Responsive surfaces: Lanthanide based Langmuir-Blodgett mono-layers for the sensing of chemical warfare agent mimics

Sensors play an important role in society, with applications in a variety of circumstances including environmental monitoring, clinical biology (e.g. disease marker detection), food safety (e.g. detection of contaminants), defence (e.g. real-time biological and chemical warfare agent (CWA) detection, explosives detection), the nuclear industry (e.g. radiation and temperature sensors), and engineering/avionics (e.g. temperature and pressure sensors, surface damage sensors) to name just a few. In all cases the early detection, or sensing, of change is paramount. One particularly important application of sensor development is in the field of CWA sensing. The highly toxic nature of the organophosphonate (OP) family of nerve agents and the potential for exposure to both military and civilian populations represents a real danger. Understandably, there is a clear requirement for adequate real-time detection capabilities for both military personal and civilian populations where advanced warning of exposure will help prevent casualties.

Current analytical technologies for sensing organophosphonates, whilst being highly sensitive, have some clear limitations including complex instrumentation, inconvenient sample preparation, lack of portability, and high cost. These drawbacks somewhat hinder the development of cost-effective field based portable devices that are easily integrated into personal protective equipment (e.g. smart textiles) and non-invasive detectors for use in public areas.
One approach that has been developed to overcome these problems is to measure signal change through interaction with responsive materials that undergo changes in chemical, electrical, optical or magnetic properties on exposure to chemical derivatives. Luminescence as a responsive medium for general sensor development has received significant attention and in particular some elegant luminescent supramolecular systems have been developed over the last 5 - 10 years for the detection of CWAs and their mimics. The majority of these have been solution based sensors (this limits the use in devices - solutions are inconvenient to store, often suffer from instability and sample preparation can be troublesome - see above), and with field based applications in mind, there is a need to move from solution responsive systems to surface immobilised receptor-reporter based sensors. This represents a significant gap in the field as luminescence sensing offers an attractive medium for immobilised sensors with potential to develop small portable devices from simple components. As such, we will use an alternative approach to overcome some of the above drawbacks. By utilising thin film (mono-layers) lanthanide based sensors where the sensor is deposited (immobilised) onto a surface (using the Langmuir-Blodgett technique) and undergoes a change in light emitting properties on exposure to low levels of CWA mimics we will overcome the limitations listed above. Throughout this research project we will explore this alternative approach for selectivity and sensitivity towards CWA mimics and ultimately assess its applicability for inclusion into functional devices. Therefore, our approach of combining the superior photophysical properties of the lanthanides, and the control over deposition afforded by the Langmuir-Blodgett technique will generate designer lanthanide luminescent sensors that can be immobilised easily and reliably, potentially transforming the field of on-surface molecular sensing.

We propose to develop new luminescent sensors for chemical warfare agents that are easily formed into thin films and hence have potential to be incorporated into functional devices. The proposed work has the potential to generate a number of types of impact.

Societal Impact. The long term impact of the proposed research is the development of new functional sensing devices for the detection of CWAs. With the ever present threat from global terrorism, it will be important to develop new sensor technologies for real-time sensing of CWAs and bio-hazards that pose significant risk to civilian and military populations. Additionally, there is potential for this research to be further developed for use in medical settings (e.g. highly sensitive sensors for point of care diagnostics and improved healthcare); environmental monitoring (e.g. pesticide detection/monitoring); and food safety (e.g. detection of poisons/toxic contaminants).

Economic Impact. Research and development into new sensor technologies is an area of considerable importance not only within academic research institutions, but also in commercial and industrial markets which are worth over £3bn annually in the UK and £50bn worldwide. Additionally, the development of defence/homeland security based sensors is experiencing significant growth with the current world political situation. It is therefore vital that the UK retains a robust presence in this sector, something that will only be realised by being prominent in the area of targeted research leading to the generation of new intellectual property. The work outlined in this proposal will help to secure the economic health of this sector.

Technological and Commercial Impact. Immobilised mono-layers of lanthanide lumiphores with readily manipulated binding sites for a range of analytes have potential to be a highly sensitive sensing medium for small molecules (e.g. organophosphonate derivatives). They are therefore ideal materials for application in sensing devices, suggesting that they have potential to make a significant technological impact as components in portable sensing devices (field based and non-invasive sensors), smart materials and smart textiles. The Langmuir-Blodgett deposition technique is robust, does not require significant substrate preparation, and can deposit films on a variety of substrate types and shapes, therefore sensors deposited onto surfaces by this method have the potential to be integrated easily into cost-effective portable sensing devices.