Three-Dimensional Dynamical Observations of Nanocolloid in Water using Diffracted Electron Tracking

Abstract

Diffracted X-Ray tracking (DXT) method has been developed for obtaining dynamical information at single protein molecule level (1). The motion of an individual single gold nanocrystal can be observed by this method, which is linked to specific site in the molecule, using a time resolved Laue diffraction technique. This method needs a very strong X-ray source, so we continue to develop a compact instrument with use of the electron beam instead of the X-ray. The Electron Back-Scattered Diffraction (EBSD) is adopted to monitor the Three-dimensional (3D) crystal orientation of the gold nanocrystal. We call this the Diffracted Electron Tracking (DET). For this purpose, we have developed the wet cell using the very thin carbon sealing film for maintained atmospheric pressure from high vacuum surroundings of a scanning electron microscope (SEM), and confirmed that the EBSD pattern (EBSP) can be obtained from the gold nanocrystals through the carbon sealing film of the wet cell. When the gold nanocrystal moved by the motion of labeled molecules, the change of the EBSP is observed. Using DET, we measured the motion of gold nanocrystal that labeled on silane-coupling-agent under different conditions; in water, in argon gas or vacuum environments. From results, the motions of gold nanocrystals in water environment were over one hundred times as large as in argon gas environment. And in vacuum environment, few motions were observed. We will discuss the difference between DXT and DET at observed gold nanocrystal motions in water environment. Recently, we confirmed EBSD can obtain from 40nm diameter of commercial colloidal gold. This finding may contribute to develop as a very general single molecular technology.1. Global twisting motion of single molecular KcsA potassium channel upon gating.H. Shimizu et al. Cell. 2008 Jan 11;132(1):67-78.