Papers by Keyword: Biosensor

Abstract: Graphene oxide (GO) is an oxidized nanosheets of graphite with a 2D planar structure. GO could be readily complexed with bio-entities as it possesses many oxygen-containing functionalities on its surface. The preparation process is fast, easy, and cost-effective. It was prepared using modified Hummers’ method in acidic solution as a primary solvent and potassium permanganate as an oxidizing agent. Afterwards, it was successfully characterized by FTIR, UV-visible spectroscopy, as well as XRD and Raman spectroscopy, and finally, SEM analysis. It was observed that the formed GO is mainly composed of carbon and oxygen elements rich in oxygen functional groups. Furthermore, the existence of (001) plane in XRD interprets the complete oxidation of graphite with d-spacing 9 Å. Moreover, Raman spectroscopy displayed the sp³ carbon hybridization, besides, the I_D/I_G ratio is found to be 0.84, which confirms the disorder between graphene oxide layers. The SEM images also pointed out that graphene oxide sheets were regularly stacked together as flake-like structures. Accordingly, the richness of oxygen-containing functionalities was confirmed. Hence, it is appropriate to be used as a base transducer for biosensing applications.

Abstract: A novel redox couple of metallic nickel (Ni) catalyst can become a great candidate of non-enzymatic detection. By taking advantage of fast electron transfer, Ni redox couples can be tailored as pseudo-enzyme in urea measurement. In this study, Ni catalyst on nitrogen doped carbon (Ni-NC) was synthesized and characterized morphological, elemental, and electrocatalytic properties in comparison to different configuration of pure nickel (Ni), Ni with carbon (Ni-C), and bare carbon electrode, assessed by cyclic voltammetry and differential pulse voltammetry. By examining various Ni redox couples in rapid electron transfer process, the prominent anodic and cathodic peaks of Ni²⁺/Ni³⁺ were applicable to detect urea in the detection range of 1-20 mM, with an excellent sensitivity and relative standard deviation of 1.634 μA.mM^-1 (R² of 0.989) and 4.89%, respectively. Therefore, Ni-NC can find practical applications for material sensing device toward non-enzymatic urea measurement.

Abstract: The study of spectroscopic ellipsometry on gold thin film with different thicknesses (30, 50, and 70 nm) for biosensor application has been done. In this work, a rotating analyzer ellipsometer (RAE) has been used to characterize gold thin film and detect microalgae. The measurement was performed at different incidence angles (60°, 65°, 70°, and 75°) assuming the gold film as an isotropic material. The light absorptions of electron represented by the ellipsometer parameter (Δ) and the extinction coefficient (k) are due to the intraband transition of free electrons in the lower photon energy and interband transition of bounded electrons from 5d to 6sp in the higher photon energy. The light absorption increases with the decrease in the thickness of Au thin film. However, for the detection of microalgae, the light absorption of the electron increases with the increase in the thickness of Au thin film due to the dominant absorption by microalgae and PVA. We report that the use of Au thin film with the thickness of 70 nm provides the most sensitive detection of microalgae which is confirmed by the change in Δ (63.1°), at the photon energy of 2.11 eV and the incidence angle of 75°.

Abstract: In this paper, the latest techniques and technologies of liquid crystal devices have been reviewed with essential conclusions made based on their applications. This work combines Liquid Crystal research from different field. Here I give an overview of Liquid Crystal instrumentation in the optical systems, focusing on a large domain of applications: photonic devices, biomedical applications, etc. I characterize common approaches and challenges. In addition, novel technique of liquid crystal that permits a new solution has been presented. I conclude with advice regarding the Liquid Crystal group at large to make concerted efforts to exchange expertise.

Abstract: This study investigated an electrocatalytic behavior of non-enzymatic glucose detection in urine by using low-cost non-precious metal CoFe catalyst on carbon (C) supported. The bimetal catalyst was prepared by the reduction of oleic acid and loaded 10% wt. metal onto the activated carbon. Due to the synergistic effect, CoFe exhibited its intrinsic electrocatalytic property, suitable for the chemisorption of glucose molecule and the d-electron of metal. For morphology and elemental composition, CoFe/C was characterized by Transmission Electron Microscopy (TEM), and X-ray Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD), exhibiting Co (111) and Fe₂O₃(104) with the nanocluster average diameter of 25 nm. More importantly, electrocatalytic behaviors of CoFe/C were assessed by cyclic voltammetry (CV) and Differential Pulse Voltammetry (DPV) on the glassy carbon rotating disk electrode for glucose detection (0-3 mM) in modified artificial urine (mAUM), and human urine specimens. In particular, excellent sensitivities from the lower range of glucose level (< 1 mM) and the higher level by DPV in mAUM were estimated to be 318.42 and 82.20 μA.cm^-2.mM^-1 with the correlation coefficient (R²) values of 0.90 and 0.94, respectively. Furthermore, the as-prepared CoFe/C biosensor also demonstrated practical measurement in human urine sample with the sensitivity of 59.72 μA.cm^-2.mM^-1 (R² = 0.99) without any electron facilitators (e.g. sodium hydroxide), thereby providing a promising cost-effective catalyst design for future technology of non-enzymatic glucose sensing applications in urine.

Abstract: Study on pyrrole electropolymerization is the preliminary step in synthesizing polypyrrole membranes, which can be used for various purposes in biosensor. In this work, electropolymerization process and electrochemical analysis of polypyrrole as an electroactive polymer have been studied by cyclic voltammetry. Pyrrole was electropolymerized to form polypyrrole in an aqueous potassium chloride solution at different pHs using phosphate buffer. The results showed that a potential range of 0-1200 mV is suitable for polypyrrole electropolymerization using the Ag|AgCl electrode as the reference. The formation of polypyrrole is stable at a scan rate of 100 mV/s. In addition, the optimized pyrrole electropolymerization was obtained using 0.1 M pyrrole and phosphate buffer at pH of 2-6. Taken together, this study can be used as a reference for the synthesis of other conducting polymers.

Abstract: Graphene has been employed as electrode materials in various electrochemical biosensors due to its excellent electrical, mechanical, thermal and optical properties. In the present study, Chemical Vapor Deposited (CVD) and epitaxial graphene on SiC were examined as material for electrochemical biosensing application. The surface of both types of graphene were characterized using Raman spectroscopy as well as with Scanning Electron Microscopy (SEM). As the key point for the comparison, the impedance spectroscopy measurements of different graphene films using deionized water and saline 0.9% NaCl solution were performed as well. The method of impedance measurements applied to graphene films expands the range of possibilities for using this material as sensitive biosensors. Based on the comparative tests results, it is possible to draw the first simple conclusions about the advantages of CVD or epitaxial graphene. Based on the results of impedance spectroscopy, it is possible to draw a simple conclusion – single layer graphene has the higher sensitivity.

Abstract: We have previously reported the surface plasmon resonance (SPR)-based biosensor ability for quantitatively differentiating bovine and porcine gelatin has been done by us before. However, it has some inaccuracies. By improving the method of detection, the results of this study shows that the difference between bovine and porcine gelatin was more distinguishable. The sensor response models acquired were nonlinear as in the previous study. However, they show different characteristics. The sensitivities of the sensor obtained are higher than those of the previous ones, i.e., 3.04^o and 4.29^o for bovine and porcine gelatin concentration change of 0.1%, respectively. And the sensor’s LOD and LOQ towards both gelatin concentrations were 0.22% and 0.74% (w/w), respectively.

Abstract: In-vitro cell culture offers the ability to grow individual cells and monitor their behaviour in a controlled environment over a certain time. During culture, different parameters have to be controlled to ensure a vital growth of cells. The most important parameters are temperature, pH-value, oxygen and carbon dioxide levels as well as the glucose concentration. All of these parameters influence the growth ability of the cell culture and should be monitored online. The online monitoring of glucose was achieved with a novel GOD based sensor which enabled a real-time measurement of glucose during cell culture. A first-time characterisation of the sensor was carried out in the culture medium DMEM. In addition, material properties of the culture system were investigated. At first to establish a baseline measurement, the sensor was placed in different glucose concentrations dissolved in Water-KCl mixture at 25 °C inside a batch chamber under constant stirring. Afterwards, the temperature was increased to 37 °C to simulate a cell culture environment. In addition, the system was transferred into a flow-through reaction chamber. The highest response signal and the most stable signal was achieved at 37 °C with DMEM during flow-through measurement. Based on these measurements online glucose monitoring in cell culture was possible to determine the glucose consumption for each cell which is important for future human-on-a-chip devices to prevent diabetic metabolisms.

Abstract: In this work a special electrode configuration with potential application in enzymatic biosensors for the detection of glyphosate was studied. The enzyme used was Horseradish Peroxidase (HRP), which was immobilized on a polyaniline film (PAni), electrodeposited on the surface of the n-type monocrystalline silicon electrode. PAni has the ability to bind to biomolecules and thereby potentiate their biocatalytic properties by favoring the transfer of electrons between enzyme and substrate. Monocrystalline silicon is one of the most used materials in electronic technology due to its semiconductor character. In this work, different parameters were investigated in the electrode preparation, including concentration of polyaniline in the electrodeposition solutions, as well as the electrodeposition times and potentials. The response of the electrode as biosensor was evaluated by the electric current density characteristic of hydroquinone oxidation in the presence of standardized glyphosate solutions. The peroxidase enzyme catalyzes the oxidation of hydroquinone to the o-quinone form in the presence of hydrogen peroxide. In turn, glyphosate inhibits the activity of HRP and causes a reduction of the electric current density in the biosensor electrode. The results obtained with glyphosate using the proposed method are in agreement with the literature and show that the n-Si/PAni/HRP biosensor maintains the catalytic activity and is of considerable interest due to the simple procedure in practical applications and a promising platform for the lack of environmental monitoring for these contaminants.