Bake your own microscope lens

Australian scientists have invented a simple way of making a high-powered lens that costs less than a cent and can transform a smartphone into a high-resolution microscope. The transformation is made by attaching the tiny polymer lens onto the camera lens of a phone.

The lens fabrication technique was invented by Dr Steve Lee from the Australian National University (ANU) Research School of Engineering, who collaborated with Dr Tri Phan from the Garvan Institute of Medical Research to find ways to transform the lens into a medical imaging tool. Their work has been published in the Optical Society journal Biomedical Optics Express.

Many conventional lenses are made by grinding and polishing a flat disk of glass into a particular curved shape. Others are made by pouring gel-like materials moulds. With the new method, all that’s needed is an oven, a microscope glass slide and a common, gel-like silicone polymer called polydimethylsiloxane (PDMS), which is used for contact lenses.

First, drop a small amount of PDMS onto the slide. Then bake it at 70°C to harden it, creating a base. Then, drop another dollop 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.

A set of droplet lenses on a microscope coverslip and a single droplet lens suspended on a fingertip. Credit: Stuart Hay.

“It’s very easy to do - in fact, I think that anyone at home could do it,” said Dr Lee. “It costs around less than a cent to make a single lens.”

Dr Lee admitted that the first droplet lenses were made by accident and he nearly threw them away.

“I happened to mention them to my colleague Tri Phan, and he got very excited,” Dr Lee said.

“So then I decided to try to find the optimum shape, to see how far I could go. When I saw the first images of yeast cells I was like, ‘Wow!’”

Comparison of a human tissue histological sample between the 1-cent PDMS lens (left) and a $300 microscope lens (right). Credit: Biomedical Optics Express.

Dr Lee found that by successively adding small amounts of fluid, creating a lens just a few millimetres thick, they could reach a magnifying power of up to 160 times with an imaging resolution of four micrometres - two times lower in optical resolution than many commercial microscopes, but more than three orders of magnitude lower in cost.

Dr Lee and his team worked with Dr Phan to design a lightweight 3D-printable frame to hold the lens, along with a couple of miniature LED lights for illumination and a coin battery. The attachment turns a smartphone camera into a dermascope - a tool to diagnose skin diseases like melanoma - which can cost $500 or more. The phone version costs just $2.

Prototype of the 3D-printed dermascope on a smartphone, used to image the top epidermis layer. Credit: Stuart Hay.

The tiny microscope has a wide range of potential uses. Dr Lee envisions that the lenses could be used by biologists to study cells in vivo; by farmers to identify pests out in their fields; or in classrooms for educational purposes. Their simplicity and low cost make them especially suitable for the third world, he added.

So far, the researchers can’t make lenses much bigger than half an inch in diameter. The team is now refining the process to make lenses as large as two inches and increasing the lens’s optical performance