The development of multisensor arrays utilising conducting polymers

• Main Author: Hinton, Andrew
• Published: Sheffield Hallam University 1997
• Subjects: 621.37; Neotronics Olfactory Sensing Equipment
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360438

This thesis is concerned with the continued development of multisensor array sensing technology for the detection and classification of aromas. The technology applies the use of conducting polymers grown across a gap between metallic conductors. The electrochemically deposited films complete a circuit and providing electrical resistance. In this format the films act as chemical resistors (chemiresistors) the current flow being influenced by the polymers' molecular electronics. Devices of this nature are potentially useful as sensors for analytes which cause the reversible modulation of the films' molecular electronics, leading to a detectable resistance change. Variation in the chemical and physical properties of the conducting polymer films has led to the generation of sensing devices capable of providing rapid, meaningful sensory information. The development of multisensor arrays containing a series of sensing devices having broad ranging sensitivities, has enabled effective discrimination of sample analytes. The information generated from such an array provides a 'fingerprint' or patterned response relating directly to the sample analyte. Complex statistical processing techniques have been coupled with the sensor technology to categorise and differentiate between the 'fingerprints' obtained. Instrumentation based on multisensor array technology has been developed by Neotronics Scientific Ltd., who currently market the NOSE (Neotronics Olfactory Sensing Equipment) based upon conducting polymer sensors. The research project resulting in this thesis was intended to develop and examine conducting polymer chemiresistor technology and explore the parameters that contribute to the production of effective discriminating sensors for use in array devices. The study involved an investigation of the variables involved in the electropolymerisation protocols, and expansion of the sensing chemiresistors available. This was achieved by analysis of polymer fabrication methods, and the variation in monomer and electrolyte feedstocks used during polymerisation. Polymer film stability was a major feature of the work performed as the long-term effectiveness of a sensing device is governed by environmental stability allowing reproducible analysis. Sensor optimisation was investigated using an individual system to determine the effect of the electrodeposition protocols, surface morphology, baseline resistance and film thickness. Polymer composition and stability were studied using a series of electrochemical, spectroscopic and surface analysis techniques. The data obtained resulted in the fabrication of chemiresistors not previously tested in electronic nose technology. Experimental optimisation studies also allowed variation in the nature of the responses obtained. A final area of investigation was the analysis of chemiresistors within a multisensor array environment using the NOSE technology. A series of arrays were prepared and the sensors exposed to a number of single, pure, organic analytes. From this data information was obtained on sensor response relating to molecular size, shape, position and nature of functional groups. The multifaceted nature of these experiments increased the number and response characteristics accessible to Neotronics, and provided a contribution to the knowledge surrounding the interactions between conducting polymer films and volatile organic analytes.