We have measured the hydrodynamic radii of magnetite nanocrystals(NCs)with an 11 nm core by fluorescence correlation spectroscopy(FCS).We found that the sizes determined from particle diffusion varied by as much as an order of magnitude for the same magnetite NC sample due to the presence of a small number of larger and brighter aggregates,which bias the fluorescence autocorrelation.By analyzing the fluorescence intensity distributions and applying a magnetic field we were able to gain insight into the size distribution of the magnetite NCs and estimate the percentage of larger aggregates present.Size-selective separation of aggregates larger than about 60 nm in diameter was achieved by applying a magnetic field of 0.24 T.
展开▼
