Argonne National Laboratory is touting work conducted using the lab’s Hard X-ray Nanoprobe, a device that can zoom in on things smaller than the wavelengths of visible light. Using high energy X-rays, the nanoprobe can display the world on the smallest biological scale, explaining how many of the fundamental body processes function.
The nanoprobe works much like an optical microcope, but uses X-rays instead of visible light. These brilliant X-rays are tailored to the requirements of individual experiments by a series of X-ray mirrors and crystal optics in the nanoprobe beamline. In the final step, a Fresnel zone plate focuses this "conditioned" beam on the specimen.
Unlike refractive lenses used in an optical microscope, Fresnel zone plates focus X-rays using diffraction. In principle, this approach could allow scientists to one day focus X-rays to spot sizes smaller than 10 nanometers. "The smaller the spot to which we can focus our beam, the smaller the structures we can observe," Maser said.
In most of the scattering experiments performed to date, scientists have been able to determine only the intensity of the X-ray that hits the detector. However, by using more sophisticated X-ray techniques – such as coherent diffraction – scientists can extract not only the intensity of the X-rays, but also their phase. "The name of the game is’how do you determine the phase of your wavefront,’" said Argonne materials scientist George Srajer. "This allows us to fully exploit the information carried from the sample by the X-rays. Amplitude and phase information go hand-in-hand."
By taking advantage of the phase information contained in coherent X-rays, Argonne’s researchers can more accurately resolve the structure of their specimens, even without advanced X-ray optics like zone plates. Synchrotron radiation sources like the APS are built expressly to provide X-rays with proper coherence. "In the end, what we are really trying to create is an ultra-high-resolution image in real space, as we would see if we could just take a picture of the sample with a camera," Maser added. "That is possible if we can determine both the amplitude and the phase, which requires coherent X-rays."
By shining hard X-rays instead of visible light onto their small samples, Argonne’s scientists can also study biological cells and tissues. In one experiment, Argonne researchers are using the APS’ X-rays to image blood vessels as they form and branch out. This process, known as angiogenesis, occurs as one of the most important steps in the healing of wounds. However, cancerous tumors can also perform angiogenesis, which allows cancer cells to grow and spread. With the unique ability to observe angiogenesis at the subcellular level, Argonne’s scientists help to discover ways to inhibit the growth of blood vessels in cancerous tissues. "It’s almost like having Superman for a doctor – using hard X-rays to find cures for problems far more severe than just broken bones," Srajer said.
In order to do these types of biological experiments, Argonne’s scientists require a device that can detect the presence of small amounts of particular compounds in highly dilute solutions. By using the nanoprobe or other APS microprobes, researchers can study trace metal distributions in cells at ever finer spatial resolution. These high-resolution tools provide Argonne researchers with the capacity to study the cellular processes important in normal physiological function and in disease.
The different types of information revealed by X-ray optics also allow researchers at the APS to investigate material processes as they occur. These experiments, known as in situ studies, give scientists a deeper understanding of material properties than they can glean from disconnected structures. The real benefit of in situ studies comes from the ability to modify materials while they are being observed.