A New Hybrid Sensitive PANI/SWCNT/Ferrocene-Based Layer for a Wearable CO Sensor.

Mihaela Savin,Costin Brasoveanu,Carmen Moldovan,Bogdan Firtat,Cristina Pachiu,Viorel Avramescu,Silviu Dinulescu,Alina Catrinel Ion,Gabriel Craciun,Andreea-Bianca Serban,Cosmin Romanitan,Carmen-Marinela Mihailescu

doi:10.3390/s21051801

Abstract

Developing a sensing layer with high electroactive properties is an important aspect for proper functionality of a wearable sensor. The polymeric nanocomposite material obtained by a simple electropolymerization on gold interdigitated electrodes (IDEs) can be optimized to have suitable conductive properties to be used with direct current (DC) measurements. A new layer based on polyaniline:poly(4-styrenesulfonate) (PANI:PSS)/single-walled carbon nanotubes (SWCNT)/ferrocene (Fc) was electrosynthesized and deposed on interdigital transducers (IDT) and was characterized in detail using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoemission spectroscopy (XPS), and X-ray diffraction (XRD). The sensor characteristics of the material towards carbon monoxide (CO) in the concentration range of 10–300 ppm were examined, showing a minimal relative humidity interference of only 1% and an increase of sensitivity with the increase of CO concentration. Humidity interference could be controlled by the number of CV cycles when a compact layer was formed and the addition of Fc played an important role in the decrease of humidity. The results for CO detection can be substantially improved by optimizing the number of deposition cycles and enhancing the Fc concentration. The material was developed for selective detection of CO in real environmental conditions and shows good potential for use in a wearable sensor.

Highlights

The synthesis of solutions based on conductive polymeric nanocomposite materials (PNCMs), as well as exploring their electrical properties, continues to be of great importance for a wide range of applications, such as sensors [1,2] and actuators, biosensors [3], micro/nanoelectronic devices, photovoltaic devices, supercapacitors [4,5], and light emitting diodes
Conductive polymers and composite solutions can be combined with other components, such as carbon nanoparticles, carbon nanotubes, graphene and graphite nanofibers, in order to obtain PNCMs, such as PEDOT:poly(4-styrenesulfonic acid) sodium salt (PSS)/graphene [13], PANI:PSS/graphene [14], PANI:PSS/multi-walled carbon nanotubes (MWCNTs) [15], and PEDOT:PSS/single-walled carbon nanotubes (SWCNTs)
The results show that the Fe is present in Fe2+ and Fe3+ states in this layer, since the most stable oxidation states of the iron centre in ferrocene are +2 and +3

Summary

Introduction

The synthesis of solutions based on conductive polymeric nanocomposite materials (PNCMs), as well as exploring their electrical properties, continues to be of great importance for a wide range of applications, such as sensors [1,2] and actuators, biosensors [3], micro/nanoelectronic devices, photovoltaic devices, supercapacitors [4,5], and light emitting diodes. (PEDOT), which manage to increase their solubility in water (improve dispersion) by combining with other hydrophilic polymers such as poly (4-styrenesulfonate) (PSS), polyacrylic acid (PAA), poly(vinylpyrrolidone) (PVP), and polyethylene glycol (PEG) This results in composite solutions, such as [6,7], PANI:PEG [8], PANI:PVP [9], PEDOT:PSS [10,11], and PPy:PSS [12], with high conductivity and good optical properties. The insertion of MWCNTs in the PANI:PSS composite, even in small amounts, generates an increase in the electrical properties of PANI, as MWCNTs ensure charge transfer efficiency [15,16] In another instance, the combination of lower mass proportion carbon nanotubes (SWCNTs), which have one-dimensional structures and nanometric dimensions, with conductive polymers will determine an improvement in the electrical and mechanical properties of the obtained conductive solutions [17,18]. These methods may include SWCNT surface functionalization, the addition of surfactants [19], the ultrasonication or the association of the other polymers, biomolecules, organic acids or organic sulfonates [20,21]

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