Mapping DNA and protein in biological samples using the scanning transmission x-ray microscope

Abstract

The Scanning Transmission soft X-ray Microscope (STXM) at the XIA beamline at the National Synchrotron Light Source, Brookhaven National Laboratory, has achieved 50 nm Rayleigh resolution and has been used to image wet biological samples using the natural absorption differences between carbon and water in the water window (between carbon and oxygen K-absorption edges). The step-like jumps in the absorption of soft x-rays by materials as a function of energy have been used for elemental mapping. Examination of these absorption "edges" with high energy resolution resolves fine absorption structures. These fine structures are strongly affected by the atom's local environment, such that they carry detailed information about the atom's chemical state. We have used this chemical sensitivity to distinguish between materials which have similar elemental composition but are chemically different. Images with 50 nm resolution and spectra from a spot size less than (0.2 (μm)2 can be acquired routinely.Figure 1 shows the x-ray absorption fine structure spectra at the carbon absorption edge from DNA and bovine serum albumin (BSA, a typical protein) taken using the STXM.