Wearable transcutaneous oxygen sensor for health monitoring

Abstract We present a wearable bandage-like photoluminescence (PL)-based transcutaneous oxygen (tcpO2) sensor consisting of a photoluminescent oxygen (O2)-sensing film, a polyvinylidene chloride (PVDC) film as an encapsulation layer, an indium tin oxide (ITO) thin-film heater, an array of micro-light-emitting diodes (μ-LED) as a light source, red cellophane paper as an optical filter, an organic photodiode (OPD) as a PL detector, and an optical isolation layer. All the components of the tcpO2 sensor were designed to be flexible and thus can be attached anywhere on the curved skin of the human body. The PVDC film with excellent O2 barrier properties and visible light transmittance was a significant additional component of the wearable sensor that improved the sensitivity of the photoluminescent O2-sensing film by minimizing the PL quenching effects of ambient atmospheric O2. Furthermore, the ITO thin-film heater increases the skin temperature, changing the structure of the stratum corneum and allowing O2 to more effectively diffuse from the skin toward the tcpO2 sensor. Therefore, the thin-film heater allows the accurate measurement of the tcpO2 variation from human skin to facilitate the determination of the severity of O2-deficiency related diseases in the tcpO2 range from 0 to 80 mmHg. The μ-LED array embedded into a polydimethylsiloxane (PDMS) film not only maintained its mechanical flexibility but also had stable light emission performance under ambient air conditions, allowing tcpO2 measurements over several cycles for as long as 60 min, which we could not previously achieve with ambient air-unstable flexible organic light-emitting diodes (f-OLEDs). The effects of the heat from the ITO thin-film heater and the skin color of the sensor user on the PL emitted by the sensing film and detected by the OPD were factored out from the tcpO2 measurements by defining two correction coefficients. The performance of the wearable tcpO2 sensor was tested using the leg elevation protocol to induce tcpO2 variation at the skin of the ankles of test volunteers. According to the experimental results, the sensing performance of our wearable bandage-like PL-based tcpO2 sensor proved to be superior to that of a commercially available tcpO2 sensor, as our wearable PL-based tcpO2 sensor demonstrated faster response times to tcpO2 variation and smaller measurement deviations between tcpO2 detection cycles.