Metal Oxide Nanostructures in Electronic Nose: Recent Advances

The inherent non-stoichiometry and ability to tailor or tune the electronic properties of the metal oxides makes them an ideal candidate for gas sensing applications. Additionally, the ease with which they can be synthesised into different nanoforms, controllable aspect ratio and position on the substrates pave the way to achieve multiple sensors in a smaller area. This is particularly important to design multiple sensors for e-nose (EN) application. For EN, use of multiple sensors with partial specificity to different analytes is required so as to improve the capability of discrimination between target gases. Both qualitative and quantitative information of the target analytes can be successfully achieved by employing numerous sensors and suitable pattern recognition algorithm. Unlike human nose, an EN cannot be used for all the applications. They are designed for a particular or at the most two applications. Herein, the detection methods like chemiresistive, electrochemical, and optical methods play an important role. The present chapter discusses and critically reviews the recent advances in the field of EN realised using different metal oxide nanostructures. Different advantages and limitations arising owing to use of metal oxide nanostructures are elaborated taking help of literature and some of our recent findings. Besides, the role of different nano-morphologies, and surface modification and doping techniques in improving the specificity and sensitivity thereby the performance of EN has been extensively reviewed. Also, recent findings with potential for commercial deployment and those already in the market are also discussed in terms of overcoming the valley-of-death syndrome. Finally, some of the daunting challenges that need to be addressed to realise the commercial product from the laboratory investigations are discussed extensively.