Microfluidics for Biologists Fundamentals and Applications

(National Geographic (Little) Kids) #1
Chapter 9

On-Chip Immunoassay for Molecular


Analysis


Andy Ng


1 Introduction


1.1 Immunoassays


The specificity and affinity of antibody-antigen interactions has long been exploited
in immunoassays for the detection of biomolecular analytes. In particular, immu-
noassays are used in a wide spectrum of applications in clinical diagnostics,
molecular biology, proteomics and biosensing, for the measurement of many pro-
teins and, to a lesser extent, small molecules due to their relatively smaller exposed
surface for recognition. Immunoassays can be categorized into two main formats:
homogeneous and heterogeneous assays. In homogeneous format, antibodies and
antigens are in solution, and their interactions that lead to the formation of the
antibody-antigen immunocomplex also occur in solution. On the other hand, in
heterogeneous format, the antibodies or antigens are immobilized on a solid
support, and their interactions take place at the boundary layer, and the unbound,
or “non-captured” antibodies or antigens, as well as other reagents can be easily
removed. Both immunoassay formats have been extensively studied and widely
implemented in microfluidic platforms.
Immunoassays can be further classified into competitive mode and
non-competitive modes. In competitive mode, known amount of labeled antigens
are introduced into the assay, and the non-labeled antigen competes with the labeled
antigens for a limited number of binding sites on the antibodies. As the amount of
non-labeled antigen in a sample increases, the amount of labeled antigens that remain
bound to the antibody decreases. The competitive immunoassay generates a signal
that is inversely proportional to the amount of the antigen, if the labeled antigen-


A. Ng (*)
Biomedical Engineering Department, McGill University, Montreal, QC, Canada
e-mail:[email protected]


©Springer International Publishing Switzerland 2016
C.K. Dixit, A. Kaushik (eds.),Microfluidics for Biologists,
DOI 10.1007/978-3-319-40036-5_9


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