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New High-Tech Tactic May Expose Stealthy Salmonella

Even the smallest quantity of Salmonella can wreak havoc for growers and food processors. But now science may be closing in on a way to easily detect the potentially deadly organism.

The technology is called “SERS,” the acronym for "surface-enhanced Raman scattering." And it has nothing to do with noodles.

U.S. Department of Agriculture 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 U.S. Centers for Disease Control and Prevention, Salmonella causes more than one million cases of illness in the United States every year.

If SERS proves successful for cornering Salmonella, the technique might be used at public health laboratories around the nation to rapidly identify this or other pathogens responsible for outbreaks of foodborne illness, according to Mr. Park, an agricultural engineer with USDA's Agricultural Research Service in Athens, Ga.

What's more, food makers might use SERS at their in-house quality control labs.

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, Mr. 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.

In work with comparatively large concentrations of two different kinds, or serotypes, of Salmonella enterica — Enteritidis and Typhimurium — Mr. Park's tests showed, apparently for the first time, that SERS can differentiate these two serotypes. 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, says Mr. Park.

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