Atto-Newton X-Ray Radiation Pressure Force on Gold Nanocrystal in Aqueous Solution

Abstract

In micro-sized force field, radiation pressure forces acting on an object surface have been widely applied as a tool for laser trapping and cooling of the visible light. In the region of short-wavelength, we confirmed the existence of atto-Newton (aN) level's radiation pressure force measured by using Diffracted X-ray Tracking (DXT) which is tracing the X-ray diffraction spots from the gold nanocrystal was labeled on the protein molecule at single molecular level [1].In this study, we succeeded in measuring the modified dynamic rotational Brownian behaviors of the gold nanocrystal in an aqueous solution at micro-sec. levels by varying the wavelength and flux of the incident X-ray probe. As a result, we observed a clear energy-dependent radiation pressure in the X-ray axial direction (2 theta) by comparing with a concentric circle direction (chi: no-pressure direction). And the observed pressures were able to be estimated from the X-ray wavelengths and flux. Furthermore, we found the presence of the resultant forces of X-ray radiation pressure on several diffracted crystal planes from analyzing the angular distributions of accelerated motions. This phenomenon expects to open a new application of X-ray science.For example, we can utilize this X-ray resultant force for the trapping of nano-probe and the crystal growth azimuth control during crystal growths. In addition, we proved that the ultra-fast DXT using protein molecules labeled the gold nanocrystal [2] can detect aN level's force field in functional protein molecules. In the future, we can detect dynamic structural changes of functional surface induced by an ultra-small force field that cannot be detected by STM and AFM.[1] Y. C. Sasaki et al., Appl. Phys. Lett., 89, 053121(2006).[2] H. Shimizu et al., Cell, 132, 67–78 (2008).