Biomedical Engineering Reference
In-Depth Information
The sensing ilm is prepared on glass or quartz substrates with
a layer-by-layer (LbL) technique. In this sensing system, Au NP/
polyelectrolyte-coated polystyrene particles of 488 nm diameters
act as quenching agents for a luorescein isothiocyanate (FITC) that
is labeled with anti-biotin immunoglobulin (anti-biotin IgG). Biotin
molecules localize on the Au NP/polyelectrolyte-coated polystyrene
particles by depositing a layer of biotinylated poly(allylamine
hydrochloride), and FITC-anti-biotin IgGs are subsequently bound
to the particles through interaction with the biotin. Transmission
electron microscopy and quartz crystal microgravimetry conirm
the multilayer formation on latex particles and planar Au surfaces,
respectively. The biotin-functionalized Au NP/polyelectrolyte-coated
polystyrene particles terminated by FITC-anti-biotin IgG exhibit a
dynamic sensing range of 1-50 nmol for biotin.
Researchers have also developed a unique, sensitive, and highly
speciic luoroimmunoassay system for antigen detection using Au
NPs and magnetic NPs.
80
The assay is based on the luorescence
quenching of FITC caused by Au NPs coated with monoclonal
antibody. To demonstrate its analytical capabilities, magnetic
nanoparticles coated with anti-α-fetoprotein polyclonal antibodies,
which speciically bind with α-fetoprotein, are used. Au NPs coated
with anti-α-fetoprotein monoclonal antibodies sandwich the α-
fetoprotein captured by the magnetic NP probes. A magnetic ield
can then be applied to separate the sandwich-type immunocomplex
formed on the surface of the magnetic NPs. The supernatant
liquid, which contains the unbound Au NPs probes, quenches
the luorescence. The luorescence intensity of FITC at 516 nm is
proportional to the α-fetoprotein concentration. This approach
provides an LOD of 0.17 nM for α-fetoprotein.
Aptamer-conjugated Au NPs (Apt-Au NPs) are useful sensors
for the detection of proteins. In these sensors, the Apt-Au NPs
act as luorescence quenchers. An Apt-Au NP-based molecular
light switching sensor has been demonstrated for the analysis
of platelet-derived growth factor (PDGF) and their receptors in
homogeneous solutions.
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Increases in the concentrations of PDGFs
are associated with a variety of disorders, including atherosclerosis;
ibroproliferative diseases of the lungs, kidneys, and joints; and
neoplasia.
82,83
PDGFs also play important roles in cell transformation
and tumor growth and progression.
84,85
The PDGF binding aptamer
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