Breakthrough discovery for accurate diagnosis and detection

University Professor of Applied Physics Stephen Arnold and his team at the New York University Tandon School of Engineering have made a discovery that could lead to Star Trek-like biosensor devices capable of flagging the barest presence in blood of a specific virus or antibody, or protein marker for a specific cancer; or sniffing out airborne chemical warfare agents while they are still far below toxic levels.

The discovery follows years of ground-breaking work by Arnold, who in 1995 discovered that an optical fiber could excite what he termed Whispering Gallery Mode (WGM) in silicon micro-beads less than one-third the diameter of a human hair. Further discoveries and patents led to WGM biosensors capable of gauging the mass of viruses, proteins and other nanoparticles by sending them into spacecraft-like orbit around the micro-bead, thanks to a photonic "tractor beam" caused by the resonating light. Arnold and collaborators then devised a way to make these WGM biosensors sensitive enough to identify even the smallest individual bio-particles from the RNA virus MS2 to single molecules down to 6 zepto-grams (a thousandth of a billionth of a billionth of a gram), below the mass of all known cancer markers. Many companies, including Genalyte, employ WGM biosensors in diagnostic products that can perform dozens of bioassays in minutes.

The WGM biosensor, is a device the size of a small smartphone comprising a tunable laser guided down a specially treated fiber optic filament with a detector at the far end of the filament measuring the light's intensity and resonance. A tiny silica bead next to the filament diverts a portion of the light beam, which begins to resonate within the bead the way sound resonates under the dome of the church gallery for which the phenomenon is named.

While the WGM biosensor's ability to identify individual nanoparticles led to highly sensitive measuring capabilities, Arnold's latest discovery could make possible biosensors tailored to very specific applications, from wearable sensors for soldiers and rescuers designed to detect extremely low concentrations of a suspected airborne nerve agent, to ways of increasing the efficiency of nanoparticle drug uptake and redistribution.

"Charge controls the ability to transport particles that are interacting with cells and other objects that possess electric fields," he said. "By determining the charge of a virus, for example, you can understand how it can be transported to the cell surface. You need to understand this mechanism in order to engineer a WGM micro-bead that has a specific antigen at a specific region of its surface so that the biosensor can attract specific pathogens or other biomolecules."

This research was supported by the National Science Foundation and the Air Force Office of Scientific Research.

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