fulltext34 - Characterization of Water-soluble Luminescent...

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Characterization of Water-soluble Luminescent Quantum Dots by Fluorescence Correlation Spectroscopy C HAOQING D ONG ,X IANGYI H UANG , AND J ICUN R EN School of Chemistry and Chemical Technology, Shanghai Jiao Tong University, Shanghai, China Quantum dots (QDs) are nanoscale inorganic particles generally composed of II–VI and III–V elements. Recently, QDs have received great interest in biological applications because of their unique and fascinating optical properties. In this short review, we introduce the synthesis of luminescent QDs in the aqueous phase and characterize certain fundamental parameters of lu- minescent QDs synthesized in the aqueous phase by fluorescence correlation spectroscopy (FCS), which include, for example, their dynamic diameters and surface charges. Meanwhile, combining with some ensemble spectroscopy techniques, we applied FCS to investigate the quenching pro- cess and mechanism of heavy metal ions (e.g., Ag + )onCdTeQDs ,aswellastheaggregationand subsequent photoactivation process of 3-mercaptopropionic acid–capping CdTe QDs induced by laser irradiation. Our preliminary results demonstrate that FCS is a sensitive and efficient tool to characterize fluorescent nanoparticles, such as QDs, at the single-molecule detection level. Key words: quantum dots; characterization; fluorescence correlation spectroscopy Introduction Quantum dots (QDs; also known as colloidal semi- conductor nanocrystals) are nanoscale inorganic par- ticles generally composed of II–VI and III–V ele- ments. 1–4 Their sizes are in the range of 1–10 nm, which can be precisely controlled by the reaction dura- tion time and temperature and ligand molecules. As we knew, when the sizes of nanocrystals are less than their Bohr radii, the energy levels of QDs are quantized and their values are related to the size of QDs. As the size of nanocrystals decreases, the bandgap increases, which results in blueshift of emission. Because of quantum confinement effects and size effects of QDs, they can manifest some unique optical properties, such as tun- able emission wavelength, broad absorption and sharp emission spectra, high quantum yield (QY), resistance to chemical degradation and photobleaching, and ver- satility in surface modification. So it can be convenient to obtain QDs with different emission wavelengths by adjusting their sizes and components. Narrow and Address for correspondence: Jicun Ren, School of Chemistry and Chemical Technology, Shanghai Jiao Tong University, 800 Dongchuan Rd., Shanghai 200240, PR China. Voice: + 86-21-54746001; fax: + 86- 21-54741297. jicunren@sjtu.edu.cn symmetric photoluminescence (PL) emission of QDs makes them ideal materials for simultaneous detection of multiple fluorophores. One light source can excite different colors of QDs because of their broad absorp- tion spectra.
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This note was uploaded on 07/11/2010 for the course SPECTOGRAP 545 taught by Professor Gdf during the Spring '10 term at AIB College of Business.

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fulltext34 - Characterization of Water-soluble Luminescent...

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