Mitigation of Gold Nanoparticle Fouling in Continuous Microreactors

Gold nanoparticles (Au-NPs) are gaining interest in food processing, with applications ranging from antimicrobial food packaging to sensing and detection of foodborne pathogens. However, scaling their synthesis in a continuous flow system remains a formidable challenge, not only requiring precise control over particle size, process stability and high throughput, but also facing the persistent problem of surface fouling. In flow-based systems, this fouling typically originates at the microreactor inlet, where gold nuclei deposit on channel walls, triggering uncontrolled particle growth and, in extreme cases, complete blockage. In this study, Au-NPs were synthesized via citrate reduction of tetrachloroauric acid in a segmented flow microreactor, with antifouling strategies explored through chemical surface modification. Coating reactor walls with silica nanoparticles and subsequent silanization created a superhydrophobic interface, which showed some success in mitigating fouling. However, the trade-off between fouling prevention and product control remained evident. Importantly, we also show that fouled reactors can be effectively cleaned with aqua regia, a practical approach to prolong continuous operation beyond single use. These findings highlight surface fouling as a critical barrier in scalable Au-NP synthesis and provide insights into the broader challenges of optimising nanoparticle production in continuous flow.