Biomedical Engineering Reference
In-Depth Information
antigen-antibody interaction showing a detection limit of 10 5 pfu/mL, which was
comparable with that of the conventional ELISA technique. They used a carbon
nanotubes were demonstrated to be efficient fluorescence quencher in biosen-
sors. 69 The carbon nanotube high stability and mechanical strength allow their
use in stringent detection environment. They used a hairpin-structured assembly
that consisted of ONT-modified SWNTs and dye-labeled complementary ONTs,
which upon the complementary recognition of oligonucleotides, quenched the
fluorescence emission from the dye tags.
4.7.1.3   Light scattering
Light scattering with metal NPs that differ in size and composition can be accom-
plished according to their distinct SPRs. Using this property, a DNA array imag-
ing technique using ONT functionalized NPs was reported. 90 This sensor was
sensitive, ultraselective, and exhibited multicolor labeling for DNA arrays for
the multiplex detection of ONT targets with AuNP probes labeled with ONTs
and Raman-active dyes. The AuNPs facilitated the formation of a silver coating
that acted as an SERS promoter for the dye-labeled oligonucleotides that were
captured with target molecules in microarray on a chip. 104 Multiplex assay for
ONT targets was performed with AuNPs labeled with ONTs and Raman-active
dyes. The AuNPs facilitated the formation of a silver coating that acted as SERS
promoter for the dye-labeled particles that were captured with target molecules
on a chip in a microarray format. The assay strategy provided high sensitivity
and high selectivity of gray-scale scanometric detection with the added attri-
butes of multiplexing resulting from a very large number of probes that can be
designed using a Raman tag as narrow-band spectroscopic fingerprint. Using
his technique, six different DNA targets with six Raman-labeled NP probes
were detected along with two RNA targets that had single-nucleotide polymor-
phisms (SNPs). The unoptimized method gave a detection limit of 20 fM. This
NP-based scattering technique can be applied to various analytes.
In another study, Qian et al. 105 described the application of biocompatible
and nontoxic PEGylated AuNPs for in vivo tumor targeting and detection based
on SERS. In this study, signal enhancements were achieved under in vivo con-
ditions for tumor detection in live animals. They exhibited that small-molecule
Raman reporters such as organic dyes were not displaced but were stabilized
by thiol-modified PEG SERS NPs that were considerably brighter than near-
infrared (NIR) emitting semiconductor QDs. The AuNPs that were conjugated
to tumor-targeting ligands such as single-chain variable fragment (ScFv) anti-
bodies were able to target tumor biomarkers such as epidermal growth factor on
human cancer cells and in xenograft tumor models.
A colorimetric detection method for identifying nucleic acid sequences based
on the distance-dependent optical properties of AuNPs is developed by Storhoff
et al. 106 In this assay, nucleic acid targets were recognized by DNA-modified
AuNP probes by using a scatter-based method that enables detection of zepto-
mole quantities of nucleic acid targets without additional signal amplification.
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