A miniaturized photodiode-based chemiluminescence sensor for measurement of fractional exhaled nitric oxide

Abstract

Fractional exhaled nitric oxide (FENO) measurement is a valuable tool in diagnosing and monitoring certain respiratory diseases, low cost and miniaturized NO sensor is highly demanded for FENO home healthcare self-monitoring. In this work, a miniature photodiode-based chemiluminescence sensor is presented for the sensitive measurement of NO concentration. Effects of various reflective film materials including stainless-steel, aluminum and silver for coating the inner surface of the optical cell were investigated for higher photon collection efficiency, and the silver reflective film displayed the best sensitivity. As the oxidation and pollution of silver film led to dramatical decay of signal, a quartz inner chamber with reflectance film layer coated on its outer surface was developed to achieve high stability and sensitivity simultaneously. The limit of detection for FENO was 6.6 ppb, the linear range of 10–100 ppb with a response time of 6.8 s was reached, which was satisfied the requirements for FENO measurement. The weight of the sensor is 96 g with a size of only 6.5 × 3 × 2 cm3, and the cost is estimated less than $1 K, which is suit for on-site monitoring of FENO. FENO50 was obtained the response difference of room air and breath air measured successively with a switching valve, the beath air was sampled into a bag at flow rate of 50 ml/s by offline sampling device, and multiple measurements were executed for better accuracy. The potential usage of the sensor was further illustrated by studying the FENO50 levels of individuals before and after consuming nitrate-rich sports drinks.