Food Biochemistry and Food Processing

Figure 31.6. A.A description of surface plasmon resonance (SPR). Polarized light is focused on a gold-coated sen-
sor chip. Energy transfer occurs at a critical angle, causing a dip in reflectance. When antigen binds to the antibody,
it causes a change in mass, and thus a change in the angle of refraction. This change in angle is measured over time
and expressed as resonance units on a sensogram. (Adapted from Hashimoto 2000, Nice and Catimel 1999.) B.A
typical sensogram of an antigen-antibody interaction. The first peak represents the capture of the antigen, recombi-
nant listeriolysin O (LLO) on the chip. After the flow of LLO stops, the resonance drops to a level representing only
the LLO bound to the chip. Fractionated serum from a llama immunized with LLO is passed across the chip, starting
at the G1 injection site. This fraction contains only heavy-chain antibodies from the llama. The increased number of
resonance units in the sensogram after the injection is over represents the binding of the antibodies to the LLO. The
drop in resonance units at the end of the sensogram represents the stripping of the LLO from the chip and the regen-
eration of the chip. (Sensogram courtesy of T. Hirama, National Research Council Canada.)