An Eco-Friendly Conductive Sensor based on Biodegradable Fibres of PANI/PHB

Electrospinning seems to be the most suitable technique to obtain long polymer fibres of submicron diameters. This technology is mostly suitable whenever the high surface area to volume ratio is required, e.g. in highly efficient filtering materials, scaffolds for tissue engineering, nano-chemical sensors, etc. In the latter case, nanofibrous interacting layers enhance the available sensing surface area, providing an increase in sensitivity and capture efficiency, due to surface area approximately one or two orders of magnitude higher than in continuous films. Among electrospun conductive polymer (CP) sensors, polyaniline (PANi) has been one of the most investigated solid state materials due to both its environmental stability (up to 300°C) and peculiar sensing mechanisms. For instance, a dedoping effect through deprotonation is expected to happen when ammonia gaseous is adsorbed onto PANi molecules. On the contrary, acidic gases (HCl, H2S, and CO2 with water) cause PANi doping through protonation. In addition, volatile organic compounds (VOCs) change conductivity of the solid state polymer. Each of these events upon polymer exposure to analytes can be measured as current variations detectable through suitable resistors [1]. Electrospun blends of PANi and insulating host polymers (HPs) have been designed, prepared and studied in our laboratory to assess the sensing features of nanofibres resulting from the combination of CP electrical conductivity and HP physical properties [2]. In order to create a new generation of environmental friendly sensors, a biocompatible and biodegradable nanofibrous sensor based on PANi and poly-3-hydroxybutyrate (PHB) was fabricated, characterized and tested to detect VOCs and gases. Specifically, the interdigitated electrodes (IDEs) coated with 10 min electrospun fibrous layers at increasing concentrations of PANi, were investigated through optical microscopy, SEM, AFM and TEM. All layers were highly porous, with interconnected void volumes and high surface-to-volume ratios. Additionally, the polymeric fibres covered both all electrodes in each IDE and the gaps between them, providing electrical connection within each transducer. The sensor retained good mechanical integrity and thermal stability until six months, at least, which reflected into reproducible sensing properties, and it was water resistant. All sensors fabricated at different PANi concentrations resulted conductive and fast responding to gases (NH3, NO2) and VOCs (acetone, acetic acid). The amount of PANi in nanofibres was a key factor for layer conductivity (low noise, increase in current), dependence on environmental parameters (humidity, temperature) and interaction with gases and VOCs.