Dear all, Sorry for this late answer, but as far as I remember, nobody pointed out this possible source of bubbles in microfluidics where fluid is driven by electroosmotic flow (or more generally in which high voltages are used): the oxidation of water to form oxygen bubbles. You can then use a "sacrificial" electrochemical species such as hydroquinone that will oxidize before water. See Moini et al, Analytical Chemistry 1999, 71, 1658-1661 Hope this helps. Kind regards Niels Lion Laboratory of Physical and Analytical Electrochemistry (Prof. Hubert H. Girault) Intitute of Chemical Sicences and Engineering Swiss Federal Institute of Technology, Lausanne (EPFL)