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X-ray-based analytics are routinely applied in many fields, including physics, chemistry, materials science, and engineering. The full potential of such techniques in the life sciences and medicine, however, has not yet been fully exploited. We highlight current and upcoming advances in this direction. We describe different X-ray-based methodologies (including those performed at synchrotron light sources and X-ray free-electron lasers) and their potentials for application to investigate the nano-bio interface. The discussion is predominantly guided by asking how such methods could better help to understand and to improve nanoparticle-based drug delivery, though the concepts also apply to nano-bio interactions in general. We discuss current limitations and how they might be overcome, particularly for future use in vivo.

CuBi2O4 has recently emerged as a promising photocathode for photo‐electrochemical (PEC) water splitting. However, its fast degradation under operation currently poses a limit to its application. Here, we report a novel method to study operando the semiconductor‐electrolyte interface during PEC operation by surface‐sensitive high‐energy X‐ray scattering. We find that a fast decrease in the generated photocurrents correlates directly with the formation of a metallic Bi phase. We further show that the slower formation of metallic Cu, as well as the dissolution of the electrode in contact with the electrolyte, further affect the CuBi2O4 activity and morphology. Our study provides a comprehensive picture of the degradation mechanisms affecting CuBi2O4 electrodes under operation and poses the methodological basis to investigate the photocorrosion processes affecting a wide range of PEC materials. [ABSTRACT FROM AUTHOR]

Photoresponsive materials feature properties that can be adjusted by light near-instantaneously, reversibly, and with high spatiotemporal precision. There is considerable interest in maximising the degree of photoswitching, and in measuring this degree during illumination in complex environments. We study the switching of photoresponsive lipid membranes that allow for precise and reversible manipulation of membrane shape, permeability, and fluidity. Though these macroscopic responses are clear, it is unclear how large the changes of trans/cis ratio are, and whether they can be improved. Here, we used small-angle X-ray scattering to measure the thickness of photoswitchable lipid membranes, and we correlate lipid bilayer thickness to trans/cis ratios. This reveals an unexpected dependency of photoswitching ratio upon aqueous phase composition. In buffer with ionic strength, we observe thickness variations twice as large as previously observed. Furthermore, soft X-rays can quantitatively isomerise photolipid membranes to the all-trans state; enabling X-ray-based membrane control. High energy X-rays do not influence the state of the photoswitches, presumably because they deposit less dose in the sample. [ABSTRACT FROM AUTHOR]

The key to fabricating complex, hierarchical materials is the control of chemical reactions at various length scales. To this end, the classical model of nucleation and growth fails to provide sufficient information. Here, we illustrate how modern X-ray spectroscopic and scattering in situ studies bridge the molecular- and macro- length scales for assemblies of polyhedrally shaped CoO nanocrystals. Utilizing high energy-resolution fluorescence-detected X-ray absorption spectroscopy, we directly access the molecular level of the nanomaterial synthesis. We reveal that initially Co(acac)3 rapidly reduces to square-planar Co(acac)2 and coordinates to two solvent molecules. Combining atomic pair distribution functions and small-angle X-ray scattering we observe that, unlike a classical nucleation and growth mechanism, nuclei as small as 2 nm assemble into superstructures of 20 nm. The individual nanoparticles and assemblies continue growing at a similar pace. The final spherical assemblies are smaller than 100 nm, while the nanoparticles reach a size of 6 nm and adopt various polyhedral, edgy shapes. Our work thus provides a comprehensive perspective on the emergence of nano-assemblies in solution. The understanding of nucleation and growth of nanostructures plays a key role in complex materials design. Here, the authors illustrate how X-ray in situ studies link transformation at the molecular- and macro- length scales during the emergence of cobalt oxide assemblies. [ABSTRACT FROM AUTHOR]

The classical nucleation theory (CNT) is the most common theoretical framework used to explain particle formation. However, nucleation is a complex process with reaction pathways which are often not covered by the CNT. Herein, we study the formation mechanism of copper nanospheres using in situ X‐ray absorption and scattering measurements. We reveal that their nucleation involves coordination polymer lamellae as pre‐nucleation structures occupying a local minimum in the reaction energy landscape. Having learned this, we achieved a superior monodispersity for Cu nanospheres of different sizes. This report exemplifies the importance of developing a more realistic picture of the mechanism involved in the formation of inorganic nanoparticles to develop a rational approach to their synthesis. [ABSTRACT FROM AUTHOR]

We developed a bioadhesive coating based on a synthetic peptide-conjugate (AK-cyclo[RGDfC]) which contains multiples of the arginyl-glycyl-aspartic acid (RGD) amino acid sequence. Biotinylated AK-cyclo[RGDfC] is bound to a supported lipid bilayer via a streptavidin interlayer. Layering, hydration and packing of the coating is quantified by X-ray and neutron reflectometry experiments. AK-cyclo[RGDfC] binds to the streptavidin interlayer in a stretched-out on edge configuration. The highly packed configuration with only 12% water content maximizes the number of accessible adhesion sites. Enhanced cell spreading of neural stem cells was observed for AK-cyclo[RGDfC] functionalized bilayers. Due to the large variety of surfaces which can be coated by physisorption of lipid bilayers, this approach is of general interest for the fabrication of biocompatible surfaces. [ABSTRACT FROM AUTHOR]

In this paper we present a concept for a microfluidic chamber optimized for x-ray reflectivity studies at solid-liquid interfaces. Experiments of this kind are usually considerably limited by strong beam attenuation due to interactions with the aqueous environment. First experiments at synchrotron sources using supported model membranes showed that the microfluidic setup yields a very effective solution for minimizing background scattering and beam absorption, which are often accompanied by radiation damage of biological samples. Additionally, the setup is also well suited for the application of fluorescence microscopy. The application of these two different techniques on the same sample offers unique possibilities for complementary studies. [ABSTRACT FROM AUTHOR]

A new method is described to prepare strongly bonded, compact monolayer films of alkyl- or arylphosphonates on the native oxide surface of Si (SiO[SUB2]/Si). This method is illustrated for octadecyl- and a-quarterthiophene-2-phosphonates. For both cases, AFM shows comprehensive coverage of the SiO[SUB2]/Si surface. The thickness of the continuous film of 4TP/SiO[SUB2]/Si was measured both by AFM and by X-ray reflectivity to be ca. 18 Å. Direct gravimetric analysis shows surface coverage by α-quarterthiophene-2-phosphonate to be about 0.66 nmol/cm[SUP2], which corresponds to molecular packing in the film close to that of crystalline α-quarterthiophene. Coverage by octadecylphosphonate was ca. 0.90 nmol/cm[SUP2], corresponding to a cross-sectional area of about 18.5 Å[SUP2]/molecule, consistent with close-packed alkyl chains. [ABSTRACT FROM AUTHOR]