Noninvasive, Ultrathin, Flexible Microneedle Electrodes for Accurate and Long-Term Biopotential Monitoring

The escalating demand for wearable electrodes in the era of digital healthcare underscores the urgent need for more efficient and accurate biopotential monitoring techniques. Here, we report a scalable and facile approach to the fabrication of microneedle electrodes (MNEs) for accurate and imperceptible biopotential monitoring, leveraging a unique micro/nanoelectroforming technique. We exploited magnetron sputtering of indium tin oxide on an inverse-microneedle mold and subsequent electrodeposition of metal layers to produce ultrathin, flexible, and highly conductive MNEs. These MNEs outperformed the planar metal electrodes and commercial silver/silver chloride gel electrodes. The microstructured surface of MNEs increases the contact area and bypasses sweat and grease on uneven skin surfaces, leading to lower electrode-skin interface impedance. This innovative design enhances the signal-to-noise ratio, enabling more accurate and noninvasive detection of electrophysiological signals, such as electromyograms and electrocardiograms. In addition, the MNEs exhibited superior mechano-electrical stability, biocompatibility, and comfort, making them suitable for long-term healthcare monitoring and human-robot interactions. This work illuminates a pathway toward more reliable and adaptable biopotential monitoring technologies.