Holograms replace lenses in low-cost, portable, dual-mode microscope

Researchers at UCLA (Los Angeles, CA) have built a compact, lightweight, dual-mode microscope that uses holograms instead of lenses. The microscope's low cost and portability—all the materials to make it add up to between $50 and $100, and it weighs about as much as a medium-sized banana—could serve doctors, nurses and field workers in remote areas of the world.

Described in a paper published in Biomedical Optics Express, the researchers' microscope prototype features a transmission mode that can probe relatively large volumes of blood or water, and a reflection mode that can image denser, opaque samples. Spatial resolution for both modes is <2 µm—comparable to what bulkier microscopes with low- to medium-power lenses can achieve.

With just a small amount of training, doctors could use devices such as their handheld microscope to improve health care in remote areas of the world with little access to diagnostic equipment, says Aydogan Ozcan, an associate professor of electrical engineering and bioengineering at UCLA and senior author of the paper. The microscope could help ensure water quality, test patients' blood for harmful bacteria, and even be used for semen-quality monitoring on animal farms. It could also prove useful in health crises such as the recent outbreak of E. coli in Europe—such as for field investigation of water, food, or maybe pathogens in blood, says Ozcan.

Instead of costly lenses that most microscopes rely on for collecting and focusing light, their microscope uses holograms. Holograms form when light bouncing off (or passing through) a 3-D object is made to interfere with a "reference beam," or light that has not hit the object. To recreate images from interfering light waves, an inexpensive light source is divided into two beams—one that interacts with microscopic cells or particles in the sample, and the other that does not. The beams then pass to an adjacent sensor chip, where their interference pattern is recorded. Software then analyzes that pattern and recreates the path taken by the light that passed through or bounced off of the objects being imaged.

Each component of the device is fairly inexpensive, says Ozcan. The laser light could come from a $5 laser pointer. The sensor chip that collects that light is the same as the ones in the backs of iPhones and Blackberrys and costs less than $15 per chip. And the whole image-collecting system runs on two AA batteries.

The microscope captures raw data, but a computer is required to reconstruct the images. Workers in the field could use their laptops to process the information or send it over the Internet or mobile phone networks to a remote server. Mobile phones could also have sufficient processing power to do the analysis on the spot.

The next steps for Ozcan's team include commercializing the device. Ozcan says he has founded a company that is developing this technology, trying to make a version of the microscopes that can be manufactured and sold to healthcare workers and hobbyists.

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