Continuous flow synthesis of monodisperse gold nanoparticles by liquid-phase reduction method on glass microfluidic device

Monodisperse gold nanoparticles (GNPs) in aqueous dispersion were synthesised using a low-cost glass microfluidic device with a Y-shaped microchannel. The effects of channel width and flow rate on the size distribution of the synthesised GNPs were investigated. An aqueous solution of tetrachloroauric (III) acid (source of Au ions), and a mixture of an aqueous solution of sodium citrate acid (reducing agent) and tannic acid (protective agent), were injected into a microchannel in the microfluidic device by using a syringe pump. The absorption spectra at low flow rates showed sharper peaks in comparison with those at high flow rates. At the channel width of 260 μm, the full width at half maximum of the absorption peak was 79.2 nm for 0.05 ml/min and 92.9 nm for 0.06 ml/min. From transmission electron microscopy images, the GNPs synthesised using a channel width of 260 μm and flow rate of 0.05 ml/min were found to have a mean diameter of 11.5 nm and coefficient of variation of 0.09. These results confirmed that the combination of a low-flow rate and a small channel width is essential to obtain monodisperse GNPs.