The increase interests in wearable device market are triggered by healthcare monitoring. Common examples are pulse, heart rate and temperature monitors. Wearable technology has opened up new path for non-invasive diagnostic and therapeutic technologies via sensing of biomarker/drug from the liquid extracted on skin including sweat (Bandodkar & Wang, 2014; Liu et al., 2017). The increasing demand of integrating electronic technology in wearable devices is driven by needs for individual monitoring remotely at home, often called as ubiquitous health care (Choudhuri et al., 2019). In addition, wearable devices allow continuous, long time monitoring at any place, anytime (Bohr et al., 2019). Mechanical and electrical responsive conducting polymers (CPs), plus high flexibility and stretch-ability contribute to recent accelerate growth of publications involving conducting polymer in wearable and skin-attachable device. Metals and silica (semiconductors) are inorganic materials that are generally regarded as highly conductive but are rigid and inflexible. The concept of organic conductors/semiconductors has arisen since the discovery of highly conducting polyacetylene by Hideki Shirakawa, working along with Alan MacDiarmid and physicist Alan Heeger in 1977 (Shirakawa et al., 1977). The most apparent advantage of organic electronics as compared to inorganic is that they are highly flexibility and they are lightweight. These properties are ideal for wearable sensors. Conducting polymers with long-term electrical and chemical stability such as polypyrrole (PPy), poly(3,4-ethylenedioxy-thiophene) (PEDOT) and polyaniline (PANi) (Figure 1) have gained popularity in this field (Puiggali-Jou et al., 2019; Talikowska et al., 2019). Doping counterions in close proximity to the extended pi-bond significantly improve CP conductivity. These doped CPs have electrical conductivities ranging from >1 S/cm to >1000 S/cm aligning CPs with the inorganic semiconductors, for example silicon
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.
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