Raman spectral signatures underlie new technique for sensitive immunoassay
Researchers at US microprocessor company Intel have developed a nanoscale particle that generates millions of different Raman spectral signatures. The particles are being developed for use in highly sensitive biomolecule-detecting immunoassays.
Raman spectra are produced when a beam of light is scattered by a collection of molecules, causing the frequency of the light to change. The change depends on the specific vibrational and rotational energy of the molecule, so the frequency change can identify the molecule. Raman spectra produced by organic molecules are often weak, but attaching gold or silver nanoparticles can increase the intensity. The researchers, led by Xing Su, created a suite of nanoparticles, generating different spectral signatures by incorporating organic compounds into the gold and silver nanoparticles. Small seed particles of gold and silver were mixed with known amounts of an organic compound, together with silver nitrate and sodium citrate. This produced nanoparticles of 50-100nm in size with the organic compound incorporated in layers of silver, which the researchers termed composite organic-inorganic nanoparticles (COINs).
Su’s team created COINs containing over 20 different organic compounds, including 6-mercaptopurine and Rhodamine-6G. COINs containing these compounds produced unique Raman spectra, and those containing different combinations of the compounds also produced unique spectra. This means that millions of COIN spectral signatures could be generated by less than 50 different organic compounds.
The researchers attached antibodies against the proteins interleukin 2 (IL-2) and IL-8 to two different COINs and demonstrated that these constructs could accurately detect the two proteins in a sample.
X. Su et al, Nano Lett., 2005, 5, 49