Recent developments in electrochemical immunoassays and immunosensors - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 118

surface of a screen-printed carbon electrode (SPCE) was modifi ed fi rst with streptavidin.
The immobilized streptavidin was used to bind biotinylated anti-rabbit IgG. The modi-
fi ed surface was then exposed to rabbit IgG and rabbit IgG that had been labeled with the
enzyme alkaline phosphatase (AP). These two antibodies compete for a limited number
of binding sites of the immobilized anti-rabbit IgG and the square wave voltammetric
signal produced is due to the oxidation of the product of an enzymatic reaction. A detec-
tion limit (based on the analytical signal that is three times greater than the blank signal)
of 50 pmol L 1 (or 7.0 ng mL 1 ) for rabbit IgG was achieved by this system.

(a) (b)

labeled
signal
antibody

labeled
analyte

analyte

capture antibody

solid phase

FIGURE 5.2

Schematic representation of (a) competitive and (b) non-competitive immunoassay formats.

1-naphthol

1-NP

Alkaline
phosphatase

ALP ALP

e

Conjugate

electrochemical
measurement

OH OH OH

Estradiol

HO HO HO

Mouse anti-estradiol mAb

Rb anti-mouse lgG

Solid Phase

FIGURE 5.3 A schematic illustrating a competitive immunoassay format used for the detection of estra-
diol. (Reprinted from [11] with permission from Elsevier.)