Insights into Nanoscale Electrophoresis of Single Dye Molecules in Highly Oriented Mesoporous Silica Channels

Abstract

Electrophoresis is a very important tool in chemistry, biochemistry, and biology and is commonly used for the separation and analysis of molecules. Typically, electrophoresis is performed at the macroscopic level. With a view on integrating molecular separations into micro- and nanofluidic and massively parallel systems, it would be highly desirable to obtain detailed knowledge about electrophoretic separation at the nanoscale. Here, we describe an in situ single molecule fluorescence imaging approach to provide insights into the controlled movement and separation of charged molecules in highly oriented silica nanochannels under the influence of an electric field. The velocity of the charged single molecules increases with increasing electric field strength and can therefore be directly controlled by an external stimulus. On the basis of the single molecule trajectories, we propose a model for the internal structure of the host and for the diffusion of charged and uncharged species in the nanoscale channels. In order to prove that the molecules move along the aligned pores, we applied an electric field diagonally to the pores. The molecules that were located in the mesopores showed a directed movement along the mesoporous silica channels, whereas molecules next to, but outside of, the structure followed the electric field lines. Leaky defects in the side walls of the pores were indicated by molecules switching into and out of the pores. In addition, we show the application of the mesoporous host material for separation of molecules according to their mobility and charge.