Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Novel approach to the synthesis of polyaniline possessing electroactivity at neutral pH Fatemeh Masdarolomoor a, ⁎ , Somayeh Hajizadeh a , Mansoor Arab Chamjangali a , Peter C. Innis b a Faculty of Chemistry, Shahrood University of Technology, P.O. Box 36155-316, Iran b ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, AIIM Facility (Building 231), Innovation Campus. Squires Way, North Wollongong, NSW, 2500, Australia ARTICLE INFO Keywords: Polyaniline Poly(2-methoxy aniline-5-sulfonic acid) Modified electrode Dopant Electropolymerization Electroactivity ABSTRACT A new approach is proposed for the synthesis of polyaniline via electrochemical polymerization of aniline at a very low concentration on a modified electrode surface. The electrode was modified with a sulfonated poly- aniline, poly(2-methoxy aniline-5-sulfonic acid) (PMAS), which acted as an electroactive conductive template for the aniline monomer. The electrode surface was modified with PMAS via a number of different methods including cyclic voltammetric and potentiostatic deposition as well as dip and drop casting water-soluble PMAS onto the electrode surface. Electrochemical polymerization of aniline was then carried out at the surface of the modified electrode. Effect of different variables such as PMAS concentration, volume and pretreatment of the modified electrode on the polymerization of aniline was studied. The polymer synthesized at the PMAS modified electrode was characterized by electrochemical and UV–vis spectrophotometic techniques. Electrochemical studies showed that even at very low concentration of aniline (5.0 mM), an adherent, uniform and stable polyaniline film was deposited on the electrode surface. Without any further treatment, this polyaniline layer was found to be electroactive at a neutral pH which is crucial for biosensing applications. 1. Introduction Conducting polymers (CPs) have been widely studied in recent years with an increasing number of publications from 1996. At present it is possible to create conducting polymers with a diverse range of che- mical, electrical and mechanical properties [1,2]. Due to this collection of dynamic properties, conducting polymers have found utility in areas such as mechanical actuators [3,4], corrosion protection [5], anti-static coatings, membranes, energy storage and conversion devices [6], polymer photovoltaics, light emitting diodes and display technologies, environmental cleaning [7], supercapacitors [8], sensors [9], biological applications such as biosensors [2,10] and tissue engineering [11,12], and catalysts [13] in sensors, energy systems and environmental pro- tection. Many conducting polymer catalysts have good biocompatibility [10,14] for their applications in bio-systems. Polyaniline is one of the most investigated polymers due to the unique electrical, chemical (pH switchability) and mechanical proper- ties. Many reviews have been published on synthesis, processing, properties, theory and applications of polyaniline [6,15–33]. Unlike polypyrrole and polythiophene, polyaniline can be found in three dif- ferent oxidation states (Scheme 1). Non-conducting leucoemeraldine (y = 1), is the fully reduced state. Non-conducting pernigraniline (y = 0) with imine links, is the fully oxidized state. Only the protonated emeraldine salt (ES) form of polyaniline (y = 0.5) is conducting while the deprotonated emeraldine base (EB) is insulting. Due to high stabi- lity at room temperature, emeraldine is the most useful form of poly- aniline. In comparison, the leucoemeraldine is easily oxidized while the pernigraniline is easily degraded [34]. Polyaniline is typically prepared by chemical or electrochemical oxidative polymerization of aniline in acidic solution [34]. Electro- chemical polymerization is carried out by employing either a constant current, a constant potential or potentiodynamic techniques in an aqueous solution of aniline. The electrolyte used is usually an acid (HA), which provides low pH as well as the dopant A - to solubilize the monomer and generate polyaniline in the doped emeraldine salt (ES) form. Electrochemical synthesis is flexible in terms of the incorporated dopant from the electrolyte and is a useful tool for the preparation and characterization of small films or coated electrodes [34,36]. CPs have been shown to act as a conductive support for im- mobilization of enzymes to improve their performance or extend their function. Incorporating biological dopants or modifiers by in-situ polymerization under mild polymerization conditions is highly https://doi.org/10.1016/j.synthmet.2019.03.011 Received 5 December 2018; Received in revised form 11 March 2019; Accepted 11 March 2019 ⁎ Corresponding author. E-mail address: fmasdar@yahoo.com (F. Masdarolomoor). Synthetic Metals 250 (2019) 121–130 0379-6779/ © 2019 Elsevier B.V. All rights reserved. T