There's been a bit of a rush of pocket/USB digital microscopes recently, but none can hold a candle to this development from the clever chaps at Caltech. They've done a neat bit of thinking and redesigned how microscopes work: their new optofluidic microscope combines microfluidics and standard chip design, and floats samples over a pinhole-camera-like detector.
As the sample moves through a metallic microfluidic channel, either by gravity or drawn by an electric field, it passes over a line of sub-micron diameter pinholes, blocking or transmitting light (sunlight works fine). The dynamic light level is then detected by a standard CCD device behind the holes. So it's lens-free, working more like a micro-sized scanner device, and yet it has comparable image quality to a top-rate glass-lensed traditional microscope.
And it's about the size of a quarter in its entirety: making it small enough to fit into a mobile-phone-sized device, with an LCD screen. It's cheap—around $10—and easy to make, and would be perfect for developing countries for easy detection of malaria in blood and such. [Physorg]