Design of Low-Frequency Impedance Measurement Sensors for Respiratory Health

Real-time monitoring of environmental exposure causing chronic diseases including asthma and COPD has assumed enormous significance due to prolific advances in materials science and electronics. Such monitoring demands low-power electronic devices for signal conditioning and measurement to be integrated with state-of-the-art environmental sensors. Ozone is a known trigger of asthma causing significant health burden worldwide. In this paper, sensitive detectors based on functionalized (i.e. high specificity) single-walled carbon nanotubes are designed to measure ambient ozone exposure. The electronic interface comprises low-power integration of the chemical sensor with a commercial device to measure the complex (sensor) impedance at a frequency between 40 kHz and 1 MHz. Simultaneous measurement of magnitude and phase on several ozone sensors reveal response change of 35% in the former and 80% in the latter, and a detection limit of only 10 ppb. This innovative chip-based impedance measurement technique has the potential for characterizing the personal exposure to ambient air pollution triggers of respiratory diseases.