Electrochemical stability ofPEDOTfor wearableon‐skinapplication

Abstract

Conducting polymers are promising candidates for wearable devices due to mechanical flexibility combined with electroactivity. While electrochemical measurements have been adopted as a central transduction method in many on‐skin sensors, less studied is the stability of the active materials (in particular poly3,4‐ethylenedioxythiophene, PEDOT) in such systems, particularly for “on‐skin” applications. In this study, several different variants of doped PEDOT are fabricated and characterized in terms of their (electrical, physical, and chemical) stability in biological fluid. PEDOT doped with tosylate (TOS) or polystyrenesulfonate (PSS) are selected as prototypical forms of conducting polymers. These are compared with a new variant of PEDOT co‐doped with both TOS and PSS. Artificial interstitial fluid (aISF) loaded with 1% wt/vol bovine serum albumin is adopted as the testing medium to demonstrate the stability in dermal applications (i.e., conducting polymer microneedles or coatings on microneedles). A range of techniques such as cyclic voltammetry and electrochemical impedance spectroscopy are used to qualify and quantify the stability of the doped conducting polymers. Furthermore, this study is extended by using human skin lysate in the aISF to demonstrate proof‐of‐concept for stable use of PEDOT in wearable “on‐skin” electronics.

Reducing the resistance for the use of electrochemical impedance spectroscopy analysis in materials chemistry

“…Here, we review EIS techniques and highlight numerous practical applications within materials science, such as for analysis of self-assembled monolayers (SAMs), 9,17,18 supercapacitors, 19–22 dye-sensitized solar cells (DSSCs), 23,24 conductive coatings, 25–27 sensors, 28,29 porous electrodes for different applications, 30–32 and other “smart” materials. 7,33,34 Very recent exciting literature examples that applied EIS to characterize, optimize or fully understand the performance of the material include analysis of on-skin or wearable sensors, 35,36 “green” microbial fuel cells, 37 and biosensors of SARS-CoV-2 antibodies. 38,39 Notably, there are different methods to illustrate and analyze EIS measurements.…”

PEDOT coated microneedles towards electrochemically assisted skin sampling

“…The fabrication of PEDOT:TOS by vapor phase polymerization (VPP) was the same as previously published works. 46,92 First, the oxidant solution was prepared containing 257 mM Fe(III) tosylate (H. C. Starck as a 54 wt% solution in butanol-Baytron CB 40) and 58 mM triblock copolymer poly(ethylene glycol-propylene glycol-ethylene glycol) (PEG-PPG-PEG, M w = 5800 g mol À1 , Sigma-Aldrich) in a 2.6 : 1 vol/vol mixture of ethanol to butanol as the solvent carrier. For the coat-cut PEDOT:TOS MN, the oxidant solution was spin-coated (400B-6NPP, Laurell Technologies Inc.) on the PMMA sheet for 25 s at 1500 rpm.…”

“…45 We have previously shown the electrochemical stability of PEDOT in the artificial ISF and skin lysate. 46 Recent works have also reported PEDOT in MNs for electroencephalography (EEG) electrodes, 47 nitric oxide sensors during endoscopy, 48 and amperometry glucose sensing. 49 Hence, in this work, PEDOT is chosen due to its desirable properties and the broad ranging research to date.…”

Recent advances in the aqueous applications of PEDOT

“… 29–40 Routinely studied variants of PEDOT, such as those doped with PSS or tosylate, are promising materials for biological applications. Mokhtar et al 37 have investigated the stability of various doped PEDOT in biological fluid, i.e. artificial interstitial fluid (aISF), and demonstrated that PEDOT shows higher electrochemical stability in biological environments when it is doped with Tos or it is co-doped with Tos/PSS, as compared to doped with just PSS.…”