Chem

VTT Technical Research Centre of Finland, P.O. Box 1000, 02044 VTT, Finland Anal. Chem., Article ASAP DOI: 10.1021/ac1027066 Publication Date (Web): November 23, 2010 Copyright © 2010 American Chemical Society * To whom correspondence should be addressed. E-mail: juuso.olkkonen@vtt.fi. Abstract This Technical Note demonstrates a simple method based on flexographic printing of polystyrene to form liquid guiding boundaries and layers on paper substrates. The method allows formation of hydrophobic barrier structures that partially or completely penetrate through the substrate. This unique property enables one to form very thin fluidic channels on paper, leading to reduced sample volumes required in