Waveguide-Based Microwave Nitric Oxide Sensor for COVID-19 Screening: Mass Transfer Modulation Effect on Hollow Confined WO3 Structures

Serious acute respiratory syndrome coronavirus-2 (SARS-CoV-2) poses a tremendous threat to global public health. Recently, the Food and Drug Administration approved the emergency use of volatile organic components as detection biomarkers for COVID-19, ushering in a new era of portable, simple, and rapid epidemiological screening based on breath diagnosis. Nitric oxide (NO) is an important biomarker indicating the degree of inflammation in the respiratory tract. In this study, a hollow multishelled structured WO₃ (HoMSs-WO₃)-based waveguide microwave gas sensor (MGS) was fabricated to detect trace levels of NO in exhaled breath for the preliminary diagnosis of COVID-19. The sensor showed excellent reusability and selectivity and efficiently detected NO in the 10–100 ppb, with a sensitivity of 39.27 dB/ppm and a detection limit of 2.52 ppb. In addition, a sound correlation was observed in the measurement results between the MGS and the Sunvou detector for detecting NO from the exhaled breath of clinical COVID-19 patients. The difference between the two measurements was within 1.96 standard bias, and the consistency range was −12 to 17 ppb, thus fully demonstrating the significant potential of the sensor in COVID-19 screening.