Mgo/zno/rgo nanocomposite based electrochemical enzymatic glucose biosensors

Abstract

Glucose biosensors are the most widely used and among the first commercialized biosensors. Various studies are carried out to improve the measurement capability of glucose biosensors for diabetes patients and other areas of use. Diabetes is a type of disease that is increasing day by day and cannot be cured. People with diabetes should pay attention to what they eat in their daily lives and constantly monitor the amount of glucose in their blood. For this reason, blood glucose determination is of great importance. Today, glucose determination can be performed quickly, sensitively and accurately with glucose biosensors. A biosensor comprises an electronic substance employed as an amplifier to read the sensed signals, a bioreceptor that can detect an analyte to be tested biologically, a transducer that will transform signals into an electrical or optical output. Biosensors can be enzyme-based, aptamer-based, antibody-based, optical, piezoelectrical and electrochemical, depending on the types of bioreceptors and transducers used. Biosensors should be sensitive, reliable, stable, low limit of detection (LOD), reusable and long-lasting. In order to manufacture and measure biosensors, their bioreceptors must be immobilized on an electrode. This electrode is known as working electrode and can be metallic, carbon-based, or polymeric. Carbon-based electrodes are generally used for glucose biosensors. Enzymatic glucose biosensors determine the amount of glucose by electrochemical methods and redox reactions occur during these methods. Glucose oxidase (GOx) enzyme should be used for glucose determination in enzymatic glucose biosensors. Electron transfer, which occurs in redox reaction that occurs as a result of the cracking of glucose bonds with GOx, which is a glucose-specific enzyme, is determined by measuring current intensity. Due to the structure of GOx enzyme, an electron transfer center is embedded in the inner part of the enzyme. For this reason, it becomes difficult to perform an electron flow from analyte to working electrode surface. Graphite electrode was chosen as a working electrode for this study. For precise and accurate measurements, enzymes must be well distributed and well attached to the graphite electrode surface. The measurement cannot be performed accurately if enzymes do not adhere to the graphite electrode surface. Modifications with various materials are possible to increase adhesion and conduct electrons. In order to increase the adhesion to the graphite electrode surface, metal oxides have been used by taking advantage of the difference between the isoelectric point (IEP) values of the materials. A material with a low IEP will adhere well to a material with a high IEP. Metal oxides are strong support materials for GOx adsorption to the graphite electrode surface and increase the surface area that GOx is well immobilized and spread, and also create a biocompatible environment for GOx. Added to this, to increase conductivity, in our design reduced graphene oxide (rGO) has been used. The originality of this project; is using a combination of MgO and ZnO which have the highest IEP among the other metal oxides 9.8-12 and 9.5, respectively. Moreover, rGO is used as a conductive agent for the development of high sensitivity glucose biosensors. In this study, 3 biosensors designed with hydrothermally synthesized nanocomposites to increase the measurement sensitivity, decrease the limit of detection value and high stability of the enzymatic glucose biosensor production was aimed. In the scope of this project; ZnO-rGO, MgO-rGO and ZnO-MgO-rGO nanocomposites have been produced by hydrothermal synthesis. X-Ray Diffractometer (XRD), Scanning Electron Microscope (SEM), particle size, Fourier Transform Infrared (FTIR), X-Ray Fluorescence Spectrometer (XRF) analyses have been performed for the characterization of nanocomposites. Then, the nanocomposites have been coated with GOx enzyme on a graphene electrode. After coating, the electrodes have been dried. Finally, electrochemical measurements; Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) have been made using a potentiostat device. In the study, 3 different nanocomposites have been produced with different morphologies via hydrothermal synthesis. SEM analyses have shown that the morphologies similar to nanorod and nanoflower obtained for ZnO-rGO nanocomposite, and MgO-rGO nanocomposite has been obtained in more spherical structure. The ZnO-MgO-rGO nanocomposite has had a combination of these two morphologies. The phases observed in the XRD analysis have been consistent with the literature. FTIR analyses have shown that C-C, O-H, Mg-O, Zn-O-C bonds were formed. Average particle size of ZR, MR and ZMR has found 300-350 nm, 325-375 nm and 375-400 nm respectively. It was discovered that the LOD values for the ZR, MR, and ZMR biosensors have been 223.1 μM (R2=0.9792), 452.1 μM (R2=0.9198), and 173.08 μM (R2=0.9874), respectively. Their sensitivities have been determined to be 70.55 μA.mM-1.cm-2, 110.12 μA.mM-1.cm-2, and 92.56 μA.mM-1.cm-2, respectively (R2=0.8685, 0.9685, and 0.9564). The ZMR electrode has performed exceptionally well in terms of repeatability, with an unusually low RSD of 0.46%. The ZR electrode displayed comparatively larger variability with an RSD of 2.89%, whereas the MR electrode followed closely behind with an RSD of 0.75%. The findings of the interference experiment gave compelling evidence that the designed glucose sensors have extraordinarily well-suited for accurate and specific glucose measurements, even when there are complex biological samples present. With the introduction of glucose, the biosensors have shown quick response times. Although there are not many studies with MgO for glucose biosensors in the literature, ZnO is a very preferred metal oxide. When the studies made with ZnO are examined in general, our biosensor, which has formed by combining MgO and ZnO, gave much better results for glucose detection and showed high sensitivity and stability due to their high surface area of nanorod morphology and high IEP values. Also, high conductivity property was achieved by rGO.