Optical Sensing

Light is ideal as a non invasive sensor of the attachment of biomolecules at a surface. Current optical detection technologies rely on measuring the shift in the surface plasmon resonance created when light strikes a suitable metal surface (usually silver or gold) at the correct angle and polarisation. The shift is measured as a change in the intensity of the reflected light at a fixed angle.

Since light is a transverse wave motion, there are two independent quantities needed to specify the changes that occur when light is reflected from a surface.

Ellipsometry is a technique that determines these two quantities, one related to the change in the amplitude of the light, and the other related to the change in its phase. The project explores the use of the phase information in light after it has interacted with a surface plasmon as a means of sensitively and conveniently detecting the attachment of a biomolecule at a surface.

Below is a diagram of a flow cell for use with optical sensing by ellipsometry. The cell is capable of applying an electric field to the solution to investigate its effect on protein attachment.