Biomedical Engineering Reference
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oxidation current of 4-aminophenol was used to relate to the quantity of analyte present.
Femtogram detection limits for murine IgG were achieved in this electrochemical
immunoassay format.
Another example is a non-competitive immunoassay system developed for the
detection of pathogenic bacteria in food samples [16]. In this work, capture antibody
was immobilized on the surface of highly dispersed carbon particles. The design of
the sensing system incorporates a fl ow-through immunosensor that contains the car-
bon particles within a disposable centrifugal fi ltration device at the base of a hollow
carbon rod (the working electrode). A hollow Ag|AgCl rod and an additional hollow
carbon rod act as the reference and counter electrodes, respectively. A schematic dia-
gram of this fl ow cell is shown in Fig. 5.4. The design is such that fl uid fl ows through
the trapped immunosorbent via the working electrode. The fl uid then fl ows through
the counter and reference electrodes before being expelled to waste. After trapping the
immunosorbent in the fl ow cell and an initial washing stage, a solution containing the
analyte cells was injected into the system to be captured by the capture antibody. Next,
horseradish peroxidase (HRP)-labeled signal antibody was introduced to complete the
two-site sandwich immunoassay. After a fi nal washing stage, amperometry was car-
ried out for quantitative determinations by fl owing sodium acetate buffer (10 mM, pH
5.6) containing the HRP substrates, hydrogen peroxide and sodium iodide (each 1 mM)
1
2
W
3
4
5
R
C
6
7
FIGURE 5.4
A schematic of the fl ow-through immunosensor equipped with (1) fl uid inlet, (2) carbon
current collector, (3) disposable immuno-column, (4) highly dispersed antibody-modifi ed carbon parti-
cles (immunosorbent), (5) carbon counter electrode, (6) Ag|AgCl reference electrode and (7) fl uid outlet.
(Reprinted from [16] with permission from Elsevier.)
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