Grating and waveguide plasmonic sensors

Femtosecond lasers produce pulses of light which are extremely short and at the same time extremely powerful. The intensities available when light from such a laser is focussed down are capable of modifying the structure of transparent materials or even ablating material from the surface. We have developed an understanding of the interaction of fs laser pulses with optical glasses so that, depending on the pulse parameters, we can create light waveguides, couplers, bends and grating structures or even machine the surface to alter its topology on a micron scale.

In this project we wish to bring these capabilities together to create a generic plasmonic sensing technology. Surface plasmons are oscillations of the free electrons in a thin metal film and these can be generated using the energy from light travelling in a waveguide close to the metal film. Importantly, the transfer of energy from the light to the plasmon only occurs at a well defined wavelength which depends strongly on the refractive index in a micron thick region above the metal film where the electric field of the plasmon extends. By sending a broad spectrum of light though the waveguide near the metal film and noting which wavelength is absorbed by the device it is possible to measure the refractive index above the metal very accurately.

If chemical or biochemical specific coatings are applied to the metal film then the sensor can detect specific species. In this proposal we plan to investigate the use of aptamers in this regard. Aptamers are oligonucleotide sequences, which can be designed to bind to specific molecules, proteins, DNA sequences or even cells, providing a highly flexible sensing technology.

An additional application for the technology is as a means of monitoring cell movement and growth. Cells contact a surface at specific points and if a cell is placed on the plasmon supporting metal film, light will be scattered from the plasmon field at the points of contact. This light may be viewed using a microscope which will allow the movement of the cells to be tracked over time. Cells respond differently depending on surface topology and the fs laser can be used to modify the sensor surface to enable studies of the effect of different surface topologies on cell movement and growth.

We are aiming to develop a generic sensing technology applicable in many areas:

- In-line measurements in chemical plants.
Beneficiaries: industry through improved efficiency and productivity

- Remote environmental sensing and monitoring of airborne and water based pollutants.
Beneficiaries: sensor manufacturers, environment agency, the public via a more healthy environment

- Multiple tests for various chemicals on one sensor, as well as the potential for multiplexed sensing arrays.
Beneficiaries: health industry and patients through more sensitive and timely analysis of biopsies, security industry and society through sensitive and timely identification of pathogenic chemical and biochemical species.

- Improved understanding of the interactions between cells and their environment for controlling the cellular status and producing biosensor-based cell assays.
Beneficiaries: Tissue engineering including stem cell research and ultimately patients

- Cellular diagnostics; automated individual cellular diagnostics for specific proteins, enzymes, carcinogens or infections by monitoring cellular metabolism along with studies of cellular properties of normal and diseased cells.
Beneficiaries: Improved information to the health care professional leading to better outcomes for patients; pharmaceutical industry through ability to quickly assess the impacts of drugs on cells and a better understanding of drug delivery at the cellular level.

Our research will of course be disseminated through the channels of international journal publications and major international conferences. In addition we will seek out potential commercial partners to exploit the technology in specific fields (for example our project partner TQ Environmental for methane detection). The photonics research group has a more than 15 year solid track record of such collaborative activity which has resulted in several spin-off companies. We will find partners through our extensive contact list and by publicising our work in more commercially focussed environments, such as via the knowledge transfer networks (this avenue has proven productive in the past) and with the assistance of the Aston University Business Partnership Unit. Further details are provided in the Pathways to Impact document.