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Luminescent nanorods as ultimate probes of fluid flow

by Anne-Marie - published on , updated on

A new method, based on the measurement of the polarized luminescence of nanorods, has been developed for the study of the flow in microchannels. This work, carried out in the framework of a Franco-Dutch collaboration between the Laboratory of Condensed Matter Physics and the Hydrodynamic Laboratory of the Ecole Polytechnique, on the one hand, and the Van’t Hoff Institute of University of Amsterdam, on the other hand, is published in the June’s edition of Nature Nanotechnology.

(a) Scanning electron microscopy image of LaPO4 nanorods. (B) and (c) Diagram showing the alignment of the nanorodets in a flow under the effect of the shearing forces. (D) Diagram of a microfluidic channel studied. (E) and (f) Experimental and theoretical mapping of the shear field in the flowing fluid.

The study of fluid flow in microchannels is relevant to many fields. For example, determining blood flow in the arteries is crucial for understanding the plaque formation in atherosclerosis. Hydrodynamic simulations are continuously improving, but their validation requires experimental feedback which run up against the difficulty of characterizing the flow on a very small scale, typically a few hundred nanometers.
The approach proposed by the Franco-Dutch research team is based on the use of monocrystalline lanthanum phosphate nanorods (LaPO4), doped with photoluminescent Europium (Eu3+) ions. Like logs floating on a river, these nanorods, 10 nm in diameter and 200 nm in length, orient themselves in the flowing liquid under the effect of shear (flow velocity gradient). Their orientation determines the polarization of the Eu3+ luminescence. The measurement of the photoluminescence polarization using a confocal microscope thus allows carrying out the tomographic cartography of the orientation of the rods and therefore of the shear in a microfluidic channel. It has therefore become possible to analyse, in real time and with unprecedented resolution, the flow of a fluid in a microfluidic channel.
This work opens promising perspectives for the fundamental understanding of phenomena related to the fluid flow in complex channel systems. Moreover, these orientation probes could also be used in biology, to study complex mechanisms related to the orientation dynamics of bio-macromolecules.

Monitoring the orientation of rare-earth doped nanorods for flow shear tomography, J. W. Kim, S. Michelin, M. Hilbers, L. Martinelli, E. Chaudan, G. Amselem, E. Fradet, J.-P. Boilot, A. M. Brouwer, C. N. Baroud, J. Peretti, T. Gacoin, Nature Nanotechnology, published online 19 June 2017. DOI: 10.1038/NNANO.2017.111

Nature Nanotechnology
Université d’Amsterdam