Chemical modification of TiO₂ nanotube arrays for label-free optical biosensing applications

Highlights: • TiO₂ nanotube arrays as versatile transducer surface in biosensor development is proposed. • The chemistry used to TiO₂ surface modification is based on stable covalent bond. • The label-free recognition mechanism relies on changes of optical TiO₂ nanotube array properties. - Abstract: In this study, we have fabricated TiO₂ nanotube arrays by the potentiostatic anodic oxidation of Ti foils in fluoride-containing electrolyte and explored them as versatile devices for biosensing applications. TiO₂ nanotubes have been chemically modified in order to bind Protein A as a specific target analyte for the optical biosensing. The obtained structures have been characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, water contact angle, fluorescence microscopy, spectroscopic reflectometry and photoluminescence. Investigations show that the prepared TiO₂ nanotubes, 2.5 μm long and 75 nm thick, can be easily and efficiently bio-modified, and the obtained structures are strongly photoluminescent, thus suitable for the label-free biosensing applications in the range of μM, due to their peculiar optical properties.