A team at the New York University Tandon School of Engineering has 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 sensor is based on the discovery that an optical fiber could excite what is termed a Whispering Gallery Mode (WGM) in polymer micro-beads less than one-third the diameter of a human hair. Further discoveries and patents led to WGMs that function by sending them into spacecraft-like orbit around the micro-bead, thanks to a photonic “tractor beam” caused by the resonating light. The researchers 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 (10-21 grams), below the mass of all known cancer markers.
The WGM biosensor, which is named for the famous Whispering Gallery in the dome of St. Paul’s Cathedral in London, 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.
They found a way to determine the density of charges on an area of a WGM micro-bead’s surface, as well as the charge of an ensnared nanoparticle. Charge controls the ability to transport particles that are interacting with cells and other objects that possess electric fields. 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.
The team was able to extract the electrostatic force between the orbiting nanoparticle and the surface of the glass bead through experiments based on the observation that the nano-orbital phenomenon requires a near balance between the electrostatic force and the known optical tractor beam force, just as a weighing scale balances the force of a spring against your body’s weight. The difference in the strength of the force being measured is extraordinarily small. The measured electrostatic force involved in keeping a nanoparticle in orbit was only 0.00000000000003 pounds. With this force measurement, both the charge on the nanoparticle and the microcavity charge density could be calculated through a series of experiments.
This 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.
For more information, visit engineering.nyu.edu.