Green Approach for the Simultaneous Synthesis and Separation of Gold Nanoparticles

Gold nanoparticles (AuNPs) have diagnostic and therapeuticapplicationsas they are biocompatible and can be surface-functionalized. The useof organic solvents in the synthesis of AuNPs hampers their applicationsin the medicinal field. The large-scale production of nanoparticlesrequires their simultaneous synthesis and separation. Self-assemblyof nanoparticles at the fluid-fluid interface facilitates theirseparation from the bulk and eliminates a downstream processing step.In this work, we exploit this in an aqueous two-phase system (ATPS)to synthesize and separate stable AuNPs. The ATPS was based on polyethyleneglycol (PEG) and trisodium citrate dihydrate (citrate) as both thesecompounds can reduce Au ions. After the synthesis of nanoparticles,using one of the solutes, a complementary solution containing theother solute is added to form a two-phase system to facilitate self-assemblyat the interface. The nanoparticles synthesized in different phasesare characterized using UV-visible spectroscopy, scanning electronmicroscopy, and transmission electron microscopy. The AuNPs synthesizedusing the citrate solution are found to be unstable. Particles synthesizedusing the ATPS with PEG-600 are trapped at the interface while thoseusing PEG-6000 remain in the bulk. Continuous synthesis and separationof nanoparticles in slug flow in a millichannel are demonstrated asa first step for large-scale controlled synthesis.

Automated summary

Gold nanoparticles (AuNPs) with biocompatibility and surface-functionalization have important diagnostic and therapeutic applications. However, the use of organic solvents in their synthesis limits their use in medicine. This study demonstrates the synthesis and separation of stable AuNPs in an aqueous two-phase system (ATPS) using polyethylene glycol (PEG) and trisodium citrate dihydrate (citrate). The self-assembly of nanoparticles at the fluid-fluid interface allows for their separation and characterization.