Metal oxide nanowires for chemiresistive gas sensors: Issues, challenges and prospects

In recent years, significant interest has emerged in the synthesis of nanoscale materials owing to their superior and enhanced functional properties. And metal oxides based nanostructures are considered to be the most attractive class of materials for realizing functional nanodevices. Of the various nanostructures, nanowires (NWs) are particularly useful for gas sensing application as they offer various advantages. These includes high surface area-to-volume ratio, pathway for electron transfer (length of NWs), enhanced and tunable surface reactivity implying possible room temperature operation, faster response and recovery time, dimensions comparable to the extension of the surface charge region, relatively simple preparation methods allowing large-scale production, convenient to use, ease of fabrication and manipulation, high integration density, smaller size and low power consumption. All the above mentioned features definitely make NWs a promising candidate for nanosensors. The present review deals with the progress made toward the effective use of NWs in particular metal oxide based for achieving superior sensing performance. The promising approaches contributing toward the further development of this field have been discussed and elaborated. Various issues related to successful utilization of NWs for commercial sensor application is discussed citing examples from the literature. In particular, different sensor configurations like single-NW based, multiple-NW based, NW films/as-grown NWs films have been critically addressed. The important steps taken toward commercialization of ultimate sensor device and the major obstacles involved are also discussed.