SERS: high-tech tactic may newly expose stealthy salmonella.At laboratories of the future, even the smallest quantity of Salmonella bacteria may be easily detected with a technology known as "SERS SERS State Employees’ Retirement System (Commonwealth of Pennsylvania)
SERS Surface-Enhanced Raman Spectroscopy
SERS School Employees Retirement System
SERS Science and Engineering Research Semester ," short for "surface-enhanced Raman scattering."
Agricultural engineer Bosoon Park, in the Agricultural Research Service's Quality and Safety Assessment Research Unit in Athens, Georgia, 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 Centers for Disease Control and Prevention (CDC), agency of the U.S. Public Health Service since 1973, with headquarters in Atlanta; it was established in 1946 as the Communicable Disease Center. , Salmonella causes more than 1 million cases of illness in this country every year.
If SERS proves successful for cornering Salmonella, the technique might be used at public health laboratories around the nation to rapidly identify pathogens responsible for outbreaks of foodborne illness. Tomorrow's foodmakers might opt to use SERS at their in-house quality-control labs to help ensure that their products are free of unsafe levels of this or other harmful bacteria.
For Salmonella testing, labs have many choices. They can opt for well-established technologies, such as monoclonal antibody assays, ELISA ELISA (e-li´sah) Enzyme-Linked Immuno-Sorbent Assay; any enzyme immunoassay using an enzyme-labeled immunoreactant and an immunosorbent.
n. (enzyme-linked immunosorbent assay enzyme-linked immunosorbent assay
Enzyme-linked immunosorbent assay (ELISA)
A diagnostic blood test used to screen patients for AIDS or other viruses. ), or PCR PCR polymerase chain reaction.
polymerase chain reaction
Polymerase chain reaction (PCR) (polymerase chain reaction) tests.
Park's team is evaluating the strengths and shortcomings of SERS in relation to these popular analytical methods and several newer ones as well, including atomic force microscopy and surface plasmon resonance.
According to Park, a SERS analysis is relatively simple to perform, an advantage when labs are swamped with samples from an outbreak of foodborne illness or a product recall.
With further research, SERS may offer superior detection capabilities, making it faster and easier to find very small quantities of bacteria in a complex, real-world background, such as a food or beverage sample. That's especially important, since it's apparently possible for as few as 10 Salmonella cells to cause illness, depending on the strain involved and other factors.
Nobel Laureate's Work is Basis of Today's SERS
Developed over the past two decades or so, SERS has expanded the power and potential of Raman spectroscopy, its parent technology. Raman spectroscopy is based on discoveries made in the early 1900s by Sir Chandrasekhara V. Raman, who received the 1930 Nobel Prize in physics The Nobel Prize in Physics (Swedish: Nobelpriset i fysik) is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the six Nobel Prizes. The first prize was awarded in 1901. for his research.
In a SERS analysis, a specimen is placed on a surface, such as a stainless steel plate, silicon wafer, or glass slide, that has been "enhanced"--or changed from smooth to rough. For example, a glass slide or silicon wafer could be etched, to roughen rough·en
tr. & intr.v. rough·ened, rough·en·ing, rough·ens
To make or become rough.
to make or become rough
Verb 1. it, or a small stainless steel plate could be coated with an extremely thin "nanolayer" of minuscule particles of a metal, such as silver, gold, or copper.
In some of its research, Park's team enhanced the surface of stainless steel plates by coating them with tiny spheres, made up of a biopolymer bi·o·pol·y·mer
A macromolecule, such as a protein or nucleic acid, that is formed in a living organism.
any protein or nucleic acid produced by a living organism. encapsulated with silver nanoparticles.
Rough surfaces and colloidal colloidal
of the nature of a colloid.
a bath containing gelatin, bran, starch or similar substances, to relieve skin irritation and pruritus. 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 spectroscope, optical instrument for producing spectral lines and measuring their wavelengths and intensities, used in spectral analysis (see spectrum). When a material is heated to incandescence it emits light that is characteristic of the atomic makeup of the forms a distinct spectral pattern known as a "Raman spectral signature," or a "Raman scattered signal."
"The idea of using a substrate of silver nanoparticles for Raman spectroscopy is not new," says Park. "But in SERS studies to detect foodborne pathogens, our use of a substrate of silver nanoparticles that encapsulate a biopolymer is novel, to the best of our knowledge."
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.
Silver-Encapsulated Spheres Tested as a Nanosubstrate
For this research, the group used a biopolymer encapsulated with silver as the nanosubstrate, and they worked with comparatively large concentrations of the serotypes (about 108 colony-forming units per milliliter of solution). The high concentrations simplified detection and showed, apparently for the first time, that SERS can differentiate the two Salmonella serotypes by their Raman signatures.
Plans call for developing a database, or library, of Raman spectral signatures of these Salmonella serotypes and other major foodborne pathogens at various concentrations. Ideally, the signatures would be posted on the Internet for public access by researchers and analytical labs worldwide.
In follow-up studies, Park intends to use less-concentrated samples of Salmonella serotypes to more rigorously challenge the technology's ability to detect and quantify the pathogen. These tests may ultimately reveal SERS's sensitivity, or detection limit--the smallest number of Salmonella cells, in a given concentration of solution, that can be accurately and reliably detected with a given combination of variables. Those variables might include the types of SERS instruments, sample preparation method, sample nanosubstrate, power and duration of the laser beam scanning, and more.
In an earlier experiment, using a different silver-based substrate, the team showed that SERS can differentiate live Salmonella cells from dead ones. That's significant. It could help quality-control labs evaluate the performance of today's food-sterilization methods, such as high-pressure processing, irradiation, and thermal processing. In addition, reliable differentiation can speed and simplify the work of researchers who are developing and testing new techniques to keep food safe to eat.
"SERS is one of several candidate technologies we are currently testing," says Park. "If we find that it continues to offer major advantages over other options, our goal would be to develop a SERS-based system that wouldn't require extensive training and would use affordable SERS instruments."
Park has presented some of these findings at an SPIE SPIE International Society for Optical Engineering
SPIE Society of Photo-Optical Instrumentation Engineers
SPIE Source Path Isolation Engine
SPIE Special Purpose Insertion Extraction
SPIE Software Process Improvement Experimentation
SPIE Standard Protocols in Effect (Society of Photo-Optical Instrumentation Engineers) conference in Orlando, Florida. His collaborators include Yao-Wen Huang and Yiping Zhao of the University of Georgia-Athens; Arthur Hinton, Jr., Kurt C. Lawrence, Jaya Sundaram, William R. Windham, and Seung Chul Yoon, all with ARS at Athens; and Yongkuk Kwon of South Korea's Animal, Plant, and Fisheries Quarantine and Inspection Agency.
The team's studies may do much to keep us safe from some of the world's worst foodborne pathogens.--By Marcia Wood, ARS.
This research supports the USDA USDA,
n.pr See United States Department of Agriculture. priority of food safety and is part of Food Safety, an ARS national program (#108) described at www.nps.ars.usda.gov.
Bosoon Park is in the USDA-ARS Quality and Safety Assessment Research Unit, Richard B. Russell Research Center, 950 College Station Rd., Athens, GA 30605; (706)546-3396, email@example.com.