The partial pressure of arterial carbon dioxide plays a critical role in assessing the acid-base and respiratory status of the human body. Typically, this measurement is invasive and can only be taken momentarily when an arterial blood sample is drawn. Transcutaneous monitoring is a noninvasive surrogate method that provides a continuous measure of arterial carbon dioxide. Unfortunately, current technology is limited to bedside instruments mainly used in intensive care units.

Here, in the ICAS Lab, we work on designing miniaturized transcutaneous carbon dioxide monitors, which will overcome the drawbacks of conventional monitors, and we develop first-of-its-kind miniaturized transcutaneous carbon dioxide monitors that are based on CO2-sensitive luminescent films [1], [2], [3].

To improve the accuracy of our measurements, we employ a method called time-domain dual lifetime referencing (t-DLR). This technique is superior to the intensity-based method commonly used with luminescence, as it reduces measurement errors caused by variations in excitation strength. With t-DLR, the maximum error is reduced from approximately 40% to around 3%, resulting in more reliable readings. We have successfully tested a discrete prototype of our miniaturized transcutaneous carbon dioxide monitor in the form of a wearable wristband on human skin, thus proving the feasibility of the t-DLR-based approach. Our current focus is on designing an integrated circuit to implement the t-DLR technique on a chip.

[1] T. B. Tufan and U. Guler, “A Fluorescent Thin Film-Based Miniaturized Transcutaneous Carbon Dioxide Monitor,” IEEE Biomedical Circuits and Systems Conference, BioCAS’21, Oct. 2021, pp. 1-5.
[2] T. B. Tufan and U. Guler, “A Miniaturized Transcutaneous Carbon Dioxide Monitor Based on Dual Lifetime Referencing,” 2022 IEEE Biomedical Circuits and Systems Conference (BioCAS), 2022, pp. 144-148
[3] T.B. Tufan and U. Guler, “A Transcutaneous Carbon Dioxide Monitor Based on Time-Domain Dual Lifetime Referencing,” IEEE Transactions on Biomedical Circuits and Systems (TBioCAS), Early Access, May 2023