Su 8 3025 negative photoresist

The SCP-Tips, including SCP-Tip containing a hook and SCP-Tip containing a hydrodynamic trap, were designed using AutoCAD software (Autodesk) and fabricated by photolithography and polydimethylsiloxane (PDMS) molding techniques. In brief, the design was printed out as five-inch glass photomasks (Photo Sciences, Inc.) and then transferred to the surface of a four-inch silicon wafer as 18-μm thick SU-8 3025 negative photoresist (MicroChem Corp.). After silanization by trimethylchlorosilane (TMCS), polydimethylsiloxane (PDMS; 10A:1B; Dow Corning Corp.) was poured onto the photoresist mold, degassed by vacuum for 15 min, and heated at 80°C for 25 min. After curing, the PDMS was peeled off and two tilted holes were punched by puncher (Harris Uni-Core). Then, the upper PDMS layer (4–5 mm thickness) with microstructure was irreversibly bonded to the bottom PDMS layer (0.5–1 mm thickness) without microstructure by using plasma treatment (Plasma ETCH, INC) to form an intact chip. The chip was left at 80°C for 30 min to enhance the bonding. Finally, the chip was cut to the appropriate size and shaped by using a scalpel to finally form a SCP-Tip.