SU-8 microneedles based dry electrodes for Electroencephalogram

• Very simple technique (low cost) for microneedle electrode fabrication
• Flexible approach
• Dry microneedle electrode measurements
• Lower resistivity from commercial ones
• Potential as chemical sensor for simultaneous recordings (EEG, O2 pH)

This work demonstrates a novel, simple method for the fabrication of dry Electroencephalogram (EEG) electrodes consisting of arrays of SU8 based microneedles. EEG electrodes fabricated this way will significantly reduce the duration and complexity of the mounting procedure as they eliminate the need for skin preparation and the application of conductive paste. Arrays of polymer based microneedles were designed and then realized using a simple, low cost photolithographic technique. The polymer used for the microneedle fabrication is epoxy based SU-8 and the microneedle array is formed on a glass carrier. A single, “back-side” photolithographic exposure is applied for the formation of sharp and appropriately-sloped microneedles. The resulting needles are cone-shaped and 500 μm in height with a base of 100 μm in diameter and a tip smaller than 30 μm. The microneedles are subsequently covered conformally with a thin film of biocompatible metal (Ag) rendering them suitable for human skin penetration. In addition, human skin penetration did not compromise the mechanical integrity of the microneedles. Initial electrical characterization results from a trial on a healthy human show that the fabricated electrodes provide excellent EEG signal strength presenting low resistivity contact.

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