December 2009

Document Type


Degree Name



Dept. of Science & Engineering


Oregon Health & Science University


We report an approach, diffusion based single particle sizing (DBSPS), to determine hydrodynamic size distributions of fluorescent nanoparticle quantum dots (QDs) and QD bioconjugates. We used fluorescence video-microscopy for determination of fluorescent particle trajectories in solution. The trajectories provide spatial and temporal information required for the determination of the diffusion coefficients (D) through mean square displacement (MSD) analysis. Subsequently, the hydrodynamic radii (R[subscript h]) of the individual particles were estimated using the Stoke-Einstein formula. DBSPS measures hydrodynamic size of single particles, rather then ensemble measurements. This allows the tracking and analysis of small single particles even when they are present in heterogeneous samples containing larger particles. Our results demonstrate that DBSPS accurately measures hydrodynamic dimensions of QD bioconjugates and pre-calibrated fluorescent polystyrene nanospheres, provides a measure of QD-biomolecule conjugation efficiency and identifies and excludes QD aggregates (multiple QD complexes). Researchers who design QD bioconjugates for aqueous settings can obtain highly tuned QD bioconjugate hydrodynamic size distributions using DBSPS.




Div. of Biomedical Engineering


School of Medicine



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