Abstract:A method for the determination of metal cations in aqueous solution Ž . using a monolithically integrated microfabricated microchip device which allows sample stacking, electrophoretic separation, and postcolumn derivatization is described. The metal cations are detected by UV laser-induced fluorescence following complexation with 8-hydroxyquinoline-5-sulfonic acid. To make use of electrokinetic stacking phenomena, the sample is added to a reservoir containing a low-conductivity buffer and is then introduced into a main separation channel using a gated injection scheme. The complexing agent is added downstream from the injection cross. For two model compounds, magnesium and calcium, detection limits were 0.5 and 18 ppb, respectively. The reproducibility for multiple injections was 1.5% relative standard deviation.

Valving characteristics on microfluidic devices were controlled through manipulation of the electric field strengths during both the sample loading and dispensing steps. Three sample loading profiles for the constant volume valve (pinched injection) in conjunction with four dispensing schemes were investigated to study valving performance. The sample confinement profiles for the sample loading step consisted of a weakly pinched sample, a medium pinched sample, and a strongly pinched sample. Four dispensing schemes varied the electric field strengths in the sample and sample waste channels relative to the analysis channel to control the volume of the sample dispensed from the valve. The axial extent of the sample plug decreased as the electric field strengths in the sample and sample waste channels were raised relative to the analysis channel. In addition, a trade-off existed between sample plug length and sensitivity.

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Herein we describe a synthetically simple strategy for increasing the lifetime of unstructured peptides in cytosolic environment via dimerization at the N-terminus to block threading into the catalytic cleft of cytosolic proteases. We establish this approach with kinase substrates, allowing for phosphorylation in cells as a demonstration of protease resistance.

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