Ultralong Tracking of Fast‐Diffusing Nano‐Objects inside Nanofluidic Channel−Enhanced Microstructured Optical Fiber

Nanoparticle tracking analysis (NTA) represents one essential technology to characterize diffusing nanoscale objects. Herein, uncovering dynamic processes and high‐precision measurements requires tracks with thousands of frames to reach high statistical significance, ideally at high frame rates. Optical fibers with nanochannels are used for NTA, successfully demonstrating acquisition of trajectories of fast diffusion nano‐objects with 100 000 frames. Due to the spatial limitation of the central nanofluidic channel, diffusion of objects illuminated by the core mode is confined, enabling the recording of Brownian motion over extraordinarily long time scales at high frame rates. The resulting benefits are discussed on a representative track of a gold nanosphere diffusing in water in over nearly 100 000 frames at 2 kHz frame rate. In addition to the verification of the fiber‐based NTA using two data processing methods, a segmented analysis reveals a correlation between precision of determined diameter and continuous time interval (i.e., number of frames per subtrajectory). The presented results demonstrate the capabilities of fiber‐based NTA in terms of 1) determining diameters with extraordinary high precision of single species and 2) monitoring dynamic processes of the object or the fluidic environment, both of which are relevant within biology, microrheology, and nano‐object characterization.