Mahmuda Akhtar, Sander van den Driesche, André Bödecker and Michael J. Vellekoop.

Sensors and Actuators B (2018) 255, 3576–3584.

https://doi.org/10.1016/j.snb.2017.08.032

We present a PDMS-based microfluidic device that allows long-term on-chip droplets storage. The droplets are used as micro-reactors, in which anaerobic bacteria can be cultivated. PDMS, the base substrate for droplet-microfluidic devices, is a porous material and causes water molecules to diffuse into the bulk. Consequently, aqueous droplets shrink fast. Our proposed method, coating the PDMS storage channels with Parylene AF4, successfully suppresses droplets shrinkage. The chemical vapor-deposited coating of Parylene AF4 was performed after realizing the PDMS channel. The diffusion suppression effect of AF4 coatings in PDMS channels has been investigated by monitoring shrinkage and by measuring the uptake of Rhodamine B for periods up to 12 h. In these devices, nanoliter droplets can be stored at 37 °C for more than two days. The application of the device is established by culturing the bacteria Escherichia coli and Enterococcus faecalis, in the stored droplets.