“There are a lot cases, like in sepsis, where pathogenic cells cannot always be grown on a plate,” says Lee, a member of Karnik’s lab. “In that case, our technique could rapidly detect these pathogens.”
“This is something that can be used to rapidly give a positive or negative answer: Is there a contaminant or not?” Tadesse says. “Because even a handful of pathogens can cause clinical symptoms.”
Study co-authors at MIT include postdoctoral associate Jongwan Lee; visiting scholar Nikiwe Mhlanga; research scientist Jeon Woong Kang; Tata professor Rohit Karnik, who is also the associate director of the Abdul Latif Jameel Water and Food Systems Lab; and assistant professor Loza Tadesse of the Department of Mechanical Engineering.
Oil and water
This research was supported, in part, by the MIT Laser Biomedical Research Center, the National Cancer Institute, and the Abdul Latif Jameel Water and Food Systems Lab at MIT.
The numbers present are so small that they must be grown in controlled environments to sufficient numbers, and their cultures stained, then studied under a microscope. The entire process can take several days to a week to yield a confident positive or negative result.
In the team’s new work, she and her colleagues found that Dynabeads also have a unique and strong Raman signature that can act as a surprisingly clear beacon.
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Tiny Magnetic Beads Could Help to Quickly Detect Pathogens
Findings point to faster way to find bacteria in food, water, and clinical samples
Dynabeads are commercially available microscopic beads made from a magnetic iron core and a polymer shell that can be coated with antibodies. The surface antibodies act as hooks to bind specific target molecules. When mixed with a fluid, such as a vial of blood or water, any molecules present will glom onto the Dynabeads. Using a magnet, scientists can gently coax the beads to the bottom of a vial and filter them out of a solution. Karnik’s lab is investigating ways to then further separate the beads into those that are bound to a target molecule and those that are not. “Still, the challenge is, how do we know that we have what we’re looking for?” Tadesse says.
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The team is particularly keen to apply the test to conditions such as sepsis, where time is of the essence, and where pathogens that trigger the condition are not rapidly detected using conventional lab tests.
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The beads themselves are not visible by eye. That’s where Tadesse’s work comes in. Her lab uses Raman spectroscopy as a way to “fingerprint” pathogens. She has found that different cell types scatter light in unique ways that can be used as a signature to identify them.
Now, MIT engineers have identified a new optical signature in a widely used class of magnetic beads, which could be used to quickly detect contaminants in a variety of diagnostic tests. For example, the team showed the signature could be used to detect signs of the food contaminant salmonella.
Both Karnik and Tadesse’s labs have independently been developing techniques to speed up various parts of the pathogen-testing process and make the process portable using Dynabeads.
As a practical demonstration, the researchers mixed Dynabeads into vials of water contaminated with salmonella. They then magnetically isolated these beads onto microscope slides and measured the way light scattered through the fluid when exposed to laser light. Within half a second, they quickly detected the Dynabeads’ Raman signature—a confirmation that bound Dynabeads, and by inference, salmonella, were present in the fluid.
The team’s new technique is significantly faster than conventional methods, using elements that could be adapted into smaller, more portable forms—a goal that the researchers are currently working toward. The approach is also highly versatile.
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“This technique would be useful in a situation where a doctor is trying to narrow down the source of an infection in order to better inform antibiotic prescription, as well as for the detection of known pathogens in food and water,” says study co-author Marissa McDonald, a graduate student in the Harvard-MIT program in health sciences and technology. “Additionally, we hope this approach will eventually lead to expanded access to advanced diagnostics in resource-limited environments.”
Published: Monday, September 4, 2023 – 12:03