Surface Modification of COC Microfluidic Devices: A Comparative Study of Nitrogen Plasma Treatment and its Advantages Over Argon and Oxygen Plasma Treatments

Control of surface properties is very important in high performance microfluidic devices because appropriate functionalization of the surface of the microchannel helps to minimize adsorption of certain analytes thus improving its performance. In this regard, both the argon and oxygen plasma techniques have been used to improve the adaption of polymer surfaces to biological environments. However, the less common nitrogen plasma technique has not been used for surface modification of cyclic olefin copolymer (COC) in microfluidic applications. This paper presents a comparative study between the argon, oxygen, and nitrogen plasma treatments with the aim to identify the most suitable process for the development of a smart, disposable chip for the Bio-MEMS application. The chemical and morphological changes of the plasma modified COC surfaces were characterized using X-ray photoelectron spectroscopy, atomic force microscopy, and water contact angle measurements. The effect of plasma treatment on the strength of thermally bonded lap-shear specimens was studied. The influence of plasma treatment on the integrity of thermally sealed microdevices was assessed using burst pressure tests. The plasma treatments had a significant impact on the electroosmosis flow mobility in the microchannels. The hemocompatibility of the various plasmamodified COC surfaces was determined using the static platelets adhesion experiment. It was shown that the nitrogen plasma treatment was more effective than the argon and oxygen treatments for the modification of COC based microfluidic devices.