Ionic complex of a rhodamine dye with aggregation-induced emission properties.

An AIE-active rhodamine based luminogen was prepared via a complexation reaction between non-emissive rhodamine hydrazide (RdH) and bulky camphorsulfonic acid (CSA). Besides acting to open the spirolactam ring of RdH, CSA also imposes a rotational restriction on the resultant ionic complex, RdH(CSA)x. Without CSA, the analogous complex RdH(HCl)3 is a luminogen with aggregation-caused quenching (ACQ) properties. The ionic bonds of RdH(CSA)3 are sensitive to several external stimuli and therefore it is a luminescent sensor for metal ions, organic amines and the blood protein bovine serum albumin (BSA). Besides being a sensor for BSA, the ionic RdH(CSA)3 is also a denaturant capable of uncoiling the peptide chain of BSA.

Subnanometer vacancy defects introduced on graphene by oxygen gas.

The basal plane of graphene has been known to be less reactive than the edges, but some studies observed vacancies in the basal plane after reaction with oxygen gas. Observation of these vacancies has typically been limited to nanometer-scale resolution using microscopic techniques. This work demonstrates the introduction and observation of subnanometer vacancies in the basal plane of graphene by heat treatment in a flow of oxygen gas at low temperature such as 533 K or lower. High-resolution transmission electron microscopy was used to directly observe vacancy structures, which were compared with image simulations. These proposed structures contain C═O, pyran-like ether, and lactone-like groups.

Shape-controlled synthesis and in situ characterisation of anisotropic Au nanomaterials using liquid cell transmission electron microscopy.

Understanding the mechanisms behind crystal nucleation and growth is a fundamental requirement for the design and production of bespoke nanomaterials with controlled sizes and morphologies. Herein, we select gold (Au) nanoparticles as the model system for our study due to their representative applications in biology, electronics and optoelectronics. We investigate the radiation-induced in situ growth of gold (Au) particles using liquid cell transmission electron microscopy (LCTEM) and study the growth kinetics of non-spherical Au structures. Under controlled electron fluence, liquid flow rate and Au3+ ion supply, we show the favoured diffusion-limited growth of multi-twinned nascent Au seed particles into branched structures when using thin liquid cells (100 nm and 250 nm) in LCTEM, whereas faceted structures (e.g., spheres, rods, and prisms) formed when using a 1 µm thick liquid cell. In addition, we observed that anisotropic Au growth could be modulated by Au-binding amyloid fibrils, which we ascribe to their capability to regulate Au3+ ion diffusion and mass transfer in solution. We anticipate that this study will provide new perspectives on the shape-controlled synthesis of anisotropic metallic nanomaterials using LCTEM.

Light-Up of Rhodamine Hydrazide to Generate Emissive Initiator for Polymerization and to Afford Photochromic Polypeptide Metal Complex.

Ring-opening polymerization (ROP) of cyclic peptide monomer of γ-propargyl-l-glutamate N-carboxyanhydride (PLG⁻NCA) was originally initiated by non-emissive, ring-close rhodamine 6G hydrazide (R-C). However, instantaneously after adding PLG⁻NCA to R-C, the spirolactam ring of R-C was opened by PLG⁻NCA, rendering emissive, ring-open R-O to initiate ROP of PLG⁻NCA. The emissive R-O moiety therefore produced fluorescent R⁻PLG with aggregation-induced emission (AIE) properties. Moreover, R⁻PLG was found to exhibit photochromic properties with good fatigue resistance and long lifetime when forming metal complexes with Sn(II) and Fe(III). In the dark, irradiated metal complexes slowly (~50 min) restored to the initial state. This research provides foundation for the development of new photochromic materials with long lifetime.

Imaging Atomic-Scale Clustering in III-V Semiconductor Alloys.

Quaternary alloys are essential for the development of high-performance optoelectronic devices. However, immiscibility of the constituent elements can make these materials vulnerable to phase segregation, which degrades the optical and electrical properties of the solid. High-efficiency III-V photovoltaic cells are particularly sensitive to this degradation. InAlAsSb lattice matched to InP is a promising candidate material for high-bandgap subcells of a multijunction photovoltaic device. However, previous studies of this material have identified characteristic signatures of compositional variation, including anomalous low-energy photoluminescence. In this work, atomic-scale clustering is observed in InAlAsSb via quantitative scanning transmission electron microscopy. Image quantification of atomic column intensity ratios enables the comparison with simulated images, confirming the presence of nonrandom compositional variation in this multispecies alloy.

Sequence-Dependent Self-Assembly and Structural Diversity of Islet Amyloid Polypeptide-Derived ß-Sheet Fibrils.

Determining the structural origins of amyloid fibrillation is essential for understanding both the pathology of amyloidosis and the rational design of inhibitors to prevent or reverse amyloid formation. In this work, the decisive roles of peptide structures on amyloid self-assembly and morphological diversity were investigated by the design of eight amyloidogenic peptides derived from islet amyloid polypeptide. Among the segments, two distinct morphologies were highlighted in the form of twisted and planar (untwisted) ribbons with varied diameters, thicknesses, and lengths. In particular, transformation of amyloid fibrils from twisted ribbons into untwisted structures was triggered by substitution of the C-terminal serine with threonine, where the side chain methyl group was responsible for the distinct morphological change. This effect was confirmed following serine substitution with alanine and valine and was ascribed to the restriction of intersheet torsional strain through the increased hydrophobic interactions and hydrogen bonding. We also studied the variation of fibril morphology (i.e., association and helicity) and peptide aggregation propensity by increasing the hydrophobicity of the peptide side group, capping the N-terminus, and extending sequence length. We anticipate that our insights into sequence-dependent fibrillation and morphological diversity will shed light on the structural interpretation of amyloidogenesis and development of structure-specific imaging agents and aggregation inhibitors.

20-nm resolution x-ray microscopy demonstrated by use of multilayer test structures [corrected].

A spatial resolution of 20 nm is demonstrated at 2.07-nm wavelength by use of a soft x-ray microscope based on Fresnel zone plate lenses and partially coherent illumination. Nanostructural test patterns, formed by sputtered multilayer coatings and transmission electron microscopy thinning techniques, provide clear experimental results.