Investigations on the influence of aspect ratio and morphology of hydrothermally grown ZnO based nanostructures towards biosensing applications

Abstract

Glucose plays a signi cant role in metabolic homeostasis. Living cells use it as both a source of energy as well as a metabolic intermediate in the synthesis of more complex molecules such as fat. Besides this, glucose covalently links to lipids and proteins which eventually lead to the formation of glycolipids and glycoproteins respectively. Therefore, an imbalance in glucose concentration in blood results in chronic diseases like diabetes mellitus. There has been tremendous increase worldwide in the number of patients su ering from diabetes in the last few decades. Moreover, India has been the second largest population of patients su ering from diabetes after China. Thus, patients su ering from diabetes need continuous monitoring of their blood glucose level. This has led to high demand for reliable, low cost and handheld point of care testing devices in the past decade. Glucose detection has been reportedly performed using various techniques viz. chromatography, chemiluminescence, electrochemistry etc. Among these, electrochemical methods, especially amperometric detection have been proven to be one of the most simplistic and most powerful methodologies. ZnO nanostructures have been proved to be materials of choice due to its excellent electronic properties, high iso-electric point, availability of wide variety of nanostructure morphologies and biocompatibility. Improving performance requires a rm understanding of how to optimize both material composition and processing parameters. This dissertation aims to achieve improved performance of an amperometric biosensor by enhancing material property. In this work, we have fabricated an enzymatic electrochemical biosensor for glucose detection utilizing ZnO nanostructures as support matrix. Di erent morphologies of ZnO was obtained by a simple and low temperature synthesis process i.e. hydrothermal growth technique. The work has been performed in three phases: (1) Aspect ratio, charge transfer resistance and surface defects tuned ZnO nanorods array was fabricated over Pt (Anode) coated glass substrates; (2) Di erent immobilization techniques viz. Physical adsorption and cross-linking were implemented and compared and (3) High aspect ratio Mn doped ZnO nanopencils were fabricated with the motive of achieving higher enzyme loading (a pre-requisite for improved biosensor response). We have explored in uence of aspect ratio, enzyme loading,surface defects, charge transfer resistance, immobilization techniques and doping on the performance of glucose biosensor in detail. The new biosensor was developed by using Mn doped ZnO nanopencils as support matrix over which Glucose oxidase was immobilized by physical adsorption process. The as fabricated biosensor device was found to exhibit high sensitivity i.e. 51 mA 􀀀 cm􀀀2 􀀀M􀀀1 with a response time of 5s and having 0.25 - 6 mM of linear range of detection. Furthermore, the biosensor retained 91% of its initial sensitivity after storage of 7 days. The observed results show that ZnO nanostructures with tuned physical properties can pave way to high performance biosensors.