Sol-gel-derived titanium oxide-cerium oxide biocompatible nanocomposite film for urea sensor
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Sol-gel-derived biocompatible titanium oxide–cerium oxide (TiO2–CeO2) nanocomposite film was deposited onto indium tin oxide (ITO)-coated glass substrate by the dip-coating method. This nanobiocomposite film has been characterized using x-ray diffraction, Fourier transform infrared, atomic force microscope, and electrochemical techniques, respectively. The particle size of the TiO2–CeO2 nanobiocomposite film was found to be 23 nm. The urea biosensor fabricated by immobilizing mixed enzyme [urease (Urs) and glutamate dehydrogenase (GLDH)] on this nanobiocomposite showed a response time of 10 s, sensitivity as 0.9165 mAcm2mM1, detection limit of 0.166 mM, and negligible effect due to interferants uric acid, cholesterol, glucose, and ascorbic acid. The value of Michaelis–Menten constant (Km) estimated using Lineweaver–Burke plot as 4.8 mM indicated enhancement in the affinity and/or activity of enzyme attached to their nanobiocomposite. This bioelectrode retained 95% of enzyme activity after 6 months at 4 C.
I. INTRODUCTION
The recent past has seen numerous investigations carried out on development and improvements on various features, such as speed, selectivity and sensitivity, and reduced cost of electrochemical biosensors.1,2 Many metal oxide-based nanomaterials, such as zinc oxide (ZnO),3–5 zirconium oxide (ZrO2),6,7 tin oxide (SnO2),8 titanium oxide (TiO2),9,10 niobium oxide (Nb2O5),11 and cerium oxide (CeO2),12 etc., have been used as immobilization matrices for the development of biosensors. Among those, nanostructured TiO2 has received much attention as an immobilization matrix for the design of desired biosensors because of its one-dimensional nanostructure, electronic conductivity, and larger specific surface area.13 It has been reported that the presence of higher valence cationic (4+) dopants enhances the ionic conductivity of TiO2 due to increase in the concentration of oxygen vacancies.14,15 It was suggested that partial orientation of TiO2 nanoparticles may have an influence on ionic conductivity of this material near the surface.16 These features are particularly attractive as potential adsorbents for enzyme immobilization as ambient temperature necessitates further development of new catalytic materials with a high surface area and well-defined reactive crystal planes with superior catalytic activity. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0212 J. Mater. Res., Vol. 24, No. 5, May 2009
Efforts have recently been made to tailor the catalytic properties of TiO2 by the addition of CeO2 to enhance thermal and electrical properties, and these novel materials have been exploited for applications toward passive counter electrodes and sensors.14,15,17 In recent years, a number of sol-gel-derived oxide substrates were used for improving characteristics of biosensors for detection of various analytes.3,4,13,17–22 Various techniques, such as radio frequency (rf) sputtering, electrochemical deposition, and sol-gel techniques, have been used to pre
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