Bilayer Nanomesh Structures for Transparent Recording and Stimulating Microelectrodes

Abstract

Nanomeshed forms of metal have emerged as a promising biocompatible electrode material for future soft bioelectronics. However, metal/electrolyte interfaces are intrinsically capacitive, severely limiting their electrochemical performance, especially for scaled electrodes, which are essential for highresolution brain mapping. Here, an innovative bilayer nanomesh approach is demonstrated to address this limitation while preserving the nanomesh advantage. Electroplating low-impedance coatings on a gold nanomesh template achieves an impedance < 30 kΩ at 1 kHz and a charge injection limit of 1 mC cm −2 for 80 × 80 µm 2 microelectrodes, a 4.3× and 12.8× improvement over uncoated electrodes, respectively, while maintaining a transparency of ≈70% at 550 nm. Systematic characterization of transmittance, impedance, charge injection limits, cyclic charge injection, and light-induced artifacts reveal an encouraging performance of the bilayer nanomesh microelectrodes. The bilayer nanomesh approach presented here is expected to enable next-generation large-scale transparent bioelectronics with broad utility in biology.

Multifunctional Flexible Biointerfaces for Simultaneous Colocalized Optophysiology and Electrophysiology

“…The impedance shows a near‐precise inverted dependence on electrode site area, indicating a capacitive interface. [ 38,39 ] The phase response in Figure 3c indicates that the Au nanogrid electrodes are capacitive (between −60° and −80°) at physiologically relevant low frequencies (e.g., 10 Hz to 1 kHz) and become more resistive at higher frequencies, consistent with that of a solid Au electrode (Figure S5, Supporting Information).…”

“…The large n value (0.95) indicates that the Au nanogrid electrodes exhibit a double‐layer capacitive interface close to that of an ideal capacitor ( n = 1), similar to other reported metal electrodes. [ 30,38 ] The capacitive electrode/tissue interface is desired for electrophysiology studies since capacitive charge transfer minimizes chemical reactions at the interface, which will otherwise cause severe tissue damage especially for chronic operations. [ 41 ]…”

Transparent Graphene/PEDOT:PSS Microelectrodes for Electro‐ and Optophysiology

“…The conductive polymer poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has been used to produce low impedance microelectrodes by coating opaque materials such as gold, iridium oxide, and carbon fiber . Although PEDOT:PSS is widely used as a transparent electrode material in field effect transistors, organic light‐emitting diodes, and polymer solar cells, its transparency has not yet been exploited for electrophysiological use.…”

“…Although PEDOT:PSS is widely used as a transparent electrode material in field effect transistors, organic light‐emitting diodes, and polymer solar cells, its transparency has not yet been exploited for electrophysiological use. PEDOT:PSS‐coated gold nanomesh electrodes achieve moderate transparency >65% with specific impedance of 0.64 Ω cm 2 by nanostructuring . Until now, the promising combination of PEDOT:PSS with transparent graphene to produce low noise microelectrodes has not been examined.…”

Advanced Electrical and Optical Microsystems for Biointerfacing

“…Current transparent microelectrodes for electrophysiology include ITO, [ 235 ] graphene, [ 236,237 ] CNTs, [ 238 ] metallic NWs, [ 239 ] metal grids, [ 240 ] and their hybrid composites. [ 241,242 ] ITO exhibits excellent transparency across the visible spectrum (85–95%) and low sheet resistance (4–40 Ω sq −1 ). [ 243,244 ] It is the most widely used transparent conductive electrodes in optoelectronic devices, such as liquid crystal displays, [ 245,246 ] OLEDs, [ 247,248 ] and solar cells.…”