$TiO_2$ nanostructured array for optical ultrasensitive biosensing.

Portable and real-time devices for biosensing are finding various application fields, including air quality for guaranteeing the occupational health, safety and security. Motivated by the request to monitor the airborne pathogens, we illustrate the steps towards the development of infrared $TiO_2$ nanostructured array. Herein, we fabricated $TiO_2$ nanotubes (NTs) by means of electrochemical anodization and investigated the prepared samples as the platform for label-free optical monitoring of biomolecules, such as SARS-CoV-2 spike glycoproteins. In order to increase the NTs sensor selectivity, we chemically modified the surface of $TiO_2$ NTs to bind the spike glycoprotein. The process of biofunctionalization was monitored and validated by using optical methods, including Infrared spectroscopy. Our results show that the $TiO_2$ NTs array can be applied as versatile platform for sensing of biochemical molecules interrogable with optical methods.