Here we propose to study the Janus character of self-assembled amphiphilic nanoparticles. For that amphiphilic core-shell nanoparticles will be synthesized with a surface consisting on two regions, one hydrogenous and hydrophilic and another deuterated and hydrophobic. The use of neutron reflectivity (NR) on a monolayer of nanoparticles oriented at the air-water interface of a Langmuir-Blodgett trough can prove the asymmetry of the nanoparticles at a macroscopic scale. To the best of our knowledge, neutron reflectivity has never been used for checking the Janus character of amphiphilic nanoparticles.