Anomalous Dielectrophoresis of Nanoparticles: A Rapid and Sensitive Characterization by Single-Particle Laser Spectroscopy

作者：Froude Victoria E; Godfroy James I; Wang Shengqin; Dombek Hannah; Zhu Yingxi^*

来源：Journal of Physical Chemistry C, 2010, 114(44): 18880-18885.

DOI：10.1021/jp108862d

Although much experimentation has focused on the dielectrophoretic behavior of submicrometer colloids, few studies have provided advanced understanding of the ac electric polarization mechanism for nanoparticles, largely due to the paucity of sensitive and rapid experimental techniques. By using ultrafast fluorescence correlation spectroscopy (FCS) at a single-particle level, we have examined the dielectrophersis (DEP) behavior of nanoparticles of varied radii, a = 10-50 nm, in aqueous media under varied ac electric fields in situ, where direct and real-time microscopic methods become inapplicable for nanoparticles of a < 50 nm. The characteristic dipole relaxation frequency (the DEP crossover frequency, omega(c)) is determined from the ac-frequency-dependent nanocolloidal concentration profile by FCS. In stark contrast to a single we predicted from classical DEP theory, we have observed two distinct omega(c)'s with a strong dependence on particle size and medium conductivity. The anomalous lower omega(c) inversely scales with the screening length and particle size, suggesting the dynamic double-layer charging effect on the interfacial polarization of nanocolloids whose size is comparable to the double-layer thickness.

• 出版日期2010-11-11