A droplet of clear liquid can bend light, acting as a lens. Using that as a guide, researchers at Australian National University have developed a new process to create very inexpensive, high quality silicone lenses that can be used in a wide range of applications, including tools to detect diseases in the field, scientific research in the lab, and optical lenses and microscopes for education.

Fig. 1 – A set of droplet lenses on a microscope coverslip held up by ANU researcher Steve Lee. (Credit: Stuart Hay)

Most conventional lenses have historically been made the same way—by grinding and polishing a flat disk of glass into a particular curved shape. Others, made with more modern methods, are made of poured gel-like materials. But both approaches can be expensive and complex. With the new method, the researchers harvest solid lenses of varying focal lengths by hanging and curing droplets of a gel-like material—a simple and inexpensive approach that, they say, avoids costly or complicated machinery. The technique was published in Biomedical Optics Express.

Steve Lee from the university’s Research School of Engineering said: “What I’m really excited about is that it opens up lens fabrication technology. What I did was to systematically fine-tune the curvature that’s formed by a simple droplet with the help of gravity, and without any molds.” (See Figure 1)

All that’s needed is an oven, a microscope glass slide, and a common, gel-like silicone polymer called polydimethylsiloxane (PDMS). The first step is to drop a small amount of PDMS onto the slide. Then bake it at 70 degrees Celsius to harden it, creating a base. Then, add another drop of PDMS onto the base and flip the slide over. Gravity pulls the new droplet down into a parabolic shape. Bake the droplet again to solidify the lens. More drops can then be added to hone the shape of the lens that also greatly increases the imaging quality of the lens. “It’s a low cost and easy lens-making recipe,” Lee explained.

The researchers made lenses about a few millimeters thick with a magnification power of 160 times and a resolution of about 4 microns, two times lower in optical resolution than many commercial microscopes, but more than three orders of magnitude lower in cost.

Disposable Lenses Can Attach to Smartphones

Their low cost allows them to be used in a variety of ways. One new use of note, Lee said, is to attach the lens to a smartphone camera, turning it into a new device—a dermascope used to diagnose skin diseases like melanoma. While normal dermascopes can cost $500 or more, the phone version costs around $2, the researcher said. Their dermascope was made using a 3D printer and is designed for use in rural areas or developing countries. It’s slated to be commercially available in just a few months, he said.

Lee also envisions that the lenses could be used in the lab as implantable lenses that biologists can use to study cells in vivo. The high cost of conventional lenses usually dissuades scientists from implanting them into mice, he says.

So far, the researchers have only been able to make lenses smaller than about half an inch in diameter. But to expand the range of applications, the team is now working to refine the process to make lenses as large as two inches and increasing its optical performance.