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From nanotech fibers and nanosensors to nanobots, nanotechnology has created so much “buzz” that it’s hard to tell where the science ends and the science fiction begins. Wherever it may lead in the future, the science of nanotechnology begins with solid particles called nanoparticles that are 1–100 nm in size. Shrinking the size of solid-phase particles to the nanometer scale—one billionth of a meter—changes their physical and chemical properties. The surprising properties of “colloidal gold” are a good example of this phenomenon. Whereas normal or “bulk” gold is bright, shiny, metallic yellow, colloidal gold nanoparticles are red or blue, and not at all shiny. Let’s investigate the preparation, properties, and uses of colloidal gold.