Self-Doping and Self-Acid-Doping of Conjugated Polymer Bioelectronics: The Case for Accuracy in Nomenclature.

Conjugated polymers are enabling the development of flexible bioelectronics, largely driven by their organic nature which facilitates modification and tuning to suit a variety of applications. As organic semiconductors, conjugated polymers require a dopant to exhibit electrical conductivity, which in physiological conditions can result in dopant loss and thereby deterioration in electronic properties. To overcome this challenge, "self-doped" and self-acid-doped conjugated polymers having ionised pendant groups covalently bound to their backbone are being developed. The ionised group in a "self-doped" polymer behaves as the counterion that mainatins electroneutrality, while an external dopant is required to induce charge transfer. The ionised group in a self-acid-doped polymer induces charge transfer and behaves as the counterion balancing the charges. Despite their doping processes being different, the two terms, self-doped and self-acid-doped, are often used interchangeably in the literature. This review highlights the differences in the doping mechanisms of self-doped and self-acid-doped polymers, and proposes that the term "self-doped" should be replaced by "self-compensated", while reserving the term self-acid-doped for polymers that are intrinsically doped without the need of an external dopant. This is followed by a summary of examples of self-acid-doping in bioelectronics, highlighting their stability in the conductive state under physiological conditions. This article is protected by copyright. All rights reserved.