Biosensor Identifies the Smallest Single Virus Particles in Solution

The ability to identify very small virus particles could cause a major change in early disease detection in a point-of-care (POC) setting and reduce waiting times for test results from weeks to minutes.

Scientists were able to detect the smallest RNA virus particle, MS2, with a mass of only 6 attograms, by amplifying the sensitivity of a biosensor. Light from a tunable laser is guided down a fiber optic cable, where its intensity is measured by a detector at the far end. A small glass sphere is brought into contact with the fiber, diverting the light's path and causing it to orbit within the sphere. This change is recorded as a resonant dip in the transmission through the fiber. When a viral particle makes contact with the sphere, it changes the sphere’s properties, resulting in a detectable shift in resonance frequency.

The technique is the result of experiments to devise a diagnostic method sensitive enough to detect and measure the size of a single virus particle in a doctor’s office or field clinic, without the need for special assay preparations or conditions. Currently such assessment requires the virus to be measured in the vacuum environment of an electron microscope, which adds time, complexity, and cost.

The smaller the particle, the harder it is to record these changes. Viruses such as influenza are fairly large and have been successfully detected with similar sensors. But many viruses such as the Polio virus are far smaller, as are antibody proteins, and these require increased sensitivity.

Stephen Arnold, professor of applied physics and member of the Othmer-Jacobs Department of Chemical and Biomolecular Engineering (Brooklyn, NY, USA), and colleagues of NYU-Poly's MicroParticle PhotoPhysics Laboratory for BioPhotonics (MP3L; Brooklyn, NY, USA) achieved extra sensitivity by attaching gold nanoreceptors to the resonant microsphere. These receptors are plasmonic, and thus enhance the electric field nearby, making even small disturbances easier to detect. Each gold hot spot is treated with specific molecules to which proteins or viruses are attracted and bind.

The scientists are now trying to detect single proteins, which would represent a major step toward early disease detection.

The scientists published their findings in the July 2012 online edition of Applied Physics Letters published by the American Institute of Physics.

“When the body encounters a foreign agent, it responds by producing massive quantities of antibody proteins, which outnumber the virus. If we can identify and detect these single proteins, we can diagnose the presence of a virus far earlier, speeding treatment,” Prof. Arnold said. “This also opens up a new realm of possibilities in proteomics,” he said, referring to the study of proteins. “All cancers generate markers, and if we have a test that can detect a single marker at the protein level, it doesn’t get more sensitive than that.”

Related Links:
Othmer-Jacobs Department of Chemical and Biomolecular Engineering
NYU-Poly's MicroParticle PhotoPhysics Laboratory for BioPhotonics