Three dimensional spatiotemporal nano-scale position retrieval of the confined diffusion of nano-objects inside optofluidic microstructured fibers

Abstract

Fiber-based 3D tracking of nano-scale objects with high spatiotemporal resolution is demonstrated for exploring dynamics at the nanoscale levels.

Three-dimensional spatiotemporal tracking of nano-objects diffusing in water-filled optofluidic microstructured fiber

“…The choice of nanosphere diameter represents a compromise between the intensity decay across the water-filled microchannel, the in-fiber power, the scattering cross section and the frame rate, allowing the nanosphere to be tracked along the transverse direction at any time. The particle diameter considered here is larger compared to our previous work [13], imposed by a smaller scattering coefficient and a faster field decay, both of which result from the smaller RI of water compared to the liquid used in our previous work.…”

“…In order to decode the axial position from the scattered intensity, an bijective function between the local intensity distribution of the evanescent field and the y-coordinate (I = f(y), y = f −1 (I)), (f −1 is the reverse of f) is required, i.e., the y-position can be uniquely determined from one certain intensity. In contrast to the water-DMSO mixture used in our previous work (RI n r = 1.44 at a wavelength of λ = 640 nm) [13], in which the field intensity can be described by a uniform exponential function within the whole channel, the intensity distribution (simulated by finite-element modeling using COMSOL) of the evanescent field inside the microchannel in case of pure water filling is substantially more complex regarding the following three aspects: (i) First, using water leads to a distinct variation of the intensity inside the microchannel not only along the y-axis but also along the x-direction in contrast to our previous work using DMSO/ water. Consequently, the mathematical function that relates y-position and intensity must be determined separately for each x-position.…”

“…2, Eq. 3leads to t d is larger compared to those of the tracked directions which is expected due to the stronger susceptibility of the intensitymediated position retrieval procedure on experimental inaccuracies (for details see the study by Jiang et al [13]).…”

“…Recently microstructured optical fibers have been introduced as a novel platform for the tracking of diffusing nano-objects over very long time scales using elastic light scattering [9][10][11][12][13]. Here tracking by means of elastic light scattering includes key advantages such as unlimited photon budget, fast data acquisition [14,15] and avoidance of labeling [16], all of which are difficult to achieve with fluorescence-based schemes.…”

“…Here tracking by means of elastic light scattering includes key advantages such as unlimited photon budget, fast data acquisition [14,15] and avoidance of labeling [16], all of which are difficult to achieve with fluorescence-based schemes. As recently demonstrated, 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 D m ≈ 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.…”