Optoelectronic Detection of Explosives

Current research in explosives detection focuses across key themes spanning the mode of signal transduction involved, including Optical, Electrical, Gravimetric and Calorimetric based solutions. Significant progress has been made in optical based detection systems and to date the most successful strategies are based upon solid state fluorescent materials and modulation of analyte interactions via electron transfer. With the exception of the conjugated polymers however, few materials have been incorporated or commercialised into device driven architectures. The future for fluorescence based sensors is in exploitable solid state technologies with enhanced sensitivity and selectivity. This proposal aims to combine the advantages of optical and electrical signal transduction to facilitate a synergistic optoelectronic sensor based upon bi-layer thin film photoconductor technology.

Bi-layer heterojunctions play key roles in optoelectronic devices such as photovoltaics, organic light emitting diodes (OLEDS) and photoreceptors. The interface is responsible for creation and dissociation of photogenerated excitons into charge carriers that are transported to the electrodes via applied bias. Compared with chemiresistors and field effect transistors, separation of the processes of charge generation and charge transport into two different films in a heterojunction facilitates a more simplistic optimisation of the physical processes involved. Analyte detection via modulation of current output from lateral bi-layer photoconductors is possible using exciton generating layers whose photoluminescence efficiency is affected by local environment. Many potential organic fluorophores that could fulfil this role are however, poorly emissive in the solid-state from aggregation induced quenching effects and rational control of these unfavourable interactions is crucial for their future realisation in functional applications.

Organic dyes and pigments are ubiquitous materials in photoconductive technologies such as xerography, upon which lateral bi-layer heterojunction sensors are based. They are effective in charge generation through careful manipulation of purity, crystallinity and morphology and as such make extremely attractive materials for the construction of bi-layer sensors. Furthermore, many dyes and pigments are amenable to organic functionalisation and crystal engineering, facilitating introduction of analyte specific recognition sites, tuneable absorption and controlled morphology to provide broadband sensor architecture. Thus, this proposal aims to develop a systematic understanding of the role of molecular design and crystal engineering on the solid state chemistry of photoluminescent dyes and pigments which can be exploited via the bi-layer approach. This aspect of the proposed research addresses several technical challenges in materials science and the fabrication of a device employing organic dyes and pigments, and metal oxides will require an in-depth understanding of their preparation, photochemistry and solid state properties. Devices based upon this structure offer significant advantages in explosives detection, providing an opportunity for high sensitivity, large dynamic range and selective target recognition with built in adaptability to changing threats. Additionally, this type of system would be non-invasive, portable and rugged, with few moving parts and the potential to offer a rapid analyte response mechanism that can be directly modulated into an electrical output.

The proposed project is timely and aligned closely with the EPSRC theme of Global Uncertainties where realisation of new technology to combat global threats will have significant societal and economical gains and potential to shape UK capabilities in fighthing terrorism. Owing to the diverse and cross-disciplinary nature of the proposal there is also a rational interface with both the Energy and Healthcare sectors which will encourage a broad impact base. An enhancement of scientific knowledge and understanding in materials research and analytical sciences will be attained with the successful undertaking of this project. Key areas in wealth creation, inward investment and new products are captured in the proposal which will benefit the economic competitiveness of the United Kingdom. Credible pathways to economic gain have been considered via intergration of an international chemical company into the project who have the infrastructure, resources, people and technical capabilities to aid in a successful outcome, particularly in relation to potential commercialisation of the dyes and pigments being studied. The project will deliver local impact and is in line with national strategic plans to foster and enhance links between Scottish universities and local companies. Integration of the Thin Film Centre (TFC) at the University of the West of Scotland will facilitate realisation channels and commercial impact opportunities for this work. The centre is a member of the Scottish Optoelectronics Association, with access to the Photonics and Plastic Electronics Knowledge Transfer Network. The centre is also linked with the Scottish Universities Physics Alliance (SUPA) with links into the DSTL Centre for Defence Enterprise who can facilitate promotion of outputs within groups such as the Materials and Structures Science and Technology Centre and at meetings such as the IED Detection Demonstration days. The TFC has strong links with the Scottish Enterprise Explosives Detection Platform who can provide pathways into companies that specialise in explosives detection. Furthermore, the TFC is sufficiently equipped to facilitate device manufacture which could help to foster local economic gain through the creation of spin off ventures with suitable project partners. The potential project outputs will achieve considerable impact in society by improving the quality of life for British citizens and influencing future government policy. Improved detection capabilities for target analytes such as explosives which can be deployed at ports and airports will enhance the safety and security of the general population. Utilisation of lightweight and portable systems in active theatres of war will also ensure increased levels of security for UK armed forces. In this sense the project is clearly positioned to shape future UK capabilities in defence which is closely aligned to the current EPSRC strategic priorities. The proposal will also enhance people based skills and fuel the European pipeline of future research excellence by providing the applicant with research independence and sustainability through the development of his academic and industrial relationships. The applicant will extend his experience in running research projects and enhance his proven leadership abilities, concurrent with the core EPSRC priority to develop future scientific leaders. The Research Assistant will have significant scope to develop practical skills, and abilities in academic leadership, development and communication. Invaluable exposure to a commercial environment will provide a balanced and realistic perspective of modern applied research. Finally, where appropriate, the theoretical and practical aspects of the proposed research will be integrated by the applicant into his academic teaching portfolio to enhance the student experience within the University of the West of Scotland and promote the enterprise, autonomy and lifelong learning that students require as graduates.