Optical tweezers are a powerful tool in the study of biological systems, where they are used to manipulate objects such as living cells at the microscale. The principle behind optical tweezers is that an object with a higher refractive index than the surrounding liquid is attracted towards the focus of a tightly focused laser beam. By using two laser beams, a living cell (e.g. a red blood cell) can be ‘grabbed’ at two different places to move, rotate or even stretch it. In optical trapping microrheology, this principle is used to study the visco-elastic properties of living cells, which provides important insights about cell structure and which can be used for diagnostics. The correlation between the movement of two optically trapped points of the cell is measured at different frequencies, either by looking at random variations due to Brownian motion (passive microrheology) or by moving one of the laser beams (active microrheology).
Figure: Schematic representation of an optical tweezers setup, artist impression of optical manipulation of a red blood cell, and an actual experiment in which a red blood cell is “stretched”.
The “Liquid Crystals and Photonics” (LCP) Group has built a double optical tweezers and accurate position detection setup, around a state-of-the-art confocal fluorescence microscope. We recently demonstrated that we can use this setup to precisely manipulate (move, rotate, stretch, …) single red blood cells (see figure). In this master thesis project, we want to extend the possibilities of our setup to perform optical trapping microrheology. Your goal will be to implement and compare the different variations of microrheology described above, and use them to study the visco-elastic properties of a number of different systems, with an emphasis on living cells. The project includes technological, experimental and theoretical work, and is of a particular interdisciplinary nature, with aspects of engineering, physics and biology.
The staff of the LCP group will provide you with all the necessary help and know-how, but we also encourage you to take the initiative to come up with your own ideas to tackle the project. Where feasible and within the scope of the project, we'll support you to develop these ideas.