Posted: Dec 17, 2009 | |
Single-molecule detection with nanodumbbells |
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(Nanowerk Spotlight) Surface-enhanced Raman scattering (SERS) offers enormous potential for chemical sensing, even though the large nonlinearity of the effect makes reproducible sensing difficult. SERS relies upon a fundamental phenomenon in physics called the Raman effect – the change in the frequency of monochromatic light, such as a laser, when it passes through a substance. | |
Properly harnessed, Raman scattering can identify specific molecules by detecting their characteristic spectral fingerprints. A novel DNA-based assembly technique developed by scientists in South Korea (Jwa-Min Nam from Seoul National University and Yung Doug Suh from Korea Research Institute of Chemical Technology) now offers a means of precise engineering of gap distances in nanoparticle dumbbells for a robust surface-enhanced Raman sensing of DNA and RNA molecules. | |
"We have demonstrated a high-yield synthetic strategy to obtain gap-tailorable gold-silver core-shell nanodumbbells (GSNDs) and subsequent hot SERS-based single-molecule detection with structurally reproducible dimetric nanostructures," Jwa-Min Nam, an assistant professor in the Department of Chemistry at Seoul National University tells Nanowerk. "We believe that our method and findings could lead to a high cross section-based SERS sensing and single DNA detection in a highly reproducible fashion. 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." | |
Reporting their findings in the December 13, 2009 online edition of Nature Materials ("Nanogap-engineerable Raman-active nanodumbbells for single-molecule detection") a team from Seoul National University and Korea Research Institute of Chemical Technology showed that these Raman-active GSNDs have single-molecule sensitivity with high structural reproducibility. The authors of this paper include Dong-Kwon Lim, Ki-Seok Jeon and Hyung Min Kim along with the leading authors, Jwa-Min Nam and Yung Doug Suh. | |
To fabricate their single-molecule detector, the researchers first modified gold nanoparticles with two different kinds of DNA sequence – a protecting sequence and a target-capture sequence. One gold nanoparticle with a diameter of 20 nm (probe A) was functionalized with two kinds of 3'-thiol-modified DNA sequence; a second, 30 nm gold nanoparticle (probe B) was functionalized by two kinds of 5'-thiol-modified DNA sequence. By modifying the molar ratios of the two kinds of sequence, the target-capture DNA per probe could be modified. A Raman-active dye (Cy3) was pre-conjugated 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 was located at the junction site between the DNA-tethered particles – the distance between the gold nanoparticles is 3-4 nm – the structure was coated with silver by means of a nanoscale silver-shell deposition process on the gold nanoparticle surface to form the GSNDs. | |
The high-yield synthetic scheme and nanogap engineering for single-DNA-tethered heterodimeric GSNDs and AFM-correlated nano-Raman spectroscopic measurement of individual GSND particles. a, A high-yield synthetic scheme for the Au nanoparticle heterodimers using stoichiometric DNA modification and magnetic purification. b, Nanometer-scale silver-shell growth-based gap-engineering in the formation of the SERS-active GSND. c, AFM-correlated nano-Raman spectroscopy set-up (laser focal diameter is 250 nm) for the detection of a Raman signal from a single GSND particle. (Reprinted with permission from Nature Publishing Group) | |
Nam explains that his team's results are important for several reasons. "First, our DNA-directed and magnetic separation-based nanostructure synthetic scheme opens opportunities in the high-yield synthesis of specific nanostructures for materials science and bio-detection applications. | |
Second, unlike the conventional strong electrolyte-induced nonspecific nanoparticle aggregation, our DNA-directed nanodimer assembly method can be easily scalable to produce targeted SERS-active nanoprobes. | |
Third, we established a silver-shell coating-based nanogap-engineering method. | |
Fourth, the nanogap-engineering of GSNDs allows for exploring hot SERS structures in an efficient and straightforward fashion. | |
Fifth, our synthetic and detection strategies provide new ways of overcoming long-standing problems in Raman and materials-research societies about controlling the nanometer-gap, nanogeometry and dye position and environment with high reliability and reproducibility." | |
The Korean scientists point out that many critical problems in Raman – especially, single molecule sensing, increasing cross section area, and quantitative Raman for eventual, practical applications of SERS – could be studied and addressed by using their method and nanodumbbells. Additionally, other optical properties including fluorescence and plasmonic coupling effect could also be studied. | |
"Finally" says Nam, "this could lead to a highly sensitive – ideally single-molecule sensitive – and quantitative biomolecule detection with great multiplexing capability. Eventually, straightforward, faster, and more accurate disease diagnosis at a lower cost could be possible using our approach." | |
According to the team, clinical test and trials are already underway. | |
By Michael Berger – Michael is author of three books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology, Nanotechnology: The Future is Tiny, and Nanoengineering: The Skills and Tools Making Technology Invisible Copyright © Nanowerk LLC | |
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