Nanostructured Metal Oxides Based Enzymatic Electrochemical Biosensors

Abstract

Studies of nanobiosensors based on semiconductor nanostructured metal oxides are of practical and theoretical importance in biological science, environmental science and analytical chemistry (Wang et al., 2005; Luo et al., 2006; Valentini & Palleschi (2008); Chopra et al., 2007). These one-dimensional nanostructured metal oxides have profound applications in optics, optoelectronics, sensors, and actuators duo to their semiconducting, piezoelectric, and pyroelectric properties (Wang et al., 2005; Chopra et al., 2007; Kerman et al., 2008; Chow et al., 2005). Nanostructured metal oxides not only possesses high surface area, nontoxicity, good biocompatibility and chemical stability, but also shows fast electron communication features made the materials to be able to function as biomimetic membrane material to fix and modify proteins (Wang et al., 2005; Chopra et al., 2007; Valentini & Palleschi (2008)). These biomimetic and high electron communication features, high surface to volume ratio and electro-catalytic activity of the nanosized materials make them ideal as immobilization matrices, as transduction platform and/or mediators. Stability, sensitivity, selectivity and other analytical characteristics of biosensors are essential features to design desirable microenviroment for the direct electron transfer between the enzyme’s active sites and the electrode. To improve these characteristics various conventional materials matrices have been proposed. Among them nanostructured metal oxides matrices not only retain the bioactivity of the immobilized enzyme but also enhanced the sensing characteristics such as sensitivity, selectivity and low detection limit of the fabricated amperomatric enzymatic biosensors. Morphology of the nanosized material is one of the most ideally suited important factor to determine the properties for biosensor applications since they are conductive, biocompatible, easily functionalized while they have very large surface area. Nanosized metal oxides based electrochemical enzymatic biosensors have active surfaces that can easily be modified for immobilization of biomolecules. However, this advantage may not apply to many non-oxide semiconductor nanomaterials because their surfaces are not stable in an air environment, which leads to formation of an insulating native oxide layer and may degrade device reliability and sensitivity. Whereas, nanostructured metal oxides based electrochemical transducer surfaces promote the direct electron transfer reactions, amplify and orient the analytic signal of the biorecognition events. When a redox protein is immobilized on a biocompatible metal oxide electrode surface, it will exhibit reasonably fast electron transfer kinetic and permit the