BIOPHYSICS: GPS on a QD

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Science  09 Jul 2004:
Vol. 305, Issue 5681, pp. 151c
DOI: 10.1126/science.305.5681.151c

Cadmium selenide-zinc sulfide (CdSe-ZnS) core-shell quantum dots (QDs) are inorganic particles (roughly 5 to 10 nm in diameter) exhibiting stable and intense luminescence. Their size and spectral properties make it feasible to consider derivatizing QDs with dye-labeled proteins in order to fabricate optical sensors possessing biochemical activity, such as the specific and sensitive binding of a ligand. Medintz et al. have performed a detailed characterization of one such QD-protein hybrid, in which maltose-binding protein (MBP) is covalently modified with a dye at one of six positions, which are distributed over the MBP surface, and then coupled to the QD via a short spacer attached at Lys370. The crystal structure of MBP is known, and thus spherical approximations of the dye locations could be calculated. By measuring fluorescent resonance energy transfer from the QD to the dye for each of the six types of MBP-QDs, the authors are able to determine the best-fitting structure of the complex, in a fashion analogous to that of a satellite-based global positioning system. — GJC

Proc. Natl. Acad. Sci. U.S.A. 101, 9612 (2004).

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