Biomedical Engineering Reference
In-Depth Information
DNA probes have been used for FISH detection of several mRNA targets [
59
,
60
]. However, QDs containing cadmium such as CdSe or CdTe are always
toxic due to the release of Cd
2
+
. In view of the inherent toxicity of the cad-
mium, an additional nontoxic ZnS shell was coated onto the CdSeTe/CdS QDs
to minimize the toxicity of NIR-emitting QDs [
35
,
61
]. Trioctylphosphine oxide
(TOPO)-capped CdSe/ZnS QDs was prepared to reduce cytotoxicity of QDs [
62
].
Amine-modified oligonucleotide probes are designed and covalently attached
to the carboxyl-terminated polymer-coated QDs via EDC chemistry (shown in
Fig.
3.16
). The resulting QD-DNA conjugates show sequence-specific hybridiza-
tion with target mRNAs. QD-DNA probes exhibit excellent sensitivity to detect
the low-expressing dorsal-related immunity factor gene. Importantly, multiplex
FISH of ribosomal protein 49 and actin 5C using green and red QD-DNA conju-
gates allows the observation of cellular distribution of the two independent genes
simultaneously.
3.3 QDs for DNA Microarrays
DNA microarrays (also commonly called gene chips, DNA chips, or biochips)
are a collection of microscopic DNA spots attached to a solid surface, such as
glass, plastic, or silicon supports [
63
,
64
]. They were born for the simultaneous
analysis of the expression levels of numerous genes in a single experiment [
65
].
Since their development in the mid-1990s, DNA microarrays have displayed
enormous potentials in various applications, such as cancer diagnosis or drug
influence on the gene expression level. DNA microarray technology has revealed
a great deal about the genetic factors involved in a number of diseases, including
multiple forms of cancer. At the beginning, microarrays were just employed for
the identification of the differences in gene expression between normal cells and
their cancerous counterparts. Later on, researchers began to apply this technol-
ogy to distinguish specific subtypes of certain cancers, as well as to determine
which treatment methods would most likely be effective for particular patients.
This also reflected the effect of medicines which was benefit for drug selection
[
66
,
67
]. DNA microarrays are usually categorized as complementary DNA
(cDNA) arrays, using either short (25-30 mer) or long ODN (60-70 mer) probes.
The core principle behind microarrays lies in their ability to provide a powerful
high-throughput system that allows for large-scale analysis of gene expression,
genetic alterations, and signal transduction pathways, which can give impor-
tant information for disease diagnosis, prognostics, and therapeutics. A typical
DNA microarray usually consists of the following step: First robotically print-
ing oligonucleotides or cDNA clone inserts onto a glass slide, then one or more
fluorescent-labeled cDNA probes generated from samples are hybridized to the
surface, later a laser is employed to excite the dye labels and record the fluores-
cent intensities by a laser confocal fluorescent scanner. Finally, the ratio of flu-
orescent intensities provides the basis for further meta-analyses. The feasibility
