materials Article Electrical Properties of Textiles Treated with Graphene Oxide Suspension Danil Valeriyevich Nikolaev 1 , Zakhar Ivanovich Evseev 1, *, Svetlana Afanasyevna Smagulova 1 and Irina Veniaminovna Antonova 2, *   Citation: Nikolaev, D.V.; Evseev, Z.I.; Smagulova, S.A.; Antonova, I.V. Electrical Properties of Textiles Treated with Graphene Oxide Suspension. Materials 2021, 14, 1999. https://doi.org/10.3390/ma14081999 Academic Editor: Antonio Di Bartolomeo Received: 26 March 2021 Accepted: 13 April 2021 Published: 16 April 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 “Graphene Nanotechnology” Laboratory, Physical-Technical Institute, North-Eastern Federal University in Yakutsk, 677000 Yakutsk, Russia; dv.nikolaev@s-vfu.ru (D.V.N.); sa.smagulova@s-vfu.ru (S.A.S.) 2 Laboratory of Physics and Technology of Three-Dimensional Nanostructures, Rzhanov Institute of Semiconductor Physics SB RAS, 630090 Novosibirsk, Russia * Correspondence: zi.evseev@s-vfu.ru (Z.I.E.); antonova@isp.nsc.ru (I.V.A.) Abstract: Two-dimensional nanomaterials such as graphene can provide various functional proper- ties to textiles, which have great potential in sportswear, healthcare etc. In this study, the properties of nylon and cotton-based electronic textiles coated with reduced graphene oxide are investigated. After reduction of graphene oxide coating in hydrazine vapor, e-textiles with a resistance of ~350 Ω/sq for nylon, and ~1 kΩ/sq for cotton were obtained. Cyclic mechanical bending tests of samples showed that the resistance increases during bending up to 10–20%. The use of bovine serum albumin as an adhesive layer improved the wash stability for samples with nylon up to 40 washing cycles. The use of BF-6 glue as a protective layer reduced changes in resistance during bending, and improved wash stability of cotton samples. It was shown that the resistance of the obtained samples is sensitive to changes in temperature and humidity. In addition, obtained e-textiles attached to a person’s wrist were able to measure heart rate. Thus, the obtained electronic textiles based on cotton and nylon coated with reduced graphene oxide demonstrates good characteristics for use as sensors for monitoring vital signs. Keywords: graphene; graphene oxide; e-textiles; wearable electronics 1. Introduction Presently, thin-film materials for wearable electronics have a wide potential for applica- tion as embedded sensors of vital signs, flexible wearable batteries, heating elements [1–3], etc., which attracts a high interest of the scientific community on this topic. The devel- opment of technologies for the production of new two-dimensional materials and their application for conductive textiles are important scientific and practical tasks [4]. In particu- lar, there are many research articles on the use of carbon nanotubes (CNTs) [5], conducting polymers [6], metal nanofibers [7] and nanoparticles [8], graphene, and its derivatives [9]. They can be used for functionalization of both natural and artificial fibers. However, the safety and biocompatibility of carbon nanotubes are under discussion [10]. It is considered that the sharp edges of CNTs can damage cell membranes and DNA, which limits their use as modifiers for wearable e-textiles. Metal nanofibers and nanoparticles also raise certain concerns about biocompatibility and environmental safety [11], and the functionalization of textiles with metal nanoparticles does not provide sufficient conductivity for practical use in wearable electronics [8]. Electrically conductive polymers are expensive and difficult to apply to organic textile materials [6]. E-textiles based on graphene and its derivatives, such as graphene oxide (GO), has been a focus of much attention due to their high conductivity, resistance to mechanical stress, and biocompatibility [12–14]. In addition, GO can form stable aqueous suspensions, due to oxygen functional groups on the surface of GO [15]. This simplifies many technological processes associated with the deposition of GO. Also, Materials 2021, 14, 1999. https://doi.org/10.3390/ma14081999 https://www.mdpi.com/journal/materials