Immunosensors
As we have learned from Chap. 1, biosensors utilize bioreceptors to capture and analyze specific biomolecules of interest. Antibodies, enzymes, and DNAs have been used commonly as bioreceptors; however, antibodies are the most common and widely studied. I
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Immunosensors
As we have learned from Chap. 1, biosensors utilize bioreceptors to capture and analyze specific biomolecules of interest. Antibodies, enzymes, and DNAs have been used commonly as bioreceptors; however, antibodies are the most common and widely studied. In addition, antigens can also be used as bioreceptors to capture and analyze specific antibodies. Biosensors that utilize antibodies or antigens as bioreceptors are called immunosensors. Immunosensors are widely being investigated and developed for practical applications such as: medical and veterinary diagnostics, food safety, and environmental monitoring. Because antibodies are very specific to proteins, viruses, bacteria, cells, etc., the sensitivity and specificity of immunosensors are much more superior to other types of biosensors. We have learned three major transducers that are commonly used in biosensor applications: optical (Chap. 8), electrochemical (Chap. 10), and piezoelectric (Chap. 11). Immunosensors are generally classified depending on the type of transducers: optical immunosensor, electrochemical immunosensor, and piezoelectric immunosensor.
12.1
Enzyme-Linked Immunosorbent Assay
Immunosensors have become very popular recently, although the use of antibodies in biological assays has been and still is a very common practice in laboratorybased analyses. One particular assay protocol that has dominated over the others is the enzyme-linked immunosorbent assay (ELISA). We have already learned briefly about the working principle of ELISA in Chap. 1. Figure 12.1 is basically identical to the sandwich immunoassay with enzyme, described previously in Fig. 1.11. In ELISA, a solid support (microwells; described later) is pre-immobilized with antibodies. Any empty spaces are further immobilized with passivating proteins, usually bovine serum albumin (BSA), to prevent any non-specific bindings. A target solution is added to this surface, and J.-Y. Yoon, Introduction to Biosensors: From Electric Circuits to Immunosensors, 199 DOI 10.1007/978-1-4419-6022-1_12, # Springer Science+Business Media New York 2013
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Immunosensors
Fig. 12.1 Typical ELISA (identical to the portion of Fig. 1.11)
antibody-antigen binding occurs if there is a complementary antigen in the target solution. The surface is then rinsed, leaving only the bound target antigens on the surface. Antibody-antigen binding is now occurred, but at this moment there is no way to tell whether the binding really occurred or not. Therefore, we need to add additional materials that will bind specifically to the target antigen as well as generating optical or electrochemical signals. To this end, the same antibody is added (called secondary antibody or 2 antibody) to the surface, which should specifically bind to the target molecule. As a result, the target molecule is sandwiched between two identical antibodies. In this sense, ELISA is often referred to as sandwich immunoassay. The surface is rinsed again to remove excess secondary antibodies. After that, antibody-to-antibody is
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