In a recent article submitted to the arXiv* preprint server, researchers have developed an imperceptible sweat sensor utilizing Ultra-High-Molecular-Weight Polyethylene (UHMWPE) nanomembranes.
This sensor represents a significant advancement in epidermal electronics for real-time monitoring of vital health signals. This technology offers comfortable and accurate monitoring capabilities, addressing the need for non-invasive health assessment tools.
Study: Breakthrough Sweat Sensor for Non-Invasive Health Monitoring. Image Credit: muse studio/Shutterstock.com
Background
Epidermal electronics have evolved to prioritize conformability and permeability, aiming to seamlessly integrate with the skin's surface while allowing the passage of necessary substances.
Traditional devices focused on physical activity monitoring face challenges in effectively capturing chemical information from sweat. Understanding the bio-electronic interface and mass transport processes within permeable systems is crucial for maximizing biomarker sensitivity and ensuring the skin's natural functions are not compromised.
The Current Study
The UHMWPE nanomembrane used in this study was prepared using a patented method developed by the research group. The membrane exhibited a thickness of 300 nm, providing full customization to the skin and enabling easy detachment for biomarker analysis post-sweat collection.
Scanning electron microscopy (SEM) was utilized to study the surface structure of the membranes. To minimize the charging effect, samples were coated with Platinum.
Fourier-transform infrared spectrometry (FTIR), Raman spectrometry, and X-ray photoelectron spectroscopy (XPS) were conducted to gain insights into the chemical structure of the membranes.
The conductivity of the UHMWPE nanomembrane was measured using a Resistivity measurement system. This allowed for the assessment of the material's electrical properties, which are crucial for the sensor's functioning in detecting biomarkers such as cortisol in sweat samples.
The air permeability of the membrane was evaluated using an air permeability tester. This test provided information on the membrane's ability to allow the passage of air, which is essential for maintaining skin breathability and comfort during sensor wear.
The composition of solutions used in the study was analyzed using high-performance liquid chromatography (HPLC) and ion chromatography (IC) instruments. These analyses helped ensure the accuracy and consistency of the solutions employed in the synthesis and functionalization processes of the UHMWPE nanomembrane.
Sweat samples were collected using the Macroduct sweat collection system. This system facilitated the noninvasive and efficient collection of sweat for subsequent analysis and biomarker detection. The collected sweat samples were crucial for evaluating the sensor's performance detecting cortisol concentrations within the desired range.
Results and Discussion
The UHMWPE nanomembrane exhibited a pseudo-skin-like structure with interconnected nanopores, enabling efficient transport of sweat and biomarkers. SEM imaging revealed the membrane's nanofibrous morphology, highlighting its high porosity and thinness.
The presence of nanopores within the membrane was crucial for creating pseudo-skin-like channels that facilitated the infusion of sweat extrudates, mimicking natural skin functions.
FTIR and Raman spectroscopy confirmed the successful synthesis and functionalization of the UHMWPE nanomembrane with MIP nanoparticles. Characteristic peaks corresponding to functional groups in the MIP@UHMWPE composite membrane indicated the successful incorporation of molecularly imprinted polymers.
XPS analysis provided further insights into the membrane's elemental composition and surface chemistry, validating the presence of the desired functional groups for selective biomarker binding.
Conductivity measurements demonstrated the electrical properties of the UHMWPE nanomembrane, which is essential for the sensor's functioning as an organic electrochemical transistor (OECT). The membrane exhibited suitable conductivity for detecting and transducing signals related to sweat biomarkers.
Air permeability testing confirmed the membrane's ability to allow air passage, ensuring skin breathability and comfort during sensor wear, which is crucial for long-term monitoring applications.
The sensor's capability to detect cortisol concentrations ranging from 0.05 to 0.5 μM was validated using sweat samples collected with the Macroduct system. The selective absorption and conductivity of the MIP@UHMWPE composite membrane enabled accurate and sensitive detection of cortisol levels in sweat, demonstrating the sensor's potential for stress monitoring applications.
The interpenetrating bio-electronic interface formed by the UHMWPE nanomembrane ensured seamless integration with the skin, preserving the skin's natural functions, and minimizing impedance.
The sensor's imperceptible and biocompatible characteristics make it suitable for continuous and noninvasive health monitoring, offering a promising solution for personalized healthcare applications.
Conclusion
The imperceptible sweat sensor based on UHMWPE nanomembranes offers a promising solution for continuous and noninvasive monitoring of vital health signals.
By leveraging the nanomembrane's unique properties, this technology has the potential to revolutionize personalized health assessment and wearable sensor applications.
Journal Reference
Feng Y., Oktavius A.K., et al. (2024). Invisible sweat sensor: ultrathin membrane mimics skin for stress monitoring. arXiv*, 2407, 07400. DOI: 10.48550/arXiv.2407.07400, https://arxiv.org/abs/2407.07400
*Important notice: arxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive or treated as established information.