Posted: April 23, 2007

Gold nanoparticles can improve the efficiency of DNA sequencing

(Nanowerk News) Not content with fluorescing and catalysing chemical reactions, gold nanoparticles have now demonstrated that they can also improve the efficiency of DNA sequencing. This follows the discovery by a team of Chinese researchers that adding gold nanoparticles to a polymer matrix enhances its ability to separate DNA by capillary electrophoresis (CE).
Gold is proving to be a fascinating and highly adaptable material for nanotechnology researchers. Although fairly non-reactive in bulk form, gold has unveiled a raft of hitherto unsuspected properties at the nanoscale. This has led scientists to explore a wide range of potential uses for gold nanoparticles, including medical imaging and the manufacture of organic chemicals.
So it was perhaps only a matter of time before analytical scientists started to investigate whether gold nanoparticles had anything to offer CE. In particular, analytical scientists are interested to discover whether incorporating gold nanoparticles into CE matrices can help enhance their separation abilities. So far, the answer appears to be that it can.
In 2003, chemists from the National Taiwan University showed that a polymer matrix containing gold nanoparticles is highly effective at separating double-stranded DNA. Now, researchers from the University of Science and Technology of China, Hefei, led by Yanmei Wang, have shown that the same is true for single-stranded DNA ("Novel quasi-interpenetrating network/gold nanoparticles composite matrices for DNA sequencing by CE").
Such highly effective CE matrices are required for DNA sequencing, which involves separating DNA strands that differ in length by only a single base. At the moment, non-gel polymers such as linear polyacrylamide (LPA) and poly(N,N-dimethylacrylamide) (PDMA) are some of the most commonly used CE matrices for separating DNA strands.
Particularly effective are versions of these polymers made up of monomers with a high molecular weight. But these polymers also tend to be highly viscous, making it difficult to inject and remove them from capillary tubes, especially the microscopic tubes used in microchip CE. Wang and his team wondered whether adding gold nanoparticles to low molecular weight versions of these polymers, which are less viscous, would make them as effective at separating single-stranded DNA as the high molecular weight versions.
To find out, they created two versions of a co-polymer comprising LPA and PDMA - a low molecular weight version and a high molecular weight version - and added gold nanoparticles at two different concentrations to the low molecular weight version. Then they tested the ability of these four polymers to act as CE matrices for sequencing a DNA strand of 1000 bases in length, which involved separating 1000 different length DNA strands.
They discovered that the low molecular weight polymer with gold nanoparticles was more effective at separating the DNA strands than the low molecular weight polymer on its own and just as effective as the high molecular weight polymer. They also found that the concentration of the gold nanoparticles in the polymer had little effective on its separation ability.
Wang and his team then used analytical techniques such as atomic absorption spectroscopy and differential scanning calorimetry to study the gold nanoparticle-containing polymer in more detail. They discovered that its enhanced separation ability seemed to be due to the gold nanoparticles improving the stability of the polymer network and thereby preventing the pores in the network, through which the DNA strands travel, from being stretched out of shape. In addition, the gold nanoparticles also helped prevent the DNA strands from sticking to the capillary walls.
Wang and his team are now investigating the influence of other factors, such as the precise size of the gold nanoparticles and the electric field strength, on the polymer's DNA separation ability.
Source: John Wiley & Sons (John Evans)
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