title: Sample pre-concentration by isotachophoresis in microfluidic devices.
abstract: We have designed microfluidic devices with the aim of coupling isotachophoresis (ITP) with zone electrophoresis (ZE) as a method to increase the concentration limit of detection in microfluidic devices. We used plastic multi-channel chips, designed with long sample injection channel segments, to increase the sample loading. The chip was designed to allow stacking of the sample into a narrow band by discontinuous ITP buffers and subsequent separation in the ZE mode. In the ITP-ZE mode, with a 2-cm long sample injection plug, sensitivity was increased by 400-fold over chip ZE and we found that the separation performance after the ITP stacking was comparable to that of regular chip ZE. We report sub-picomolar limits of detection of fluorescently labeled ACLARA eTag reporter molecules electrokinetically injected from cell lysate sample matrixes containing moderate salt concentrations. We evaluated sample injections from buffers with varied ionic strengths and found that efficient stacking and separations were obtained in both low and high conductivity buffers, including physiological buffer with at least 140 mM salt. We applied ITP-ZE to the analysis of a cell surface protease (ADAM 17) which used live intact cells in physiological buffers with detection limits below 10 cells/assay.
authors.affiliation: ACLARA BioSciences, 1288 Pear Avenue, Mountain View, CA 94043-1432, USA. awainright@aclara.com
authors.forename: Ann
authors.initials: A
authors.lastname: Wainright
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Williams
authors.forename: Gary
authors.initials: G
authors.lastname: Ciambrone
authors.forename: Qifeng
authors.initials: Q
authors.lastname: Xue
authors.forename: Jing
authors.initials: J
authors.lastname: Wei
authors.forename: Dennis
authors.initials: D
authors.lastname: Harris
mesh_terms: D002021:Buffers; D002460:Cell Line; D004586:Electrophoresis / Q000295:instrumentation*; D004867:Equipment Design; D006801:Humans; D012680:Sensitivity and Specificity
chemical_list: D002021:Buffers