Magnetic resonance identification tags for ultra-flexible electrodes

Abstract Ultra-flexible electrodes, due to their superior biocompatibility, are likely to lead the future of neuroprosthetics. However, identifying the locations of high-density ultra-flexible electrodes in the brain for accurately assigning neural signals to specific structures remains a major challenge. To address this, we developed magnetic resonance identification (MRID) -tags. Each ultra-flexible electrode bundle carries an MRID-tag with unique barcode patterns visible in MRI (MRI-barcodes) for identification of the bundle and the anatomical positions of individual electrodes. We generate the MRI-barcodes by patterning superparamagnetic iron-oxide nanoparticles into electrode fibers (10µm 2 ) with dot-matrix nanoparticle coating technique. We chronically tested MRID-tagged ultra-flexible electrodes in vivo in the dorsal hippocampus of freely-moving rats, where distinct electrophysiological landmarks validated our electrode localization results. We were able to localize individual electrodes with a mean accuracy of 83 µm. MRID-tagged ultra-flexible electrodes demonstrated months-long recording stability with mean single-unit signal-to-noise ratios as high as 20.