Make Your Own Droplet Microscope Lens for a Penny

794 Make Your Own Droplet Microscope Lens for a Penny
A set of droplet lenses on a microscope coverslip with ANU’s Steve Lee / Stuart Hay, ANU
Clear liquid droplets can bend light, acting like a lens. By exploiting this well-known phenomenon, scientists have devised a cheap and simple way to turn a smartphone into a high-resolution microscope. The high-powered lenses cost less than a cent apiece to make, and all you need is a cover slip or glass slide, some common polymer, and an oven. The method would be immensely helpful for diagnosing medical conditions in remote areas and developing countries. 
Conventional lenses are usually made in one of two ways. You can grind and polish a flat disk of glass into a particular curved shape, or you can pour gel into molds. These new lentil-sized lenses simply retain the natural shape of liquid droplets. They're made of a gel-like silicon polymer called polydimethylsiloxane (PDMS) -- the same unbreakable, scratch-free stuff used for contact lenses. 
And it really sounds quite simple to make. “We put a droplet of polymer onto a microscope cover slip and then invert it. Then we let gravity do the work, to pull it into the perfect curvature,” study author Steve Lee from Australia National University explains in a news release
By adding small amounts of fluid to the droplet successively after baking the base drop, they managed to reach a (surprisingly high) magnifying power of 160 times with an imaging resolution of four micrometers. They varied the focal lengths by letting the drop hang and then curing (or hardening) them further in the oven. 
"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," Lee explains. No complicated machinery needed. Here’s the step-by-step easy-bake recipe: 
  • 1. Drop a small amount of PDMS onto the slide. 
  • 2. Bake at 70 degrees Celsius to harden it and create a base. 
  • 3. Afterwards, drop another dollop of PDMS onto the base and flip the slide over. 
  • 4. Watch as gravity pulls the new droplet down into a parabolic shape. 
  • 5. Bake the droplet again to solidify the lens. 
  • 6. Add more drops as needed to hone the lens shape and enhance the imaging quality of the lens. 
The whole lens was only a few millimeters thick and just over a centimeter in diameter. The team then designed a lightweight 3D-printable frame to hold the lens, along with a couple mini LEDs and a coin battery for watches. The attachment turns a smartphone camera into a dermascope to diagnose skin diseases like melanoma. Dermascopes can cost $500; this new prototype dermascope add-on comes to about $2. You can check out this comparison of the magnified images.
The new dermascope could be commercially available in just a few months, according to Lee. With a different app, a similar tool can help farmers identify pests in the field. And to think, the first droplet lens was made by accident. Serendipitous.  
The work was published in the Optical Society’s Biomedical Optics Express this week. 
Images: Stuart Hay, ANU



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