No Virus Too Small for NYU-Poly Microscope

Viruses are small, and the most miniscule of them can only be seen by an electron microscope. However, electron microscopy can be a time consuming, and expensive, process.

Scientists at Polytechnic Institute of New York University (NYU-Poly) have developed a novel method that's been used to set a record for the smallest virus detected in solution, the bacteriophage MS2 (weighing only 6 attograms [6.0 x 10-18 grams]). The team has hopes of the technology working into clinical point-of-care devices that will rapidly detect just about any infectious disease.

The device works by guiding a tunable laser down a fiber optic cable, where its intensity is measured by a detector located 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. The change is recorded as a resonant dip in the transmission through the fiber. When a viral particle comes into contact with the sphere, it changes the sphere's overall properties, and emits a detectable shift in resonance frequency.

Arnold and his co-researchers achieved this by affixing gold nano-receptors to the resonant microsphere. The plasmonic receptors enhance the electric field nearby, making even small disturbances easier to detect. Each gold "hot spot" is treated with specific molecules to which proteins and viruses are attracted and bind.

Arnold explains that his inspiration for the unusual technique came to him while watching 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?"

The sensor itself, called a Whispering Gallery-Mode Biosensor, is completely unique to Arnold's work. Its name comes from the famous Whispering Gallery in the dome of St. Paul's Cathedral in London. The name is appropriate, in that the cathedral room allows a whisper to be heard anywhere within its circular gallery, light traveling within the glass sphere of the biosensor orbits many times, and nothing on the surface is missed.

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