Vol.:(0123456789) 1 3 Chemical Papers https://doi.org/10.1007/s11696-018-0481-z ORIGINAL PAPER Ultrasensitive bioelectronic devices based on conducting polymers for electrophysiology studies Sanaz Asgarifar 1,2  · Pedro M. C. Inácio 1,2  · Ana L. G. Mestre 1,2  · Henrique Leonel Gomes 1,2 Received: 8 January 2018 / Accepted: 20 April 2018 © Institute of Chemistry, Slovak Academy of Sciences 2018 Abstract Conducting polymer electrodes based on poly(3,4-ethylenedioxythiophene doped with poly(styrenesulfonate) (PEDOT:PSS) are evaluated as transducers to record extracellular signals in cell populations. The performance of the polymer electrode is compared with a gold electrode. A small-signal impedance analysis shows that in the presence of an electrolyte, the polymer electrode establishes for frequencies below 100 Hz a higher capacitive electrical double layer at the electrode/electrolyte interface. Furthermore, the polymer/electrolyte interfacial resistance is several orders of magnitude lower than the resistance of the gold/electrolyte interface. The polymer low interfacial resistance minimizes the intrinsic thermal noise and increases the system sensitivity. The ultra-sensitivity of the polymer-based transducer system was demonstrated by recording the electrical activity of cancer cells of the nervous system. Keywords Organic bioelectronics · Polymer electrodes · Extracellular signals · PEDOT:PSS Introduction Conducting polymer-based electrodes are particularly attrac- tive to fabricate electrophysiological transducers. Polymer- based electrodes yield better electrophysiological recordings when compared with metal electrodes (Blau et al. 2011; Cui and Martin 2003; Leleux et al. 2014; Löfer et al. 2015; Sessolo et al. 2013; Svennersten et al. 2011; Tsukada et al. 2012). Polymers ofer a low impedance interface that facili- tates signal transduction from the cells and tissues to the recording electrode. Moreover, conducting polymers can exhibit desired mechanical compliance with soft biological matter, in terms of fexibility, elasticity, and morphology, and with a surface chemistry that promotes biocompatibility and stability over extended periods. Conducting polymers are now being incorporated into devices to measure electrophysiological signals. As an exam- ple, the conducting polymer poly(3,4-ethylenedioxythio- phene) doped with poly (styrenesulfonate) (PEDOT:PSS) has been used to coat microelectrode arrays (MEAs) (Pas et al. 2017). MEAs are substrate-integrated extracellu- lar electrode matrices kept in contact with cells in culture (Obien et al. 2015; Spira and Hai 2013). MEAs are consid- ered to be the state-of-the-art platform for the development of cell-based sensors. Current available MEAs are capable of measuring electrophysiological activity of multiple cells simultaneously, providing information about the activity of individual cells at high spatiotemporal resolution. This technology has been optimized to detect signals generated by electrogenic cells, such as neurons and cardiac cells. Neu- rons generate relatively strong signals reaching several mil- livolts in amplitude; these signals also propagate at speeds of meters per second. Therefore, when detected by external, microelectrodes give rise to fast varying signals occurring in a time scale of milliseconds. They are refereed as action potentials. With the goal to understand how the Brain works, action potentials have been under intense research for many years. However, all the biological cells produce a membrane poten- tial that is specifc for its type and tissue, which is also spe- cifc for its degree of diferentiation. The electric nature of This work was presented at the 81st Prague Meeting on Macromolecules held on September 10–14, 2017. * Henrique Leonel Gomes hgomes@ualg.pt 1 Faculdade de Ciências e Tecnologia, Universidade do Algarve, 8005-139 Faro, Portugal 2 Instituto de Telecomunicações, Avenida Rovisco, Pais 1, 1049-001 Lisbon, Portugal