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Diffracted X-ray Blinking Tracks Single Protein Motions
摘要： Single molecule dynamics studies have begun to use quantum probes. Single particle analysis using cryo-transmission electron microscopy has dramatically improved the resolution when studying protein structures and is shifting towards molecular motion observations. X-ray free-electron lasers are also being explored as routes for determining single molecule structures of biological entities. Here, we propose a new X-ray single molecule technology that allows observation of molecular internal motion over long time scales, ranging from milliseconds up to 103 seconds. Our method uses both low-dose monochromatic X-rays and nanocrystal labelling technology. During monochromatic X-ray diffraction experiments, the intensity of X-ray diffraction from moving single nanocrystals appears to blink because of Brownian motion in aqueous solutions. X-ray diffraction spots from moving nanocrystals were observed to cycle in and out of the Bragg condition. Consequently, the internal motions of a protein molecule labelled with nanocrystals could be extracted from the time trajectory using this diffracted X-ray blinking (DXB) approach. Finally, we succeeded in distinguishing the degree of fluctuation motions of an individual acetylcholine-binding protein (AChBP) interacting with acetylcholine (ACh) using a laboratory X-ray source.
关键词： Acetylcholine-binding protein,Brownian motion,Nanocrystal labelling,Single molecule dynamics,X-ray diffraction
更新于2025-09-09 09:28:46
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Monolithic silicon carbide with interconnected and hierarchical pores fabricated by reaction‐induced phase separation
摘要： Hierarchically porous silicon carbide (SiC) monoliths were fabricated based on polycarbosilane (PCS), divinyl benzene (DVB), and decalin, by a sequence of procedures including catalyst-free hydrosilylation reaction-induced phase separation, ambient-pressure drying, calcination, and HF etching. The influences of ratios of each component on the phase separation were systematically studied. It was found that isotactic polypropylene added as a nonreactive additive could effectively tailor the microstructure and improve the mechanical properties of SiC monoliths. The resultant SiC monoliths mainly consisted of β-SiC nanocrystals, and possessed low bulk density (0.7 g/cm3), high porosity (78%), large specific area (100.6 m2/g), high compressive strength (13.5 ± 1.6 MPa), and hierarchical pores (macropores around 350 nm, mesopores around 4 nm and 20 nm). These properties make SiC monoliths promising materials for catalyst/catalyst support, gas separator, and the reinforcement of high-temperature composites.
关键词： nanocrystal,reaction induced phase separation,hierarchical pore,ambient pressure drying,SiC monolith
更新于2025-09-09 09:28:46
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Surfactant-Assisted Synthesis of Monodisperse Methylammonium Lead Iodide Perovskite Nanocrystals
摘要： Lead iodide based perovskites are promising optoelectronic materials ideal for solar cells. Recently emerged perovskite nanocrystals (NCs) offer more advantages including improved size-tunable band gap, structural stability, and solvent-based processing. Here we report a simple surfactant-assisted two-step synthesis to produce monodisperse PbI2 NCs which are then converted to methylammonium lead iodide perovskite NCs. Based on electron microscopy characterization, these NCs showed competitive monodispersity. Combined results from X-ray diffraction patterns, optical absorption, and photoluminescence confirmed the formation of high quality methylammonium lead iodide perovskite NCs. More importantly, by avoiding the use of hard-to-remove chemicals, the resulted perovskite NCs can be readily integrated in applications, especially solar cells through versatile solution/colloidal-based methods.
关键词： Surfactant,Perovskite,Nanoparticle,Methylammonium Lead Iodide,Micelle,Nanocrystal
更新于2025-09-04 15:30:14
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Influence of Cracks on the Optical Properties of Silver Nanocrystals Supracrystal Films
摘要： Physical properties of nanocrystals self-assembled into 3D superlattices called supracrystals are highly specific with unexpected behavior. The best example to support such claim was given, through STM/STS experiments at low temperature, of very thick supracrystals (around 1000 layers) where it was possible to image the surpracrystal surface and study their electronic properties. From previous studies, we know the optical properties of Ag nanocrystals self-assembled in hexagonal network (2D) or forming small 3D superlattices (from around 2 to 7 layers) are governed by dipolar interactions. Here, we challenge to study the optical properties of Ag supracrystals film characterized by large thicknesses (from around 27 to 180 Ag nanocrystals layers). In such experimental conditions, according to the classical Beer-Lambert law, the absorption of Ag films is expected to be very large and the film transmission is closed to zero. Very surprisingly, we observe reduced transmission intensity with an increase of the notch linewidth, in the 300-800 nm wavelength range, as the supracrystal film thickness increased. By calculating the transmission through the supracrystal films, we deduced that the films were dominated by the presence of cracks with wetting layers existing at their bottoms. This result was also confirmed by optical micrographs. The cracks widths increased with increasing the film thickness leading to more complex wetting layers. We also demonstrated the formation of small Ag clusters at the nanocrystal surface. These results provide some implications towards the design of plasmonic materials.
关键词： localized surface plasmon resonance,supracrystals,silver nanocrystal,optical properties,cracks
更新于2025-09-04 15:30:14
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Cs Oleate Precursor Preparation for Lead Halide Perovskite Nanocrystal Synthesis: The Influence of Excess Oleic Acid on Achieving Solubility, Conversion, and Reproducibility.
摘要： In the colloidal synthesis of inorganic perovskite materials, cesium oleate (CsOL) is the most commonly used Cs precursor. Yet despite its ubiquitous use in literature, CsOL has been observed to be insoluble at room temperature and leads to surprisingly inconsistent results in CsPbX3 nanocrystal synthesis depending on the Cs salt from which the precursor is derived. We show that under the conditions used in most reports, the amount of oleic acid (OA) added, while stoichiometrically sufficient, still leads to incomplete conversion of the Cs salts to CsOL. This results in a mixture of Cs sources being present during the reaction, causing decreased homogeneity and reproducibility. When a 1:5 Cs:OA ratio is used, complete conversion is readily obtained even under mild conditions, resulting in a precursor solution that is soluble at room temperature and yields identical synthetic results regardless of the initial Cs source. Further, 1H nuclear magnetic resonance (NMR) of solutions prepared using varying Cs:OA ratios shows that the maximum ratio of Cs:OA obtainable in solution is 1:5, with any excess Cs present in the precipitate. We believe the use of a soluble, fully converted CsOL reagent will improve reproducibility for Cs-based perovskite synthesis and directly benefit synthetic methods based on microfluidics.
关键词： reproducibility,inorganic perovskite materials,microfluidics,CsPbX3 nanocrystal synthesis,colloidal synthesis,oleic acid,solubility,cesium oleate
更新于2025-09-04 15:30:14
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Printing Birefringent Figures by Surface Tension-Directed Self-Assembly of a Cellulose Nanocrystal/Polymer Ink Components
摘要： Photonic printing on transparent substrates using emerging synthetic photonic crystals is in high demand, especially for anti-fraud applications. However, photonic printing is faced with grand challenges including lack of the full invisibility of printed patterns before stimulation or after stimuli removal and absence of the long-lasting stability. Natural anisotropic crystal structures and artificially molecularly arranged polymers show an optically anisotropic property known as birefringence. Crystalline cellulose is the most abundant birefringent bio-crystal on the earth. Here, we introduce a printing method based on using a cellulose nanocrystal/polymer ink that is governed by surface evaporation phenomenon and divided surface tension forces to direct the self-assembly of ink components at the nanoscale and print 3D birefringent micro-figures on transparent substrates. This type of printing is from now on referred to as Birefringent Printing (BP). Unlike previously reported photonic crystal printing methods, this method is accurate, has high-contrast, is virtually impossible to forge and at the same time is very simple, inexpensive and non-toxic.
关键词： polymer ink,cellulose nanocrystal,directed self-assembly,birefringence,surface tension,invisible printing
更新于2025-09-04 15:30:14
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Highly Stable Luminous “Snakes” from CsPbX3 Perovskite Nanocrystals Anchored on Amine-Coated Silica Nanowires
摘要： CsPbX3 (X=Cl, Br and I) perovskite nanocrystals (NCs) are known for their exceptional optoelectronic properties, yet the material’s instability towards polar solvents, heat or UV irradiation greatly limits its further applications. Herein, an efficient in-situ growing strategy has been developed to give highly stable perovskite NC composites (abbr. CsPbX3@CA-SiO2) by anchoring CsPbX3 NCs onto silica nanowires (NWs), which effectively depresses the optical degradation of their photoluminescence (PL) and enhances stability. The preparation of surface-functionalized serpentine silica NWs is realized by a sol-gel process involving hydrolysis of a mixture of tetraethylorthosilicate (TEOS), 3-aminopropyltriethoxysilane (APTES) and trimethoxy(octadecyl)silane (TMODS) in a water/oil emulsion. The serpentine NWs are formed via an anisotropic growth with lengths up to 8 μm. The free amino groups are employed as surface ligands for growing perovskite NCs, yielding distributed monodisperse NCs (~8 nm) around the NW matrix. The emission wavelength is tunable by simple variation of the halide compositions (CsPbX3, X=Cl, Br or I) and the composites demonstrate a high photoluminescence quantum yield (PLQY 32-69%). Additionally, we have demonstrated the composites CsPbX3@CA-SiO2 can be self-woven to form a porous 3D hierarchical NWs membrane, giving rise to a superhydrophobic surface with hierarchical micro/nano structural features. The resulting composites exhibit high stability towards water, heat and UV irradiation. This work elucidates an effective strategy to incorporate perovskite nanocrystals onto functional matrices as multifunctional stable light sources.
关键词： colloidal CsPbX3 nanocrystal,superhydrophobic,photostability,assembled hierarchical membrane,serpentine silica nanowires
更新于2025-09-04 15:30:14