IT SOUNDS like a claim as bold as turning base metals into gold or travelling faster than light. Viewing nanoscale particles with a light microscope just can't be done. But the red dots visible down a specially equipped light microscope tell a different story. The dots are particles just 100 nanometres across.

"There's nothing magical about it," says Bob Carr, chief technical officer of Nanosight, based in Salisbury, UK, which developed the device. Dubbed Halo, it can be attached to any light microscope to let you view moving particles as small as 10 nanometres. And Halo could become more than a curiosity, says Carr, with applications from detecting bioweapons to quality control in paints, pharmaceuticals and sunblocks.

Light microscopes fail at the nanoscale because they cannot resolve objects smaller than half the wavelength of visible light. Nano-sized objects also scatter back too few photons, so they cannot be seen against ...