Stimuli-Responsive Reagent System for Enabling Microfluidic Immunoassays with Biomarker Purification and Enrichment

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• 作者：John M. Hoffman ; Patrick S. Stayton ; Allan S. Hoffman ; James J. Lai
• 刊名：Bioconjugate Chemistry
• 出版年：2015
• 出版时间：January 21, 2015
• 年：2015
• 卷：26
• 期：1
• 页码：29-38
• 全文大小：458K
• ISSN：1520-4812

文摘

Immunoassays have been translated into microfluidic device formats, but significant challenges relating to upstream sample processing still limit their applications. Here, stimuli-responsive polymer鈥揳ntibody conjugates are utilized in a microfluidic immunoassay to enable rapid biomarker purification and enrichment as well as sensitive detection. The conjugates were constructed by covalently grafting poly(N-isopropylacrylamide) (PNIPAAm), a thermally responsive polymer, to the lysine residues of anti-prostate specific antigen (PSA) Immunoglobulin G (IgG) using carbodiimide chemistry via the polymer end-carboxylate. The antibody-PNIPAAm (capture) conjugates and antibody-alkaline phosphatase (detection) conjugates formed sandwich immunocomplexes via PSA binding in 50% human plasma. The complexes were loaded into a recirculating poly(dimethylsiloxane) microreactor, equipped with micropumps and transverse flow features, for subsequent separation, enrichment, and quantification. The immunocomplexes were captured by heating the solution to 39 掳C, mixed over the transverse features for 2 min, and washed with warm buffer. In one approach, the assay utilized immunocomplex solution that was contained in an 80 nL microreactor, which was loaded with solution at room temperature and subsequently heated to 39 掳C. The assay took 25 min and resulted in 37 pM PSA limit of detection (LOD), which is comparable to a plate ELISA employing the same antibody pair. In another approach, the microreactor was preheated to 39 掳C, and immunocomplex solution was flowed through the reactor, mixed, and washed. When the specimen volume was increased to 7.5 渭L by repeating the capture process three times, the higher specimen volume led to immunocomplex enrichment within the microreactor. The resulting assay LOD was 0.5 pM, which is 2 orders of magnitude lower than the plate ELISA. Both approaches generate antigen specific signal over a clinically significant range. The sample processing capabilities and subsequent utility in a biomarker assay demonstrate the opportunity for stimuli-responsive polymer鈥損rotein conjugates in novel diagnostic technologies.