Tiny Magnetic Beads Could Help to Quickly Detect Pathogens

“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.”

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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“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.”

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“We were initially seeking to identify the signatures of bacteria, but the signature of the Dynabeads was actually very strong,” Tadesse says. “We realized this signal could be a means of reporting to you whether you have that bacteria or not.”

Testing beacon

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.


Dynabeads, which are antibody-coated superparamagnetic beads, served as a strong Raman reporter for the simultaneous capture and detection of pathogenic bacterium such as salmonella. This image shows the Dynabeads (grey spheres) interacting with salmonella bacterium (in green). The inset shows the Y-shaped antibodies coating the Dynabeads. Image courtesy of the researchers.

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Looking for diseased cells and pathogens in fluid samples is an exercise in patience. “It’s kind of a needle-in-a-haystack problem,” Tadesse says.

“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.”

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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.

The researchers found that Dynabeads have an unusually strong Raman signature that can be easily detected, much like a fluorescent tag. This signature, they found, can act as a “reporter.” If detected, the signal can serve as a quick confirmation, within less than one second, that a target pathogen is indeed present in a given sample. The team is currently working to develop a portable device for quickly detecting a range of bacterial pathogens, and their results will appear in an “Emerging Investigators” special issue of the Journal of Raman Spectroscopy.

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.

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.

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.

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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

The MIT team found a faster way to confirm the presence of Dynabead-bound pathogens using optics, specifically, Raman spectroscopy. This optical technique identifies specific molecules based on their “Raman signature,” or the unique way in which a molecule scatters light.

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Published: Monday, September 4, 2023 – 12:03

Published Aug. 25, 2023, in MIT News.