Rapid synthesis of gold nanoparticles with carbon monoxide in a microfluidic segmented flow system

A microfluidic reactor was developed to enhance the speed (reaction time <4 min) and control of the synthesis of gold nanoparticles (3–25 nm) with or without capping agents using carbon monoxide as gaseous reductant, which is easy to remove from the reaction mixture by venting. Gas–liquid segmented flow was formed inside a 1 mm inner diameter coiled flow inverter with aqueous gold precursor and the reducing gas to produce gold nanoparticles with polydispersity as low as 5%. The uncapped gold nanoparticles make the product attractive for surface-enhanced Raman scattering, and showed an average enhancement factor of 1.94 × 105. Various capping agents (tri-sodium citrate, polysorbate 80, oleylamine and poly(ethyleneglycol) 2-mercaptoethyl ether acetic acid) and different operational parameters were also tested, demonstrating that the proposed synthesis is flexible and can continuously produce a variety of gold nanoparticles, with potential for other applications.