User: Pok Man Mendy Chan, Mount Sinai School of Medicine, New York

The project: Studying expression of G-protein coupled receptors in striatal neurons and their involvement Parkinson's disease.

The problem: Metabolically active tissue from postmortem brains in Chan's studies shows high levels of background fluorescence.

The solution: To examine coexpressed receptors at the single-cell level, Chan chooses as many as four dyes (Invitrogen, Carlsbad, CA) with nonoverlapping spectra, then fits in quantum dots (Evident Technologies) between dye-emission wavelengths for a maximum of eight colors per experiment. Because of their brightness, dots stand out against autofluorescence much better than dye, says Chan. Brightness is also advantageous when working with low-quality tissue such as tumor samples, says Sealfon. When using dots alone, he notes, the background can be bleached out with light exposure, he says. While organic dyes...

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