Recently, it has been shown that nanoparticles made of biological active principle are more efficient than the molecule itself. The linkage between a nucleoside analogue (anti cancer activity) to a squalene leads to nanoparticles formation with an average size of 100nm. This increases the therapeutic index and the efficiency of the administration. Up to day, for these new systems, the control of size and polydispersity with nanoprecipitation is not optimized and the mechanism of the nanoparticle formation not fully understood. The aim of this proposal is to obtain the time resolved small neutron scattering signal from squalene derivative nanoparticles in D2O during their formation. A non toxic model (squalenic acid) with similar behavior will be used. The mixing is ensured by a home made millifluidic set-up with a continuous flow after the mixer allowing to access second time resolution by coupling space and time. Different concentrations and different solvent ratio will be studied to identify the key parameters that control the final size and polydispersity. The experimental results will be modeled by nucleation and growth theory to elucidate the underlined mechanism