Portable measurement system for breath analysis by real-time fluctuation enhanced sensing method

Abstract

Resistance flicker noise of gas sensors gives a new opportunity to improve gas detection by enhancing selectivity and sensitivity of cheap and popular gas sensors. The improvement at low gas concentrations can be even increased further by UV light irradiating the gas sensing layers exhibiting photocatalytic effect (e.g., WO 3 or TiO 2 gas sensing layers). A new system has been developed recently to utilize low frequency noise measurement method but controlling a set of sensors applied for breath analysis and medical check-up. The system measures DC resistance and resistance noise in an array of four prototype resistive gas sensors. An operating temperature of each sensor can be set independently by the software controlling the system. Some sensors can be irradiated by the UV light as well. Humidity, temperature and pressure within a miniature gas chamber, of a volume about 40 ml, is monitored to secure repeatable conditions during the measurements and to avoid humidity condensation in the exhaled breath. The setup is controlled by an FPGA circuit performing necessary computations (power spectrum density estimation) and data transmission. Further processing by applying selected detection or gas concentration estimation methods can be done by a smartphone or a PC controlling the measurement setup. The system was prepared for fast and non-invasive medical diagnosis of patients suffering from tropical diseases.