Functionalised Nanostructured TiO2 Layers for Sensor and Biosensor Applications

The immobilization of biomolecules on solid surfaces is a hot topic in modern bioelectrochemistry, since it is of great interest for several applications such as biological fuel cells, chemical and biological sensing. Furthermore, the development of biosensors on miniaturized platforms appears fundamental to overcome the extensive packaging, the complex electronic interfacing and the regular maintenance of conventional biosensors. The crucial aspect involved in the realization of a bioelectronic system is the immobilization of biological components on electrodes surfaces, able to ensure an effective electronic communication between the biomaterials and the electronic transducers. In latest years, the functionalisation of solid electrodes with thin films of biocompatible materials reveals very attractive, since these configurations could provide a rapid translation of the biological processes occurring on the surface to electronic outputs. In this study we report the realization of functionalised TiO thin films onto silicon substrates for the immobilization of several enzymes and biological molecules. TiO films with different characteristics were realized by MOCVD and Sol-Gel techniques. Deposition processes revealed to be the key parameters for the determination of chemical and microstructural features of the films, which influenced the immobilization. Surface roughness, chemical composition and microstructural features of TiO films were investigated by Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and FT-IR Spectrometry. Nanostructured TiO films deposited at different conditions exhibited a homogeneous microstructure, characterised by low roughness values. The presence of residual carbonylic and carboxylic groups was detected on TiO surfaces deposited at lowest temperatures. Glucose Oxidase and Horseradish Peroxidase immobilized onto TiO nanostructured surfaces exhibited a pair of well-defined and quasi-reversible cyclic voltammetric peaks. The electron exchange between the enzyme and TiO electrodes was greatly enhanced in the TiO nanostructured environment. In addition, several biological molecules, as neurotransmitters were also investigated by Cyclic Voltammetry (CV) and detected with the Differential Pulse Voltammetry (DPV) technique. For dopamine, epinephrine and norepinephrine very high current values, a wide range of potential, and a shift of their oxidation potential (very important to minimize the interference effects) were observed by CV. The study of the interactions between TiO film surfaces and biologic components performed by XPS and FT-IR revealed that the presence of residual carbonylic and carboxylic groups promotes their immobilization TiO surfaces. The electrocatalytic activity of HRP and GOD embedded in TiO electrodes toward HO and glucose, respectively, may have a potential perspective in fabricating the third-generation biosensors based on direct electrochemistry of enzymes. 22222222222