Size-controlled synthesis of gold nanoparticles using a micro-mixing system

A new microfluidic reaction chip capable of mixing, transporting and controlling reactions has been developed for the size-tunable synthesis of gold nanoparticles. This chip allows for an accelerated and efficient approach for the synthesis of gold nanoparticles. The microfluidic reaction chip is made by computer-numerically controlled machining and PDMS casting processes, which integrate a micro-mixer, a normally closed valve and a micro-pump onto a single chip. The micro-mixer is capable of generating a vortex-type flow field, which achieves a mixing efficiency as high as 95% within 1 s. Successful synthesis of dispersed gold nanoparticles has been demonstrated within an 83% shorter period of time (13 min), as compared to traditional methods (around 2 h). By using different volumes of reagents, the dispersed gold nanoparticles are found to have average diameters of 19, 28, 37 and 58 nm. The optical absorption spectra indicate that these synthesized nanoparticles have different surface plasmon resonance peaks, which are 521, 525, 530 and 537 nm, respectively. The development of this microfluidic reaction system holds promise for the synthesis of functional nanoparticles for further biomedical applications.