Biomedical Engineering Reference
In-Depth Information
method to quantify the captured gold nanoparticle tracers and avoid the dissolution step
and the use of an enzyme label and substrate. The stripping signal of gold nanoparticles
is related to the concentration of target IgG in the sample solution. The detection limit
of 0.02
g mL
1
of IgG was obtained under optimum experimental conditions.
The above immunosensors and immunoassays based on a gold nanoparticle label
are used to detect one target analyte and cannot be used for multiple target assays. An
electrochemical immunoassay protocol for the simultaneous measurements of pro-
teins, based on the use of different inorganic nanocrystal tracers, was reported by Liu
et al.
[29]. The multi-protein electrical detection capability is coupled to the amplifi -
cation feature of electrochemical stripping transduction (to yield fmol detection limits)
and with an effi cient magnetic separation (to minimize non-specifi c adsorption effects).
The multianalyte electrical sandwich immunoassay involves a dual binding event, based
on antibodies linked to the nanocrystal tags and magnetic beads (Fig. 14.5). Carbamate
linkage is used for conjugating the hydroxyl-terminated nanocrystals with the secondary
antibodies. Each biorecognition event yields a distinct voltammetric peak, whose posi-
tion and size refl ects the identity and level, respectively, of the corresponding antigen.
ยต
(b)
Ab
1
Ag
3
Ag
2
Ag
1
ZnS-Ab
1
CdS-Ab
2
PbS-Ab
3
(c)
Ab
2
Ab
3
(a)
Acid Dissolution
Zn
Cd
Pb
(d)
M
M
LE
E (v)
FIGURE 14.5
Multiprotein electrical detection protocol based on different inorganic colloid nanocrystal
tracers. (a) Introduction of antibody-modifi ed magnetic beads; (b) binding of the antigens to the antibodies
on the magnetic beads; (c) capture of the nanocrystal-labeled secondary antibodies; (d) dissolution of nanoc-
rystals and electrochemical stripping detection (reproduced from [29] with permission).
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