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With the company’s name and logo taped to the glass door, the unpacked boxes, an empty reception desk, and young scientists bustling about, it could be any Silicon Valley company in the chaos of starting up. But this, it quickly becomes apparent, is not an ordinary startup. You begin to notice the difference a few doors past the coffee maker. Just down the hall, in a windowless room lit by the faint glow of a green laser shooting through a maze of optical equipment, you’ll find the company’s crown jewels, tiny particles emitting a variety of colors. These are quantum dots-crystals made up of only a few hundred atoms. Viewed through an ordinary optical microscope, they twinkle like stars in a moonless sky.

Quantum Dot Corporation-and its handful of high-profile venture capital investors-is betting these glowing specks will change how biologists view the cellular world. The particles measure only a few nanometers (billionths of a meter) across. Because this is about the same size as a protein molecule or a short sequence of DNA, quantum dots could be near-perfect beacons for lighting up biological events. They come in a nearly unlimited palette of colors and can be linked to biomolecules to form sensitive probes to identify specific compounds and track biological events.

Fluorescent tags are ubiquitous in medicine and biology-used in everything from HIV tests to imaging the inner functions of cells. But the dyes that biologists now rely on have serious drawbacks. For one thing, different types of dye molecules must be used for each color, and a matching laser must be used to get a dye to fluoresce: a green laser for a green dye, yellow for a yellow dye, and so on. The colors emitted by the dyes tend to bleed together, and using a combination of lasers is unwieldy. These limitations mean that, in practice, you cannot look for more than a few types of biomolecules at a time. What’s more, dyes fade quickly, so imaging is a one-shot affair.

Quantum dots have none of these shortcomings. You can make sharply colored dots simply by varying the size of the nanoparticles and make a rainbow of these colors fluoresce with white light or a single-color laser. Furthermore, the nanoparticles continue to shine for much longer than dyes do. These improvements allow you to simultaneously tag various biological components-say different proteins or various sequences of DNA-with specific colored nanodots.

That kind of flexibility could mean a cheap and easy way to screen a blood sample for the presence of a number of different viruses at the same time. It could also give physicians a quick take on a patient’s condition. For instance, the presence of a particular set of proteins is a strong indicator that a person is having a heart attack; quantum dots could offer a rapid and simple test to detect these proteins. On the research front, the ability to simultaneously tag multiple biomolecules could provide a powerful way to watch the complex cellular changes and events associated with diseases, providing clues for drug discovery.

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