Plasmonic Gold Nanorods as Probes of Soft Matter and Biological Systems

Doctoral thesis, 2026

Motion and structure at the nanoscale encode information about local forces, mechanical
properties, and dynamic interactions that are difficult to access using conventional
measurement techniques. This challenge is particularly pronounced in biological and
soft-matter systems, where fluctuations and structural changes demand probes combining
minimal perturbation with high spatial and temporal sensitivity. Plasmonic gold
nanorods provide such a platform. Their localized surface plasmon resonance gives rise
to strong light scattering for sensitive optical readout, while optical forces and torques
enable controlled trapping, translation and rotation.

This thesis explores gold nanorods as nanoscale probes in complex biological and physical
environments. Single nanorods are optically trapped and driven to rotate by circularly
polarized light, transducing local mechanical activity into rotational-frequency
fluctuations. Applied to living endothelial cells, this light-driven nanomotor platform
resolves heterogeneous nanoscale motions across the nucleus, perinuclear region, and
cell periphery, and uncovers transient oscillations that reveal short-lived mechanical
events typically inaccessible to conventional methods. The same rotational control,
applied beyond biology, enables low-contact profilometry through lateral scanning of
a trapped nanorod over nanoscale surface features. In another approach, nanorods
serve as intracellular tracers of vesicular motion. Dark-field microscopy combined with
deep-learning-based particle tracking and state segmentation enables long-duration,
high-throughput analysis of intracellular transport in prostate cancer cells, resolving
confined, diffusive, and directed motion across large trajectory ensembles. This reveals
distinct transport phenotypes, with diffusion dominating in both cell lines and directed
transport occurring as short-lived bursts. Nanorod surface chemistry further shapes
this behavior, modulating the coupling between vesicle loading and active transport.
Together, these studies establish plasmonic gold nanorods as a versatile platform for
probing nanoscale dynamics with minimal perturbation across biological and physical
systems. The results highlight the pronounced heterogeneity of such environments and
demonstrate how a single nanoscale probe, viewed through light, can resolve motion
and structure across diverse complex systems.