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Single-Molecule Measurements of Gold-Quenched Quantum Dots

Zoher Gueroui, Ph.D.

Quantum dots (Qdots), also called nanocrystals, can be viewed as artificial atoms intermediate between molecular and bulk forms of matter. Given their photostability properties and their bright luminescence, tunable across the visible spectrum, they have proven to be useful as sensors, laser, and single photon sources. Recently, the discovery of new coatings protecting these nanocrystals from the watery environment, led to numerous applications to label living cells. Among the numerous applications for biological science that could be undertaken, we addressed the possibility of energy transfer of Qdot with another inorganic particle, a nanometer-sized gold cluster. Double-stranded DNA was used as a rigid spacer to tune the distance between the two nanoparticles. Using epi-fluorescent microscopy, the intensity of single and isolated fluorescent Qdot-DNA-Gold complexes was quantified. The fluorescence distribution emitted by single CdSe nanocrystals can easily be distinguished from the fluorescence of partially quenched CdSe. Our results show that the distance dependence quenching is compatible with a Forster-type process. This, in turn, allows us to characterize the homogeneity of the sample studied and opens new perspectives for probing molecular interactions on bulk or on surfaces.

Reference

(1) Gueroui Z. and Libchaber A. (2004) Single-molecule measurements of gold-quenched quantum dots. Phys Rev Lett. 93, 166108-166111.