Zinc Oxide Nanorod Films for Electrochemical Urea Biosensor
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Zinc Oxide Nanorod Films for Electrochemical Urea Biosensor Netzahualcóyotl Palomera1, Marcia Balaguera2, Sunil K. Arya 5, Samuel Hernández2, Maharaj S. Tomar3, Jaime E. Ramírez-Vick4 and Surinder P. Singh4 1 Department of Mechanical Engineering, 2Department of Chemistry, 3Department of Physics, 4 Department of Engineering Science & Materials, University of Puerto Rico, Call Box 9000, Mayagüez, PR 00681-9000. 5 Bio-MEMS and Microsystem Lab, Department of Electrical Engineering, University of South Florida, Tampa, FL 33620, United States. ABSTRACT Metal oxide nanostructures have shown significant promise for biosensors, gas sensors, photocatalyst and other biomedical applications. Among these, zinc oxide (ZnO) nanostructures, exhibiting interesting properties such as high catalytic activity, biocompatibility, high isoelectric point, large surface to volume ratio, make them a good candidate for biosensing applications. Here we report the synthesis of ZnO nanorods (ZnONR) on ITO films in aqueous phase and its application in Urea biosensor fabrication. ZnONR have been synthesized by a two-step method, first seed growth of ZnO by sputtering on ITO films followed by decomposition of zinc nitrate hexahydrate / hexamethylenetetramine (HMT) in aqueous phase. Exploiting the high isoelectric point of ZnO, a Urease/ZnONR/ITO bioelectrode has been fabricated by physical binding of Urease (Urs) onto ZnONRs. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and cyclic voltammetry (CV) have been used to characterize ZnONR and the Urs/ZnONR/ITO bioelectrode. The FE-SEM and XRD measurements confirm the formation of ZnONR. The electrochemical data from the Urs/ZnONR/ITO biolectrode reveal linearity between 1-11 mM with sensitivity of 0.9 µA/mM and a relatively low MichaelisMenten constant (Km) of 5.01 mM for urea sensing. The results indicate the potential of ZnONR films for fabrication of commercial biosensors. INTRODUCTION Electrochemical biosensors exhibit fast and accurate responses for detection of desired analytes have shown great promise for improved healthcare monitoring. Choice of materials such as SiO2, Si, CeO2, TiO2, ZnO, and conducting polymers, play a vital role in defining the sensitivity and other performance parameters of biosensor. Nanostructured metal oxides have recently gained much interest, owing to their large surface area and biocompatibility. They are known to provide high loading capacity of the sensing biomolecule in mild environment. Furthermore, due to differences in isoelectric point (IEP) with respect to biomolecule, they permit direct immobilization of the biomolecule by physical adsorption via electrostatic interactions between the enzyme and the material [1,2]. Among metal oxides, ZnO nanostructures possess a high isolectric point of 9.5, biocompatibility and good redox properties in electrochemical procedures making them good candidate materials for enzymatic biosensor electrodes with preserved/enhanced enzymatic activity [3-5]. Urea is a biologically important analyte, w
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