Electrochemical Detection in Polymer Microchannels J. S. Rossier, M. A. Roberts, R. Ferrigno, and H. H. Girault* Laboratoire d'E Ä lectrochimie, E Ä cole Polytechnique Fe ´ de ´ rale de Lausanne, 1015 CH-Lausanne, Switzerland A method, using UV laser photoablation, is presented for the fabrication and the integration of an electrochemical detector in a microchannel device, where carbon mi- croband electrodes are placed either in the bottom or in the side walls of the rectangular microchannel. The different electrochemical cell geometries are tested with a model compound (ferrocenecarboxylic acid) in 4 0 - and 100-μm-wide capillaries fabricated in planar polymer substrates. The experimental results are compared to numerical simulations for stagnant stream conditions. Depending on the scan rate and on the microchannel depth, the system behaves as a microband electrode until a linear diffusion field develops within the channel. The limit of detection for a one electron redox species within the 1 2 0 -pL detection volume is ∼1 fmol with both cyclic voltammetry and chronoamperometric detection. The miniaturization of analytical tools has played a significant role in the development of fast analysis systems using ever decreasing volumes. 1-4 The advantages of speed and separation efficiency in such systems have been well documented; 5 however, problems have also arisen concerning the handling and detection of very small amounts of sample, inherent to a miniaturized device. Electroosmotic pumping has been used to efficiently handle small sample volumes, thereby addressing the handling problem. 6 Miniaturized analytical systems have also been coupled with various detectors including laser-induced fluorescence (LIF) for ultrasensitive detection 7,8 or even mass spectrometry, 9,10 demon- strating the ability to detect small sample amounts. These detection techniques require significant off-chip instrumentation which increases expense and often necessitates time-consuming alignment procedures. Electroanalytical tools have taken advantage of microfabrication techniques for many years in order to produce microelectrodes. The ability to minimize iR drop distortion of experimental data and their low capacitance is part of the properties that are suited for a fast analysis. 11 The possibility of micromachining electrodes by standard microfabrication techniques, 12 photoablation, 13 or using glass or epoxy resin encapsulation 14-17 is now well estab- lished. 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