Optically Driven Nanomotors for Cellular Motion Detection at the Nano-Scale

Licentiate thesis, 2024

Studying cells, the fundamental units of life, is crucial for advancements in fields like medicine and biotechnology. Advances in cellular research are closely linked to the development of methods that can measure nanoscale biological processes, both in time and space. A particularly important area is the study of mechanical motions in single cells, which are connected to cell viability and health. To study these nanomotions, a highly sensitive, non-invasive method is essential.

This thesis presents a method for detecting nanomotions in living cells using a single rotating nanomotor trapped with optical tweezers. Optical tweezers are a popular tool used in biological research due to their ability to sense and apply minute forces and torques to microscopic objects, as well as their ease of implementation allowing for precise studies of biological samples. In this approach, a nanorod supporting plasmonic resonances is trapped in two dimensions against a glass surface and rotated through torque transfer from a circularly polarized laser beam. The rotation frequency of the nanomotor is proportional to the optical torque, which is determined by the light intensity. By manipulating the nanomotor along the beam’s focus, this thesis demonstrates a near-linear relationship between its rotation frequency and position. Fluctuations of the cell membrane can displace the nanomotor along the laser beam, allowing for the detection of cellular nanomotions ranging from tens of nanometers to up to a micrometer. This opens new opportunities to study specific cellular processes, and in turn facilitating a deeper understanding of single-cell pathology.