Gold nanoparticles linked to single-stranded DNA create a simple but versatile genetic testing kit
Gold
nanoparticles linked to single-stranded DNA create a simple but versatile
genetic testing kit
Posted by: Tarun Kumar
Tests for identifying
genetic variations among individuals, which can be used to develop precisely
targeted drug therapies, are a current focus in the emerging field of
pharmacogenomics. A*STAR researchers have now developed and patented a
customized and elegant nanoprobe for assessing sensitivity to the drug
warfarin.
To develop the nanoprobe, Jackie Ying at the A*STAR Institute of Bioengineering and Nanotechnology and co-workers in Singapore, Taiwan and Japan devised a relatively simple procedure that uses standard laboratory equipment and can be easily adapted for other genetic tests.
"Our method is
faster, more cost-effective and more accurate than existing alternatives,"
says Ying.
Ying's method detects
genetic variations known as single-nucleotide polymorphisms (SNPs) that differ
in only a single-nucleotide building block of DNA. In the case of warfarin—the
most frequently prescribed anticoagulant—there are SNP differences in specific
parts of the genome that indicate whether a patient will tolerate the drug or
suffer serious side effects.
The researchers used
gold nanoparticles attached to short sections of DNA that bind to specific
complementary sequences of DNA through the base pairing that holds together
double-stranded DNA. These nanoprobes were exposed to fragments of DNA that had
been cut out and amplified from a patient's genome.
The nanoprobes are
initially pink due to surface plasmonic effects involving ripples of electric
charge. When analyzed, if the probes do not bind to the DNA fragments, they
aggregate and become colorless on exposure to a salt solution. If they do bind
to the target, they will not aggregate but will remain pink until heated to a
'melting temperature' at which the base pairing is disrupted and the DNA
strands of the probe and the genome fragments separate. For cases of partial
complementarity—in which the fragments are mismatched by a single
nucleotide—the melting temperature is lowered by an amount depending on the
level of mismatch. This allows SNPs to be detected through their different
melting temperatures.
The resulting color
change is easily visible to the human eye but can also be evaluated
automatically (see image). The system can also distinguish between homozygous
genotypes (where a person caries the same SNP on each member of a pair of
chromosomes) and heterozygous genotypes (where a person carries different SNPs
on each chromosome).
"The patented
warfarin test kit is available for commercialization or licensing," says
Ying. "We have developed and are validating assay kits for several other
applications in pathogen detection, pharmacogenomics and genetic disease screening."
More information: Zu, Y., Tan, M.-H., Chowbay, B., Lee, S.
C., Yap, H., et al. "Nanoprobe-based genetic testing." Nano
Today 9, 166–171 (2014). dx.doi.org/10.1016/j.nantod.2014.04.003
