Conformable Sensors for Healthcare and Environmental Sensing Applications
Creators: name: Elango, Peter Francis Mathew
Publisher: name: RMIT University
Year: 2025
Subjects: classificationCode: 401804
subject: Nanoelectronics
classificationCode: 401605
subject: Functional materials

description: With quantum leaps in technology in the electronics sector, demand for the miniaturisation of devices while retaining their functionality is on the increase. Such miniaturized sensors, with the ability to be skin-conformable, offers the potential to monitor healthcare and environmental parameters. Environmental parameters such as temperature changes that need to be continuously and accurately monitored requires a highly sensitive material that can accurately detect these changes and also take humidity fluctuations into consideration. Metal oxide-based thermal sensors are desired, owing to their enhanced sensing capabilities and low cost of operation. Highly sensitive metal oxide sensors can enable stable, accurate and miniaturised thermal sensors tailored to different operational ranges. The biggest challenges the healthcare sector faces include the growing workload on healthcare professionals, escalating costs, and lack of continuous medical data. To address these challenges, wearable sensors capable of point-of-care diagnostics are the need of the hour. Unlike their rigid counterparts, which are clunky and predominantly used as non-invasive platforms, conformable sensors facilitate a closer and more intimate anatomical contact between the sensing platform and the human body. By integrating with wireless communication capabilities, continuous monitoring of biometric data and environmental parameters is achievable. The adoption of such conformable sensing devices holds significant potential for revolutionizing monitoring of environmental parameters and healthcare practices by addressing the challenges posed by increasing workloads and rising costs. This work is comprised of three components. In the first part, a vanadium dioxide (VO2)-based thin film thermal sensor was developed and studied under the influence of varying humidity conditions. The effect of different humidity levels on the overall thermal sensing behaviour and the insulator-to-metal transition (IMT) phenomenon was investigated. Further, density functional theory (DFT) studies were conducted to understand the thermal sensing mechanism under changing humidity conditions. The developed sensor exhibited a very good response over a broad temperature range of –100 oC to 100 oC, with a TCR of –0.00243%, high sensitivity and cyclic repeatability. Wireless measurement capabilities were also demonstrated. Such sensors could potentially be used in environmental and wearable sensing applications. The second part focuses on developing a compact and wearable ECG monitor. Among the various biophysical parameters that are of interest in a wearable device, an electrocardiogram (ECG) is critical as it enables detection of cardiovascular-related ailments and assessment of overall cardiac health. In a wearable ECG device, the choice of electrode design and material plays a key role in the performance of the sensor. Various dry electrode-based sensor design geometries have been explored to realise a compact, lightweight, portable, gel-free wearable ECG patch that would aid in point-of-care (PoC) diagnostics. Further, the influence of the region of the body at which the measurements were made was studied under different body positions across varying external stimuli. The influence of surface area, perimeter and resistance offered by the electrodes on the ECG signal acquisition, its effects on device performance were investigated and it was concluded that the hexagonal labyrinth configuration was the most suitable candidate. A prototype of a wearable ECG patch was made by combining this electrode configuration and interfacing it with wireless communication capabilities, and the results were compared with commercially available portable ECG monitor. Such a device could find potential application in remote healthcare and ambulatory care settings, and as a PoC and a preventive medical device. Finally, the third part focuses on developing a wearable cutaneous wound healing monitor, specifically for monitoring the wound healing progression in chronic wounds. A unique approach employing a multiplexed combination of SMD temperature sensors, thin-pH sensors, and conductometric biosensors employing highly resistive Silicon (HR-Si) technology to monitor proteins key to wound healing indication such as C-reactive protein and Interleukin-6 concentrations was developed to monitor the progression (or lack thereof) of chronic wound healing. This helps to monitor the various phases of wound healing such as haemostasis, inflammation, proliferation, and remodelling. Normal skin and healed wounds typically have temperature between 31.10 oC – 35.40 oC. Wounded skin when healing has a temperature between 36.0 oC – 38.0 oC. Any temperature &gt;38.0 oC is critical and might lead to amputation. Healthy skin has a pH &lt;5. Normal wounds have a pH &lt;7, and a pH &gt;7 would indicate the presence of a chronic wound. A CRP concentration of &lt;40 nM indicates the wound is healing, and if this value moves &gt;40 nM, this is a sure sign that chronic wound infection is getting worse. Similarly, an IL-6 concentration of &lt;45 nM is indication of wound healing, and &gt;45 nM indicates that the wound is getting adverse. By using a triangulated approach of combining miniaturized temperature, pH, CRP, and IL-6 sensors, accurate and continuous monitoring wound healing at the site of inspection is possible. This developed sensor was found to efficiently monitor the changes in these biophysical parameters and the protein biomarkers under ideal conditions and also under the influence of fluctuating temperature. Further, this cutaneous wound healing monitor was enabled with wireless NFC capabilities which helps in its application as a PoC diagnostic device. The findings related to these studies is expected to potentially lead to the development of an entire system of sensors for monitoring healthcare and environmental parameters.