Abstract:
The aim of this research was to carry out synthesis and characterization of series of dithienyl pyrrole (SNS) based conducting polymers and their applications as chemical gas sensors in the perspective of development of flexible multisensing radio frequency identification (RFID) system for perishable goods monitoring, the aim of the EU project ‘FlexSmell’.
In this context, number of dithienyl pyrrole derivatives were synthesized and polymerized by both chemical and electrochemical methods. The synthesis of SNS based polymers with different functionalities on their backbone was undertaken in order to study the effect of electron donating/withdrawing substituents on the properties of the polymers. The SNS polymers with halogen atoms (F, Cl, Br and I) were also prepared and studied for their effects on the properties of the polymers. Flexible chemoresistive sensors were fabricated by electrochemical deposition of the SNS polymers onto interdigitated electrodes (IDE) substrates. The sensors were characterized against the analytes responsible for decay of perishable goods, such as humidity, ammonia, ethanol etc.
The optical absorption spectra of the SNS conducting polymers showed well defined absorption bands due to π-π* transition or to the transitions among polaron, bipolaron and band states. These features correlate with the good conductivity shown by the investigated compounds when regarded in the frame of the conduction models for organic materials owning delocalised π bonds. The influence of the substituents on the electrical conductivities of the polymers was analysed. The polymers have their electrical conductivity linked to the electron donating character and electronegativity (for the polymers with halogen atoms) of the substituents. The polymers are also studied for their thermal stability, morphology etc. The SNS polymers characterized for their sensing performances against humidity, ammonia and ethanol showed linear increase in their resistances with the relative humidity and a power function one in respect with the concentrations of the other analytes.
Attempts have also been made towards the synthesis of dithienyl pyrrole-dialkylbithiazoles copolymers for the synthesis of easily soluble and environmentally stable polymeric materials intended to be used for chemical sensing.
The main goal of the FlexSmell project, development of flexible multisensing RFID system was achieved by working in collaboration with Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland, The University of Manchester (UK) and Holst Centre (The Netherlands). The multisensor platform was developed at EPFL whereas RFID tag at Holst Centre. Multisensor platforms with sensors of different transduction principles were fabricated by ink-jet printing of Ag-nanoparticle ink on flexible polyethylene terephthalate foils. The platforms have two IDE capacitors for humidity sensing, one resistive temperature detector for temperature measurement and two IDE resistive devices for ammonia and VOCs detection. The capacitive devices were functionalised with cellulose acetate butyrate or polyether urethane layers at University of Tübingen whereas resistive ones with polyaniline and polypyrrole layers at The University of Manchester. The RFID tag was integrated with the multisensor platform through a hybrid approach. In comparison with the currently available RFID sensing systems based on silicon technology, our prototype of low cost flexible multisensing platform with wireless communication capabilities represents a very promising approach for the next generations of smart RFID tags.
Another part of the work explored the possibility to incorporate porcine odorant binding proteins in the structure of field effect gas biosensors through chemical and physical immobilization of the biological material on gold coated substrates. The concept has been tested by differential Kelvin probe measurements. This investigation was also performed in the frame of FlexSmell project for future developments of biosensor based RFID systems.
Keywords: Conducting polymers, Dithienyl pyrrole, Chemical gas sensors, Smart multisensing RFID, Biosensors.
Chemical sensors