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High-tech tactic to expose stealthy Salmonella

Even the smallest quantity of Salmonella may, in the future, be easily detected with the technology known as SERS, short for “surface-enhanced Raman scattering”.

A US Department of Agriculture (USDA) scientist, Bosoon Park, is leading exploratory studies of this analytical technique’s potential for quick, easy and reliable detection of Salmonella and other foodborne pathogens.

According to the US Centers for Disease Control and Prevention, Salmonella causes more than one million cases of illness in the United States every year.

Developed over the past two decades or so, SERS has expanded the power and potential of Raman spectroscopy, its parent technology.

In a SERS analysis, a specimen is placed on a surface, such as a stainless steel plate, that has been “enhanced” or changed from smooth to rough. For some of their research, Park’s team enhanced the surface of stainless steel plates by coating them with tiny spheres, made up of a biopolymer encapsulated with nanoparticles of silver.

Rough surfaces, and colloidal metals such as silver, can enhance the scattering of light that occurs when a specimen, placed on this “nanosubstrate,” is scanned with the Raman spectrometer’s laser beam.

The scattered light that comes back to the spectroscope forms a distinct spectral pattern known as a Raman spectral signature, or Raman scattered signal. Researchers expect to prove the concept that all molecules, such as those that make up Salmonella, have their own unique Raman spectral signature.

The idea of using a substrate of silver nanoparticles for Raman spectroscopy is not new. But in SERS studies to detect foodborne pathogens, the use of a surface — enhanced with biopolymers coated with silver nanoparticles — is apparently novel.

Though SERS research with biological specimens is still in comparatively early stages, researchers expect to prove the concept that all molecules, such as those that make up Salmonella, have their own unique Raman spectral signature. In the future, the Raman signature of an unidentified biological specimen could be compared to known Raman signatures to find a match and thus identify the unknown specimen.

Park’s team has already developed preliminary Raman spectral signatures for two common pathogenic kinds, or serotypes, of S. enterica —Enteritidis and Typhimurium— collected from raw chicken.

With further research, SERS may prove superior for finding very small quantities of bacteria in a complex, real-world background, such as a food or beverage sample, Park notes.

Read the full story: “SERS: High-Tech Tactic May Newly Expose Stealthy Salmonella was published in the April 2012 issue of Agricultural Research magazine.

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