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Could your smartphone one day tell you you're pregnant?

02 July 2015

Small add-on devices could turn a smartphone's optical components into a biosensor to monitor diabetes, test for pregnancy and detect hazardous gases.

A fibre optic surface plasmon resonance sensor developed for smartphones (photo: Kort Bremer, Hanover Centre for Optical Technologies)

Researchers at the Hanover Centre for Optical Technologies (HOT), University of Hanover, have developed a self-contained fibre optic sensor for smartphones with the potential for use in a wide variety of biomolecular tests, including those for detecting pregnancy or monitoring diabetes. A special smartphone app uses the sensor readings to provide real-time results. 

The sensor uses the optical phenomenon of surface plasmon resonance (SPR) to detect the composition of a liquid or the presence of particular biomolecules or trace gases.

Surface plasmon resonance occurs when a fixed beam of light strikes a metallic film; most of the light is reflected, but a small band is absorbed by the film's surface electrons, causing them to resonate. When the metallic film is placed in contact with a fluid, the index of refraction of the liquid changes the absorbed band's size and location in the light spectrum.

By adding recognition elements to the film that cause a shift in the index of refraction when bound to targeted biomolecules or trace gases, important information about a biological sample's composition can be determined, based on which light is reflected and which is absorbed.

"We have the potential to develop small and robust lab-on-a-chip devices for smartphones," says Kort Bremer, inventor and co-author of an article describing the work, pubilshed in the journal, Optics Express. The other author is HOT director, Bernhard Roth.

Surface plasmon resonance is a phenomenon commonly used for biosensing, but typically requires bulky lab equipment involving both a light detector and light source. Fortunately, smartphones already have both of these, allowing the minimalist, U-shaped device the researchers have designed to consist solely of a 400-micrometre diameter core multi-mode fibre with a silver-coated sensing region.

In a proof-of-concept version of the sensor, Bremer carefully excised the polymer coating from a 10-millimetre segment of the optics cable to expose the bare 400-micrometre diameter glass fibre core. He then cleaned the segment, subjected it to a silver-coating process, added a small well in which to pour the solutions being observed, and polished both ends of the fibre to 45° angled faces. They were then bonded to the phone's case and to its LED and camera, the latter being fitted with a diffraction grating to separate the light beam into an emission spectrum.

In subsequent experiments, the device's sensitivity was tested using various concentrations of glycerol, and the team confirmed it was on par with current equipment, at a fraction of the cost and size.

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