A Graphene-Based Microfluidic Platform for Electrocrystallization and In Situ X-ray Diffraction

Here, we describe a novel microfluidic platform for use in electrocrystallization experiments. The device incorporates ultra-thin graphene-based films as electrodes and as X-ray transparent windows to enable in situ X-ray diffraction analysis. Furthermore, large-area graphene films serve as a gas barrier, creating a stable sample environment over time. We characterize different methods for fabricating graphene electrodes, and validate the electrical capabilities of our device through the use of methyl viologen, a redox-sensitive dye. Proof-of-concept electrocrystallization experiments using an internal electric field at constant potential were performed using hen egg-white lysozyme (HEWL) as a model system. We observed faster nucleation and crystal growth, as well as a higher signal-to-noise for diffraction data obtained from crystals prepared in the presence of an applied electric field. Although this work is focused on the electrocrystallization of proteins for structural biology, we anticipate that this technology should also find utility in a broad range of both X-ray technologies and other applications of microfluidic technology

Bacteria-Resistant, Transparent, Free-standing Films Prepared from Complex Coacervates

We report the fabrication, properties, and bacteria-resistance of polyelectrolyte complex (PEC) coatings and free-standing films. Poly(4-styrenesulfonic acid), poly(diallyldimethylammonium chloride), and salt were spin-coated into PEC films. After thermal annealing in a humid environment, highly transparent, mechanically strong, and chemically robust films were formed. Notably, we demonstrate that PEC coatings significantly reduce the attachment of Escherichia coli K12 without killing the microorganisms. We suggest that forming bacteria-resistant surface coatings from commercially available polymers holds the potential for use across a wide range of applications, including high-touch surfaces in medical settings

Graphene-Based Microfluidics for Serial Crystallography

Microfluidic strategies to enable the growth and subsequent serial crystallographic analysis of micro-crystals have the potential to facilitate both structural characterization and dynamic structural studies of protein targets that have been resistant to single-crystal strategies. However, adapting microfluidic crystallization platforms for micro-crystallography requires a dramatic decrease in the overall device thickness. We report a robust strategy for the straightforward incorporation of single-layer graphene into ultra-thin microfluidic devices. This architecture allows for a total material thickness of only ∼1 μm, facilitating on-chip X-ray diffraction analysis while creating a sample environment that is stable against significant water loss over several weeks. We demonstrate excellent signal-to-noise in our X-ray diffraction measurements using a 1.5 μs polychromatic X-ray exposure, and validate our approach via on-chip structure determination using hen egg white lysozyme (HEWL) as a model system. Although this work is focused on the use of graphene for protein crystallography, we anticipate that this technology should find utility in a wide range of both X-ray and other lab on a chip applications

Microfluidic Platforms for Advanced Crystallography

X-ray crystallography has played a critical role in structural biology, allowing for the direct study of the interplay between protein structure and function. However, the fragile nature of protein crystals creates significant challenges with respect to crystal handling, including the potential for physical damage and crystal dehydration. Microfluidic and microscale technologies have the potential to facilitate protein crystallization and structure determination in a protected environment, as well as high-throughput in situ data collection, without the need to manipulate crystals after growth. Furthermore, X-ray compatible microfluidics can enable advanced structural studies that would be otherwise inaccessible if more traditional crystal mounting strategies were employed. Our goal is to establish innovative microfluidic platforms as next-generation sample delivery strategies for X-ray crystallography. We developed a novel microfluidic device architecture that takes advantage of large-area sheets of graphene to facilitate X-ray crystallographic analysis of protein crystals. The use of atomically-thin graphene films minimizes the amount of material surrounding a crystal while serving as a vapor-diffusion barrier that is stable against significant water loss over the course of weeks. This approach enables long-term incubation of protein crystallization trials and direct in situ analysis of the resulting crystals. Building on this capability, we demonstrated the potential for using this device architecture to enable the collection of high quality X-ray diffraction data under the presence of an electric field, and have applied this platform to enable new protein crystallization techniques, such as electro-crystallization. We have also used microfluidic technology to address limitations in the high-throughput workflow associated with screening of potential drug targets. We used an innovative fabrication strategy to develop photoresist-based microfluidic array devices to accelerate compound screening efforts in early-stage drug discovery We demonstrated a new compound screening workflow based on our microfluidic platform with significantly improved efficiency in both sample preparation and data collection. We validated our devices by obtaining high-resolution ligand-protein complex structures from protein crystals soaked with ligands in various conditions. This work paves way for the adoption of microfluidics as a strategy for advanced sample delivery at synchrotron X-ray sources, particularly for large-scale pharmaceutical endeavor

A Graphene-Based Microfluidic Platform for Electrocrystallization and In Situ X-ray Diffraction

Here, we describe a novel microfluidic platform for use in electrocrystallization experiments. The device incorporates ultra-thin graphene-based films as electrodes and as X-ray transparent windows to enable in situ X-ray diffraction analysis. Furthermore, large-area graphene films serve as a gas barrier, creating a stable sample environment over time. We characterize different methods for fabricating graphene electrodes, and validate the electrical capabilities of our device through the use of methyl viologen, a redox-sensitive dye. Proof-of-concept electrocrystallization experiments using an internal electric field at constant potential were performed using hen egg-white lysozyme (HEWL) as a model system. We observed faster nucleation and crystal growth, as well as a higher signal-to-noise for diffraction data obtained from crystals prepared in the presence of an applied electric field. Although this work is focused on the electrocrystallization of proteins for structural biology, we anticipate that this technology should also find utility in a broad range of both X-ray technologies and other applications of microfluidic technology

Channel and Spatial Attention Regression Network for Cup-to-Disc Ratio Estimation

Cup-to-disc ratio (CDR) is of great importance during assessing structural changes at the optic nerve head (ONH) and diagnosis of glaucoma. While most efforts have been put on acquiring the CDR number through CNN-based segmentation algorithms followed by the calculation of CDR, these methods usually only focus on the features in the convolution kernel, which is, after all, the operation of the local region, ignoring the contribution of rich global features (such as distant pixels) to the current features. In this paper, a new end-to-end channel and spatial attention regression deep learning network is proposed to deduces CDR number from the regression perspective and combine the self-attention mechanism with the regression network. Our network consists of four modules: the feature extraction module to extract deep features expressing the complicated pattern of optic disc (OD) and optic cup (OC), the attention module including the channel attention block (CAB) and the spatial attention block (SAB) to improve feature representation by aggregating long-range contextual information, the regression module to deduce CDR number directly, and the segmentation-auxiliary module to focus the model’s attention on the relevant features instead of the background region. Especially, the CAB selects relatively important feature maps in channel dimension, shifting the emphasis on the OD and OC region; meanwhile, the SAB learns the discriminative ability of feature representation at pixel level by capturing the relationship of intra-feature map. The experimental results of ORIGA dataset show that our method obtains absolute CDR error of 0.067 and the Pearson’s correlation coefficient of 0.694 in estimating CDR and our method has a great potential in predicting the CDR number

Knowledge domain and emerging trends in Alzheimer’s disease: a scientometric review based on CiteSpace analysis

Alzheimer’s disease is the most common cause of dementia. It is an increasingly serious global health problem and has a significant impact on individuals and society. However, the precise cause of Alzheimer’s disease is still unknown. In this study, 11,748 Web-of-Science-indexed manuscripts regarding Alzheimer’s disease, all published from 2015 to 2019, and their 693,938 references were analyzed. A document co-citation network map was drawn using CiteSpace software. Research frontiers and development trends were determined by retrieving subject headings with apparent changing word frequency trends, which can be used to forecast future research developments in Alzheimer’s disease

EFFECTS OF COMPOSITION OF FLY ASH-BASED ALKALI-ACTIVATED MATERIALS ON COMPRESSIVE STRENGTH: A REVIEW

A fly ash-based alkali-activated material (FAAM) is an important member of the alkali-activated geopolymeric family. The compressive strength is one of most important mechanical properties for FAAMs in its use as a construction material. The effects of the components of the precursors from fly ash, an alkali-activator, or additives on the compressive strengths of FAAMs have been reviewed. The SiO₂/Al₂O₃, Al₂O₃/Na₂O, and water/solid (W/S) ratios are crucial in developing the compressive strengths of FAAMs. The strength map, as a function of the change in the SiO₂/Al₂O₃ and SiO₂/Na₂O ratios has been established. There is a critical value of the SiO₂/Al₂O₃ ratio at about 4.20 to 4.30, in which the increase or decrease of the compressive strengths at a constant SiO₂/Al₂O₃ ratio with various Al₂O₃/Na2O ratios is found. The active CaO resource, originating from a ground blast-furnace slag (GBFS), ordinary Portland cement (OPC), or chemical agents, such as Ca(OH)₂ or CaO, is of benefit to the improvement in the strength of FAAMs: however, to avoid the dominant formation of C-A-S-H, N-C-A-S-H, and C-S-H gels instead of N-A-S-H and A-S-H gels, an optimal addition of 7.5% to 10% OPC and a 15% to 20% GBFS replacement is recommended by considering the setting time, workability, and strength development. The effects of Fe₂O₃ in the fly ash and the silica on the compressive strengths of the FAAMs are also generalised