The invention relates to a method of synthesis of substantially pure nanoparticles in a continuous-flow system, in which a precursor substance solution undergoes reduction reaction using a reducing agent solution and nanoparticles are produced, wherein the reduction reaction is terminated by adding an agent neutralizing the reducing agent and a stable nanoparticle colloid is produced. In the method of the invention a need for using surfactants or other organic molecules for nanoparticle stabilization has been eliminated.
