A three-dimensional flow focusing microsecond mixer for dynamic assessment of nanoparticle formation

This paper reports the design, fabrication, and characterization of a three-dimensional (3D) flow focusing microfluidic mixer. By hydrodynamically focusing the sample into a very confined stream in both vertical and horizontal directions, the mixer can achieve ultrarapid mixing of the sample stream with the reagent streams within ~3 ± 1 μs, which allows us to study the reaction kinetics on the microsecond timescale. Using the mixer, we investigated the formation of the hexaphenylsilole (HPS) nanoparticles. The HPS nanoparticles formed in the mixer have smaller size with narrower size distribution, compared to those formed by bulk nanoprecipitation. We also demonstrated the mixer can resolve the microsecond kinetics of nanoparticle self-assembly in two distinct steps, suggesting the nanoparticle formation follows the classical nucleation and growth theory.