Sustained Synthesis of Ultra‐Long Gold Wires via an Open Microfluidic System

Ultra-long metal nano/microwires have broad applications in fields such as electronics, sensing, and catalysis. With the advantage of laminar flow, the microfluidic approach enables the efficient synthesis of metal micro- and even nanowires. However, the synthesized metal wires typically broaden over time due to diffusion as their length increases within microchannels, making it challenging to achieve long metal wires without widening. Herein, an open microfluidic system for the synthesis of ultra-long metal wires with size controllability is presented. The system creates a mixing area where two coflowing laminar streams interact, allowing reactions to occur in metal wire synthesis. Besides, the coflowing laminar streams are truncated through aspiration to restrict their diffusion over time, demonstrating the potential to synthesize ultra-long metal wires with size controllability. The conditions for gold nanowire synthesis are investigated, and gold nanowire with a width of 370 nm is synthesized. Two ultra-long gold wires, each exceeding 3600 μm in length, have also been successfully obtained. Finally, a gold wire has been directly assembled on patterned ITO chips for resistance monitoring.