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 ).