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 bio-microfluidic 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 O₂ plasma and polyethylene glycol (PEG) coating. Three kinds of surface treatment namely the O₂ plasma treatment, PEG coating and O₂ 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° ± 3°. Using only O₂ 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 O₂ 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.