Biomedical Engineering Reference
In-Depth Information
FIGURE 4.4
Schematic diagram of IOMNP that is used as the capture platform in an assay.
(For
color version of this figure, the reader is referred to the online version of this topic)
substrate. The 200-nm streptavidin-coated magnetic iron oxide nanoparticles
(IOMNPs) with an iron oxide content of about 70% were used to immobilize 5′
biotinylated DNA probes using the strong biotin-streptavidin interaction. A layer
of these functionalized IOMNPs was directly immobilized on bare gold electrode
using a magnet. Using this technique, the values of
Z
real measured in the case
of HIV DNA detection were lower compared to those obtained with HBV DNA.
For the same concentration (12.65 nmol/mL), a value of
Z
real of 98.38 KΩ cm
2
was recorded for HBV DNA detection and only 15.88 KΩ cm
2
in the case of HIV
DNA. This can be explained in terms of the length of the DNA target being 74
base pairs (bp) in the case of the HBV target and only 33 bp in the case of the HIV
target because at the same concentration, the value of
Z
real is an increasing func-
tion of the DNA target length. For both biosensors, saturation was reached at the
same concentration, 12.65 nmol/mL, because the same quantity of DNA probes
was immobilized on the surface of the magnetic NPs. Using non-faradic imped-
ance spectroscopy detected 50 pmol of HBV DNA and 160 pmol of HIV DNA
from 20-µL sample that may be a function of the shorter HIV target sequence.
In oncology, NM-based immunoassays that detect the presence of tumor
markers are important for in vitro cancer diagnosis. Gong et al.
80
used silica-
coated magnetic NMs with modified amino groups for immobilization and
separation of human alpha-fetoprotein (AFP), a tumor marker in hepatocellular
carcinoma. The system used novel nanostructured rhodamine B isothiocyanate
dye molecule Raman tags that gave high stability compared with traditional tags.
The system comprising silica-coated magnetic NPs as immobilization matrix and
separation tool was simpler than traditional techniques. This sensitive and spe-
cific immunoassay for human alpha-fetoprotein used Ag/SiO
2
core-shell NMs
that resulted in detection of human AFP at concentrations as low as 11.5 pg/mL.
4.4.1 Covalent Conjugation Protocols
Covalent conjugation of biomolecules to NMs may be done following conven-
tional bioconjugation techniques with slight modification.
81
These methods are
useful for the conjugation of proteins, ONTs,
69
or other molecules to various
