The team was encouraged they might find a way to enhance the signal by recent experiments showing that coupling certain molecules with metallic nanoparticles could greatly increase their response to light (see: http://www.bnl.gov/newsroom/news.php?a=11157). Theoretical work even suggested that these so-called plasmonic particles-which induce a collective oscillation of the material's conductive electrons, leading to stronger absorption of a particular wavelength-could bump the signal into the visible light portion of the spectroscopic fingerprint, where it would be easier to measure.
The group experimented with different shapes and compositions of nanoparticles, and found that cubes with a gold center surrounded by a silver shell are not only able to show a chiral optical signal in the near-visible range, but even more striking, were effective signal amplifiers. For their test biomolecule, they used synthetic strands of DNA-a molecule they were familiar with using as "glue" for sticking nanoparticles together.
When DNA was attached to the silver-coated nanocubes, the signal was approximately 100 times stronger than it was for free DNA in the solution. That is, the cubic nanoparticles allowed the scientists to detect the optical signal from the chiral molecules (making them "visible") at 100 times lower concentrations.
"This is a very large optical amplification relative to what was previously observed," said Fang Lu, the first author on the paper.
|Contact: Karen McNulty Walsh|
DOE/Brookhaven National Laboratory