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Single-Molecule Colocalization Studies Shed Light on the Idea of Fully Emitting versus Dark Single Quantum Dots

Authors

  • Thomas Pons,

    1. US Naval Research Laboratory, Division of Optical Sciences, Washington, DC 20375, USA
    Current affiliation:
    1. Laboratoire Physique et Etude des Matériaux, ESPCI-CNRS UMR8213, Ecole de Physique et Chimie Industrielle (ESPCI), 10 rue Vauquelin, 75005 Paris, France
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  • Igor L. Medintz,

    1. US Naval Research Laboratory, Division of Optical Sciences, Washington, DC 20375, USA
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  • Dorothy Farrell,

    1. US Naval Research Laboratory, Division of Optical Sciences, Washington, DC 20375, USA
    Current affiliation:
    1. National Cancer Institute, Building 31, Room 10A52, Bethesda, MD 20892, USA
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  • Xiang Wang,

    1. Dept. of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
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  • Amy F. Grimes,

    1. Dept. of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
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  • Douglas S. English,

    1. Dept. of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
    Current affiliation:
    1. Department of Chemistry, Wichita State University, 1845 Fairmount, Wichita, KS 67260, USA
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  • Lorenzo Berti,

    1. Department of Biochemistry and Molecular Medicine, University of California, Davis School of Medicine, Sacramento, CA 95817, USA
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  • Hedi Mattoussi

    Corresponding author
    1. US Naval Research Laboratory, Division of Optical Sciences, Washington, DC 20375, USA
    Current affiliation:
    1. Florida State University, Department of Chemistry and Biochemistry, Tallahassee, FL 32306, USA
    • US Naval Research Laboratory, Division of Optical Sciences, Washington, DC 20375, USA.
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Abstract

In this report the correlation between the solution photoluminescence (PL) quantum yield and the fluorescence emission of individual semiconductor quantum dots (QDs) is investigated. This is done by taking advantage of previously reported enhancement in the macroscopic quantum yield of water-soluble QDs capped with dihydrolipoic acid (DHLA) when self-assembled with polyhistidine-appended proteins, and by using fluorescence coincidence analysis (FCA) to detect the presence of “bright” and “dark” single QDs in solution. This allows for changes in the fraction of the two QD species to be tracked as the PL yield of the solution is progressively altered. The results clearly indicate that in a dispersion of luminescent nanocrystals, “bright” (intermittently emitting) single QDs coexist with “permanently dark” (non-emitting) QDs. Furthermore, the increase in the fraction of emitting QDs accompanies the increase in the PL quantum yield of the solution. These findings support the idea that a dispersion of QDs consists of two optically distinct populations of nanocrystals—one is “bright” while the other is “dark;” and that the relative fraction of these two populations defines the overall PL yield.

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