Fabrication of the microchannels
The master mold was obtained using standard photolithography techniques. AutoCAD 2017, (AutoDesk, USA) software was used to design the two-turn spiral channel. It was printed on a Mylar mask. A negative photoresist SU-8 was spin-coated on to a 4-inch silicon wafer. It was exposed to a UV light source through the Mylar mask and was developed using SU-8 developer to obtain the channel design onto the silicon wafer that was ordered from micro resist technology, Germany. A PDMS replica was produced using a soft lithography technique where Sylgard 184 silicon elastomer and curing agent was mixed in a 10:1 ratio. The silicon elastomer was poured onto the SU-8 master and was cured for a minimum of 6 hr. at 65oC. The PDMS mold was cut and holes were punched using a 0.75 mm diameter Harris Uni-Core puncher to obtain inlets and outlets. Clean glass and the PDMS mold was bonded using an oxygen plasma treatment using FEMTO SCIENCE CUTE plasma system, South Korea and incubation at 110oC for 10 min to ensure robust bonding.