Scaling Effects on the Electrochemical Performance of poly(3,4‐ethylenedioxythiophene (PEDOT), Au, and Pt for Electrocorticography Recording

Abstract

Reduced contact size would permit higher resolution cortical recordings, but the effects of diameter on crucial recording and stimulation properties are poorly understood. Here, the first systematic study of scaling effects on the electrochemical properties of metallic Pt and Au and organic poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes is presented. PEDOT:PSS exhibits better faradaic charge transfer and capacitive charge coupling than metal electrodes, and these characteristics lead to improved electrochemical performance and reduced noise at smaller electrode diameters. PEDOT:PSS coating reduces the impedances of metallic electrodes by up to 18x for diameters <200 µm, but has no effect for millimeter scale contacts due to the dominance of series resistances. Therefore, the performance gains are especially significant at smaller diameters and lower frequencies essential for recording cognitive and pathological activities. Additionally, the overall reduced noise of the PEDOT:PSS electrodes enables a lower noise floor for recording action potentials. These results permit quantitative optimization of contact material and diameter for different electrocorticography applications.

Selective Formation of Porous Pt Nanorods for Highly Electrochemically Efficient Neural Electrode Interfaces

“…The low impedance of PtNR microelectrodes across frequencies is essential for the high fidelity recording of a broad range of brain activity such as local field potentials (ranging from ~0 to 300 Hz) to single and multiunit activity >300 Hz. 25 It has also become increasingly important to be able to use microelectrodes to modulate neural activity. 26 Stimulation capability is assessed by the charge injection capacity (CIC), the maximum amount of charge that can be injected through the electrode prior to building a potential across the electrode/ electrolyte interface that can cause water hydrolysis ( Figure 2e).…”

A Scalable and Low Stress Post-CMOS Processing Technique for Implantable Microsensors

“…Since PEDOT:PSS offers biocompatible interfaces between electrode and biological tissue and improves the efficiency of stimulation current delivery due to its low contact impedance, it has emerged as one of the promising electrically conductive polymers to be used as microelectrode material [ 19 , 20 , 21 , 22 , 23 , 24 ]. For our impedance measurement, we fabricated 70 μm square Au and PEDOT:PSS-coated Au electrodes with extended structures, including additional pads on the chip surface.…”

“…In a CMOS process, aluminum that is often used as a top metal is oxidized over time, which can disrupt the electrical interface with biological tissue, as one example [ 8 , 9 ]. For this problem, stable and biocompatible alternative materials such as gold (Au), platinum–iridium alloy, and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) are attractive to provide long-term reliability of the electrode–tissue interface and electrode–electrolyte impedance optimization [ 19 , 20 , 21 , 22 , 23 , 24 ]. One post-CMOS strategy has made use of the sacrificial carrier substrate accompanying the bare die that holds the individual microdevices, using deep-etched silicon, silicon oxide substrate [ 25 , 26 , 27 ], or rigid polymer [ 5 , 6 , 28 , 29 , 30 ].…”

Advanced Electrical and Optical Microsystems for Biointerfacing

“…[ 75 ] PEDOT:PSS‐coated gold and platinum microelectrodes exhibit impedance values <100 kΩ at 1 kHz, which is one order of magnitude smaller than pristine platinum and gold microelectrodes, respectively (Figure 1h). [ 76 ] In addition, conductive polymers can act as a mediator at the interface to mitigate the mechanical mismatch and reduce the foreign‐body responses. [ 77 ]…”