Organic Sensor Devices
Many organic and organic/inorganic hybrid materials display specific chemical or physical interactions with the odours of e.g. air pollutants, food contaminants, or explosives. They are in principle useful as sensors for the monitoring of such materials in the environment, or the food chain. We are interesting in developing and testing transducers that translate molecular recognition into measurable physical quantities. We focus on electronic transducers, including chemiresistors and organic field effect transistors (OFETs). Figure 1 shows an image of a series of our OFET devices alongside a graph showing the final device characteristics. Note the low operating voltages attained by the use of novel gate insulators.
Above: A photograph of OFET devices designed and built by the group, alongside a graph showing the final device characteristics.
We study chemiresistors that consist of core/shell nanoparticle films. These films swell in some odours, leading to a change in their electric resistance, and thus providing a convenient sensor readout. An example of a atomic-fore microscope image of a core/shell nanoparticle film is shown in Figure 2.
Figure 2, above: An example of a atomic-force microscope image of a core/shell nanoparticle film
The electric characteristics of OFETs depend on various parameters, which all may be affected by odours. Real- time measurement and multi-parameter analysis of OFET characteristics therefore reveals particularly rich information on odours, and can discriminate between target analytes and interferants. The d evelopment of portable, cost efficient and fast equipment for the detailed and accurate characterization of sensor OFETs, and the interpretation of the recorded data, is therefore equally important to us as the development of the transducers themselves. The Electric response (orange) of an n- type organic transistor under voltage drive (blue), as characterized by our bespoke measurement circuit is shown in the figures below:
Figure 3, above left: Transistor characteristics under plain air, the semiconductor material is shown as inset. Right: Exposed to an amine odour, which is one of the indicators of food spoilage.
