Droplet lens | Day 27

Whenever I cook lentils, I’m fascinated by the wonderful geometric shape that an uncooked lentil possesses. A disk bulging in the middle and tapered at the edges, the lentil is shaped just like a classic convex lens. In fact, I just learnt that the Latin word for lentils is what gave lenses their name.

A convex lens bends entering light waves, causing them to focus at a particular point upon exiting on the other side: here’s an extremely simple video demonstration of that. This produces a magnification effect. To produce the right lens shape, they are either polished and ground out of flat pieces of glass (very expensive) or made out of modern gel-like materials in specially shaped molds (still not that cheap).

However, droplets of water have the properties of a lens, too. Hence the genius invention that swiped a Eureka Prize for Innovative Use of Technology his year — a droplet lens. Steve Lee from Australian National University paired with Tri Phan from the Garvan institute in Sydney, and produced an innovation that can turn the measly camera of a smartphone into a microscope.

To do this, all you need is an oven, a gel consistency silicone polymer called PDMS, and a microscope glass slide. By dropping PDMS onto the slide, hanging it upside down and baking in a fairly cool oven at 70° C, gravity helps you make a tiny, perfectly good lens with the magnification power of up to 160x. That’s powerful enough to see human blood cells. Attach a simple 3-D printed lens mount to the smartphone you already own, stick in the cheap and powerful lens, turn on a custom-made app and there you go, a pretty good microscope that costs just a few dollars.

While fancy, commercial microscopes do have higher resolution and even more powerful optics than the DIY droplet versions, they are also expensive. The inventors believe that a cheap, disposable droplet solution can have a wide range of uses — from exploring the backyard with your kids to citizen science, to helping diagnose skin diseases like melanoma in rural areas where a dermascope may not be easily available.

It’s such a clever invention one almost wonders why nobody stumbled upon it sooner. But it’s here now, and I’ll be keeping an eye out for DIY smartphone microscope kits in the shops.

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