New miniaturized exhaled nitric oxide sensor based on a high Q/V mid-infrared 1D photonic crystal cavity

A high Q/V mid-infrared 1D photonic crystal cavity in chalcogenide glass AMTIR-1 (Ge₃₃As₁₂Se₅₅) resonating at λ_R=5.26  μm has been proposed as a key element of a sensor able to evaluate the nitric oxide (NO) concentration in the exhaled breath, namely fraction exhaled NO. The cavity design has been carried out through 3D finite-element method simulations. A Q-factor of 1.1×10⁴ and a mode volume V=0.8  (λ/n)³, corresponding to a Q/V ratio of 1.4×10⁴(λ/n)^-3, have been obtained with a resonance transmission coefficient T=15%. A sensitivity of 10 ppb has been calculated with reference to the photothermal physical property of the material. Such a result is lower than the state-of-the-art of NO sensors proposed in literature, where hundreds of parts per trillion-level detection seem to have been achieved, but comparable with the performance obtained by commercial devices. The main advantages of the new device are in terms of footprint (=150  μm²), smaller at least 1 order of magnitude than those in literature, fast response time (only few seconds), and potential low cost. Such properties make possible in a handheld device the sensor integration in a multi-analysis system for detecting the presence of several trace gases, improving prevention, and reducing the duration of drug treatment for asthma and viral infections.