Microdrop analysis of a bead-based immunoassay |
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Authors: | Jennifer H Thomas Niina J Ronkainen-Matsuno Svetlana Farrell H Brian Halsall William R Heineman |
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Institution: | Department of Chemistry, University of Cincinnati, P.O. Box 210172, Cincinnati, OH 45221-0172, USA |
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Abstract: | The progress to electrochemical detection of a microbead-based immunoassay in small volumes has led to a reduced assay time and lower detection limits. Three electrochemical techniques are described for an immunoassay with detection in a microdrop. The techniques are amperometric detection with a rotating disk electrode (RDE), a microelectrode, and an interdigitated array (IDA) electrode. An enzyme-labeled sandwich immunoassay with mouse IgG as the model analyte is used to demonstrate the three techniques. The microbead assay is carried out in a test tube using a magnet to control bead collection. Once the immunocomplex is formed on the microbead, the beads are transferred to a microdrop where the enzyme, either alkaline phosphatase or β-galactosidase, generates 4-aminophenol (PAP). PAP is oxidized at the electrode with an applied potential of +290 mV vs. Ag/AgCl. For all three techniques, the upper limit of the dynamic range was 1000 ng/ml mouse IgG, and the detection limits were: 50 ng/ml for the RDE, 40 ng/ml for the microelectrode, and 26 ng/ml for the IDA electrode. |
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Keywords: | Microbead-based immunoassay Electrochemical immunoassay Rotating disk electrode Microelectrode Interdigitated array electrode |
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