Abstract Twelve nanometer Au nanoparticles generated by citrate reduction were handled in a chip-based interdiffusion microreactor without significant adsorption to the surfaces at flow rates in the _l/min-range. Furthermore, the microreactor was tested for the generation and growth of colloidal gold nanoparticles. Following a seeding growth approach, starting from 12 nm citrate-stabilised gold seeds, larger particles of diameters ranging from 15 to 24 nm were prepared. This method makes use of ascorbic acid as reducing agent, while the 12 nm seeds serve as nucleation centers. For particle stabilization polyvinyl pyrrolidone was employed. Particle size distributions were determined by an analytical centrifugation method or atomic force microscopy. UV-Vis spectra of the colloidal solutions were recorded. The size distribution of the produced particles is altered by the flow rate of the reactants, their concentration ratio as well as the order of the reactant addition. In the conducted experiments the mean particle diameter increases with decreasing flow rate and particle growth was only observed, if the concentration of seeds was equal or lower than the concentration of Au3+. Without the addition of polyvinyl pyrrolidone, the produced colloidal solutions were unstable and decomposed within 7 days. © 2003 Elsevier B.V. All rights reserved. CPS 高精度納米粒度分析儀