Biosensors and Bioelectronics: X
2022
Skin stimulation and recording: Moving towards metal-free electrodes
SHANER, SEBASTIAN W.; ISLAM, MONSUR; KRISTOFFERSEN, MORTEN B.; AZMI, RAHELEH; HEISSLER, STEFAN; ORTIZ-CATALÁN, MAX; KORVINK, JAN G.; ASPLUND, MARIA. 

Highlights

– A metal-free hydrogel electrode that yields stable DC stimulation and recording.   

– Parallelizable and cleanroom-free protocol with sustainable materials

– More durable stimulation compared to clinical-standard silver-silver chloride.

Link to source: https://www.sciencedirect.com/science/article/pii/S2590137022000383

When one thinks about electrodes, especially ones meant for humans, they typically think of some kind of metal. Whether on the skin or in the brain, metal electrodes are characteristically expensive, stiff, non-efficient in electron-ion transduction, and prone to toxic metal ion by-products during stimulation. In order to circumvent these disadvantages, electrically-conductive laser-induced graphene (LIG) and mixed electron-ion conducting polymer (poly(3, 4‐ethylenedioxythiophene) polystyrene sulfonate – PEDOT:PSS) was leveraged to create a metal-free electrode combination that allows for an economical, soft, and organic electrode for applications on human skin. Compared to clinical-standard silver – silver chloride (Ag/AgCl) skin electrodes, the metal-free hydrogel electrodes show notable improvement in electrochemical stability and prolonged stable potentials during long-term DC stimulation (0.5–24 hours). Recording and stimulation performance on human participants rivals that of Ag/AgCl, thus fortifying the notion that they are an appropriate progression to their noble metal counterparts.

 

2.2. Surface-functionalization of LIG

Polyurethane (AdvanSource HydroMed D3, USA) was deposited onto HMDA-treated LIG electrodes using a dip-coater (Nadetech ND-DC Dip Coater, Spain). PU was dissolved in ethanol (90%) to a final PU concentration of 1% w/v. The PU is covalently bonded to the amine groups on the treated LIG electrodes. The dip-coating (Nadetech NC-DC Dip Coater, Spain) immersion speed of 300 mm/min and retraction speed of 10 mm/min.

Keywords: Bioelectronics; Conducting hydrogels; Direct current stimulation; Skin electrodes