Observations of X-Ray Radiation Pressure Force Using High-Speed Diffracted X-Ray Tracking

Abstract

In single molecular science and technology, it is very important to control dynamical Brownian motions of individual functional protein molecules. Optical trap and tweezer using visible light is the first demonstration of controlling micron-sized particles or molecules. In order to improve both monitoring and controlling internal molecular motions from single molecular units with more super-precisions under in vitro or in vivo physiological conditions, we have proposed new single molecular techniques using shorten wavelength, for example, X-rays, electrons, and neutron. Recently, we observed directed Brownian motions of individual single gold nanocrystals using high-speed Diffracted X-ray Tracking (DXT). We confirmed that this motion is dependent upon X-ray Intensity and the sized of observed gold nanocrystal. The observed force is estimated at atto-Newton level. In my previous research, we utilized the adsorbed protein molecules, and the gold nanocrystals are linked to the adsorbed ones. Because we can not observe free Brownian motions of the individual gold nanocrystals in aqueous solutions using normal speed DXT. In this new experiment of high-speed DXT, a diffraction spot in high-speed DXT was monitored with an X-ray image intensifier (Hamamatsu Photonics, V5445P) and a CMOS CCD camera (FASTCAM SA1.1, Photron) with 128 x 112 pixels. Additionally we utilized high-speed X-ray shutters. The averaged exposure time in single shot was 5μsec.-20μsec. In these experiments, we controlled the size of gold nanocrystals and the energy of quasi-white x-rays. In the future, we will be able to control and measure dynamics of micro- or nano-crystalline materials or labeled single molecular units using x-ray radiation pressure force.