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Letter

Experimental Determination of Quantum Dot Size Distributions, Ligand Packing Densities, and Bioconjugation Using Analytical Ultracentrifugation

Supporting Info

Emma E. Lees^†^‡, Menachem J. Gunzburg^†, Tich-Lam Nguyen^†, Geoffrey J. Howlett^§, Julie Rothacker^‡, Edouard C. Nice^‡, Andrew H. A. Clayton^‡ and Paul Mulvaney*^†

School of Chemistry and Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia, The Department of Biochemistry and Molecular Biology and Bio21 Institute, University of Melbourne, Parkville, Victoria 3010, Australia, and Ludwig Institute for Cancer Research, PO Box 2008, Royal Melbourne Hospital, Parkville, Victoria 3050, Australia

Nano Lett., 2008, 8 (9), pp 2883–2890

DOI: 10.1021/nl801629f

Publication Date (Web): July 30, 2008

†

School of Chemistry and Bio21 Institute, University of Melbourne.

‡

Ludwig Institute for Cancer Research, Royal Melbourne Hospital.

The Department of Biochemistry and Molecular Biology and Bio21 Institute, University of Melbourne.

* Corresponding author. Telephone: (61)3-8344-2420. Fax: (61)3-9348-1595. E-mail: mulvaney@unimelb.edu.au.

Abstract

Analytical ultracentrifugation (AUC) was used to characterize the size distribution and surface chemistry of quantum dots (QDs). AUC was found to be highly sensitive to nanocrystal size, resolving nanocrystal sizes that differ by a single lattice plane. Sedimentation velocity data were used to calculate the ligand packing density at the crystal surface for different sized nanocrystals. Dihydrolipoic acid poly(ethylene glycol) was found to bind between 66 and 60% of the surface cadmium atoms for CdSe nanocrystals in the 1.54−2.59 nm radius size regime. The surface ligand chemistry was found to affect QD sedimentation, with larger ligands decreasing the sedimentation rate through an increase in particle volume and increase in frictional coefficient. Finally, AUC was used to detect and analyze protein association to QDs. Addition of bovine serum albumin (BSA) to the QD sample resulted in a reduced sedimentation rate, which may be attributed to an associated frictional drag. We calculated that one to two BSA molecules bind per QD with an associated frictional ratio of 1.2.

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