4. Use 1 mm thick stainless steel substrate for the photolithogra-

phy process. Here, the aim is to transfer the design on the

acetate paper to the stainless steel substrate.

5. Clean stainless steel substrate with baby shampoo, acetone,

isopropyl alcohol (IPA) and distilled water, respectively. Dry it

with nitrogen gun to leave no residue on steel substrate.

6. Place cleaned steel substrate on the spin coater and coat

PR-1828 photoresist on it to obtain an average photoresist

layer thickness of 5 μm using 2000 rotation-per-minute (rpm).

7. Implement soft baking process for 2 min at 95
C on hot plate

to the photoresist coated steel substrate.

8. Superimpose acetate paper with design on the coated steel

substrate and apply UV light (365 nm wavelength, 20 mW/

cm² power density) for 3 min.

9. Develop the exposed photoresist on the steel substrate by

dipping it into the developer solution (MF319 solution).

10. Rinse with distilled water and dry the steel substrate to reveal

the design made of photoresist.

11. Check the patterns of the design under the microscope and

hard bake photoresist layer on the hot plate for 3 h at 110
C.

Fig. 2 (a) AutoCAD drawing of designed microfluidic device. (b) Fabricated microfluidic device (reproduced

from ref. 15 with permission from Biomedical Microdevices). (c) Fabricated microfluidic device with electro-

des. (Reproduced from ref. 16 with permission from Biomicrofluidics)

Fabrication Protocol for Thermoplastic Microfluidic Devices: Nanoliter. . .

31