Improvement of the performance of a photoacoustic transcutaneous CO2 sensor: optimization of response time and sensitivity

The development of a novel miniaturized photoacoustic transcutaneous carbon dioxide (CO2) sensor has marked a significant advancement in non-invasive monitoring of arterial CO2 levels in patients. This study focuses on optimizing the sensor performance by enhancing its response time and sensitivity. By optimizing the photoacoustic design, we achieved a reduction in reaction time after application on the skin (arterialization time tart) from tart ≈ 170 minutes to tart ≈ 7 minutes, enabling real-time monitoring. Reducing the sensor’s response time by decreasing the absorption-path diameter shortens gas-exchange time but also lowers the signal-to-noise-ratio (SNR), thereby increasing the limit of detection. Therefore, the sensitivity of the sensor was improved through the implementation of an Interband Cascade (IC) LED as a powerful light source, which enables more precise detection of CO2 concentrations in the transcutaneous environment. A novel setup of the photoacoustic detection chamber was developed and characterized, showing a clear trend towards optimization of the SNR through small geometric structures within the chamber. Experimental laboratory results demonstrate that the enhanced sensor improves the SNR by ≈ 35 dB compared to our state-of-the-art, achieving an SNR of nearly 105 dB when averaging over n = 10 measurement points. The combination of rapid response and high sensitivity make the photoacoustic sensor a promising tool for clinical applications, particularly in the management of respiratory conditions and monitoring of metabolic processes. The advancements pave the way for future research into the integration of this technology not only in clinical settings, but also smart personal health trackers, which could lead to better diagnoses through timely and accurate monitoring of CO2 levels.