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 Connection to bio-molecules Future directions

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

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: Ǻ

QD Properties QD 630Alexa 488

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

Methods for preparing QD bioconjugates Production of CdSe TOPO dried by heating to 200 o C at 1 Torr for 20 min Reaction flask stabilized at 300 o C at 1atm of argon A:1.00 mL of Me 2 Cd 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 o C, then heated to restore the temp to o C 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

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

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

The End Thank you for your attention Questions?