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2007, 111, 32-35 Published on Web 12/14/2006
Rapid and Quantitative Sizing of Nanoparticles Using Three-Dimensional Single-Particle Tracking C. Shan Xu, Hu Cang, Daniel Montiel, and Haw Yang* Department of Chemistry, UniVersity of California at Berkeley, and Physical Biosciences DiVision Lawrence Berkeley National Laboratories, Berkeley, California 94720 ReceiVed: October 31, 2006; In Final Form: NoVember 26, 2006
We report the first application of three-dimensional (3D) single-particle tracking (SPT) to hydrodynamic size characterization of gold nanoparticles in water. Nanoparticles undergoing Brownian motion were dynamically locked at the focal point of a microscope objective, one at a time, by rapid counteractive movements of the sample container. The hydrodynamic radius was derived from the recorded trajectory of each individual nanoparticle. The directly measured size and size distribution using 3D-SPT were in agreement with those obtained using the conventional dynamic light scattering (DLS) and using transmission electron microscopy (TEM), respectively.
An important direction in creating materials of novel properties has been the use of nanoparticles as building blocks for more complicated structures.1-3 Yet, our fundamental understanding of the manner by which nanoscale particles assemble and disassemble remains incomplete. Rapid characterizations of nanostructures in terms of their size and size distribution through direct experimental observation are therefore expected to contribute to this general area. Electron microscopy is the most commonly used method offering an accurate determination of both the size and distribution; however, it can be timeconsuming and is difficult to operate under the more relevant in situ conditions. Single-particle light-scattering techniques offer an alternative size measurement of colloidal particles one at a time,4 although their accuracy can be impaired by the particle shape and structure. Hydrodynamic behavior, on the other hand, is a direct representation of the kinetically pertinent particle size in the solution phase. Ensemble-averaged photon correlation approaches such as DLS5 allow fast characterization of the average hydrodynamic properties of a nearly monodispersed sample in a homogeneous solution. However, they only provide a qualitative measure on the distribution.6 SPT records the motion of a nanoparticle and, thus, should offer an unmitigated solution to this problem. To date, however, no successful application of SPT for studying nonfluorescent nanoscale particles (
