Biosensor speeds up disease diagnosis

Researchers at Polytechnic Institute of New York University (NYU-Poly) have created an ultra-sensitive biosensor capable of identifying the smallest single virus particles in solution.

Their technique is a major advance in a series of experiments to devise a diagnostic method sensitive enough to detect and size a single virus particle in a doctor’s office or field clinic, without the need for special assay preparations or conditions.

Normally, such assessment requires the virus to be measured in the vacuum environment of an electron microscope, which adds time, complexity and considerable cost.

Instead, the researchers were able to detect the smallest RNA virus particle MS2, with a mass of only 6 attograms, by amplifying the sensitivity of a biosensor.

Within it, light from a tunable laser is guided down a fiber optic cable, where its intensity is measured by a detector on 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 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 in the past. But many viruses such as Polio are far smaller, as are antibody proteins, and these require increased sensitivity.

Stephen Arnold and his co-researchers achieved this by attaching gold nano-receptors 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.

Arnold explained that the inspiration for this breakthrough technique came to him during a concert by violinist Itzhak Perlman: “I was watching Perlman play, and suddenly I wondered what would happen if a particle of dust landed on one of the strings. The frequency would change slightly, but the shift would be imperceptible. Then I wondered what if something sticky was on the string that would only respond to certain kinds of dust?”

In experiments, the researchers successfully detected the smallest RNA virus in solution, and they are now training their sights on detecting single proteins, which would represent a major step toward early disease detection.