Abstract
Abstract Three-dimensional (3D) tracking of nano-objects represents a novel pathway for understanding dynamic nanoscale processes within bioanalytics and life science. Here we demonstrate 3D tracking of diffusing 100 nm gold nanosphere within a water-filled optofluidic fiber via elastic light scattering–based position retrieval. Specifically, the correlation between intensity and position inside a region of a fiber-integrated microchannel has been used to decode the axial position from the scattered intensity, while image processing–based tracking was used in the image plane. The 3D trajectory of a diffusing gold nanosphere has been experimentally determined, while the determined diameter analysis matches expectations. Beside key advantages such as homogenous light-line illumination, low-background scattering, long observation time, large number of frames, high temporal and spatial resolution and compatibility with standard microscope, the particular properties of operating with water defines a new bioanalytical platform that is highly relevant for medical and life science applications.
Highlights
Measuring the trajectory of diffusing nano-objects that have dimensions substantially below the diffraction limit represents a powerful approach particular within bioanalytics and life science
The slope parameter obtained from experiment pexp shows a very good agreement with its simulated counterpart psim (Dmx, sim 1.2 μm, Dmy, sim 1.1 μm) (Figure 4a) which is remarkable considering that this parameter has been determined from two pairs of values only and that the simulations include several assumptions such as a perfect ellipse shape of the channel or a simple concentric refractive index (RI) distribution in the core
The non-ideal ellipse shape of the channel contributes to the error which is not considered in both simulations and experimental data analysis
Summary
Measuring the trajectory of diffusing nano-objects that have dimensions substantially below the diffraction limit represents a powerful approach particular within bioanalytics and life science This allows us to understand processes at the nanoscale level, examples of which include protein folding [1] or for measuring virus concentrations [2]. One configuration of the fiber-based approach allows full 3D tracking of a diffusing nanosphere over thousands of frames at kHz frames rates via elastic light scattering–based position retrieval [13] This approach uses a microstructured optical fiber including a liquid-filled microchannel (diameter Dm ≈ 1 μm) running parallel to the light guiding glass core (with a center-to-center distance of about 2 μm) allowing to retrieve the position of the nano-object along the direction of the microscopic detection via the intensity of the light scattered at the evanescent field of the core mode.
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