ja061762i - Published on Web Metal-Enhanced Fluorescence...

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Metal-Enhanced Fluorescence from CdTe Nanocrystals: A Single-Molecule Fluorescence Study Krishanu Ray, Ramachandram Badugu, and Joseph R. Lakowicz* Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, Uni V ersity of Maryland School of Medicine, 725 West Lombard Street, Baltimore, Maryland 21201 Received March 14, 2006; E-mail: [email protected] Signal detection is a challenging task in chemistry and biology. Most often, background noise hinders the detection of the signal of interest. This can be prevailed if one has a signal enhancing and/or directing technique. In this regard, Metal-Enhanced Fluo- rescence (MEF) is a newly recognized technology, where we study the interactions of fluorophores with metallic colloids or surfaces, which provides fluorescence enhancement. 1 Along with signal enhancement, MEF also provides several other important spectral changes, such as increased photostability, decreased lifetime due to increased rates of radiative decay, and increased distance for fluorescence resonance energy transfer (RET). 1c Because of this exceptional improvement in signal detectability provided by the MEF, we were able to increase the intrinsic DNA fluorescence, which is otherwise impractical to perceive. 1d Accordingly, we have made considerable progress with MEF studies, where we used wide varieties of fluorophores that can be potentially used in different applications. 2 Single-molecule fluorescence spectroscopy provides several advantages over ensemble measurements. 3 For instance, it eliminates averaging of the spectral properties over all members of the ensemble and can reveal fundamental features otherwise masked in ensemble experiments. Accordingly, using single-molecule fluorescence studies, we anticipate that the metal - fluorophore interactions in the MEF studies can be better revealed, especially at the single-molecule level. For this, we choose CdTe nanocrystals (QDots) as fluorophores. QDots having few nanometer sizes, tunable absorption, and fluorescence spectral properties are widely used as probes in various fields, including biological labeling and imaging. 4 Potential applications of QDots are rapidly increasing. Single QDot fluorescence spectroscopy has been accomplished successfully for several colloidal semiconductor materials, including CdSe, 5a CdS, 5b CdTe, 5c Si, 5d and InP. 5e Additionally, quantum dot fluorescence spectral properties are reported in the presence of metallic nanoparticles at the ensemble level with little details. 6,7 In this communication, we describe the ensemble and single- molecule fluorescence spectral properties of CdTe nanocrystals spin coated in polyvinyl alcohol (PVA) matrix on glass and silver island films (SIFs). CdTe nanocrystals were prepared using a modified Weller method (for further details, see Supporting Information). 8
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This note was uploaded on 09/30/2010 for the course MATH Math 117 taught by Professor Notsure during the Spring '10 term at École Normale Supérieure.

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ja061762i - Published on Web Metal-Enhanced Fluorescence...

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