tions which depend on large interfacial area; for example, in membraneless fuel cells [42] or for use in combination with the liquid junction potential [43]. We are grateful for support from the National Institute for Nanotechnology, the Natural Science and Engineering Council of Canada, the informatics Circle of Research Excellence, and the Canada Research Chairs program. We thank CMC for fabrication of the devices. We would like to thank Zhe Wang for help in the laboratory and with data analysis, and Dave Fortin for creating the illustrated contents image. Acknowledgments [1] K.L. Helton and P. Yager, Lab Chip , 2007, 7 , 1581. [2] G.B. Thurston, Biophysical Journal , 1972, 12 , 1205. [3] R.G. Larson, The Structure and Rheology of Complex Fluids , Oxford University Press, 1999. [4] T.M. Squires and S.R. Quake, Rev. Mod. Phys. , 2005, 77 , 977. [5] A. Groisman and V. Steinberg, Nature , 2001, 410 , 905. [6] J.M. Ottino and S. Wiggins, Phil. Trans. R. Soc. Lond. A , 2004, 362 , 923. [7] P. Garstecki, M.A. Fischbach, and G.M. Whitesides, Appl Phys. Lett. , 2005, 86 , 244108. [8] C.H. Chen, H. Lin, S.K. Lele, and J.G. Santiago J. Fluid Mech. , 2005, 524 , 263. [9] J.B. Knight, A. Vishwanath, J.P. Brody, and R.H. Austin Phys. Rev. Lett. , 1998, 80 , 3863. [10] A.D. Stroock, S.K.W. Dertinger, A. Ajdari, I. Mezic, H.A. Stone, and G.M. Whitesides Sci- ence , 2002, 295 , 647. [11] R.B. Bird, R.C. Armstrong, and O. Hassage, Dynamics of Polymeric Liquids , Wiley, 1987. [12] P. Pakdel and G.H. McKinley, Phys. Rev. Lett. , 1996, 77 , 2459. [13] A. Groisman and V. Steinberg, Nature , 2000, 405 , 53. [14] T. Burghelea, E. Segre, I. Bar-Yosef, A. Groisman and V. Steinberg, Phys. Rev. E , 2004, 69 , 066305. [15] P.S. Virk, AlChE Journal , 1975, 21 , 626. [16] P. E. Arratia, C. C. Thomas, J. Diorio, and J. P. Gollub, Phys. Rev. Lett. , 2006, 96 , 144502. [17] J.A. Pathak, D. Ross, and K.B. Migler, Phys. Fluids , 2004, 16 , 4028. 13