Serial small- and wide-angle X-ray scattering with laboratory sources.

Recent advances in X-ray instrumentation and sample injection systems have enabled serial crystallography of protein nanocrystals and the rapid structural analysis of dynamic processes. However, this progress has been restricted to large-scale X-ray free-electron laser (XFEL) and synchrotron facilities, which are often oversubscribed and have long waiting times. Here, we explore the potential of state-of-the-art laboratory X-ray systems to perform comparable analyses when coupled to micro- and millifluidic sample environments. Our results demonstrate that commercial small- and wide-angle X-ray scattering (SAXS/WAXS) instruments and X-ray diffractometers are ready to access samples and timescales (≳5 ms) relevant to many processes in materials science including the preparation of pharmaceuticals, nanoparticles and functional crystalline materials. Tests of different X-ray instruments highlighted the importance of the optical configuration and revealed that serial WAXS/XRD analysis of the investigated samples was only possible with the higher flux of a microfocus setup. We expect that these results will also stimulate similar developments for structural biology.

Millimeter-scale topography facilitates coral larval settlement in wave-driven oscillatory flow.

Larval settlement in wave-dominated, nearshore environments is the most critical life stage for a vast array of marine invertebrates, yet it is poorly understood and virtually impossible to observe in situ. Using a custom-built flume tank that mimics the oscillatory fluid flow over a shallow coral reef, we isolated the effect of millimeter-scale benthic topography and showed that it increases the settlement of slow-swimming coral larvae by an order of magnitude relative to flat substrates. Particle tracking velocimetry of flow fields revealed that millimeter-scale ridges introduced regions of flow recirculation that redirected larvae toward the substrate surface and decreased the local fluid speed, effectively increasing the window of time for larvae to settle. Regions of recirculation were quantified using the Q-criterion method of vortex identification and correlated with the settlement locations of larvae for the first time. In agreement with experiments, computational fluid dynamics modeling and agent-based larval simulations also showed significantly higher settlement onto ridged substrates. Additionally, in contrast to previous reports on the effect of micro-scale substrate topography, we found that these topographies did not produce key hydrodynamic features linked to increased settlement. These findings highlight how physics-based substrate design can create new opportunities to increase larval recruitment for ecosystem restoration.

Characterising a PDMS based 3D cell culturing microfluidic platform for screening chemotherapeutic drug cytotoxic activity.

Three-dimensional (3D) spheroidal cell cultures are now recognised as better models of cancers as compared to traditional cell cultures. However, established 3D cell culturing protocols and techniques are time-consuming, manually laborious and often expensive due to the excessive consumption of reagents. Microfluidics allows for traditional laboratory-based biological experiments to be scaled down into miniature custom fabricated devices, where cost-effective experiments can be performed through the manipulation and flow of small volumes of fluid. In this study, we characterise a 3D cell culturing microfluidic device fabricated from a 3D printed master. HT29 cells were seeded into the device and 3D spheroids were generated and cultured through the perfusion of cell media. Spheroids were treated with 5-Fluorouracil for five days through continuous perfusion and cell viability was analysed on-chip at different time points using fluorescence microscopy and Lactate dehydrogenase (LDH) assay on the supernatant. Increasing cell death was observed in the HT29 spheroids over the five-day period. The 3D cell culturing microfluidic device described in this study, permits on-chip anti-cancer treatment and viability analysis, and forms the basis of an effective platform for the high-throughput screening of anti-cancer drugs in 3D tumour spheroids.

Ptychographic X-ray tomography reveals additive zoning in nanocomposite single crystals.

Single crystals containing nanoparticles represent a unique class of nanocomposites whose properties are defined by both their compositions and the structural organization of the dispersed phase in the crystalline host. Yet, there is still a poor understanding of the relationship between the synthesis conditions and the structures of these materials. Here ptychographic X-ray computed tomography is used to visualize the three-dimensional structures of two nanocomposite crystals - single crystals of calcite occluding diblock copolymer worms and vesicles. This provides unique information about the distribution of the copolymer nano-objects within entire, micron-sized crystals with nanometer spatial resolution and reveals how occlusion is governed by factors including the supersaturation and calcium concentration. Both nanocomposite crystals are seen to exhibit zoning effects that are governed by the solution composition and interactions of the additives with specific steps on the crystal surface. Additionally, the size and shape of the occluded vesicles varies according to their location within the crystal, and therefore the solution composition at the time of occlusion. This work contributes to our understanding of the factors that govern nanoparticle occlusion within crystalline materials, where this will ultimately inform the design of next generation nanocomposite materials with specific structure/property relationships.

Evaluation of microflow configurations for scale inhibition and serial X-ray diffraction analysis of crystallization processes.

The clean and reproducible conditions provided by microfluidic devices are ideal sample environments for in situ analyses of chemical and biochemical reactions and assembly processes. However, the small size of microchannels makes investigating the crystallization of poorly soluble materials on-chip challenging due to crystal nucleation and growth that result in channel fouling and blockage. Here, we demonstrate a reusable insert-based microfluidic platform for serial X-ray diffraction analysis and examine scale formation in response to continuous and segmented flow configurations across a range of temperatures. Under continuous flow, scale formation on the reactor walls begins almost immediately on mixing of the crystallizing species, which over time results in occlusion of the channel. Depletion of ions at the start of the channel results in reduced crystallization towards the end of the channel. Conversely, segmented flow can control crystallization, so it occurs entirely within the droplet. Consequently, the spatial location within the channel represents a temporal point in the crystallization process. Whilst each method can provide useful crystallographic information, time-resolved information is lost when reactor fouling occurs and changes the solution conditions with time. The flow within a single device can be manipulated to give a broad range of information addressing surface interaction or solution crystallization.

Dynamic Crystallization Pathways of Polymorphic Pharmaceuticals Revealed in Segmented Flow with Inline Powder X-ray Diffraction.

Understanding the transitions between polymorphs is essential in the development of strategies for manufacturing and maximizing the efficiency of pharmaceuticals. However, this can be extremely challenging: crystallization can be influenced by subtle changes in environment, such as temperature and mixing intensity or even imperfections in the crystallizer walls. Here, we highlight the importance of in situ measurements in understanding crystallization mechanisms, where a segmented flow crystallizer was used to study the crystallization of the pharmaceuticals urea: barbituric acid (UBA) and carbamazepine (CBZ). The reactor provides highly reproducible reaction conditions, while in situ synchrotron powder X-ray diffraction (PXRD) enables us to monitor the evolution of this system. UBA has two polymorphs of almost equivalent free-energy and so is typically obtained as a polymorphic mixture. In situ PXRD analysis uncovered a progression of polymorphs from UBA III to the thermodynamic polymorph UBA I, where different positions along the length of the tubular flow crystallizer correspond to different reaction times. Addition of UBA I seed crystals modified this pathway such that only UBA I was observed throughout, while transformation from UBA III into UBA I still occurred in the presence of UBA III seeds. Information regarding the mixing-dependent kinetics of the CBZ form II to III transformation was also uncovered in a series of seeded and unseeded flow crystallization runs, despite atypical habit expression. These results illustrate the importance of coupling controlled reaction environments with in situ XRD to study the phase relationships in polymorphic materials.

Controlling the fluorescence and room-temperature phosphorescence behaviour of carbon nanodots with inorganic crystalline nanocomposites.

There is a significant drive to identify alternative materials that exhibit room temperature phosphorescence for technologies including bio-imaging, photodynamic therapy and organic light-emitting diodes. Ideally, these materials should be non-toxic and cheap, and it will be possible to control their photoluminescent properties. This was achieved here by embedding carbon nanodots within crystalline particles of alkaline earth carbonates, sulphates and oxalates. The resultant nanocomposites are luminescent and exhibit a bright, sub-second lifetime afterglow. Importantly, the excited state lifetimes, and steady-state and afterglow colours can all be systematically controlled by varying the cations and anions in the host inorganic phase, due to the influence of the cation size and material density on emissive and non-emissive electronic transitions. This simple strategy provides a flexible route for generating materials with specific, phosphorescent properties and is an exciting alternative to approaches relying on the synthesis of custom-made luminescent organic molecules.

Rapid Mapping of Protein Interactions Using Tag-Transfer Photocrosslinkers.

Analysing protein complexes by chemical crosslinking-mass spectrometry (XL-MS) is limited by the side-chain reactivities and sizes of available crosslinkers, their slow reaction rates, and difficulties in crosslink enrichment, especially for rare, transient or dynamic complexes. Here we describe two new XL reagents that incorporate a methanethiosulfonate (MTS) group to label a reactive cysteine introduced into the bait protein, and a residue-unbiased diazirine-based photoactivatable XL group to trap its interacting partner(s). Reductive removal of the bait transfers a thiol-containing fragment of the crosslinking reagent onto the target that can be alkylated and located by MS sequencing and exploited for enrichment, enabling the detection of low abundance crosslinks. Using these reagents and a bespoke UV LED irradiation platform, we show that maximum crosslinking yield is achieved within 10 seconds. The utility of this "tag and transfer" approach is demonstrated using a well-defined peptide/protein regulatory interaction (BID80-102 /MCL-1), and the dynamic interaction interface of a chaperone/substrate complex (Skp/OmpA).

The Effect of Additives on the Early Stages of Growth of Calcite Single Crystals.

As crystallization processes are often rapid, it can be difficult to monitor their growth mechanisms. In this study, we made use of the fact that crystallization proceeds more slowly in small volumes than in bulk solution to investigate the effects of the soluble additives Mg2+ and poly(styrene sulfonate) (PSS) on the early stages of growth of calcite crystals. Using a "Crystal Hotel" microfluidic device to provide well-defined, nanoliter volumes, we observed that calcite crystals form via an amorphous precursor phase. Surprisingly, the first calcite crystals formed are perfect rhombohedra, and the soluble additives have no influence on the morphology until the crystals reach sizes of 0.1-0.5 µm for Mg2+ and 1-2 µm for PSS. The crystals then continue to grow to develop morphologies characteristic of these additives. These results can be rationalized by considering additive binding to kink sites, which is consistent with crystal growth by a classical mechanism.

3D visualization of additive occlusion and tunable full-spectrum fluorescence in calcite.

From biomineralization to synthesis, organic additives provide an effective means of controlling crystallization processes. There is growing evidence that these additives are often occluded within the crystal lattice. This promises an elegant means of creating nanocomposites and tuning physical properties. Here we use the incorporation of sulfonated fluorescent dyes to gain new understanding of additive occlusion in calcite (CaCO3), and to link morphological changes to occlusion mechanisms. We demonstrate that these additives are incorporated within specific zones, as defined by the growth conditions, and show how occlusion can govern changes in crystal shape. Fluorescence spectroscopy and lifetime imaging microscopy also show that the dyes experience unique local environments within different zones. Our strategy is then extended to simultaneously incorporate mixtures of dyes, whose fluorescence cascade creates calcite nanoparticles that fluoresce white. This offers a simple strategy for generating biocompatible and stable fluorescent nanoparticles whose output can be tuned as required.