The development of nanotechnology based nowdays on the assembly (or even self-assembly) of building blocks that are nanoparticles. The goal is to make use of the intrinsic properties of nanoparticles such as their plasmonic capacities, high surface area or reactivity and of their assembly, to obtain new functional devices such as nanofiltration membranes or photonic crystals. In all cases, the first step is to control the synthesis of these objects in terms of quantity, size and distribution. This control cannot only be obtained by the conventional method of trials and errors. The laboratory therefore had developed a mechanistic analysis of the processes of nucleation and growth of these objects by coupling (i) mixing controlled reactors (microfluidics), (ii) soft chemistry (mainly ambiant temperature and in water) (iii) to study using techniques of in situ sensors (light, SAXS, WAXS, XAS, SANS) the kinetis of synthesis with the adapted resolutions (down to the millisecond when necessary) and theoretical analysis of both conventional (CNT) as well as atomistic. The potential impacts of these objects towards the environment is also a major subject of interest for the LIONS researchers who in parallel study in parallel.