A vacuum-pumped microfluidic device for automated in-line mixing and focusing processes

Microfluidic devices with multi-functional features have been a highly promising tool to implement mixing, reaction, transport, separation, and detection of bio-samples on a solitary microchip for applications in the biochemistry, biophysics and medical fields. This work presents a unified vacuum-pumped microfluidic device consisting of a micromixer module and a microflow cytometer module to complete an automated in-line sequence of mixing and focusing procedures for possible rapid screening of the marker cell detection. For the former module, an in-plane passive micromixer with optimum Tesla structures was adopted to achieve good mixing performance. We also devised a microcytometer as the latter module to attain planar symmetric hydrodynamic focusing in microchannels. Using the coupled mixing and hydrodynamic focusing analysis to predict the suction-driven flow behavior for guiding the chip design, the microfluidic device was fabricated through SU-8 lithography and a PDMS replica molding technique to construct reverse structures from the patterned SU-8 molds on a silicon substrate. Numerical and experimental results have demonstrated the capability of the developed microfluidic device to realize a 93% mixing index and to control the focused stream within a width of 20 μm in tests.