iPhone turns into a spectrometer

Adding to the thousands of apps already available for the iPhone, US scientists have developed an app that turns the iPhone into a spectrometer. In conjunction with a specially-developed cradle, the app can use the iPhone's built-in camera to detect a whole range of analytes, including toxins, proteins, bacteria, viruses and other molecules.

The cradle contains a suite of lenses and filters, with the centrepiece being a microscope slide coated with a photonic crystal and aligned with the iPhone's camera. Between them, these lenses and filters cost around $200, but according to the scientists they allow the iPhone to replicate the function of a $50,000 spectrometer.

This novel spectrometer takes advantage of the fact that photonic crystals can be tuned to reflect a narrow band of light while letting all other wavelengths pass through. When combined with the iPhone's camera and the app, this produces a spectrum with a single black line representing the missing wavelengths. Any analytes that bind with the photonic crystal cause the reflected band to shift to longer wavelengths, moving the position of the black line in the spectrum, with a larger shift meaning a higher concentration of analytes.

By coating the microscope slide with both photonic crystals and biological receptors such as proteins or antibodies, the spectrometer can detect specific analytes based on this wavelength shift. Because the slide can easily be replaced in the cradle, the spectrometer can detect a whole range of different analytes by simply using slides coated with different receptors. In a first test of the spectrometer described in a recent paper in Lab on a Chip, the scientists used it to detect a specific antibody.

Now, they are progressing to detecting toxins in harvested corn and soybeans and pathogens in food and water. '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,' said team leader Brian Cunningham at the University of Illinois at Urbana-Champaign. 'We'll use the phone and one cradle to perform four of the most widely used biosensing assays that are available.' They're also developing a version of the cradle and app for Android phones.

A video of the app in action can be viewed at http://www.youtube.com/watch?v=Kh7MUjIYuyw.

(Photo of iPhone in cradle courtesy of Brain T. Cunningham.)