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Gold nanoparticles improve sensitivity and specificity of genetic analysis and diagnosis
Good as Gold
June 27, 2005
Even though they don't shine, they're still worth their
weight in gold: nanoscopic particles made of gold are used
for a number of technical and scientific purposes. Now
these tiny golden particles are being put to use in another
area. Chinese scientists have discovered that the
polymerase chain reaction (PCR), the basis for modern
genetic testing methods, works markedly better in the
presence of gold nanoparticles.
As we all know from murder mysteries, a few flakes of skin
under the victim's fingernails or saliva residue on an
envelope's adhesive strip are enough to reveal the
perpetrator. The tiny amount of genetic material in these
samples is enough to give a genetic fingerprint that can be
compared with known samples and assigned unambiguously to a
single person. PCR takes all the credit for this; this
tremendously efficient technique allows the complete
genotype or a select region of the genome to be copied.
Within a few hours, there is enough material for a variety
of biological and medical tests. PCR is indispensable not
only for forensics but also in research and diagnosis, for
the identification and quantification of pathogens.
Here's how PCR works: the genetic material is in the form
of double strands of DNA, which are first separated into
single strands. A segment of the DNA sequence to be
examined is marked with a short synthetic piece of single-
stranded DNA, the primer. Starting at the primer, an enzyme
then gets to work copying the strand, building block by
building block. This procedure, splitting the DNA into
single strands and copying it, is repeated again and again.
Each cycle doubles the amount of DNA. Errors do occur in
this process, which are then passed on in the copies,
compromising sensitivity and specificity. This is where
Chunhai Fan, Jun Hu, Zhizhou Zhang and their team step in.
Their nanogold binds substantially more tightly to single-
stranded than to double-stranded DNA. This effect seems to
be responsible for the fact that in the presence of gold
particles, fewer errors occur in the PCR and the yield is
improved. This makes it possible to use smaller DNA samples
from the start.
The effect of the nanogold particles is not completely
understood. It is clearly analogous to a natural error
avoidance system: in cells, the protein SSB binds to
single-stranded DNA, but not to double-stranded DNA,
hindering mismatches between the strand to be copied and
the natural primer.
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