An iPhone app and an optics-rich smartphone cradle are enabling sensitive yet inexpensive biosensing of toxins, proteins, bacteria, viruses, and other molecules. The handheld system targets a variety of applications, including on-the-spot tracking of groundwater and food contamination, real-time medical diagnostics, and—combined with a phone's GPS data—mapping of epidemics.
The wedge-shaped cradle holds the phone's camera in alignment with its integrated optical components—including lenses and filters typically found in bulky and expensive laboratory systems. Though the cradle incorporates only about $200 worth of optics, it performs as accurately as a $50,000 lab-based spectrophotometer.
At the heart of the system is a crystal that acts like a mirror, but reflects only one wavelength of light while letting the rest of the spectrum pass through. When anything biological attaches to the photonic crystal—such as protein, cells, pathogens, or DNA—the reflected color shifts to a longer wavelength.
The app walks the user step by step through the test process, which involves a normal microscope slide coated with the photonic material and primed to react to a specific target molecule. The slide fits into a slot on the cradle, and the system measures the spectrum: the reflecting wavelength shows up as a black gap in the spectrum. After exposure to a test sample, the spectrum is re-measured; 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 just a few minutes.
Professor Brian Cunningham, who leads a team of University of Illinois at Urbana-Champaign (U of I) researchers working on the platform, says the group wants to facilitate biodetection "outside of the laboratory." Smartphones provide a natural platform to leverage because of the huge impact they are making on society—and because of their computing and imaging power. "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."
The team explained sensing of an immune system protein for their publication,1 but the slide could be primed for any type of biological molecule or cell type. In fact, the research team is collaborating with other U of I groups to explore applications such as a test for iron and vitamin A deficiencies in expectant mothers and children, and detection of toxins in crops. A recent National Science Foundation grant aims to expand the range of biological experiments it is able to perform. The researchers are working to improve the manufacturing process for the iPhone cradle, while also working on a cradle for Android phones.
1. D. Gallegos et al., Lab Chip, 13, 2124–2132 (2013).