Polarized luminescent nanoprobes and their application for in situ flow shear measurements

In this work, we use monocrystalline LaPO4:Eu nanorods as polarized luminescent probes. By distinguishing between emission peaks originating from magnetic and electric dipole transitions, we can derive the three-dimensional orientation of the nanorods through measurements of their polarized luminescence. This spectroscopy-based orientation analysis can furthermore be used to characterize microfluidic media, as the collective orientation of nanorods is directly related to flow conditions they are subjected to. Using a confocal microscope, we can locally determine their collective orientation which provides a direct measure of the shear stress. We demonstrate this method to map the shear stress profile in different microfluidic channel geometries and monitor the shear stress in an energy harvesting device.