Nanoparticle tracking analysis based on microstructured waveguides

The thesis focuses on the approach of fiber-assisted nanoparticle tracking analysis based on elastic light scattering, clarifies its capability of ultralong and fast-tracking of label-free nanoparticles, points out the limitations in the current schemes, and proposes related solutions. Firstly, the thesis reviews the fundamentals of fiber optics and Brownian motion and presents the data methods used in this study. Secondly, a trajectory of 50 nm gold nanosphere with a typical length of 10$^5$ frames and duration of 40 seconds is obtained by using optofluidic nanobore optical fiber, and the results are compared with state-of-the-art methods. Although the nanochannel transversely confines nanoparticles in the focal plane, the spatial-dependent modal fields cause the scattered intensity to fluctuate with the motion of the target. The third part hence presents a pathway to generate flattened modes within nanofluidic fiber, which allows constant intensity in all three dimensions. As a result, the focal depth is remarkably improved for particle tracking measurements. Also, the general flat-field condition is given for other types of waveguides. Lastly, a novel fiber-integrated optofluidic chip is explored for nanoparticle detection. The concept employs a freely propagating Gaussian beam as illumination for the specimen that is filled in a core-less capillary fiber, aiming to establish a near-flat light field and break through the limits of the flat-field condition in optical fibers.