Gas-phase biosensors: A review

In this review, we describe advances in biosensors and bioimaging techniques for gas-phase biochemical molecules. These techniques exploit the high specificity of biorecognition elements for the selective sensing of volatile biochemicals. The review begins with a discussion of gas-phase biosensors using enzymes as recognition elements, in which redox reactions of volatile biochemicals provide detectable products such as fluorescent molecules. Then, biosensors using other biorecognition elements, including antibodies, molecularly imprinted polymers, olfactory receptors, and cells, are introduced. Combinations of these elements with optical, electrochemical, and acoustic wave transducers are also described. A unique and powerful feature of biosensors is that they are little influenced by humidity because biorecognition elements are used in the liquid phase. This notable advantage makes it possible for biosensors to measure volatile biochemicals in the breath and other humid environments. We also discuss progress in capturing the spatiotemporal distribution of volatile biochemicals with improved continuity and the use of imaging technologies. These new technologies are expected to be utilized for determining the relationship between spatiotemporal changes in volatile biochemicals in the breath or skin gas and health, which has not been explored, and for high-precision monitoring of volatile biochemicals in the environment.