Tracking the motion of single nanoparticles inside living cells: New insights into intracellular crowdedness

How biomolecules move inside living cells, in space and time, is not only a fundamental research question but is key to the understanding of many biological processes. With the development of advanced single-particle tracking techniques, it has become apparent that biomolecules inside cells exhibit complicated types of motion, which cannot be simply described as random from thermal diffusion or directed motion via molecular motors. This is because the cell contains a cytoplasm crowded with large biomolecules and organelles, and a heterogeneous network of cytoskeletal protein filaments.

Key to the in depth understanding of biomolecular motion inside living cells is the development of new techniques capable to track single particles in 3D with high localisation precision and speed, alongside mathematical models that can describe the experiments according to physics' law, and eventually reveal new insights into the highly complex living cell's interior.

In this project, you will apply an advanced laser micro-spectroscopy technique called resonant Four-Wave Mixing, pioneered by the supervisory team, to image and track single small gold nanoparticles background free inside cells with precision at the nanoscale in 3D. Nanoparticles will be micro-injected into eggs (oocytes). These are large cells actively studied by the supervisory team (from mammals and invertebrates). They have ATP levels and metabolic rates closely linked to their ability to mature, be fertilised, and further develop into good quality embryos. Notably, movement of particles can be influenced by molecular motors that are ATP-driven. Hence, studies of intracellular motion in these cells will be a platform for new technologies to monitor embryo metabolism and predict viability.

Experimental single particle trajectories will be measured in eggs under different metabolic conditions, and will be compared with mathematical models of diffusion, reflecting expertise in mathematical and computational methods by the supervisory team. Measured time trajectories will reveal combinations of random, directed, transiently stalled and constrained motions related to crowded environments. The aim will be to develop a causal link between the nanostructure of the environment and particle motion. This in turn will stimulate hypothesis to be verified experimentally, and will provide an unprecedented insight on the cell's interior.