Confined nucleation and growth of molecular nanocrystals for biophotonics: fluorescence imaging and photodynamic therapy

An original process of sono crystallization allows to confine and favor the nucleation and growth of organic nanocrystals (NCs) in droplets by applying ultrasounds ...
An original process of sonocrystallization (in solution to the crystallization solution) allow to confine and favor the nucleation and growth of organic nanocrystals (NCs) in droplets by applying ultrasounds. This results in highly fluorescent tracers for biological imaging based on two-photon fluorescence scanning microscopy. These tracers (40-100 nm) are based on molecular NCs, which combine the good photostability of crystals with a high number of molecules (105-106) constituting each NC, thus enhancing strongly the absorption cross section and fluorescence emission. This leads to bright tracers that greatly increase fluorescence contrasts for deep 3D imaging in biological tissues. On the other hand, we have started, in collaboration with biologists, to test the possibility of preparing molecular NCs for photodynamic therapy (PDT). Finally, some specific molecular NCs (non-centrosymmetric structure or highly conjugated molecules) will be involved in the characterization of optical nonlinear properties of nanocrystals (two-photon absorption, second harmonic generation, exaltation of excitonic properties, etc.) in collaboration with physicists.
The main objective of this internship will be to control the confined crystallization of molecular NCs in droplets of organic solvents. For that, organic compounds will be dissolved in organic solvents miscible with water (alcohols, THF, dioxane…). The resulting solutions will be suddenly sprayed and dispersed in water through ultrasounds. As water is generally a non-solvent for molecular phases, the corresponding NCs will nucleate and grow when the solvent droplets will be gradually mixed in water.  We recently made a step-forward in the control of this process by producing nanometer-sized crystals (50 nm in diameter). Based on a fully developed reactor, the goal is now to produce monodisperse initial droplets to obtain narrow size distributions of NCs (50-100 nm) by adjusting accurately the confined nanocrystallization conditions. The resulting NCs will be characterized by X-ray diffraction, electron microscopies (SEM and TEM), dynamic light scattering, Raman and fluorescence spectroscopies. Finally, we will plan to couple this confined nanocrystallization method in solutions to sol-gel chemistry to cover in a second step the NCs with a thin amorphous shell to produce biocompatible NCs and allow then their bio-functionalization for in vitro or in vivo studies (fluorescence imaging, see image below, and PDT experiments).
 

Nanochemistry

Chemistry, material science. Strong interest in the development and characterizations of nanomaterials with spectroscopic properties for biological or nanomedicine applications.
 

Published on October 15, 2021
Updated on September 7, 2022