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Cradle turns iPhone into biosensor

Photonics Spectra
Aug 2013

CHAMPAIGN, Ill. – A unique cradle and app for the iPhone use the phone’s own camera and processing power to create a handheld biosensor capable of detecting any kind of biological molecules or cells. The system, developed at the University of Illinois, could allow the use of smart-phones to conduct environmental, medical, food safety and other tests.

“We’re interested in biodetection that needs to be performed outside of the laboratory,” said team leader Brian Cunningham, a professor of electrical and computer engineering and of bioengineering at the university. “Smartphones ... have really powerful computing capability and imaging. A lot of medical conditions might be monitored very inexpensively and noninvasively using mobile platforms like phones. They can detect molecular things like pathogens, disease biomarkers or DNA – things that are currently only done in big diagnostic labs with lots of expense and large volumes of blood.”


A cradle and app for the iPhone make a handheld biosensor that uses the phone’s own camera and processing power to detect any kind of biological molecules or cells.


The wedge-shaped cradle contains optical components such as lenses and filters usually found in much larger and more expensive laboratory devices. It holds the phone’s camera in alignment with the optical components.

At the heart of the biosensor is a photonic crystal that reflects only one wavelength of light while the rest of the spectrum passes through. When anything biological – proteins, cells, pathogens or DNA – attaches to the crystal, the reflected color shifts from a shorter wavelength to a longer one.

To use the iPhone biosensor, a normal microscope slide is primed to react to a specific target molecule and coated with the photonic material. The slide is inserted into a slot on the cradle, and the spectrum is measured. Its reflecting wavelength shows up as a black gap in the spectrum. After exposure to the test sample, the spectrum is measured again. The degree of shift in the reflected wavelength tells the app how much of the target molecule is in the sample.

The entire test takes only a few minutes; the app walks the user through the process step by step. Although the cradle holds only about $200 in optical components, the setup performs as accurately as a large $50,000 spectrophotometer in the laboratory.

The team is working to improve the manufacturing process for the cradle and to create one for Android phones; the group hopes to make them available starting next year. Through a National Science Foundation (NSF) grant, they also are working with others on campus to develop a test for iron and vitamin A deficiencies in expectant mothers and children, to field-test for toxins and pathogens in food and water, and more.

“It’s our goal to expand the range of biological experiments that can be performed with a phone and its camera being used as a spectrometer,” Cunningham said. “In our first paper, we showed the ability to use a photonic crystal biosensor, but in our NSF grant, we’re creating a multimode biosensor. We’ll use the phone and one cradle to perform four of the most widely used biosensing assays that are available.”

The work appears in Lab on a Chip (doi: 10.1039/C3LC40991K).


GLOSSARY
camera
A light-tight box that receives light from an object or scene and focuses it to form an image on a light-sensitive material or a detector. The camera generally contains a lens of variable aperture and a shutter of variable speed to precisely control the exposure. In an electronic imaging system, the camera does not use chemical means to store the image, but takes advantage of the sensitivity of various detectors to different bands of the electromagnetic spectrum. These sensors are transducers...
microscope
An instrument consisting essentially of a tube 160 mm long, with an objective lens at the distant end and an eyepiece at the near end. The objective forms a real aerial image of the object in the focal plane of the eyepiece where it is observed by the eye. The overall magnifying power is equal to the linear magnification of the objective multiplied by the magnifying power of the eyepiece. The eyepiece can be replaced by a film to photograph the primary image, or a positive or negative relay...
photonic crystal
spectrometer
A kind of spectrograph in which some form of detector, other than a photographic film, is used to measure the distribution of radiation in a particular wavelength region.  
spectrophotometer
An instrument for measuring spectral transmittance or reflectance.
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