Development of an analytical chip for nitrogen monoxide detection using porous glass impregnated with 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl

Nitrogen monoxide (NO) is an important bio-regulatory molecule. NO presence in exhaled breath is a biomarker for an airway inflammation. Thus, measuring NO in the exhaled air is considered a noninvasive method for disease screening. In this study, we developed an analytical chip made of porous glass impregnated with 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (PTIO) for NO gas detection. The analytical chip had an absorption peaks at 338 and 567 nm, which decreased when exposed to NO, whereas the absorbance at 413 nm increased with an isosbestic point at 477 nm. It was found that there is a linear relationship between the logarithmic change in the absorbance at 338 nm and 567 nm and the cumulative NO concentration. Additionally, the spectrum of the analytical chip was affected by humidity. There was a linear relationship between the PTIO's molar absorption coefficient at 567 nm and the relative humidity. Therefore, the absorbance of PTIO can be corrected in order to take the effect of humidity into consideration. The working ranges of the analytical chip were between 0.15 and 3.7 ppm x h of cumulative NO concentration and at a relative humidity between 40% and 90%. We also measured NO in a small amount of air (1.8 L to mimic the actual exhaled air volume) and we were able to measure the NO concentration of 30 ppb for 24 h.