A micro-flow-through system comprising a manifold for segment generation and mixing, a set of PC-controlled syringe pumps for fluid actuation and an optical multi-channel system for particle characterization were applied for combinatorial variation of reaction mixtures for the synthesis of plasmonic nanoparticles. The complete space of combinations of reactant concentrations was realized by an automated generation of micro-fluid segment sequences by a combined slowly shifting flow rate of one component, and a periodically fast shifting flow rate of a second solution, both against water. The nanoparticles colloidal product solutions are characterized by differential centrifugal sedimentation spectroscopy (DCS), UV/VIS and SEM. The size distribution spectra and the optical spectra indicate the effect of composition on the particle quality. In case of nanoparticle synthesis screenings, the concentration of metal salts, reducing agent, ion strength and pH can be varied. The multi-dimensional addressing of parameter spaces can be used for finding optimal reaction conditions for a narrow size or shape distribution as well as for a tuning of the optical properties.