The disadvantage of hollow optical fiber is that the light is guided through the core, and the inner channel is illuminated through an evanescent field (@Faez2015Fast, Label-Free Tracking of Single Viruses and Weakly Scattering Nanoparticles in a Nanofluidic Optical Fiber). To overcome this, it is possible to use hollow core fibers with channel diameters of several micrometers (@Fo2020Tracking and Analyzing the Brownian Motion of Nano-objects Inside Hollow Core Fibers). However, in such case, the particles can diffuse transversely over several frames. This can be used to track the position in 3D (see 202010261531), but adds to the overall difficulty of the experimental setup.
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