Optical chemical gas sensor based on spectral autocorrelation: A method for online detection of nitric oxide and ammonia in exhaled breath

Abstract

The detection of nitric oxide (NO) and ammonia (NH₃) in exhaled breath (EB) plays a crucial role in non-invasive diagnosis of airway inflammatory and kidney diseases. Here we report an optical chemical gas sensor for NO and NH₃ based on spectral autocorrelation. In our sensor system, the target gas is removed through a chemical reaction with a sensing material and the spectrum of the target gas is extracted from the spectra obtained before and after the reaction by autocorrelation. Our method focuses on the ability of the material to eliminate the target gas without the need for detecting signals of the reaction, greatly relaxing the requirements on material properties. Fundamentally different from optical sensors that obtain spectra by spectral decoupling, our sensor relies on autocorrelation operation to acquire the spectrum of the target gas, thereby overcoming spectra overlap. Lab-based results show that the sensor enables detection of NO (2.28–451.82 ppb) and NH₃ (11.52–12,725.42 ppb) with mean absolute errors (MAEs) of 0.79 ppb and 6.13 ppb and measurement accuracies of 0.8 % and 1.4 %, respectively. The EB experiment proves that the sensor can detect exhaled NO and NH₃ and distinguish EB between healthy subjects and simulated patients.