Paraffin was deposited and patterned by lift-off on a 3 in.
diameter 1 mm thick cyclic olefin copolymer (COC) wafer using
positive AZ P4620 photoresist (Clariant Inc.). The process is
illustrated in Fig. 3. After cleaning with isopropyl alcohol, the
COC wafer was spin coated with a 20m thick layer of AZ
P4620. The photoresist was soft baked in a 65 ◦C oven for
12 min. Following standard UV exposure, the resist was developed
in AZ400K developer diluted with water in a ratio of 1:3.5
(v:v). Paraffin was deposited on the COC surface by spin coating.
Tissue Prep paraffin pellets and organic solvent OpticlearTM
(Logitech) were mixed in a ratio of 1:2 (v:v). The mixture was
heated inside a 60 ◦C convection oven to speedup the paraffin
dissolution. A conventional 150 W light bulb was used to preheat
the COC wafer surface for 2 min prior to deposition. The
paraffin–OpticlearTM mixture was poured onto the preheated
COC surface, and paraffin was spin coated using a 10 s spread
at 500 rpm followed by a 20 s coat at 3000 rpm. OpticlearTM
was evaporated by placing the coated COC wafers on a leveled
35 ◦C hotplate for 12 h. Following paraffin deposition, AZ
P4620 was lifted-off using pure, undiluted AZ400K developer
under controlled agitation. Final thickness of the paraffin film