Measurement of Exhaled Ammonia Based on Mid-Infrared EC-QCL and Flexible Hollow Waveguide: A New Idea for Early Diagnosis of Nephropathy

A high-resolution spectroscopic sensor system based on wavelength modulation spectroscopy was proposed for exhaled ammonia detection, aiming to explore its feasibility for kidney dis-ease diagnosis. A mirrorless, flexible hollow waveguide with a sam-ple volume of 8.8 mL was selected as the gas cell, effectively ad-dressing the issues of long response time and large gas sample vol-ume seen in traditional gas cells. A mid-infrared external cavity quantum cascade laser (EC-QCL) was used, targeting the NH<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ab-sorption line around 1046.4 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup>. The system achieved a detection limit of 1.30 ppb with an optimal averaging time of 79 s, and the average response time for gas detection was less than 1.5 s. The results showed that the system could effectively identify exhaled ammonia in kidney disease patients, demonstrating its reliability. This paves the way for further advancements in breath-based di-agnostic technologies for kidney disease.