How to Perform Microscopy, Spectroscopy with an iPhone
DAVIS, Calif., Oct. 4, 2011 — Researchers at the University of California, Davis, have transformed everyday iPhones into medical-quality imaging and chemical detection devices. With materials that cost about as much as a typical app, the decked-out smartphones use their heightened senses to perform detailed microscopy and spectroscopy.
The enhanced iPhones could help doctors and nurses diagnose blood diseases in developing nations where many hospitals and rural clinics have limited or no access to laboratory equipment. In addition to bringing new sensing capabilities where they are needed most, the modified phones can transmit real-time data to colleagues around the globe for further analysis and diagnosis.
"Field workers could put a blood sample on a slide, take a picture and send it to specialists to analyze," said Sebastian Wachsmann-Hogiu, of the university’s department of pathology and laboratory medicine and the lead author of the research that led to the smartphone’s adaptation to serious imaging.
An iPhone microscope, which consists of a 1-mm-diameter ball lens embedded in a rubber sheet and taped over the smartphone’s camera. (Photos: Z.J. Smith, K. Chu, A.R. Espenson, M. Rahimzadeh, A. Gryshuk, M. Molinaro, D.M. Dwyre, S. Lane, D. Matthews, S. Wachsmann-Hogiu, University of California, Davis)
The group is not the first to build a smartphone microscope. "But we thought we could make something simpler and less expensive," Wachsmann-Hogiu said.
Ultimately, the team turned to ball lenses, finely ground glass spheres that act as low-power magnifying glasses. The team used a 1-mm-diameter ball lens that costs $30 to $40 in its prototype, but to reduce the price, mass-produced lenses could be substituted.
To build the microscope’s lens, Kaiqin Chu, a postdoctoral researcher in optics, inserted a ball lens into a hole in a rubber sheet and then simply taped the sheet over the smartphone’s camera.
At 5× magnification, the ball lens is no more powerful than a child's magnifying glass. Yet when paired with the camera of a smartphone, the microscope could resolve features on the order of 1.5 μm — small enough to identify different types of blood cells.
Stained samples of pollen (left images) and plant stems (right two images). Top row: commercial microscope; bottom row: cell phone microscope.
There are two reasons why such low magnification produces such high-resolution images. First, ball lenses excel at gathering light, which determines resolution. Second, the camera's semiconductor sensor consists of millions of light-capturing cells. Each cell is only about 1.7 μm across — small enough to capture precisely the tiny image that comes through the lens.
Ball lenses pose some unique problems. The curvature of their sphere bends light as it enters the ball, distorting the image, except for a very small spot in the center. The researchers used digital image processing software to correct for this distortion. They also used the software to stitch together overlapping photos of the tiny in-focus areas into a single image large enough for analysis.
Even though smartphone micrographs are not as sharp as those from laboratory microscopes, they are able to reveal important medical information, such as the reduced number and increased variation of cells in iron-deficiency anemia, and the banana-shaped red blood cells characteristic of sickle cell anemia.
Wachsmann-Hogiu’s team is working with the University of California, Davis, Medical Center to validate the device and to determine how to use it in the field. They may also add features, such as larger lenses, to diagnose skin diseases as well as software to count and classify blood cells automatically to provide instant feedback and perhaps recognize a wider range of diseases.
Images of a sugar crystal taken through polarized light filters. Left: traditional microscope; right: cell phone microscope.
When researchers need additional diagnostic tools, the microscope could be swapped for a simple spectrometer that also uses light collected by the iPhone’s camera. Like the microscope, the iPhone-based spectrometer takes advantage of the phone’s imaging capabilities. "We had worked with spectrometers for diagnostics and didn't think it would be too far a stretch," Wachsmann-Hogiu said.
The spectrometer that the researchers added to the iPhone is easy to build. It starts with a short plastic tube covered at both ends with black electrical tape. Narrow slits cut into the tape allow only roughly parallel beams of light from the sample to enter and exit the tube. This grating spreads the light into a spectrum can be used to identify various molecules.
"If you didn't have the slits, light would come in from all different angles and you could never separate it properly," said Zachary Smith, a postdoctoral optics researcher in the lab.
Though the spectrometer is still in its early stages, the researchers believe it could measure the amount of oxygen in the blood and help diagnose chemical markers of disease.
The scientists will present their findings at Frontiers in Optics 2011, the Optical Society’s annual meeting, which will take place in San Jose, Calif., from Oct. 16 to 20.
For more information, visit: www.ucdavis.edu
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