Available online at www.sciencedirect.com Talanta 74 (2008) 1414–1419 Direct electrochemistry and electrocatalysis of hemoglobin immobilized in TiO 2 nanotube films W. Zheng a,b , Y.F. Zheng a,∗ , K.W. Jin c , N. Wang c a LTCS and Department of Advanced Materials and Nanotechnology, College of Engineering, Peking University, Beijing 100871, China b Center for Biomedical Materials and Engineering, Harbin Engineering University, Harbin 150001, China c Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, China Received 1 June 2007; received in revised form 18 September 2007; accepted 20 September 2007 Available online 29 September 2007 Abstract Titanium oxide nanotubes (TiO 2 -NTs) synthesized by the hydrothermal method had been prepared as the co-immobilization matrix to incorporate hemoglobin (Hb) successfully. The nanostructures of TiO 2 -NTs were investigated by X-ray diffraction and high-resolution electron microscopy. The Hb immobilized in TiO 2 -NTs had a similar structure to the native of Hb and retained its near-native conformations as characterized by the UV–vis and FT-IR spectroscopy. A couple of quasi-reversible redox peaks with a formal potential of -0.34 V (vs. SCE) in 0.10 M pH 7.0 phosphate buffered saline (PBS) were observed. The amperometric response of the immobilized Hb linearly to H 2 O 2 concentration ranged from 4 M to 64 M with a detection limit of 4.637 × 10 -6 M and the high stability of the immobilized Hb in TiO 2 -NTs constituted a promising platform for the development of biosensors. © 2007 Elsevier B.V. All rights reserved. Keywords: Titanium oxide nanotubes; Hemoglobin; Electrochemistry; Hydrogen peroxide; Biosensors 1. Introduction The direct electrochemistry of redox proteins, particularly enzymes, has received increasing attention in view of its impor- tance in elucidating the intrinsic thermodynamic and kinetic properties of proteins and its potential application in bio- electronic devices [1–3]. However, the proteins or enzymes exhibit a rather slow rate of heterogeneous electron-transfer at conventional electrodes, because of the deep burying of the electroactive prosthetic groups, the adsorptive denaturation of proteins onto electrodes and the unfavorable orientations at electrodes, although their electron-transfer is quite fast in biological systems [2]. Therefore, an understanding of the interactions between proteins and device/material surfaces is critically important in many fields of biomedical science, from biosensors to biocompatible materials. Since the discovery of carbon nanotubes [4], much attention has been given to the study of preparation, structural charac- ∗ Corresponding author. Tel.: +86 10 6276 7411; fax: +86 10 6276 7411. E-mail address: yfzheng@pku.edu.cn (Y.F. Zheng). teristics, properties, and applications for their unique physical and mechanical properties [5,6]. One-dimensional nanomateri- als usually exhibit special properties and potential applications, therefore, inorganic one-dimensional nanostructured materials have attracted considerable research attention in the recent 10 years [7–9]. The oxide-nanotubes became the research hot spot due to their superior performance and extensive applications in various research and industrial fields [10]. Many oxide one- dimensional nanomaterials have been successfully synthesized, such as TiO 2 , ZnO, ZrO 2 , Al 2 O 3 and so on [11–14]. Titanium dioxide is a widely used, inorganic material, which occurs in various structural types and can be engineered into many different forms such as nanoparticles, sol–gels, nanofibers, and nanotubes [11,15,16]. It shows good biocompatibility, stability and environmental safety. One-dimensional TiO 2 nan- otubes (TiO 2 -NTs), owing to their large length–diameter ratio, have physical, electronic and chemical properties that are dif- ferent from other forms. Since the first report claiming the hydrothermal synthesis of TiO 2 -NTs [17], there have been many studies on the growth and structure of this kind of peculiar nanotubes. Recent studies have shown that the structures of TiO 2 -NTs are diverse, the different synthesis parameters, such 0039-9140/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2007.09.017