Graphene-based tunable plasmonic metamaterials for nitric oxide in breath-sensing application

Research has shown that breath exhaled from human lungs contains hundreds of volatile organic compounds (VOCs), from which illnesses and physical phenomena of organ systems can be detected. We can use exhaled nitric oxide (ENO) concentration to test whether a patient has a chronic obstructive pulmonary disease (COPD). One significant advantage of using exhaled breath to examine the existence of illness is that the examination is non-invasive, posing no extra risks to human bodies. In the past two decades, some studies applied electronic sensors in detecting the concentration of nitric oxide, and the sensors needed to operate at high temperatures. However, few studies are about optical detection with a measuring range from ultraviolet to visible light, and the range could cause harm to human skin. In this paper, we used tunable metamaterial to build a split-ring resonator (SRR) that resonates in the region of terahertz (THz) frequency. The resonant peak was designed to appear at 0.250 THz, which is the resonant peak of nitric oxide. In order to increase the total volume of gas adsorption, we laid a compound layer that consisted of a layer of zinc titanium oxide and a layer of graphene on the metamaterial's surface to enhance the sensitivity (ΔT/Δn) of the component from 2% to 12.6%. We hope to develop the research result into a component that monitors and examines the physical conditions of human bodies and expect to apply the component in the development of wearable electronic components.