Characterization and Manipulation of Single Nanoparticles Using Electrokinetic Trapping Near Nanopores*

Manipulation and detection of micro/nanoparticles are of great importance in a broad spectrum of applications ranging from medical diagnostics and environmental monitoring to basic research in physics and biology. Although a variety of methods that can selectively trap and detect microparticles have been developed over the last decade, it remains a great challenge to extend these methods to the nanoscale. Here we report a new approach for single nanoparticle manipulation and detection based on electrokinetic trapping of nanoparticles near a low-aspect ratio nanopore. We discover that this trapping results from a balance between electrophoretic and electroosmotic forces and that the motion of a trapped nanoparticle can be modeled as a harmonic oscillator. We demonstrate that, by analyzing ionic current through the nanopore, it is possible to characterize the size and surface charge density of the trapped nanoparticle. We also demonstrate that the position of trapping and force exerted on the nanoparticle can be easily tuned by changing the applied voltage. We envision that further development of this technique will enable various advanced tools for drug delivery, transport control, and biosensing.