A DNA-based assembly technique can precisely engineer gap distances in nanoparticle dumbbells to optimise the sensing capability of DNA and RNA molecules using surface-enhanced Raman scattering (SERS). Potential pplications of the research include nano-optical sensors, in vitro diagnostic devices and medical imaging. “This could lead to a highly sensitive—ideally single-molecule-sensitive—and quantitative biomolecule detection with great multiplexing capability,” comments Jwa-Min Nam, an assistant professor in the department of chemistry at Seoul National University. “Eventually, straightforward, faster, and more-accurate disease diagnosis at a lower cost could be possible using our approach.” The technique could be used to quickly detect cancer and diseases such as AIDS, hepatitis and even the slow-to-diagnose h1N1 flu strain.
The imaging technique relies on Raman scattering, which is related to the change in the frequency of monochromatic light, such as a laser, when it passes through a substance—SERS can identify specific molecules by detecting their characteristic spectral fingerprints. However, while the technology has great potential for chemical sensing, the large nonlinearity of the effect makes reproducible SERS sensing difficult, according to an article at Nanowerk.
Reporting their findings in “Nanogap-Engineerable Raman-Active Nanodumbbells for Single-Molecule Detection,” the researchers from Seoul National University and the Korea Research Institute of Chemical Technology show that Raman-active gap-tailorable gold-silver core-shell nanodumbbells (GSNDs) have single-molecule sensitivity with high structural reproducibility. To fabricate a single-molecule detector, the scientists modified gold nanoparticles with two different kinds of DNA sequences—a protecting one and a target-capture one. A gold nanoparticle with a diameter of 20 nm (probe A) was functionalised with two kinds of a 3′-thiol-modified DNA sequence while a 30-nm gold nanoparticle (probe B), was functionalised by two kinds of a 5′-thiol-modified DNA sequence. By modifying the molar ratios of the two kinds of sequences, the target-capture DNA per probe can be adjusted. Cy3, a Raman-active dye, was preconjugated to the target-capture sequence (probe B alone) so that the dye could be located at the junction of the single-DNA interconnected probes A and B.
With the Cy3-modified DNA located at the junction site between the DNA-tethered gold nanoparticles—a distance of 3 to 4 nm—the gold nanoparticle surface was coated with silver by means of a nanoscale silver-shell deposition process to form the GSNDs.
“We believe that our method and findings could lead to high cross section–based SERS sensing and single DNA detection in a highly reproducible fashion,” Nam comments. “Since our DNA-based nanostructure fabrication synthetic strategy is pretty flexible and many other nanostructures could be generated for various other applications, this work could be a breakthrough for the field.”Brian Buntz