Metal oxides nanowires chemical/gas sensors: recent advances E. Comini Sensor, University of Brescia, Via Valotti 9, 25133, Italy article info Article history: Received 26 May 2020 Received in revised form 9 July 2020 Accepted 13 July 2020 Available online xxx Keywords: Chemical sensing Gas sensing Oxide semiconductors Nanostructures Functional materials abstract Chemical/gas sensors are playing and will play a crucial role in smart building, smart houses, environ- mental monitoring, food quality monitoring and in the customization of personalized medicine, as they allow a constant data collection to monitor all the parameters needed for a preventive intervention related to health and wealth of human beings together with the environment. Nanowires (NWs) and NW-based heterostructures thanks to their peculiar properties such as high crystallinity, flexibility, conductivity, and optical activity are key components of future sensing devices. Notwithstanding a rapid growth in smart, portable, and wearable chemical sensing devices, the development of reliable devices for the detection of chemicals, gases, and vapors is still needed together with the possibility to correlate the sensing data with health and wealth of the analyzed system: food, environment, and human beings. In this short review, I am going to report few recent studies and achievements devoted to increase the functional performances of chemical sensing devices, keeping the focus on materials, sensing trans- duction, and data extraction/evaluation. © 2020 The Author. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction Nanomaterials have attracted the attention of researchers since long time ago, but among the different morphologies that can be found in literature, nanowires (NWs) related ones present the ad- vantages of superior material quality together with an impressive design freedom. These are the characteristics that make NWs structures ready for pushing advancements in materials engineer- ing and fundamental science. NWs represent a novel material category moving from conventional 2-dimensional films to 3- dimensional devices. The ability to control material composition at a nanometric level is extremely relevant, especially for semiconducting materials. As different bandgap semiconductors are aligned, heterostructures (HSs) are formed and, due to the internal electric fields produced, carriers are displaced and localized [1]. In the specific case of NWs, there are several peculiarities and interesting possibilities that arise, as 3-dimensional HS can be prepared. Starting from a NW, a second nucleation can be achieved on the NW external surface resulting in hierarchical or branched HSs, increasing the surface-to-volume ratio that is critical for some applications such as catalysts, chemical, gas, or biosensors [2], and may be exploited also for electronic devices [3]. Moreover, lattice matching for having epitaxy is not a big constrain in NWs because the eventual strain can relax easily over an interface of few nanometers (as in the case of axial structures) [4]. Normally, the strain due to lattice mismatch combining two different constituents in NWs may relax elastically at the interface with no dislocations. Therefore, there is the capability to achieve HSs without looking for lattice matching, concentrating on the bandgap engineering [5e11]. In addition, in NW HSs, in the even- tual case dislocations arise, they are misfit dislocations [12]. As we prepare HSs with NWs, the doping profile can be controlled on a 3-dimensional level; not only linear HSs but also radial ones can be easily achieved forming junctions [13e15]. In addition, NW HSs decoration with nanocluster or quantum dots is another frequently used possibility to change the material functional properties increasing specificities and tailoring real ap- plications requirements [16]. All these capabilities to integrate different compounds, with no need of lattice matching, may really be used for bandgaps engineering to achieve superior devices performances. Bandgap engineering is an essential property especially for semiconductors. Furthermore, the manifold possibilities and freedom in designing the shape and morphology allowed with NWs can open new and innovative ma- terial combinations and configurations. When we are dealing with NWs, we can exploit also their exceptional flexibility. NWs can bear large mechanical E-mail address: Elisabetta.comini@unibs.it. Contents lists available at ScienceDirect Materials Today Advances journal homepage: www.journals.elsevier.com/materials-today-advances/ https://doi.org/10.1016/j.mtadv.2020.100099 2590-0498/© 2020 The Author. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Materials Today Advances 7 (2020) 100099