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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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Quantum dot bioconjugates for imaging labelling and sensing l.jpg

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 l.jpg

Outline

  • Applications

  • Benefits of QDs

  • Current Capabilities

  • Manufacturing process

  • Connection to bio-molecules

  • Future directions


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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


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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


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QD Properties

Alexa 488

QD 630


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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


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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


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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


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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


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The End

Thank you for your attention

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