Researchers at the University of Houston have found a way to create a very cheap (3 cents) lens that can be easily attached to your smartphone camera just by sticking it on the lens of the camera.
The lens is made of polydimethylsiloxane (plastic...), PDMS, and is produced using an ink-jet like printer. The trick is to have the droplet of PDMS fall onto a surface that is heated at a fixed temperature. Depending on the temperature and on the time it rests on the surface the curvature of the lens changes and along with it its magnifying power.
The researchers have tested the lens on the smartphone finding a resolution of 1 µm, corresponding to 120x magnification with a very good quality comparing to the one of a normal microscope. At this resolution you can see cells and their inner structure making this a very inexpensive microscope to use on the field.
I can easily imagine myself roaming and snapping picture of Nature at microscopic level... and the researchers are explicitly mentioning students as the first users having fun and learning in the field.
Once you are done with the shooting session you just peel out the lens and discard it, although you can reuse it but at 3 cents a lens discarding is something you can afford. The actual lens material cost is 1 cent, the other two cover production, packaging...
Greater magnifications (like 400x) can also be obtained but quality decreases.
To produce the lens they have used a modified ink-jet printer. Now they have opened a crowdfunding campaign to harvest 12,000$ to develop a specific printing device.