Steve Lee holds a slide with four droplet lenses. (Stuart Hay, Australian National University)
25 April 2014. Engineers at Australian National University in Canberra devised an inexpensive process to make an add-on lens that turns a smartphone into a high-powered microscope. The team led by ANU’s Woei Ming (Steve) Lee published its technique in the May 2014 issue of the journal Biomedical Optics Express.
The university filed for a patent in Australia earlier this year on the fabrication process. Lee says a group in Germany already expressed interest interested in adapting the lenses for remote dermatology diagnostics.
Lee, with colleagues from Australia’s University of New South Wales and Garvan Institute of Medical Research, sought a simpler and lower cost way to mass produce lenses that can be attached to mobile devices for applications in telemedicine and agriculture, as well as science education. The authors say the lenses can be produced for less than a penny each.
The lenses are made with polydimethylsiloxane or PDMS, a common polymer widely used in contact lenses and consumer products, such as shampoo. The material is optically clear, non-toxic, and non-flammable. When used to make contact lenses today, PDMS is injected into a mold, than stamped by machines. This industrial process can produce lenses in high volume at low unit costs for consumers, but it still requires a high initial investment in equipment, as well as packaging and distribution steps to get the lenses to customers.
The method designed by Lee and colleagues still makes it possible to produce a lens from PDMS with a low unit cost, but in small quantities. The fabrication method starts with a small drop of PDMS in liquid form on a clean surface. By inverting the surface with the drop of PDMS, forces of gravity and surface tension combine to form the curvature needed for a short focal length and magnification.
The authors then adapted techniques of additive manufacturing to produce a lens with higher magnification. After oven-curing the first PDMS drop, more drops of the liquid were deposited, inverted, and cured. The researchers found with each drop of PDMS they added, the focal length became shorter and magnification increased. Moreover, the team discovered they could calibrate the lens properties by adjusting the size of liquid drops added to the lens, settling on 100 microliters as the optimum drop volume.
“By successively adding small amounts of fluid to the droplet,” says Lee in a university statement, “we discovered that we can reach a magnifying power of up to 160 times with an imaging resolution of four micrometers.”
The researchers tested the lenses with a commercial 5 megapixel image sensor and compared the images to a standard upright research microscope. The tests showed the droplet lenses could produce images similar in quality to the microscope for subjects like medical specimens and pollen grains, as well as a standard industry test pattern.
Working with Tri Phan at Garvan Institute of Medical Research in Sydney, the team designed a prototype system for attaching the lens to a smartphone. The system has plastic frame for the lens that can be printed with a 3-D printer, as well as two miniature LEDs for illumination and a coin-sized battery for power.
The team tested the system with a Google Nexus smartphone to produce clear 60X images of a human finger tip with the smartphone’s camera, showing individual fingerprint ridges and sweat pores. The system, says the authors, would cost about $US 2.00 and weigh about 0.5 grams (0.02 ounces).
“This is a whole new era of miniaturization and portability,” adds Phan. “Image analysis software could instantly transform most smartphones into sophisticated mobile laboratories.”
Lee tells more about the device in the following video.
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