A team from the University of California at Davis has developed an affordable way to give the iPhone surprisingly capable chemical detection and imaging powers. We've reported on cellphone microscopes before, but this version claims to be simpler in concept and less expensive, plus it adds spectroscopy to its list of abilities. The team's findings will be presented at the Optical Society's (OSA) annual meeting next week.
Already powerful computers in their own right, iPhones with such added senses can be especially useful to medical professionals in developing nations where access to quality laboratory equipment can be sketchy at best.
"Field workers could put a blood sample on a slide, take a picture, and send it to specialists to analyze," says Sebastian Wachsmann-Hogiu, a physicist with UC Davis' Department of Pathology and Laboratory Medicine and the Center for Biophotonics, Science and Technology, and lead author of the soon-to-be-presented research.
Initially, Wachsmann-Hogiu probed the limits of simplicity. "We started with a drop of water on the camera's lens. The water formed a meniscus, and its curved surface acted like a magnifying lens. It worked fine, but the water evaporated too fast."
To get around that problem, the team went "solid state" and began experimenting with ball lenses- finely polished glass spheres with the imaging properties of low-powered (5X) magnifying glasses. For their prototype, the team used a fairly pricey (US$30-40) 1-millimeter diameter ball lens, but the price could be substantially reduced by substituting similar quality mass-produced lenses instead.
Post-doctoral optics researcher Kaiqin Chu built the microscope "lens" by punching a hole in a rubber sheet into which he secured one of the glass balls. He then taped this assembly over the iPhone's lens port and voila.
Because ball lenses are so adept at gathering light, they can yield surprising feature resolution - close to 1.5 microns - which is enough to allow specialists to discern between different blood cell types. Coupled with the iPhone's semiconductor sensor, which is composed of light-capturing pixels roughly 1.7 microns wide, enough information can be gathered to render a decent image.
Still, ball lenses have distinct limitations which the team needed to address. Since the curved spheres bend light as it enters, the images they yield, except for a very small region in the center, are distorted. The team used special software to address the distortion and piece together tiny in-focus regions into larger images suitable for interpretation.
To enhance the iPhone's value in the field, Wachsmann-Hogiu's team is also developing a simple spectrometer that could be switched out with the microscope attachment. "We had worked with spectrometers for diagnostics, and didn't think it would be too far a stretch," Wachsmann-Hogiu said.
Spectrometers "spread out" light reflected by an object, not unlike the rainbow that results from white light sent through a prism. When a substance is exposed to light, its atoms and molecules absorb very specific wavelengths, the analysis of which makes it possible to determine that substance's chemical composition.
The proposed iPhone spectrometer turns out to be relatively simple to construct. The team began by covering both ends of a short plastic tube with black electrician's tape. They then cut thin slits in the tape which blocked all but roughly parallel beams of light reflected by the sample from entering and exiting the tube. While not as sensitive as lab-based devices, this modest tool reliably expands the light into specific spectra of colors which scientists can match with individual compounds.
Further work on how to use the device in the field is being undertaken in conjunction with UC Davis Medical Center. While no price point is currently available, once it hits the market, this new application promises an appreciable addition to the iPhone's already long list of abilities.
The presentation, "Microscopy and Spectroscopy on a Cell Phone," by Kaiqin Chu, Zachary J. Smith, Alyssa R. Espenson, Denis Dwyre, Stephen Lane, Dennis Matthews, and Sebastian Wachsmann-Hogiu of the Center for Biophotonics, University of California, Davis, Medical Center, Sacramento, Calif. will take place Wednesday, Oct. 19 at 12 p.m. at the Fairmont San Jose Hotel.
Image credit (all): : Z. J. Smith, K. Chu, A. R. Espenson, M. Rahimzadeh, A. Gryshuk, M. Molinaro, D. M. Dwyre, S. Lane, D. Matthews, S. Wachsmann-Hogiu
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