Scientists have now demonstrated that gold and silver nanostars are more effective than commonly used nanorods and nanospheres for chemical and biological sensing and imaging. They have used surface-enhanced Raman spectroscopy (SERS)for this purpose.
The National Institute of Standards and Technology (NIST) researchers found that gold and silver nanostars improved the sensitivity of SERS 10 to 100,000 times that of other commonly used nanoparticles.
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SERS relies on metallic nanoparticles, usually gold and silver, to amplify signals from molecules present in only trace quantities.
In such experiments, scientists shine laser light on an aqueous solution containing the nanoparticles and the molecule of interest and monitor the scattered light.
The detailed characteristics of both the molecule and the nanoparticle affect the strength of scattered light, which contains an identifying fingerprint for the molecule known as its vibrational signature.
It is possible to detect a very low concentration of molecules in a solution, with nanoparticles amplifying the signature.
The researchers used two target molecules, 2-mercaptopyridine and crystal violet for testing optical properties of the nanostars
It was found that the Raman signal of 2-mercaptopyridine was 100,000 stronger when nanostars were present in the solution.
Also, the stars were found to be particularly capable of enhancing the signature of crystal violet, delivering a signal about 10 times stronger than the previous winner, nanorods. Both the nanostars and the nanorods outperformed the nanospheres commonly used for Raman enhancement.
Researchers led by NIST physicist Angela Hight Walker perfected the process for making gold nanostars, building them from the bottom-up using surface alterations to manipulate their growth and control their shape.
When suspended in a solution, the team guided the nanostars to gather together to form multiple "hot spots," where the enhancement is dramatically larger than for a single nanostar.
Hight Walker said that the nanostars can now be created en masse and have desirable optical properties, which may encourage researchers to examine their possible applications.
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