Ammonia measurement in exhaled human breath using PCF sensor for medical applications

Diagnosis of diseases through exhalation is a new, noninvasive method. In this study, a new photonic crystal fiber (PCF) has been proposed for detecting ammonia gas in breath. The spectroscopy system contains a tunable laser source, a monochromator that sets the wavelength at the absorption line of ammonia gas, a PCF used as a cell gas, a detector, and a computer to monitor and show the results. The gas sensing attributes of photonic crystal fiber are analyzed through the Finite Element Method (FEM). According to the simulated result, the high relative sensitivity of 63.18% is obtained when the core is filled by ammonia gas at 1.544 mu m wavelength. The effect of water vapor on ammonia gas is investigated. It is shown that with the addition of respiratory moisture, the sensor still has high sensitivity and less confinement loss. Therefore, it is almost insensitive to moisture. These results illustrate the high performance of the sensor designed and that it can be helpful for medical applications, especially in diagnosing renal failure.