Electrochemical methods for neural interface electrodes

Abstract

Objective. Neural interfaces often rely on charge transfer processes between electrodes and the tissue or electrolyte. Electrochemical processes are at the core of electrode function and, therefore, the key to neural interface stability, electrode performance characterization, and utilization of electrodes as chemical sensors. Electrochemical techniques offer a variety of options to investigate the charge transfer and electrocatalytic properties of electrodes. Approach. In this tutorial, we present various experiments to illustrate the power of electrochemical methods, serve as a reference and guideline, and stimulate deeper understanding of the subject. Main results. As a basis for the following experiments, we discuss the platinum cyclic voltammogram and focus on understanding surface processes and roughness determination. We highlight the importance of appropriate instrumentation using potentiostats and how strongly it can influence results. We then discuss a number of potential-controlled and current-controlled methods for electrode characterization, including chronocoulometry, chronoamperometry, (active) potentiometry, and chronopotentiometry. They illustrate charge transfer caused by both electrode surface processes and the presence of redox-active species, such as dissolved oxygen and hydrogen, or hydrogen peroxide. We also discuss the electrode potential with respect to a reference electrode under various conditions and how it affects its electrochemical properties like surface state, catalytic properties and capability to transfer charge. Significance. Electrochemical methods are still underutilized in neural engineering, and valuable information is therefore often not accessed. Many studies on electrode characterization would benefit from a more consistent and target-oriented electrochemical methodology and instrumentation. That ranges from the investigation of new materials and processes, over electrode performance assessment to the development of more long-term stable and biocompatible neural interfaces. Ultimately, standardization, consistency and comparability will play a key role in the translation of microtechnology into biomedical and clinical applications.

Implantable Multi-Cross-Linked Membrane-Ionogel Assembly for Reversible Non-Faradaic Neurostimulation

“…While conventional neurostimulation is commonly demonstrated using only the potential difference between two electrodes without a reference electrode, we systematically used chronoamperometry and chronopotentiometry to compare the differences in electric potential and current responses between faradaic charge injection of the metallic electrode and nonfaradaic (capacitive) charge injection of the McMiA-based neural interface (Figure f). In the chronoamperometric studies (potential-controlled method), different voltage amplitudes (300–900 mV vs Ag/AgCl) were specified, which can cause gas evolution (Figure g, left) . Therefore, in the water window region (700–900 mV vs Ag/AgCl), a small potential change strongly increases the faradaic currents for the Au electrode.…”

“…In the chronoamperometric studies (potential-controlled method), different voltage amplitudes (300−900 mV vs Ag/AgCl) were specified, which can cause gas evolution (Figure 2g, left). 35 Therefore, in the water window region (700−900 mV vs Ag/AgCl), a small potential change strongly increases the faradaic currents for the Au electrode. However, it was observed that the anodic and cathodic currents did not show a significant increase at the Au electrode/McMiA interface.…”

Cyclic Voltammetry Study of Noble Metals and Their Alloys for Use in Implantable Electrodes

“…It is important to note that any differences seen between aerated and sparged scans in the region greater than 0.2 V may be due to the averaging of several trials between each material as well as differences in pH caused by different oxygen partial pressures or the gas pressure variation between aerated and sparged conditions. , These slight variations are insignificant and do not affect the evaluation of the materials or any resulting conclusions.…”

High‐Conductivity Stoichiometric Titanium Nitride for Bioelectronics

“…Capacitance was estimated using a 100 m m KCl electrolyte and E step of 0.001 V using a True Linear scan mode. [ 21 ] CV measurements for establishing the water window and estimating capacitance were done on “bulk” samples with an active area of 7 mm 2 . Furthermore, from wide range cyclic voltammograms, it was possible to extrapolate the value of charge storage capacity obtained from the time integral of the cathodic current within the water electrochemical passive window, for the three different conditions of O 2 content in the electrolyte (0% O 2 , 21% O 2 (ambient), and 100% O 2 ).…”