Tunable gold nanoparticle synthesis using microfluidic flow focusing enabled by reusable 3D-printed multimaterial connectors.

The design and fabrication of reusable, cost-effective, and leakage-resistant microfluidic connectors using a commercial multi-material 3D printer (Connex Objet 3D, Tri-Tech 3D, UK) is reported. The connectors, comprising plugs, adapters, and ports, were fabricated from VeroClear™ (rigid polymer) and incorporated TangoBlack (elastomeric soft polymer) as integrated ferrules and gaskets. This multi-material approach enabled the attachment of the connectors using physical locking mechanisms; thus eliminating the need for adhesives and so enabling reusability without mechanical failure. These 3D printed plugs and ports are demonstrated by the synthesis of gold nanoparticles (AuNPs) in a HEPES-mediated microfluidic system under different flow rate ratios (FRR). The resulting AuNPs are evaluated for catalytic performance in the model reduction of 4-nitrophenol to 4-aminophenol. Precise control overflow FRR enabled tunable modulation of AuNPs size, polydispersity, and surface plasmonic responses (SPR). The resulting NPs demonstrated excellent batch-to-batch consistency, critical for reproducible analytical performance. This work presents a scalable interfacing strategy by featuring 3D printed microfluidic connectors, for microfluidic based NPs synthesis platforms and highlights that variation of FRR serves as an effective tool to tailor nanoparticle properties while offering mechanistic insight into AuNP formation dynamics under varying flow conditions.