specificity. Hence, the need for portable and highly sensitive sensor with fast detection is utmost required to diagnose AMI for fast treatments. Herein, a label-free impedimetric-based cTnI immunosensors were fabricated and their analytical performances were assessed and reported in this thesis. Reduced graphene oxide (rGO) and gold interdigitated electrode (Au-IDE) were employed to develop the immunosensors. The research work is divided into two main sections; first is to obtain a uniform deposition of rGO through single-droplet drop-casting technique and second is to fabricate the cTnI immunosensor aided by rGO. The deposition results revealed the method-3 involving post-sonication technique produces a large and self-assembled of rGO nanoflakes through single-droplet drop-casting without the use of any chemical solvent. Furthermore, the rGO modified Au-IDE devices show an excellent electron mobility, whereby the electrical conductivity was enhanced approximately ~1000-fold compared to the bare devices. Thus, the as-prepared rGO suspension was used to fabricate the immunosensors. Four different surface modification strategies on respective bioelectrodes mediated by the as-prepared rGO suspension were investigated. Electrochemical impedance spectroscopy (EIS) was performed to characterize the immunosensors by sweeping frequencies from 0.1 - 500 kHz at a small AC voltage (25 mV). Results revealed that one of the four immunosensors developed through strategy-4 shows an excellent analytical performance for the cTnI antigen detection in spiked buffer and human serum. A potential surface functionalization mediated by rGO basal plane functional groups was postulated based on XPS and FTIR analyses. The as-fabricated immunosensor showed a wide linear range (10 ag/mL – 100 ng/mL) of cTnI antigen detection in human serum with a linear regression coefficient (R2) of 0.9716 and the lowest analytes detected was 10 ag/mL, whereby it shows highly selective and sensitive trait. The immunosensor also showed a fast-detection that only required 5 minutes for probe and targets binding and stable for nine days. The bioelectrodes were highly reproducible. Hence, such an electrode sensing surface modifications strategy can be further extrapolated for later applications in various biomarker mediated disease diagnoses.
      19  4
  • 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
    Reduced graphene oxide-multi walled carbon nanotubes hybrid material as electrode for DNA biosensor
    ( 2017)
    Saeed Salem Saeed Ba Hashwan
    This thesis presents a novel thin film of reduced graphene oxide-multiwalled carbon nanotubes (rGO-MWCNTs) composites as a sensing film electrode for Deoxyribonucleic acid (DNA) immobilization and hybridization detection. This project consisted of three parts, which are the rGO-MWCNTs composite thin film preparation and characterization, the device fabrication processes description, and followed by the DNA immobilization and hybridization. In the first part, the thesis describes the graphene oxide preparation from graphite powder using improved Hummers’ method. Whereas, the multiwalled carbon nanotubes (MWCNTs) was functionalized through nitric acid oxidation process. Chemical reduction process was used to obtain the reduced graphene oxide using hydrazine as reduced agent. The MWCNTs, GO, and rGO-MWCNTs materials were mechanically sprayed on the silicon dioxide (SiO2) surface of the device channel using spray technique. Chitosan solution was mixed with the materials and sprayed on the device surface in order to increase the viscosity of the materials and strengthen their adhesion with the silicon dioxide surface by changing the surface characteristic from hydrophobic to hydrophilic. The morphology of the rGO-MWCNTs composite thin films were observed by field emission scanning electron microscope. The bonding of the rGOMWCNTs were examined using Fourier transform infrared spectroscopy. The phase structure of the materials were confirmed via X-ray powder diffraction. Secondly, the design, fabrication and evaluation of the device were descripted in details. In addition, the device fabrication processes contained of oxidation process for silicon dioxide layer growing, physical vapor deposition process which was used to deposit an aluminum layer on the silicon substrate to form the source and drain, mask designed, printed, and utilized in the pattern transfer process, and photolithography process which was carried out to create the channel of the device. The operation of the electrode is based on the surface charge adsorption of the film material interface. Finally, in the DNA immobilization and hybridization section where the novelty of the research introduced, the biosensor demonstrated high sensitivity to the complementary DNA target with a linear range from 500 pM to 100 pM. Furthermore, the biosensor demonstrated good selectivity, reproducibility, and long-term stability for DNA detection. The device has shown sufficient capability to distinguish between targets complementary DNA and different DNA sequences, such as non-complementary and single-mismatched DNA. The hybridization process of the non-complementary DNA has the smallest response (39 μA) due to the double standard DNA was not effectively formed. Whereas, the singlemismatched DNA has shown less response (55 μA) comparing with the complementary DNA (65 μA) due to the single mismatched base. The device accuracy was investigated and found to be 11.28 %. Since, the biosensor responded very well and demonstrated excellent detection capabilities, it is highly recommended to be used in detecting specific biomarkers and other targeted proteins.
      2  6