The present invention provides a process for producing nanoparticles, comprising : providing a first liquid comprising a metal salt and at least one species of ligand having a functional group capable of binding to a metal surface, providing a second liquid comprising a reducing agent; providing at least one liquid droplet generator operable to generate liquid droplets, causing the at least one liquid droplet generator to form liquid droplets of the first liquid, passing the liquid droplets through a gas to contact the second liquid so as to cause the metal salt and the at least one species of ligand to come into contact with the reducing agent, thereby causing self-assembly of nanoparticles, said nanoparticles having a core of said metal and a corona comprising a plurality of said ligands covalently bound to the core. Also provided are nanoparticles produced by the process of the invention and use of such nano particles in medicine.