Biomedical Engineering Reference
In-Depth Information
proteins.
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By using smaller particles, the magnetosandwich assay performance
was enhanced with respect to dynamic range and sensitivity but the detection
limit was strongly hampered by the high amount of nonspecific background,
especially for the smallest 125-nm particles used, which showed the most prom-
ising results. This problem was solved by applying a more stringent blocking
procedure detecting S100ββ, a diagnostic marker for stroke and minor head
injury, in serum samples down to ~0.2 ng/mL over a broad dynamic range (ca.
two decades). However, the smaller particles might generate smaller magnetic
responses because of their lower magnetization, leading to a tradeoff between
MNP size for magnetic signal generation and for assay performance.
Magnetic sensors offer rapid, sensitive, and low background methods of
detecting important disease biomarkers. With proper choice of MNPs, sig-
nificant degree of clustering that could lead to irreproducible magnetic sensor
results could be avoided with strong blockers. Furthermore, smaller particles
allow for improved sensitivity and wider dynamic range of concentration
detected. However, smaller particles may generate smaller magnetic responses
because of their lower magnetization showing a tradeoff between MNP size for
magnetic signal generation and for assay performance. More studies are on-
going to launch this system for clinical diagnostics.
4.7.3.2 Lateral Flow Devices
NPs have been successfully integrated with lateral flow immunoassay (LFIA)
devices or strip tests. The first dry-reagent strip test system using ONT-conju-
gated AuNPs as probes maybe the one reported by Glynou.
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The highly specific
molecular recognition properties of ONTs was combined with the unique optical
properties of AuNPs for the development of a dry-reagent strip-type biosensor
for visual detection of dsDNA within minutes. The assay does not require mul-
tiple incubation and washing steps in most current assays and also avoids the
instrumentation through the color reaction involving the AuNPs reporters with
oligo(dT) attached to their surface form an integral part of the strip. PCR products
(233 or 495 bp) with biotin labels are hybridized (5 min) with a poly(dA)-tailed
oligo and applied on the strip. As the buffer diffuses along the strip, it rehydrates
the NPs that become linked to the tDNA through poly(dA)/(dT) hybridization.
The hybrids are captured by immobilized streptavidin in the test zone of the strip
that resulted in a characteristic red band. A second red band is formed in the con-
trol zone of the strip to indicate proper test performance. The sensor offered about
8 times higher sensitivity than ethidium bromide staining of agarose gels. Quanti-
fication was obtained by densitometric analysis of the bands resulting in detection
of as low as 2 fmol of amplified DNA and 500 copies of prostate-specific antigen
complementary DNA by combining PCR and the strip sensor. The sensor was
used for 20 patient plasma samples in the detection of hepatitis C virus.
Herpes simplex virus type 2 (HSV-2) IgG-specific antibody LFIA based on col-
loidal AuNPs has been reported.
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A total of 359 serum samples and 100 whole-
blood samples were tested and compared to those from the HerpeSelect HSV-2
