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Quantum Dot Bioconjugates for Imaging, Labelling and Sensing

Quantum Dot Bioconjugates for Imaging, Labelling and Sensing. By: Igor L. Medintz, H. Tetsuo Uyeda, Ellen R. Goldman, and Hedi Mattoussi Nature Materials , June 2005 Presented by: Marshal Miller. Outline. Applications Benefits of QDs Current Capabilities Manufacturing process

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Quantum Dot Bioconjugates for Imaging, Labelling and Sensing

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  1. Quantum Dot Bioconjugates for Imaging, Labelling and Sensing By: Igor L. Medintz, H. Tetsuo Uyeda, Ellen R. Goldman, and Hedi Mattoussi Nature Materials, June 2005 Presented by: Marshal Miller

  2. Outline • Applications • Benefits of QDs • Current Capabilities • Manufacturing process • Connection to bio-molecules • Future directions

  3. Bio-Applications • in vivo and in vitro flourophores • Cellular labelling (cancer cells) • Deep-tissue imaging • Efficient fluorescence resonance energy transfer (FRET) donors • Understand interplay of biomolecules

  4. QD vs Organic Labelling • Organic and genetic fluorophores • Low photobleaching threshold • Broad absorption and emission profiles • QDs properties • High resistance to photobleaching and photo and chemical degradation • Broad absorption, but narrow emission (FWHM ~25-40nm) • High quantum yield • High molar extinction coefficients (~10-100x organic) • Wide range (UV – IR) • Large Stokes shifts CdSe core: 13.5-24.0 Ǻ

  5. QD Properties Alexa 488 QD 630

  6. Current Capabilities • Best QDs for bio-applications (June 2005) are CdSe cores with ZnS layer • Easily reproducible/Refined chemistry • Wide range of emission • ZnS: • Passivates the core surface • Protects core from oxidation • Prevents Cd/Se from leeching into surrounding solution • Produces higher photoluminescence yield • Other colloidal nanocrystals: ZnS, CdS, ZnSe, CdTe, PbSe • Problems with reproducibility • Inorganic passivation

  7. Methods for preparing QD bioconjugates • Production of CdSe • TOPO dried by heating to 200 oC at 1 Torr for 20 min • Reaction flask stabilized at 300 oC at 1atm of argon • A:1.00 mL of Me2Cd added to 25.0 mL of TOP in drybox • B: 10.0 mL of TOPSe added to 15.0mL of TOP • A added to B • Removed from heat put in vigorously stirring reaction flask • Temp falls to 180 oC, then heated to restore the temp to 230-260 oC • Absorption spectra taken every 5-10 mins to monitor growth • Raising the temp increases growth rate • Once desired size is observed, portion of growth solution transferred to a vial • Can isolate a series of sizes (15 to 115 Ǻ) from one batch TOP = trioctyl phosphine, TOPO = trioctyl phosphine oxide, Me2Cd = Dimethylcadmium Process from: Synthesis and Characterization of Nearly Monodisperse CdE Semiconductor Nanocrystals, Murray et. al. J. Am. Chem. Soc. 1993

  8. Connecting to Biomolecules • Uses ‘cap exchange’ by substituting TOP/TOPO with bifunctional ligands (ex thiol) • Formation of polymerized silica shells functionalized with polar groups • Preserves TOP/TOPO and uses amphiphilic ‘diblock’ and ‘triblock’ copolymers and phospholipids

  9. Problems/Future Directions • Toxicity of inorganic Cd, Se, Zn, Te, Hg, Pb • Toxins, neurotoxins, teratogens • Reports of QDs damaging DNA • Have been some long-term in vivo studies showing no evidence of toxicity • No long term animal studies • How are particles cleared metabolically? • Do QDs mirror true in vivo behavior? • Multiplexing (6-10 signals at varying intensities) bar codes for synthetic products • Flexible bioconjugation • Make processes more reproducible

  10. The End Thank you for your attention Questions?

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