Electronic nose based on metal oxide semiconductor sensors for medical diagnosis

As malignant diseases are responsible for high mortality rates invariably, there is presently a pressing need to develop innovative medical diagnostic techniques due to the limitations of current approaches, including non-invasiveness, inability to monitor real-time, and the associated high cost of the equipment. Specifically, breath analysis has received a great deal of attention over the past two decades. Volatile organic compounds (VOCs) in exhaled breath could reflect the metabolic and physiological processes of the human body. Thus the electronic nose (E-nose) which comprises an array of gas sensors, signal acquisition, a pre-processing unit, and a pattern recognition algorithm that mimics the human sense of smell, can diagnose illnesses by analyzing exhaled breath fingerprints accurately, showing their irreplaceable features of non-invasive, real-time monitoring, quick diagnosis, and low cost. By combining the advantages of metal oxide semiconductor (MOS) gas sensors (fast-responding, affordable, and highly sensitive), the preponderance of MOS E-nose is further enhanced. This article focuses on metal oxide semiconductor gas sensors for detecting volatile organic compounds. The sensing principle and modification methods of binary and ternary metal oxide sensing materials are reviewed. It also encompasses a review of the metal oxide semiconductor electronic nose for detecting cancer and respiratory diseases.