By attaching pathogen-specific antibodies to vanishingly small gold nanoparticles—so minuscule that 25,000 would fit across the width of a human hair—scientists at Jackson State University in Mississippi can detect various strains of Salmonella with a simple five-minute test. Assays currently on the market as “rapid” Salmonella detection methods still usually require at least 12 to 18 hours for results.
The nanoparticles can also be used as a vector for pathogen elimination using a technique called photothermal nanotherapy.
Paresh C. Ray, PhD and his colleagues have been working on this nanoparticle technology for several years, originally developing it for use in cancer treatment.
The nanoparticles have a shape that, under the microscope, looks like a piece of popcorn, with splayed “tips” that make them easier to detect using Raman spectroscopy. On a piece of produce, such as lettuce, when the nanoparticles encounter the specific strain of Salmonella to which they carry an antibody, they bind to it and cause a pink-to-blue color change on the assay that can be detected within a few minutes.
“You can choose the antibody and detect any type of pathogen,” said Dr. Ray, an associate professor of chemistry and biochemistry who has previously published similar findings on other pathogens, such as E. coli. Only a few drops of the nanoparticle solution are needed to detect the bacteria in a produce sample, and gallons of it can be made from just $90 worth of gold. Although long-term testing is still ongoing, Dr. Ray said that there have been no signs of toxicity from the nanoparticles so far.
The nanoparticles can also be used as a vector for pathogen elimination using a technique called photothermal nanotherapy. If researchers shine the right wavelength of light at a contaminated product, the nanoparticles absorb that light and heat up. “Those hot particles burn through the outer membrane of the Salmonella bacteria, killing the bacteria,” Dr. Ray said.
The research was presented at the meeting of the American Chemical Society in late March and also appears in Chemical Reviews.