Flexible nanostructured TiO2-based gas and UV sensors: a review

Flexible sensors have been attracting an ever-growing attention over the last years due to their outstanding characteristics, that include their lightweight and cost-effective characteristics, high stretchability, biocompatibility, and conformability. Moreover, the pursue of such devices has exponentially raised, with the IoT (Internet of Things) technology and the integration of several kinds of sensor devices that allow exchanging information on the internet, as well as remotely operating devices and collecting data. In fact, IoT is bringing sensor usage to a new level, where gas and ultraviolet (UV) sensors are largely integrated, guaranteeing the well-being and safety of people, with the immediate detection and response to changes in an environment. Gas and UV sensors based on titanium dioxide (TiO2) have been largely reported, where numerous efforts have been devoted to improving its sensing performance, especially when employing TiO2 at the nanoscale. TiO2 has the advantage of being chemical stable, non-toxic, inexpensive, and compatible with low-cost wet-chemical synthesis routes. This review outlines the current state of flexible gas and UV sensor technologies having TiO2 as the sensing layer and the impact of this nanostructured material on the field.