Organic heterojunctions for sensor applications

Lead Research Organisation: Imperial College London
Department Name: Dept of Physics

Abstract

Organic bioelectronics is a field of research that combines the use of organic electronics with applications related to biological systems. These devices can extend the range of biosensors, wearable textiles (e-skins), neural probes and many other novel applications. This project will concentrate on sensor applications that utilise organic electrochemical transistors (OECT). Biosensors, a particular of area of research that has developed novel biomimetic devices will be introduced.
Biosensors are a low-cost and effective method of delivering point-of-care healthcare i.e. portable diagnostic devices.

The OECT is one of the newest variants of transistor types; they offer potential in communicating with biological milieu.
However, due to its complex nature in using mixed conduction polymers such as PEDOT:PSS, the device mechanisms are not well understood. One of the challenges that arise from using OECTs is understanding the role of the ions from the electrolyte. How do the ions interact with the PEDOT:PSS when transported into the film? Can it be considered as electrochemical dedoping when there is no charge transfer species formed or is it still an electrostatic interaction when the ions penetrate and interact in the bulk of the film? Upon the interaction between ions from the electrolyte and the CP, it is possible that CP properties such as charge carrier mobilities and densities are affected. We can attempt improve our understanding of the ionic component in OECTs. This could help optimise newer device applications to increase transconductance and response times.

It may be beneficial to study already established devices as the OECT operation can differ depending on the application due to differences in electrolyte, biofunctionalization etc. For example, in relation to current devices, Pappa et al. hypothesised that their initial PLL layer on top of the PEDOT:PSS could possibly dedope the film. This could have been confirmed or disproven using in situ Raman spectroscopy to observe the changes in the doping levels upon the attachment of PLL. APS could also be used to support the Raman findings by observing any changes in the work function if there is any dedoping process in this case. Therefore, in situ characterisation could help clarify device operation mechanisms. This is because there is usually a difference when characterising individual materials and devices under operation. For example, certain devices only become unstable when there is an applied bias. This can be detected by characterisation with in situ electrochemical Raman spectroscopy, where the bias is controlled and current is recorded alongside any changes to the intramolecular structure of the CP. A large area of research is dedicated to improving conductivity within materials. With more studies focusing on film modifications with ionic liquids and solvents as secondary dopants, it is important to monitor what happens to the intramolecular structure when the CP is modified. This is because it can be correlated to changes in the intermolecular scale such as morphology and packing. Studying the effects of these changes could lead to the fabrication of improved OECTs using different geometries, electrolytes or dopants.

A more thorough understanding of PEDOT:PSS and OECTs can be established through in situ characterisation of the device. Then, novel devices such as the 3D scaffolds mentioned previously, could be studied. One of the challenges in the scaffold research was identifying the different phases of CP and cells within the 3D structure. This could be investigated via Raman mapping of multiple cross-sections of the scaffold. As new materials for OECTs and devices for bioelectronics are developed, there is opportunity to study and characterise. Eventually, after understanding the limitations of the devices and materials, fabricating higher performance and stable OECT-based devices is a possibility.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/R512540/1 01/10/2017 31/03/2022
2494970 Studentship EP/R512540/1 01/10/2017 31/12/2021 Ellasia TAN