Page 60 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

58 CHAPTER 3 Immune assay assisted cancer diagnostic

3.4 Antibody-based immunosensors

Biosensor is an analytical device with the aim to detect chemical substances. Its
works is based on the combination of the physicochemical detector and biological
component. This biological component could be tissue, microorganism, enzymes,
antibodies, antigens, nucleic acid which could interact and bind with specific analytic
[38]. Immunosensors are kind of biosensors based on interactions between an anti-
body and an antigen on a transducer surface (Fig. 3.3). Antibodies and antigens can
bind together with great strength, therefore they can be immobilized on a transducer,
and detect each other. It also brings high sensitivity to these techniques too. Moreover,
as each antibody or antigen can interact with their own antigen or antibody, there-
fore, immunosensor-based antibody has high selectivity too. Immunosensors based
on its detection ways have divided into three parts: 1—electrochemical, 2—opti-
cal, 3—piezoelectric immunosensors (electrochemical quartz crystal microbalance).
Immunosensors can be either direct or indirect. It means they have operated directly
via the Ab/Ag interaction, or indirectly with a further label, such as an enzyme or
fluorescent molecule, in order to detect whether a binding event has occurred.
Electrochemical immunosensors explore measurements of an electrical signal
produced on an electrochemical transductor. Immunosensors based on electrochemi-
cal detection is used more in research because this technique is portable, simple and
has an automated detection, meaning that it does not require handling by a person.
Immunosensors have several parts, and each part is important and impacts devel-
opment. An electrode surface is the first part. An electrode surface can be modi-
fied with gold nanoparticles, carbon nanotubes, nanofibers or any other conducting
polymer. What is important in this part is using materials that increase conductivity,
allowing for high sensitivity in detection. This conductive electrode has stayed on

FIGURE 3.3 Schematic representation of antibody-based immounosensors.