Food Biochemistry and Food Processing (2 edition)

BLBS102-c45 BLBS102-Simpson March 21, 2012 14:38 Trim: 276mm X 219mm Printer Name: Yet to Come

45 Biosensors for Sensitive Detection of Agricultural Contaminants, Pathogens and Food-Borne Toxins 863

Inhibition assay Competition assay

Gold layer

Linker layer

Glass layer

Dextran matrix

Antigen Antibody Conjugated antigen

Figure 45.3.Formats for inhibition and competition assays. For illustration, a Biacore surface is represented.

Inhibition: Free analyte inhibits binding of the antibody to the immobilised analyte on the chip. The signal generated when the antibody binds

to the immobilised analyte is inversely proportional to the concentration of free analyte in the sample.

Competition: Free () and conjugated ( ) analyte compete for binding to the immobilised antibody. The signal generated is inversely

proportional to the amount of free analyte in the sample.

Complementarity determining regions Heavy chain

Light chain

y

V

VH

Intrachain disulphide bond

CL

VL

CH 1

Hinge region

Carbohydrate

CH

CH

VH

2

Interchain

disulphide bond

CH 3

Figure 45.4.Structure of an IgG antibody. CH1–3refers to constant heavy regions 1 to 3, respectively. VH, variable heavy; VL, variable light.