Tape-based facile surface passivation for digital microfluidics

Digital microfluidics (DMF) has transformed lab-on-a-chip systems by enabling programmable manipulation of microscale droplets for biochemical analysis, diagnostics, and portable biomedical applications. A key requirement in DMF devices is a dielectric layer to prevent electrolysis and a hydrophobic layer to ensure an appropriate contact angle and minimize droplet adhesion. However, conventional fabrication of these layers typically involves microfabrication processes requiring specialized facilities, and once formed, the layers are difficult to remove or replace, rendering the devices non-reusable. Here, we present a facile strategy for rapid and convenient surface passivation of DMF devices using a commercially available fluoropolymer (polytetrafluoroethylene, PTFE) tape. Passivation is achieved through a simple press-bonding step that imparts dielectric and hydrophobic properties (contact angle >110°) with appropriate surface roughness (Ra < 10 nm) for reliable DMF operation. Importantly, the PTFE layer can be rejuvenated by simply replacing the bonded tape, instantly refreshing the device. We demonstrate stable droplet manipulation and consistent electrode conductivity after ten replacement cycles. Residual testing with fluorescent dyes and deoxyribonucleic acid (DNA) molecules confirms the anti-fouling properties of PTFE tape, verifying its applicability in bioanalytical applications. These results establish a simple and directly replaceable passivation route for printed circuit board (PCB)-based DMF devices, while the relatively high actuation voltage and limited durability assessment define the current scope of the approach.