Electrochemical Synthesis of Self-Doped Poly(3,4-ethylenedioxythiophene) and Application to Flexible Biosensors

Wet-processable and highly conductive polymers are promising candidates for key materials in organic electronics. Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), commercially available as a water dispersion of colloidal particles, has potential applications to organic electronics because of its high electrical conductivity, transparency and thermal stability 1). However, the PEDOT:PSS has some technical issues owing to the PSS: The ultra-thin layers thinner than the colloidal particle size is difficult; The PEDOT:PSS colloids aggregate and precipitate when stored for an extended period; The pristine PEDOT:PSS exhibits poor electrical conductivity without secondary dopants such as ethylene glycol and DMSO. Recently, we have developed a novel fully soluble self-doped PEDOT (S-PEDOT) by chemical oxidative polymerization having a high conductivity without secondary dopants 2). This presentation deals with the first study on synthesis of the S-PEDOT by a facile electrochemical polymerization and characterization by means of cyclic voltammetry (CV), reflection spectroscopy, X-ray diffraction analysis (XRD), and the four-point technique. The S-PEDOT was electrochemically synthesized at different current densities ranging from 0.5 to 5 mA/cm2. It was found that the electrical conductivity increased with increasing current density and attained as high as 427 S/cm at 5 mA/cm2 which was one order of magnitude higher than those so far reported in the literature. Further investigation has been made to clarify the role and effect of current density on molecular weight, crystallinity, and carrier transport properties in more detail. For the application to biosensors, flexible organic electronic circuits consisting of working, counter, and reference electrodes were fabricated by line-patterning 3) the S-PEDOT water solution as a conductive ink on a Kapton film as a flexible substrate. The flexible glucose sensor was then fabricated by coating the bioink containing glucose oxidase, ferrocene, and chitosan on the working electrode. It was found that the flexible biosensor successfully worked where the electric current during the CV measurement increased with increasing the glucose concentration. 1) H. Okuzaki ed., PEDOT: Materials Properties and Device Applications, S&T (2012). 2) H. Yano, K. Kudo, K. Marumo, H. Okuzaki, Sci. Adv., 5, eaav9492 (2019). 3) D. Hohnholz, H. Okuzaki, and A. G. MacDiarmid, Adv. Funct. Mater., 15, 51 (2005).