3.1.2

Electrochemical

Wet Etching

In order to have a positive stainless steel mold, electrochemical wet

etching process is used [17]. Once the master mold is created, it can

be used in the fabrication of thermoplastic chips with or without

electrodes (Fig. 2b, c).

1. Prepare NaCl: Distilled water solution at a ratio of 1:4 (w/w).

2. Place photoresist coated steel substrate and a blank steel plate

in a container facing each other and pour NaCl solution in it.

3. Use blank steel plate as cathode and use photoresist coated steel

substrate as anode.

4. Apply DC current of 60 A between the steel plates for 20 s,

resulting in an etch depth of around 12 μm. Check the patterns

of the design under the microscope. If the desired depth is

achieved on the steel substrate, remove photoresist patterns in

acetone, IPA and distilled water. Rinse and dry the steel mold.

3.2

Fabrication of

Electrodes

Electrodes integrated to microfluidic devices can be used to study

the effects of electric fields on cells or as actuators to control liquid

flow or sort cells on chip [16].

3.2.1

Creating an

Electrode Design

1. Use L-edit software to design the electrodes.

2. Draw interdigitated electrodes considering the cell size and

fixed substrate size of 7.5  2.5 cm².

3. Transfer finalized drawing to the acetate paper and obtain

electrode mask.

3.2.2

Chromium and

Gold Deposition on Blank

COP Substrate

1. Use thermal evaporator with high vacuum capability in

this step.

2. Place pure chromium (99.99%) and gold (99.99%) in the spe-

cific chambers within the evaporator.

3. Check the lifetime of the evaporator’s crystal, which measures

the sample thickness before deposition process.

4. Place blank COP sample, washed with baby shampoo, acetone,

IPA and distilled water, respectively and dried with nitrogen,

on the round compartment of evaporator.

5. Close shutter and the chamber of the evaporator and start the

vacuum.

6. Leave the system pumping for 24 h and attain 10^6 Torr (see

Note 1) vacuum level.

7. Begin the rotation of the sample and open cooling water of the

equipment (see Note 2).

8. First, deposit chromium on the blank COP sample of thickness

around 8–10 nm using 50 A electrical current (see Note 3).

This is achieved after stable reading is established on the crystal

32

Elif Gencturk et al.