Polyethylene glycol coating for hydrophilicity enhancement of polydimethylsiloxane self-driven microfluidic chip

The hydrophilic microfluidic chip that can self-actuate fluidic flow effectively with no extra pump is an important device for bio lab-on-a-chip (LOC) application. Polydimethylsiloxane (PDMS) is a common material for biomicrofluidic chip but suffers from hydrophobic surface problem. In this article, the surface modification of PDMS material for long-term hydrophilicity improvement has been studied by O-2 plasma and polyethylene glycol (PEG) coating. Three kinds of surface treatment namely the O-2 plasma treatment, PEG coating and O-2 plasma followed by PEG coating were performed for hydrophilic enhancement on pristine PDMS. The contact angle measurement was used for examining hydrophilic duration after treatment. The contact angle of pristine PDMS is hydrophobic around 100 degrees +/- 3 degrees Using only O-2 plasma treatment made the contact angle of PDMS below 10 initially but its hydrophobicity recovered quickly after 2 h that hindered practical application. Adding PEG coating on the O-2 plasma treated PDMS surface can make hydrophilic behavior retained longer than 400 h. The Fourier transform infrared spectrometer and contact angle variation were used for identifying the evolution of hydrophilicity enhancement. The cross form microchip was used for testing the self-driven flow of rhodamine droplet into the microchannel successfully. This method is low-cost, disposable and easy to integrate with the microfluidic LOC system. (C) 2016 Elsevier B.V. All rights reserved.