Micro Gas Analyzer Measurement of Nitric Oxide in Breath by Direct Wet Scrubbing and Fluorescence Detection

A novel method is proposed to measure NO in breath. Breath NO is a useful diagnostic measure for asthma patients. Due to the low water solubility of NO, existing wet chemical NO measurements are conducted on NO2 after removal of pre-existing NO2 and conversion of NO to NO2. In contrast, this study utilizes direct measurement of NO by wet chemistry. Gaseous NO was collected into an aqueous phase by a honeycomb-patterned microchannel scrubber and reacted with diaminofluorescein-2 (DAF-2). Fluorescence of the product was measured using a miniature detector, comprising a blue light-emitting diode (LED) and a photodiode. The response intensity was found to dramatically increase following addition of NO2 into the absorbing solution or air sample. By optimizing the conditions, the sensitivity obtained was sufficient to measure parts per billion by volume levels of NO continuously. The system was applied to real analysis of NO in breath, and the effect of coexisting compounds was investigated. The proposed system could successfully measure breath NO.