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New Technique to Boost Sensitivity of Biological Detectors

Biosensors in-built into smartwatches, smartphones, and other gadgets will SOON become a reality. Scientists at the Moscow Institute of Physics and Technology have now developed a technique to boost the sensitivity of biological detectors to enable their use in wearable and mobile devices.

Biosensor layout (a, c). The waveguide is inside the dielectric substrate. The resonator, realized as a ring waveguide, is positioned at the interface between the dielectric material and the biological fluid that is analyzed. A change in the fluid’s refractive index shifts the resonant curve (b). Image Credit: Kirill Voronin et al./Sensors.

The study has been described in a paper featured on the cover of the January issue of Sensors, and has been funded by the Russian Science Foundation.

A biosensor is described as an electrochemical device that identifies the composition of biological fluids in real time. Blood glucose meters that diabetic patients use could be the only mass-produced biosensing devices in use at present.

However, according to futurologists, soon, household appliances would be able to analyze saliva, sweat, aqueous humor, and other bodily fluids to recognize a person, perform medical tests, diagnose disease, or continuously track an individual’s health and recommend ideal diet accordingly.

Until recently, applications such as those were not taken seriously, since the available devices were not adequately sensitive and were exorbitantly priced to hit the consumer market. But there could be a silver lining very soon.

A research team at the MIPT Center for Photonics and 2D Materials has come up with a radically innovative biosensor design that could boost detector sensitivity several times and provide a similarly notable decrease in costs.

A conventional biosensor incorporates a ring resonator and a waveguide positioned in the same plane. We decided to separate the two elements and put them in two different planes, with the ring above the waveguide.

Kirill Voronin, Graduate Student, Laboratory of Nanooptics and Plasmonics, MIPT

It was Voronin who proposed the concept used in this research work.

The researchers did not investigate that sensor layout previously, because it is easier to manufacture a flat, single-level device inside a lab. A waveguide and a ring resonator were produced simultaneously by depositing a thin film and etching it.

The alternative two-level design is not so easy to use to manufacture exclusive experimental devices. However, it was found to be relatively inexpensive for the mass-production of sensors. This is because the technological processes followed at an electronics plant are oriented toward layer-by-layer placement of active component.

More significantly, the new two-tier biosensor design led to several times higher sensitivity.

A biosensor works by registering the trivial changes in the refractive index at its surface. These changes are due to organic molecule adsorption and are detected using a resonator whose resonance conditions are based on the external medium’s refractive index.

A significant resonant peak shift is caused by even slightest changes in the refractive index. Therefore, a biosensor responds to almost every molecule that comes into contact with its surface.

We have positioned the strip waveguide under the resonator, in the bulk dielectric. The resonator, in turn, is at the interface between the dielectric substrate and the external environment. By optimizing the refractive indices of the two surrounding media, we achieve a significantly higher sensitivity.

Aleksey Arsenin, Study Co-Author and Leading Researcher, Laboratory of Nanooptics and Plasmonics, MIPT

In the newly proposed biosensor design, both the detector and the source of light are placed within the dielectric. The sensitive element is the only component that remains on the outer side. In other words, the diameter of the gold ring is several dozen micrometers and its thickness is one-thousandth of that.

Voronin stated that the team’s technique for rendering biosensors more responsive will take the technology to a qualitatively new level.

The new layout is intended to make biosensors much easier to manufacture, and therefore cheaper. Optical lithography is the only technique necessary to produce detectors based on our principle. No moving parts are involved, and a tunable laser operating in a tight frequency range will suffice.

Kirill Voronin, Graduate Student, Laboratory of Nanooptics and Plasmonics, MIPT

Valentyn Volkov, head of the MIPT Center for Photonics and 2D Materials, has predicted that developing an industrial design on the basis of the newly proposed technology could take nearly three years.


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