Nanostructured platinum grass enables superior impedance reduction for neural microelectrodes

Abstract

Micro-sized electrodes are essential for highly sensitive communication at the neural interface with superior spatial resolution. However, such small electrodes inevitably suffer from high electrical impedance and thus high levels of thermal noise deteriorating the signal to noise ratio. In order to overcome this problem, a nanostructured Pt-coating was introduced as add-on functionalization for impedance reduction of small electrodes. In comparison to platinum black deposition, all used chemicals in the deposition process are free from cytotoxic components. The grass-like nanostructure was found to reduce the impedance by almost two orders of magnitude compared to untreated samples which was lower than what could be achieved with conventional electrode coatings like IrOx or PEDOT. The realization of the Pt-grass coating is performed via a simple electrochemical process which can be applied to virtually any possible electrode type and accordingly shows potential as a universal impedance reduction strategy. Elution tests revealed non-toxicity of the Pt-grass and the coating was found to exhibit strong adhesion to the metallized substrate.

Electrodeposited PEDOT:Nafion Composite for Neural Recording and Stimulation

“…As shown in Figure e,f, negligible variation of the impedance was observed for both NAF and PSS after stimulation with respect to the initial state, confirming comparable stability when the materials were subjected to three million pulses of electrical stimulation stress under similar experimental conditions. It should be noted that the mechanical adhesion of PEDOT films can be significantly improved through the roughening of the underlying metal surface or, more efficiently, through the formation of covalent chemical bonds between the conductive film and the underlying surface …”

Attenuated Glial Reactivity on Topographically Functionalized Poly(3,4‐Ethylenedioxythiophene):P‐Toluene Sulfonate (PEDOT:PTS) Neuroelectrodes Fabricated by Microimprint Lithography

“…Topographical surface modification of the neural electrodes has shown promise in improving the electrochemical performance through high aspect ratio structures, increasing the active surface area of the electrodes . The electrochemical performance and the evaluation of the resulting effective‐active surface area of the functionalized microelectrodes were subsequently assessed.…”

“…From this perspective, the field of neuroelectrode engineering has encouraged the use of alternative electroactive materials over conventional metallic strategies such as gold and platinum as an approach to provide an electrochemical platform for the immobilization of biological molecules, or in order to promote physicomechanical mimicry through soft or topographically rough interfaces . Specifically, semiconducting polymers, including polypyrrole and poly(3,4‐ethylenedioxythiophene) (PEDOT), and their hybrids have been employed widely in neural engineering because of their versatility as electrode coatings through electrodeposition processes, and have been employed to enhance the neuroelectrode electrochemical profile, and provide a platform for chemical and morphological functionalization to meet particular requirements …”

Wafer‐Scale Fabrication of Conducting Polymer Hydrogels for Microelectrodes and Flexible Bioelectronics

“…These values are substantially higher than the charge injection limits of 50–150 µC cm − 2 per phase as is reported for standard Pt electrodes at a pulse width of 200 µs . In contrast, for sputtered IrO x (SIROF) films, charge injection limits of 1–5 mC cm − 2 were reported . Although the PDMAAp/PEDOT may not substantially improve the CIC of IrO x electrodes, it offers an opportunity to further functionalize the electrodes without losing in stimulation performance.…”

“…The current was increased until the voltage drop ( V PB ) reached the potential limits of −0.6 V or 0.8 V, which were calculated with respect to the measured open cell potential. The here chosen cathodic pulse width of 200 µs is a commonly used stimulation parameter to characterize materials for neural interface applications . The anodic pulse duration of 800 µs was used to enable large cathodic stimulation currents without reaching the anodic water window limit.…”