Figure 1. Fabrication of the interdigitated gold electrode
arrays and microfluidic chip . a) Schematic of the process flow
for the fabrication of gold electrodes, which includes photolithography
of a positive photoresist followed by evaporation of gold and lift-off
of the positive photoresist. b) Different layers of the
microfluidic chip, which includes a SiO2/Si substrate,
interdigitated gold electrodes, a PSA-based microchannel, and a PMMA
cover with inlet and outlet holes.
To facilitate the fabrication process, a negative pattern was fabricated
using photolithography of a positive photoresist (AZ1505, 1 µm
thickness) on a silicon oxide coated silicon wafer. Once the positive
resist was patterned, 40 nm thick gold layer was deposited on the entire
substrate using an evaporation machine. The coated substrate was further
ultra-sonicated in acetone for 5 minutes to lift off the positive resist
on the substrate, which left behind the interdigitated gold electrode
patterns on the substrate. In a parallel process, we patterned
microfluidic channels within a double-sided pressure-sensitive adhesive
(PSA) sheet (PSA thickness= 100 µm) using a cutting plotter machine
(Graphtec CE6000-40, Japan) and prepared a poly (methyl methacrylate)
(PMMA, 3 mm thickness) cover featuring inlet and outlet holes using a
CO2 Laser Engraving machine (ULS Versa Laser 3.50,
wavelength 10.6 μm). The electrode arrays on the substrate, the
PSA-patterned microchannel and the PMMA cover were aligned and assembled
to complete the microfluidic device for dielectrophoresis
(Figure 1b ).