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Fluorescence-Based Assessment of Plasma-Induced Hydrophilicity in Microfluidic Devices via Nile Red Adsorption and Depletion

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journal contribution
posted on 17.12.2015, 03:35 by David J. Guckenberger, Erwin Berthier, Edmond W. K. Young, David J. Beebe
We present a simple method, called fluorescence-based assessment of plasma-induced hydrophilicity (FAPH), that enables spatial mapping of the local hydrophilicity of surfaces normally inaccessible by traditional contact angle measurement techniques. The method leverages the change in fluorescence of a dye, Nile Red, which is adsorbed on an oxygen plasma-treated surface, and its correlation with the contact angle of water. Using FAPH, we explored the effect of microchannel geometries on the penetration distance of oxygen plasma into a microchannel and found that entrance effects prevent uniform treatment. We showed that these variations have a significant impact on cell culture, and thus the design of cell-based microfluidic assays must consider this phenomenon to obtain repeatable and homogeneous results.