ARS researchers shed light on stealthy Salmonella detection

US Department of Agriculture (USDA) Agricultural Research Service (ARS) researchers are experimenting with the technology, known as surface-enhanced Raman scattering (SERS), with the sole aim of detecting even the smallest quantity of Salmonella on food surfaces.

SERS are light scatterings created when a specimen is scanned with a Raman spectrometer laser beam. Different Salmonella serogroups form unique spectral pattern which the ARS researchers have already been able to differentiate between.

If it proves to be a success, the process could be adopted by food safety laboratories and the food industry to detect Salmonella and other pathogens responsible for foodborne outbreaks.

ARS scientist Bosoon Park, who is leading the SERS research, told FoodQualityNews.com that future developments based on the research could detect small quantities of the pathogen – those that cannot be easily seen or identified - at early stages of contamination.

Early stages of contamination​

“This method is simpler, quicker and needs minimum sample preparation time. It could detect Salmonella in earlier state of contamination with acceptable detection limit after calibration,”​ said Park.

“It can be adopted for other foodborne pathogens detection such as E.coli, Campylobacter, Listeria and so on. E.coli is being tested with SERS at present.”​

“This research could be developed further in terms of applications of this technology for various foodborne pathogens.”​

According to Park, the research could be broadened to develop a portable instrument and Salmonella serotype spectral library for field-based quick detection.

“This can be used at a food industry, federal (FDA, FSIS, CDC), state laboratory in relation with food pathogen outbreaks,”​ he added.

Unique spectral signature​

During the SERS analysis process, a specimen is placed on a surface, such as a stainless steel plate, that has been changed from smooth to rough by coating the surface with biopolymers encapsulated with silver nanoparticles.

These rough surfaces can enhance the scattering of light that occurs when a specimen is scanned with the Raman laser.

The scattered light that returns into the spectroscope forms a distinct spectral pattern known as a Raman spectral signature. Researchers are hoping to prove that all molecules, including those that make up Salmonella, have their own unique spectral signature

This idea is not new, but the use of SERS to detect foodborne pathogens is.

During tests using large concentrations of two Salmonella serotypes – Enteritidis and Typhimurium – the SERS process was able to differentiate between the two strains.

“This scattered signal carries their characteristics of molecular information. From this information, the type of cells could be identified accordingly,”​ Park added.