Solution-based Methods Research Articles

Hydrogel-Based Stamping Technology for Solution-Free Blood Cell Staining.

An accurate microscopical analysis of blood smears requires a reproducible and convenient method of staining. Solution-based staining procedures can be cumbersome. Especially in low- and middle-income countries, the lack of skilled technicians and adequate laboratory facilities, as well as insufficient water and reagent quality, often become confounding factors. To overcome these obstacles, we developed a new cell staining method based on sequential stamping of agarose gel patches that contain eosin, methylene blue/oxidized methylene blue, Azure B, and buffer, respectively. Our method, termed "hydrogel staining", provides a simple, reproducible, solution-free, and inexpensive approach to stain blood cells. We have optimized incubation times to achieve the optimal transfer of dyes to fixed blood cells on a glass slide, with outcomes comparable to conventional solution-based methods for white blood cells and malaria-infected red blood cells. This hydrogel staining method does not require special skills to produce excellent quality stained blood film slides. The new method could enhance the accuracy of microscopical examination of blood smears, especially in resource-limited settings.

Variable angle spectroscopic ellipsometry characterization of spin-coated MoS2 films

Amongst emerging Transition Metal Dichalcogenides (TMDCs), molybdenum disulfide (MoS2) has attracted a remarkable interest thanks to many possible applications. In particular, MoS2 has potentialities not yet fully realized in solution-based applications. However, the lack of knowledge of the optical properties of MoS2 has significantly limited its use in many exciting photonic fields. Films prepared by solution-based exfoliation methods have never been studied to our best knowledge.The optical properties of MoS2 films prepared by solution-based exfoliation methods have never been studied to our best knowledge.Herein, the broadband optical properties of ~20 nm-thick MoS2 films deposited by spin-coating onto Si/SiO2 substrates were studied by means of micro-Raman spectroscopy and Variable Angle Spectroscopic Ellipsometry (VASE).

Ultrasonic Transducer From Piezoelectric Polymer Multilayer Through Electrophoretic Deposition for Photoacoustic Imaging.

Emerging ultrasound imaging modality based on optical-generated acoustic waves, such as photoacoustic (PA) imaging, has enabled novel functional imaging on biological samples. The performance of the ultrasonic transducer plays a critical role in producing higher quality PA images. However, the high electrical impedance of the small piezoelectric elements in the transducer array causes an electrical mismatch with external circuitry and results in degraded sensitivity. One effective method for reducing the electrical impedance is to implement a piezoelectric multilayer configuration instead of the conventional single layer for the transducer. In this work, we introduced an ultrasonic transducer comprising a piezoelectric polymer multilayer structure produced by an innovative multicycle powder-based electrophoretic deposition, using a suspension of polymer nanoparticles. The multicycle electrophoretic deposition overcomes the redissolution issue in solution-based methods. The ultrasonic transducer comprising the piezoelectric polymer multilayer exhibits significantly enhanced receiving sensitivity as compared to the ultrasonic transducer using a single layer. Ultrasonic transducer with multielement array configuration is obtained using the piezoelectric polymer multilayer, and PA imaging with improved resolution is demonstrated. Theoretical analysis shows that the enhanced transducer performance is mainly attributed to the improved electrical impedance match between the piezoelectric polymer element in the transducer and external receiving circuit.

A Versatile Surface Modification Method via Vapor-phase Deposited Functional Polymer Films for Biomedical Device Applications.

For last two decades, the demand for precisely engineered three-dimensional structures has increased continuously for the developments of biomaterials. With the recent advances in micro- and nano-fabrication techniques, various devices with complex surface geometries have been devised and produced in the pharmaceutical and medical fields for various biomedical applications including drug delivery and biosensors. These advanced biomaterials have been designed to mimic the natural environments of tissues more closely and to enhance the performance for their corresponding biomedical applications. One of the important aspects in the rational design of biomaterials is how to configure the surface of the biomedical devices for better control of the chemical and physical properties of the bioactive surfaces without compromising their bulk characteristics. In this viewpoint, it of critical importance to secure a versatile method to modify the surface of various biomedical devices. Recently, a vapor phase method, termed initiated chemical vapor deposition (iCVD) has emerged as damage-free method highly beneficial for the conformal deposition of various functional polymer films onto many kinds of micro- and nano-structured surfaces without restrictions on the substrate material or geometry, which is not trivial to achieve by conventional solution-based surface functionalization methods. With proper structural design, the functional polymer thin film via iCVD can impart required functionality to the biomaterial surfaces while maintaining the fine structure thereon. We believe the iCVD technique can be not only a valuable approach towards fundamental cell-material studies, but also of great importance as a platform technology to extend to other prospective biomaterial designs and material interface modifications for biomedical applications.

Rapid Fabrication by Lyotropic Self-Assembly of Thin Nanofiltration Membranes with Uniform 1 Nanometer Pores.

Nanostructured materials with precisely defined and water-bicontinuous 1-nm-scale pores are highly sought after as advanced materials for next-generation nanofiltration membranes. While several self-assembled systems appear to satisfy this need, straightforward fabrication of such materials as submicron films with high-fidelity retention of their ordered nanostructure represents a nontrivial challenge. We report the development of a lyotropic liquid crystal mesophase that addresses the aforementioned issue. Films as thin as ∼200 nm are prepared on conventional support membranes using solution-based methods. Within these films, the system is composed of a hexagonally ordered array of ∼3 nm diameter cylinders of cross-linked polymer, embedded in an aqueous medium. The cylinders are uniformly oriented in the plane of the film, providing a transport-limiting dimension of ∼1 nm, associated with the space between the outer surfaces of nearest-neighbor cylinders. These membranes exhibit molecular weight cutoffs of ∼300 Da for organic solutes and are effective in rejecting dissolved salts, and in particular, divalent species, while exhibiting water permeabilities that rival or exceed current state-of-the-art commercial nanofiltration membranes. These materials have the ability to address a broad range of nanofiltration applications, while structure-property considerations suggest several avenues for potential performance improvements.

Rapid Denaturing Organic Digestion Method for Targeted Protein Identification and Characterization.

Bottom-up mass spectrometry-based protein analysis methods employing protease digestion are routinely used to identify and characterize proteins with high specificity and sensitivity. Method performance is generally measured by sequence coverage capability and the total number of characteristic peptides identified, when compared to predicted databases. Limitations to commonly used solvent-based digestion methods currently employed include long digestion times (18-24 h or more), leading to protease autolysis, which also precludes automation, decreases sensitivity, and increases both intra- and inter-day performance variability. This report describes the development and validation of a simple, 5 min tryptic denaturing organic digestion (DOD) method for use with tandem mass spectrometry in bottom-up protein identification and characterization. It has been evaluated across select protein toxins and diagnostic clinical protein targets, substantially improving digestion performance when compared to other solution-based and enzyme-immobilized methods. The method was compared to two currently used bottom-up methods, the 24 h filter-aided sample prep (FASP) and Flash Digest (1 and 4 h) methods. Single proteins used to compare the methods included the ricin light chain, ricin heavy chain, ricin holotoxin, serotype A Clostridium botulinum toxin, Staphylococcus enterotoxin B, ribonuclease A, and thyroglobulin. In tests, across the proteins investigated, the 5 min DOD digestion method resulted in sequence coverages ranging from 55 to 100%, with relatively high reproducibility and precision; results were better than or equal to FASP method results and were greatly enhanced when compared to Flash method results. Importantly, DOD method intra- and inter-day precision was much improved as compared to results for both FASP and Flash digestions. These data indicated that the DOD method, when compared to the FASP and Flash Digest methods, dramatically reduced digestion time, while maintaining or improving the ability to detect and characterize targeted proteins, and reduced analytical variability for tryptic digestion, resulting in markedly faster and more precise analyses.

Vapor Sublimation and Deposition to Fabricate a Porous Methyl Propiolate-Functionalized Poly-p-xylylene Material for Copper-Free Click Chemistry.

Conventional porous materials are mostly synthesized in solution-based methods involving solvents and initiators, and the functionalization of these porous materials usually requires additional and complex steps. In the current study, a methyl propiolate-functionalized porous poly-p-xylylene material was fabricated based on a unique vapor sublimation and deposition process. The process used a water solution and ice as the template with a customizable shape and dimensions, and the conventional chemical vapor deposition (CVD) polymerization of poly-p-xylylene on such an ice template formed a three-dimensional, porous poly-p-xylylene material with interconnected porous structures. More importantly, the functionality of methyl propiolate was well preserved by using methyl propiolate-substituted [2,2]-paracyclophane during the vapor deposition polymerization process and was installed in one step on the final porous poly-p-xylylene products. This functionality exhibited an intact structure and reactivity during the proposed vapor sublimation and deposition process and was proven to have no decomposition or side products after further characterization and conjugation experiments. The electron-withdrawing methyl propiolate group readily provided efficient alkynes as click azide-terminated molecules under copper-free and mild conditions at room temperature and in environmentally friendly solvents, such as water. The resulting methyl propiolate-functionalized porous poly-p-xylylene exhibited interface properties with clickable specific covalent attachment toward azide-terminated target molecules, which are widely available for drugs and biomolecules. The fabricated functional porous materials represent an advanced material featuring porous structures, a straightforward synthetic approach, and precise and controlled interface click chemistry, rendering long-term stability and efficacy to conjugate target functionalities that are expected to attract a variety of new applications.

Solution-processed pseudo-vertical organic transistors based on TIPS-pentacene

Powerful and versatile transistors are indispensable to realize the vision of future flexible electronics, e.g., for wearable active-matrix displays, smart sensors, or radio-frequency identification tags. Organic thin-film transistors are considered to be a perfect match for flexible electronics. However, conventional organic thin-film transistors still do not match the demanding performance targets of many applications. Furthermore, often complex and expensive fabrication steps are employed for the fabrication of hero-devices, which is not compatible with the paradigm of low-cost production of flexible electronics.In this contribution, we present the first solution-processed vertical organic field-effect transistor (VOFET) with good on-state performance comparable to vacuum-processed VOFETs. This approach unites the advantages of a low-temperature, low-cost solution processing with an ultra-short channel transistor concept possibly enabling large-area, low-cost flexible electronics. We examine the influence of different crystal morphologies (spherulitic and ribbons) on the transistor performance by using spin- and shear-coating as solution-based deposition methods. The solution-processed VOFETs reach channel width-normalized transconductances of up to 0.26 μS/μm with a charge carrier mobility of 4.8 cm2/V. S-parameter measurements finally verify that transition frequencies up to 6 MHz are reachable with shear-coated TIPS-pentacene. However, compared to small molecule-based VOFETs, the solution-processed VOFETs show an unfavorably high off-state current and hysteresis, which are explained by background doping and charge carrier trapping. Hence, in order to advance with, further optimization of the semiconductor material and the insulator–semiconductor interface is thus required to qualify solution-processed VOFETs for commercial applications.

Anisotropic optical behavior of an amorphous organic polymer locally aligned by inkjet-printing

The molecular arrangement of polymeric organic semiconductors alter the macroscopic optoelectronic properties of the material. Most existing solution-based deposition methods are however, limited in both resolution as well as pattern design and often result in molecular disorder upon drying. Here, a method for aligning the amorphous polymer polyindenofluoren-8-triarylamine (PIF8-TAA) via inkjet printing is presented. By tuning the printing speed and including different amounts of the solid solvent crystallization agent 1,3,5-trichlorobenzene (TCB), fibrous structures with varying morphology can be fabricated. The resulting optical properties are analyzed using photoluminescence and Raman spectroscopy. The findings show an optical anisotropic behavior dependent on the fiber size and alignment. This is likely caused by the increased molecular arrangement within the structures. Methods enabling tailored structuring of the molecular arrangement in a material, provide the possibility to develop novel applications, as well as to optimize existing devices with improved properties such as, charge carrier transport and emission efficiency.

GPVI (Glycoprotein VI) Interaction With Fibrinogen Is Mediated by Avidity and the Fibrinogen αC-Region.

GPVI (glycoprotein VI) is a key molecular player in collagen-induced platelet signaling and aggregation. Recent evidence indicates that it also plays important role in platelet aggregation and thrombus growth through interaction with fibrin(ogen). However, there are discrepancies in the literature regarding whether the monomeric or dimeric form of GPVI binds to fibrinogen at high affinity. The mechanisms of interaction are also not clear, including which region of fibrinogen is responsible for GPVI binding. We aimed to gain further understanding of the mechanisms of interaction at molecular level and to identify the regions on fibrinogen important for GPVI binding. Approach and Results: Using multiple surface- and solution-based protein-protein interaction methods, we observe that dimeric GPVI binds to fibrinogen with much higher affinity and has a slower dissociation rate constant than the monomer due to avidity effects. Moreover, our data show that the highest affinity interaction of GPVI is with the αC-region of fibrinogen. We further show that GPVI interacts with immobilized fibrinogen and fibrin variants at a similar level, including a nonpolymerizing fibrin variant, suggesting that GPVI binding is independent of fibrin polymerization. Based on the above findings, we conclude that the higher affinity of dimeric GPVI over the monomer for fibrinogen interaction is achieved by avidity. The αC-region of fibrinogen appears essential for GPVI binding. We propose that fibrin polymerization into fibers during coagulation will cluster GPVI through its αC-region, leading to downstream signaling, further activation of platelets, and potentially stimulating clot growth. Graphic Abstract: A graphic abstract is available for this article.

Solution-Based Synthesis of Sulvanite Cu3TaS4 and Cu3TaSe4 Nanocrystals

Sulvanites have the parent formula Cu3MCh4. The metal M belongs to group 5 and Ch is a chalcogen. The tantalum sulvanites Cu3TaS4 and Cu3TaSe4 are predicted to have wide band gaps and p-type conductivity and show promise in optoelectronic applications. Their potential as p-type transparent conductors or efficient photocatalysts for visible-light water splitting is a valuable incentive to explore these materials in their nanoscale form, toward bottom-up processing opportunities. Reported herein are the first syntheses of nanosized Cu3TaS4 and Cu3TaSe4 sulvanites, which preserve the parent cubic crystal structure but show that morphology at the nanoscale is dependent of the reaction conditions. The two solution-based methods for synthesizing the tantalum S and Se sulvanites result in Cu3TaS4 or Cu3TaSe4 nanocrystals (NCs) with prismatic morphology, or, in the case of Cu3TaSe4, could lead to core-shell spherical nanostructures. The Cu3TaS4 NCs and Cu3TaSe4 NCs have good absorption in the UV-Vis region, while the Cu3TaSe4 core-shell NCs possess broad absorption bands not only in the UV-Vis but also in the near-infrared region. Photoluminescence measurements of Cu3TaS4 and Cu3TaSe4 reveal optical bandgaps of 2.54 and 2.32 eV, respectively, consistent with the values measured in bulk. Additionally, the current–voltage (I-V) curve of Cu3TaS4 NCs proves its electrical conductivity.

Precursor chemistry of metal nitride nanocrystals.

Metal nitride nanocrystals are a versatile class of nanomaterials. Depending on their chemical composition, the optical properties vary from those of traditional semiconductor nanocrystals (called quantum dots) to more metallic character (featuring a plasmon resonance). However, the synthesis of colloidal metal nitride nanocrystals is challenging since the underlying precursor chemistry is much less developed compared to the chemistry of metal, metal chalcogenide or metal phosphide nanocrystals. Here, we review chemical approaches that lead (or could lead) to the formation of colloidally stable metal nitride nanocrystals. By systematically comparing different synthetic approaches, we uncover trends and gain insight into the chemistry of these challenging materials. We also discuss and critically evaluate the plausibility of certain suggested mechanisms. This review is meant as a guide for the further development of colloidal nitride nanocrystals.

Hydrogen bond synthons affect the coordination geometry of d10-metal halide complexes: synthetic methods, theoretical studies, and supramolecular architectures

The tendency of the pyrazine nitrogen atom to form hydrogen bond supramolecular synthons affects the coordination geometry of new d10-metal halide complexes which have been prepared by solution-based methods in comparison with solid-state reactions.

Large-area synthesis of transition metal dichalcogenides via CVD and solution-based approaches and their device applications.

For the last decade, two-dimensional transition metal dichalcogenides (TMDCs) have attracted considerable attention due to their unique physical and chemical properties. Novel devices based on these materials are commonly fabricated using the exfoliated samples, which lacks control of the thickness and cannot be scaled. Therefore, the synthesis of large-area TMDC thin films with a high uniformity to advance the field is required. This article reviews the latest advances in the synthesis of wafer-scale thin films using chemical vapor deposition methods. The key factors that determine the electrical performance of TMDCs are introduced, including the interfacial properties and defects. The latest solution-based techniques which suggest the opportunity to obtain large-area TMDC thin films with a low-cost process and the potential applications in electronics and optoelectronics are also discussed. The outlook for future research directions, challenges, and possible development of 2D materials are further discussed.

Type-II Heterojunctions in SnO2-Coated TiO2 Core-Shell Nanoparticles

Titanium dioxide (TiO2) and tin oxide (SnO2) are two popular wide band-gap semiconductors for photocatalytic and electronic applications such as solar cells, optoelectronic devices, and lithium-ion batteries. Nanosized TiO2 structures have strong absorption in the UV region while SnO2 is a powerful transparent conducting oxide. Composites of TiO2 and SnO2 are especially attractive since they form a type-II heterojunction extending the lifetime of charge carriers and enhancing photoconversion efficiency. In this study, the synthesis of TiO2 nanoparticles as well as their uniform and controlled coating with SnO2 shells are described, providing the first utilization of sodium stannate to grow SnO2 shells on a metal-oxide core. The step-growth method utilized here shows the ability to vary the shell thickness between 5-40 nm while maintaining uniformity of the shell. As such, the complete synthesis route involves facile and reproducible surfactant-free solution-based methods at moderate temperatures. The nanoparticles were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Overall, this paper represents reliable nanoscale fabrication techniques offering key advancements in photovoltaic and optoelectronic applications. Keywords: TiO2, SnO2, Heterojunction, Core-shell, Nanoparticles, Wide Band-gap Semiconductor

Colloidal Quantum Dots as Platforms for Quantum Information Science.

Colloidal quantum dots (QDs) are nanoscale semiconductor crystals with surface ligands that enable their dispersion in solvents. Quantum confinement effects facilitate wave function engineering to sculpt the spatial distribution of charge and spin states and thus the energy and dynamics of QD optical transitions. Colloidal QDs can be integrated in devices using solution-based assembly methods to position single QDs and to create ordered QD arrays. Here, we describe the synthesis, assembly, and photophysical properties of colloidal QDs that have captured scientific imagination and have been harnessed in optical applications. We focus especially on the current understanding of their quantum coherent effects and opportunities to exploit QDs as platforms for quantum information science. Freedom in QD design to isolate and control the quantum mechanical properties of charge, spin, and light presents various approaches to create systems with robust, addressable quantum states. We consider the attributes of QDs for optically addressable qubits in emerging quantum computation, sensing, simulation, and communication technologies, e.g., as robust sources of indistinguishable, single photons that can be integrated into photonic structures to amplify, direct, and tune their emission or as hosts for isolated, coherent spin states that can be coupled to light or to other spins in QD arrays.

Pressing challenges of halide perovskite thin film growth

The adoption of new thin-film materials in high-end technologies, such as monolithic tandem solar cells and integrated circuits, demands fabrication processes that allow a high level of control over film properties such as thickness, conformality, composition, and crystal structure. Achieving this with traditional optoelectronic materials, such as silicon, indium phosphide, gallium arsenide, silicon nitride, and several metal oxides, has opened the way for applications such as high-efficiency photovoltaics, light emitting devices, and integrated photonics. More recently, halide perovskites have demonstrated huge potential in optoelectronic applications, showing exceptional photovoltaic properties, light emission, and lasing performance. Common growth techniques for these halide perovskites have been solution-based methods. Optimized solution-based processes yield high quality thin films well-suited for applications, such as single-junction solar cells, but remain incompatible with integration into complex devices such as monolithic tandem photovoltaics and photonic circuits. Therefore, new fabrication methods allowing atomic, structural, and compositional precision with the conformal growth of hybrid and multi-compound halide perovskite thin films are of utmost importance for material exploration and for their application in complex devices. This Perspective reviews the progress on synthesis methods of halide perovskite thin films, discusses pressing challenges, and proposes strategies for growth control, versatile film deposition, monolithic device integration, epitaxial growth, and high-throughput synthesis to discover novel and non-toxic stable metal halide compositions.

Development of Cryogenic Electrohydrodynamic Jet Printing for Fabrication of Fine Scaffolds with Extra Filament Surface Topography.

Electrohydrodynamic jet printing (EJP) is a developing additive manufacture technology that enables the fabrication of fine scaffolds directly from polymer solutions or melt. Timely solidification of the polymer jet is the key factor for the success of EJP process. In conventional solution-based EJP methods, it is usually achieved by rapid solvent evaporation and producing a scaffold with smooth filaments. In current study, by combining solution-based EJP with a cryogenic workbench, a cryogenic electrohydrodynamic jet printing (CEJP) system was developed, in which the polymer jet was frozen and solidified quickly at the freezing temperature rather than solvent evaporation. The feasibility and versatility of the CEJP system were verified by successful printing of scaffolds with different hole shapes and pore sizes. Meanwhile, the resulting scaffolds not only had a resolution in the range of 50-80 μm but also possessed oriented "ridges" and "valleys" on surface of the filaments, which was conductive to cell orientation. Therefore, this work provides a novel method to print fine scaffolds with extra surface topography.

Pressure-Induced Selective Amorphization of CsPbBr3 for the Purification of Cs4PbBr6

Lead halide perovskites have been of great interest due to their promising optoelectronic applications. While solution-based synthetic methods have been well developed, they often form mixtures of perovskites having several different phases, which cannot be easily purified by conventional purification methods. Here we report a high-pressure purification method of 0D Cs4PbBr6 perovskite containing a trace of 3D CsPbBr3. The synthesized 0D Cs4PbBr6 perovskites exhibit strong photoluminescence at λpeak = ∼520 nm because of the trace amount of CsPbBr3 embedded in the Cs4PbBr6. With the application of high pressure (20 GPa), the crystalline CsPbBr3 phase turns amorphous, while the crystal structure of Cs4PbBr6 is retained without change. Almost 95% of the CsPbBr3 phase can be removed by one cycle of compression (1 atm to 20 GPa, and to 1 atm). Due to the removal of CsPbBr3, Cs4PbBr6 perovskites which originally show strong green fluorescence become nonfluorescent after one cycle of compression.

Structural and magnetic properties of highly Fe-doped ZnO nanoparticles synthesized by one-step solution plasma process

Among many preparation methods for the synthesis of Fe-doped ZnO nanoparticles which have been widely investigated due to versatile properties and potential applications in optoelectronics, photovoltaics, and spintronic devices, solution-based methods such as sol-gel, hydrothermal, and precipitation processes usually consume many reagents and involve numerous steps. In this study, we report a one-step synthesis of highly Fe-doped ZnO nanoparticles (NPs) by a solution plasma process (SPP) using FeCl2 and FeCl3 as precursors without any addition of chemicals. Breakdown of water bubbles caused by plasma discharge led to the formation of hydroxyl radicals, which reacted with the dissolved Zn2+ ions producing Zn(OH)2 that was indeed converted to ZnO through thermal dehydration. Meanwhile, Fe ions were incorporated into the host ZnO lattice during the synthesis process. Fe-doping levels in Zn1-xFexO NPs are easily controllable by changing the Fe precursor concentration and plasma discharging time. We achieved a high doping content (x = 0.14–0.46) within 30 min, which is difficult to achieve using traditional solution-based synthesis approaches. All the Fe-doped NPs exhibit ferromagnetic behavior, but the magnitude is strongly dependent on the Fe content and doping ratio of Fe2+ to Fe3+ ions, which are explained by the dominance and competition between the ferromagnetic and antiferromagnetic exchange interactions through the presence of mixed Fe2+ and Fe3+ ions. The observed optimal ratio of Fe2+ to Fe3+ for maximizing the magnetization is approximately 3:7. It is noteworthy that the magnetization of Fe-doped ZnO NPs can be simply controlled by manipulating the Fe content and composition of Fe2+ and Fe3+ ions achieved through the SPP. This result provides a platform for studying fundamental magnetic properties of TM-doped semiconductors for potential spintronic applications. Thus, the SPP has great potential as an alternative strategy for the synthesis of highly Fe-doped ZnO NPs, which can be expanded to the synthesis of other doped metal-oxide nanostructures for a broad range of research applications.