Recent developments in electrochemical immunoassays and immunosensors - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 124

Protein A
modified electrode

biotin anti-RIgG

anti-RIgG

RIgG

(a) Immobilization of RIgG

(b) Competitive immunoassay

H 2 O 2

H 2 O

HRP-streptavidin conjugate

ox HRP red

red

HQ ox

ne

E -0.100 V

(c) Enxymatic labeling (d) Enzyme activity determination

FIGURE 5.6 Schematic representation of the immunosensor based on a Protein A-GEB biocomposite
as a transducer. (a) Immobilization of RIgG on the surface via interaction with Protein A, (b) competitive
immunoassay using anti-RIgG and biotinylated anti-RIgG, (c) enzyme labeling using HRP-streptavidin and
(d) electrochemical enzyme activity determination. (Reprinted from [31] with permission from Elsevier.)

who have developed a renewable microfl uidic immunosensor using Protein G as the
immobilization aid [33]. In this work, Protein G was covalently bound to a silicon
microchip to trap immunocomplexes that were formed off-line in a competitive assay
between antibody and either labeled or unlabeled analyte antigen. Following injec-
tion of these complexes and processing of the immunoassay, the Protein G bound to
the silicon microchip was regenerated by removing the immunocomplexes. This
was achieved by injecting glycine-HCl buffer (0.4 mol L 1 , pH 2.2) at a fl ow rate of
50 L min 1 for 2-3 min. The Protein G chip lost no activity after more than 8 months. µ

5.4.3 Conducting polymers
The application of conducting polymers such as polyaniline, polypyrrole, and polythi-
ophene for immobilizing capture antibodies in immunoassay systems is widespread.