Luminescent probes are universally used to observe life and matter in small scale. However, many dynamic processes at the cellular and molecular levels remain unknown because they involve complex motions such as rotation, twisting, and bending that occur at scales below the optical diffraction limit. 
We develop novel fluorescent probes that emit light signaling the three-dimensional orientation of the probes. We utilized lanthanide-doped-nanocrystals, which emit peculiarly polarized luminescence [1, 2, 3]. These nanocrystals exhibit emission spectra with a number of sharp peaks, which varies dramatically as the probes rotate. The unique nature of lanthanide luminescence, including both electric and magnetic dipole transitions, allows to measure the orientations of individual probes [4, 5, 6] as well as their ensemble [7, 8]. We deliberately tune the host nanocrystal structure to maximize the efficiency of emission and the degrees of polarization [9], achieving unprecedented sensitivity to the orientation of nanoscale objects [4]. These nanocrystal probes can be labeled with enzymes, DNA strands, or cell surfaces in order to monitor their complex dynamics and unveil the biochemical and biomechanical processes. 

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​[1] J Kim, A de la Cotte, R Deloncle, S Archambeau, C Biver, J-P Cano, K Lahlil, J-P Boilot, E Grelet, T Gacoin*, “LaPO4 mineral liquid crystalline suspensions with outstanding colloidal stability for electro-optical applications” Adv. Funct. Mater. 22, 4949–4956 (2012). [Link]

[2] J Kim, J Peretti, K Lahlil, J-P Boilot, T Gacoin*, “Optically anisotropic thin films by shear-oriented assembly of colloidal nanorods” Adv. Mater. 25, 3295-3300 (2013). [Link] 

[3] J 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* “Monitoring the orientation of rare-earth doped nanorods for flow shear tomography”

Nature Nanotechnology. 12, 914-919 (2017). [Link] 

[4] J.-M. Kim, R. Chacón, Z. Wang, E. Larquet, K. Lahlil, A. Leray, G. Colas des Francs, J. Kim*, T. Gacoin “Measuring 3D Orientation of Nanocrystals via Polarized Luminescence of Rare-Earth Dopants” Nature Communications. 12, 1943 (2021). [Link]

[5] R Chacon, A Leray, JM Kim, K Lahlil, S Mathew, A Bouhelier, J Kim, T Gacoin, G Colas Des Francs* “Measuring the Magnetic Dipole Transition of Single Nanorods by Spectroscopy and Fourier Microscopy” Physical Review Applied. 14, 5, 054011 (2020). [Link]

[6] A Kumar, JM Kim, K Lahlil G Julie, S N Chormaic, J Kim, T Gacoin, J Fick* “Optical trapping and orientation-resolved spectroscopy of europium-doped nanorods” Journal of Physics: Photonics. 2, 2, 025007 (2020). [Link]

[7] J.-M. Kim, K. Lahlil, T. Gacoin*, J. Kim*, “Measuring the order parameter of vertically aligned nanorod assemblies” Nanoscale. 13, 16, 7630 (2021). [Link] 

[8] L. Magermans, J-M. Kim, R. Chacon, A. Leray, T. Atherton, T. Gacoin, J. Kim* “Morphogenesis and Topological Evolution of Nematic Colloids under Confinement” under review

[9] E Chaudan, J Kim*, S Tusseau-Nenez, P Goldner, O L Malta, J Peretti, T Gacoin* “Polarized luminescence of anisotropic LaPO4:Eu nanocrystal polymorphs” Journal of American Chemical Society. 140, 9512-9517 (2018). [Link]

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