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.