Detection of molecules in water with liquid crystal lasers
Begeleider(s): dr. ir. Inge Nys


Liquid crystals are materials that combine the properties of liquids and solid crystals.The molecules exhibit a certain degree of ordering while the material is still fluid. It is know since the pioneering work of Abbot and coworkers that the orientation of the liquid crystal at the interface with water can change when adding surfactant to the water. The figures below show a microscope image of a metallic grid used in TEM measurements. The squares of the grid are filled with liquid crystal. Depending on the presence (and concentration) of surfactant in the water, the image under the microscope changes from almost black to colorful. This is due to the fact that the liquid crystel changes its orientation at the interface. But due to the elastic nature of liquid crystals also the liquid crystal orientation in the rest of the volume changes. The liquid crystal can thus be used as an 'ampflifier' of reactions at the interface. Very recently (January 2015) it was shown (again by Abbott and coworkers ) that the reaction of the liquid crystal can be made specific for certain types of proteins.


In this thesis the aim is to use a TEM grid filled with liquid crystals to detect the presence of surfactant molecules in water, similar to the experiments described above. But instead of using a microscope to detect reactions at the interface, we will use a different type of liquid crystal which is chiral. Due to the chirality, there is an inherent periodicity in the material. When the periodicity is matched to optical wavelengths the liquid crystal layer can be easily transformed into a laser. The properties of the lasing signal can then be used to acquire information about the presence of biological entities in the water, thus avoiding the need for an expensive microscope setup.

The thesis work is divided into two parts: