MIT engineers use light in beads to swiftly detect pathogens

Known as Dynabeads, a novel optical signature within them confirms a target pathogen's presence in under a second.
Sade Agard
Dynabeads, which are antibody-coated superparamagnetic beads, served as a strong optical reporter for the capture and detection of pathogens.
Dynabeads, which are antibody-coated superparamagnetic beads, served as a strong optical reporter for the capture and detection of pathogens.

Jongwan Lee et al.  

MIT engineers have discovered a new optical signature in a widely employed class of magnetic beads, enabling rapid detection of contaminants in various diagnostic tests. 

For instance, their study, accessible on ArXiv (awaiting peer review), highlighted the beads' newfound capacity to swiftly expose traces of the foodborne pathogen Salmonella.

Besides its effect on food safety, the innovation could provide medical experts with a method to promptly and accurately identify the source of illness in a given sample.

Pathogen-detection in a second

In the world of diagnostics, waiting for test results can be frustrating and time-consuming. Whether it's a blood test, a water pollution analysis, or checking for food contamination, the turnaround time often hinges on laborious sample processing and analysis steps. 

Now, MIT engineers might soon revolutionize this scenario, offering swift and accurate detection of contaminants.

The key to their advancement lies in a commercial laboratory tool – microscopic magnetic beads known as Dynabeads. Coated with antibodies that latch onto specific target molecules, these beads have been a staple in experimental setups for years. 

Yet, researchers have grappled with the need for additional steps to confirm the presence of molecules attached to the beads. 

Enter the power of optics, specifically Raman spectroscopy, leveraged for rapid pathogen detection. 

MIT engineers use light in beads to swiftly detect pathogens
Dynabeads, which are antibody-coated superparamagnetic beads, served as a strong optical reporter for the capture and detection of pathogens.

The new study unveiled the extraordinary optical properties of Dynabeads that can expedite the confirmation process. The researchers harnessed the unique scattering of light, or "Raman signature," exhibited by different molecules.

Upon detection, it provides nearly instantaneous confirmation – in less than a second – of the presence of a target pathogen within a sample. 

The team's primary focus was on detecting the notorious food contaminant Salmonella. By showcasing the applicability of their technique, the researchers highlighted the potential to identify bacterial pathogens that pose health risks swiftly. 

A 'super strong' signal

“You could purchase Dynabeads with E.coli antibodies, and the same thing would happen," explained co-author Assistant Professor Loza Tadesse of the Department of Mechanical Engineering in a press release.

"It would bind to the bacteria, and we’d be able to detect the Dynabead signature because the signal is super strong."

The implications are wide-reaching and could impact medical diagnostics. 

"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," said 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."

Currently in the works is the development of a portable device that can expedite the detection process for a range of bacterial pathogens. 

As MIT engineers illuminate a faster path to confirming the presence of pathogens, the landscape of diagnostics stands on the brink of transformation. 

With their innovative use of Raman spectroscopy, the wait time for critical results might soon be a thing of the past. As the team continues refining its approach, the world anticipates a future where rapid and reliable detection is the new norm.

The complete study, yet to be peer-reviewed, was published in Arxiv and can be found here.

Study abstract:

Dynabeads are superparamagnetic particles used for immunomagnetic purification of cells and biomolecules. Post-capture, however, target identification relies on tedious culturing, fluorescence staining and/or target amplification. Raman spectroscopy presents a rapid detection alternative, but current implementations target cells themselves with weak Raman signals. We present antibody-coated Dynabeads as strong Raman reporter labels whose effect can be considered a Raman parallel of immunofluorescent probes. Recent developments in techniques for separating target-bound Dynabeads from unbound Dynabeads makes such an implementation feasible. We deploy Dynabeads anti-Salmonella to bind and identify Salmonella enterica, a major foodborne pathogen. Dynabeads present signature peaks at 1000 and 1600 1/cm from aliphatic and aromatic C-C stretching of polystyrene, and 1350 1/cm and 1600 1/cm from amide, alpha-helix and beta-sheet of antibody coatings of the Fe2O3 core, confirmed with electron dispersive X-ray (EDX) imaging. Their Raman signature can be measured in dry and liquid samples even at single shot ~30 x 30-micrometer area imaging using 0.5 s, 7 mW laser acquisition with single and clustered beads providing a 44- and 68-fold larger Raman intensity compared to signature from cells. Higher polystyrene and antibody content in clusters yields to the larger signal intensity and conjugation to bacteria strengthens clustering as a bacterium can bind to more than one bead as observed via transmission electron microscopy (TEM). Our findings shed light on the intrinsic Raman reporter nature of Dynabeads, demonstrating their dual function for target isolation and detection without additional sample preparation, staining, or unique plasmonic substrate engineering, advancing their applications in heterogeneous samples like food, water, and blood.