Publication detail

Shattering the Water Window: Comprehensive Mapping of Faradaic Reactions on Bioelectronics Electrodes

EHLICH, J. VAŠÍČEK, Č. DOBEŠ, J. RUGGIERO, A. VEJVODOVÁ, M. GLOWACKI, E.

Original Title

Shattering the Water Window: Comprehensive Mapping of Faradaic Reactions on Bioelectronics Electrodes

Type

journal article in Web of Science

Language

English

Original Abstract

It is generally accepted that for safe use of neural interface electrodes, irreversible faradaic reactions should be avoided in favor of capacitive charge injection. However, in some cases, faradaic reactions can be desirable for controlling specific (electro)physiological outcomes or for biosensing purposes. This study aims to systematically map the basic faradaic reactions occurring at bioelectronic electrode interfaces. We analyze archetypical platinum-iridium (PtIr), the most commonly used electrode material in biomedical implants. By providing a detailed guide to these reactions and the factors that influence them, we offer a valuable resource for researchers seeking to suppress or exploit faradaic reactions in various electrode materials. We employed a combination of electrochemical techniques and direct quantification methods, including amperometric, potentiometric, and spectrophotometric assays, to measure O-2, H-2, pH, H2O2, Cl-2/OCl-, and soluble platinum and iridium ions. We compared phosphate-buffered saline (PBS) with an unbuffered electrolyte and complex cell culture media containing proteins. Our results reveal that the "water window" the potential range without significant water electrolysis varies depending on the electrolyte used. In the culture medium that is rich with redox-active species, a window of potentials where no faradaic process occurs essentially does not exist. Under cathodic polarizations, significant pH increases (alkalization) were observed, while anodic water splitting competes with other processes in media, preventing prevalent acidification. We quantified the oxygen reduction reaction and accumulation of H2O2 as a byproduct. PtIr efficiently deoxygenates the electrolyte under low cathodic polarizations, generating local hypoxia. Under anodic polarizations, chloride oxidation competes with oxygen evolution, producing relatively high and cytotoxic concentrations of hypochlorite (OCl-) under certain conditions. These oxidative processes occur alongside PtIr dissolution through the formation of soluble salts. Our findings indicate that the conventional understanding of the water window is an oversimplification. Important faradaic reactions, such as oxygen reduction and chloride oxidation, occur within or near the edges of the water window. Furthermore, the definition of the water window significantly depends on the electrolyte composition, with PBS yielding different results compared with culture media.

Keywords

electrochemistry; neurostimulation; platinumelectrodes; bioelectronics; reactive oxygen species; reactive chlorine species; water window

Authors

EHLICH, J.; VAŠÍČEK, Č.; DOBEŠ, J.; RUGGIERO, A.; VEJVODOVÁ, M.; GLOWACKI, E.

Released

1. 10. 2024

Publisher

AMER CHEMICAL SOC

Location

WASHINGTON

ISBN

1944-8252

Periodical

ACS applied materials & interfaces

Year of study

16

Number

40

State

United States of America

Pages from

53567

Pages to

53576

Pages count

10

URL

https://pubs.acs.org/doi/10.1021/acsami.4c12268

Full text in the Digital Library

http://hdl.handle.net/11012/250787

BibTex

@article{BUT191212,
  author="Jiří {Ehlich} and Čeněk {Vašíček} and Jan {Dobeš} and Amedeo {Ruggiero} and Markéta {Vejvodová} and Eric Daniel {Glowacki}",
  title="Shattering the Water Window: Comprehensive Mapping of Faradaic Reactions on Bioelectronics Electrodes",
  journal="ACS applied materials & interfaces",
  year="2024",
  volume="16",
  number="40",
  pages="53567--53576",
  doi="10.1021/acsami.4c12268",
  issn="1944-8252",
  url="https://pubs.acs.org/doi/10.1021/acsami.4c12268"
}