High-Speed On-Chip Mixing by Microvortex Generated by Controlling Local Jet Flow Using Dual Membrane Pumps

Robot integrated microfluidic chip is a key technology for microscale applications. Recently, the technology has been applied to on-chip mixing, which mix solutions on a microfluidic chip because it is a promising tool to analyze not only the chemical reaction with the small sample volume, but also the response of cells to environmental changes. However, these conventional mixing methods require the mixing time of millisecond-order due to the difficulty of mixing in the laminar condition of a microchannel whose Reynolds number tends to be low. In this letter, we propose a high-speed on-chip mixing by the microvortex generated by controlling local jet flow using dual-membrane pumps. First, we confirmed that vortex was successfully generated within 20 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>s by the local jet flow. The velocity and Reynolds number were analytically estimated as approximately 20 m/s and <inline-formula><tex-math notation="LaTeX">${\text{1.6}} \times \text{10}^{\text{3}}$</tex-math></inline-formula>, respectively. Second, we evaluated the response time of the mixing using the microvortex. We mixed 200-nm nanobead suspension and the DI water in the velocity of main flow of 1 m/s. By measuring the intensity at the certain observation area, we confirmed that our method successfully mixed solutions and the mixing time was approximately 500 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>s, whose speed has not been achieved by conventional robot integrated on-chip mixers. Moreover, we confirmed that our system can control the concentration of mixed flow by controlling flow rate ratio of sample and sheath flow. From these results, we confirmed that we achieved high-speed on-demand on-chip mixing by the microvortex.