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New surface could streamline medical tests

Light waves have been harnessed to reveal molecules in blood and other samples in real time. It could change the way allergies are diagnosed and enable new discoveries in the life sciences.| Medium Read
EnlargeIn the image on the left, the light from the DNA molecules stuck to the surface is cancelled out, so the background fluorescence appears as a green haze. In the image on the right, the light form the DNA molecules is amplified.
IMAGE:  In the image on the left, the light from the DNA molecules stuck to the surface is cancelled out, so the background fluorescence appears as a green haze. In the image on the right, the light form the DNA molecules is amplified. Credit: Lahann's Lab

Light waves have been harnessed to reveal molecules in blood and other samples in real time. Researchers from the University of Michigan and Columbia University have developed a surface that takes advantage of optics to separate the signals of target molecules from background light. It could change the way allergies are diagnosed and enable new discoveries in the life sciences.

“We can watch single molecules binding to our surface in real time,” said Joerg Lahann, a professor of chemical engineering. “To be able to do this in an opaque environment, such as blood serum, could lead to entirely different medical test methods and may streamline current approaches towards detection of chemical and biological threats.”

Blood is a great source of information about goings-on in the body, but it is complicated—whatever a doctor seeks is typically lost in a sea of cells, proteins, enzymes and other molecules. Fluorescence microscopy is a way to find a particular disease marker in the mess, and the new surface developed by Lahann’s lab streamlines this process by monitoring the binding of important molecules in real time.

When using fluorescence microscopy on a blood sample, researchers and lab technicians first remove the blood cells, leaving behind serum. Next, they mix in fluorescent tags that attach to the molecules of interest—antibodies, for instance, if they are looking for an allergy. Then they typically expose a surface covered in antigen—the molecule that triggers the allergy—to the fluorescent serum and wait for the antibodies to attach to the antigen.

Because fluorescent molecules are all over in the serum, researchers and technicians have to rinse the surface off before they can measure how many antibodies they captured. To quantify how many antibodies are in the sample, they have to run the experiment multiple times, waiting for different lengths of time before making the measurement.

The new surface, developed in Lahann’s lab, now allows researchers and technicians to monitor the rate at which antibodies bind to the antigen layer in real time. It does this by using a basic optics phenomenon to amplify and cancel out the signal from the antibodies in different locations on the surface so that the background can be measured.

When light waves reflect off a mirrored surface, they can interfere with one another. Depending on the distance between the fluorescent molecule and the mirror, they can build one another up or they can cancel each other out.

The new surface is carefully designed so that when the target antibody is stuck to the antigen, the light will be amplified so that it shows up brightly in the microscope image. In other regions, where light from the antibodies cancels itself out, researchers can measure the background coming from the fluorescent serum.

The team used the new technique to identify single molecules of DNA and measure the capacity of a protein to bind. In the near future, they say the new technique could be useful in diagnosing allergies and other illnesses, as well as discovering identifying information from very small samples, such as might be found in a fingerprint.

Lahann is also director of the U-M Biointerfaces Institute and a professor of materials science and engineering, biomedical engineering, and macromolecular science and engineering.

This work has been funded by the Defense Threat Reduction Agency (DTRA).

In the image on the left, the light from the DNA molecules stuck to the surface is cancelled out, so the background fluorescence appears as a green haze. In the image on the right, the light form the DNA molecules is amplified.
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