Direct Integration of Perovskite Solar Cells with Carbon Fiber Substrates.

Integrating photovoltaic devices onto the surface of carbon-fiber-reinforced polymer substrates should create materials with high mechanical strength that are also able to generate electrical power. Such devices are anticipated to find ready applications as structural, energy-harvesting systems in both the automotive and aeronautical sectors. Here, the fabrication of triple-cation perovskite n-i-p solar cells onto the surface of planarized carbon-fiber-reinforced polymer substrates is demonstrated, with devices utilizing a transparent top ITO contact. These devices also contain a "wrinkled" SiO2 interlayer placed between the device and substrate that alleviates thermally induced cracking of the bottom ITO layer. Devices are found to have a maximum stabilized power conversion efficiency of 14.5% and a specific power (power per weight) of 21.4 W g-1 (without encapsulation), making them highly suitable for mobile power applications.

Transition Metal Dichalcogenide Dimer Nanoantennas for Tailored Light-Matter Interactions.

Transition metal dichalcogenides have emerged as promising materials for nanophotonic resonators because of their large refractive index, low absorption within a large portion of the visible spectrum, and compatibility with a wide range of substrates. Herein, we use these properties to fabricate WS2 double-pillar nanoantennas in a variety of geometries enabled by the anisotropy in the crystal structure. Using dark-field spectroscopy, we reveal multiple Mie resonances, to which we couple WSe2 monolayer photoluminescence and achieve Purcell enhancement and an increased fluorescence by factors up to 240 for dimer gaps of 150 nm. We introduce postfabrication atomic force microscope repositioning and rotation of dimer nanoantennas, achieving gaps as small as 10 ± 5 nm, which enables a host of potential applications, including strong Purcell enhancement of single-photon emitters and optical trapping, which we study in simulations. Our findings highlight the advantages of using transition metal dichalcogenides for nanophotonics by exploring applications enabled by their properties.

Atomic force microscopy reveals the mechanical properties of breast cancer bone metastases.

Mechanically dependent processes are essential in cancer metastases. However, reliable mechanical characterization of metastatic cancer remains challenging whilst maintaining the tissue complexity and an intact sample. Using atomic force microscopy, we quantified the micro-mechanical properties of relatively intact metastatic breast tumours and their surrounding bone microenvironment isolated from mice, and compared with other breast cancer models both ex vivo and in vitro. A mechanical distribution of extremely low elastic modulus and viscosity was identified on metastatic tumours, which were significantly more compliant than both 2D in vitro cultured cancer cells and subcutaneous tumour explants. The presence of mechanically distinct metastatic tumour did not result in alterations of the mechanical properties of the surrounding microenvironment at meso-scale distances (>200 µm). These findings demonstrate the utility of atomic force microscopy in studies of complex tissues and provide new insights into the mechanical properties of cancer metastases in bone.

Emergence of Highly Linearly Polarized Interlayer Exciton Emission in MoSe2/WSe2 Heterobilayers with Transfer-Induced Layer Corrugation.

The availability of accessible fabrication methods based on deterministic transfer of atomically thin crystals has been essential for the rapid expansion of research into van der Waals heterostructures. An inherent issue of these techniques is the deformation of the polymer carrier film during the transfer, which can lead to highly nonuniform strain induced in the transferred two-dimensional material. Here, using a combination of optical spectroscopy, atomic force, and Kelvin probe force microscopy, we show that the presence of nanometer scale wrinkles formed due to transfer-induced stress relaxation can lead to strong changes in the optical properties of MoSe2/WSe2 heterostructures and the emergence of linearly polarized interlayer exciton photoluminescence. We attribute these changes to local breaking of crystal symmetry in the nanowrinkles, which act as efficient accumulation centers for interlayer excitons due to the strain-induced interlayer band gap reduction. Surface potential images of the rippled heterobilayer samples acquired using Kelvin probe force microscopy reveal variations of the local work function consistent with strain-induced band gap modulation, while the potential offset observed at the ridges of the wrinkles shows a clear correlation with the value of the tensile strain estimated from the wrinkle geometry. Our findings highlight the important role of the residual strain in defining optical properties of van der Waals heterostructures and suggest effective approaches for interlayer exciton manipulation by local strain engineering.

Mechanical Heterogeneity in the Bone Microenvironment as Characterized by Atomic Force Microscopy.

Bones are structurally heterogeneous organs with diverse functions that undergo mechanical stimuli across multiple length scales. Mechanical characterization of the bone microenvironment is important for understanding how bones function in health and disease. Here, we describe the mechanical architecture of cortical bone, the growth plate, metaphysis, and marrow in fresh murine bones, probed using atomic force microscopy in physiological buffer. Both elastic and viscoelastic properties are found to be highly heterogeneous with moduli ranging over three to five orders of magnitude, both within and across regions. All regions include extremely compliant areas, with moduli of a few pascal and viscosities as low as tens of Pa·s. Aging impacts the viscoelasticity of the bone marrow strongly but has a limited effect on the other regions studied. Our approach provides the opportunity to explore the mechanical properties of complex tissues at the length scale relevant to cellular processes and how these impact aging and disease.

Architecture and Self-Assembly of Clostridium sporogenes and Clostridium botulinum Spore Surfaces Illustrate a General Protective Strategy across Spore Formers.

Spores, the infectious agents of many Firmicutes, are remarkably resilient cell forms. Even distant relatives can have similar spore architectures although some display unique features; they all incorporate protective proteinaceous envelopes. We previously found that Bacillus spores can achieve these protective properties through extensive disulfide cross-linking of self-assembled arrays of cysteine-rich proteins. We predicted that this could be a mechanism employed by spore formers in general, even those from other genera. Here, we tested this by revealing in nanometer detail how the outer envelope (exosporium) in Clostridium sporogenes (surrogate for C. botulinum group I), and in other clostridial relatives, forms a hexagonally symmetric semipermeable array. A cysteine-rich protein, CsxA, when expressed in Escherichia coli, self-assembles into a highly thermally stable structure identical to that of the native exosporium. Like the exosporium, CsxA arrays require harsh "reducing" conditions for disassembly. We conclude that in vivo, CsxA self-organizes into a highly resilient, disulfide cross-linked array decorated with additional protein appendages enveloping the forespore. This pattern is remarkably similar to that in Bacillus spores, despite a lack of protein homology. In both cases, intracellular disulfide formation is favored by the high lattice symmetry. We have identified cysteine-rich proteins in many distantly related spore formers and propose that they may adopt a similar strategy for intracellular assembly of robust protective structures.IMPORTANCE Bacteria such as those causing botulism and anthrax survive harsh conditions and spread disease as spores. Distantly related species have similar spore architectures with protective proteinaceous layers aiding adhesion and targeting. The structures that confer these common properties are largely unstudied, and the proteins involved can be very dissimilar in sequence. We identify CsxA as a cysteine-rich protein that self-assembles in a two-dimensional lattice enveloping the spores of several Clostridium species. We show that apparently unrelated cysteine-rich proteins from very different species can self-assemble to form remarkably similar and robust structures. We propose that diverse cysteine-rich proteins identified in the genomes of a broad range of spore formers may adopt a similar strategy for assembly.

From Monochrome to Technicolor: Simple Generic Approaches to Multicomponent Protein Nanopatterning Using Siloxanes with Photoremovable Protein-Resistant Protecting Groups.

We show that sequential protein deposition is possible by photodeprotection of films formed from a tetraethylene-glycol functionalized nitrophenylethoxycarbonyl-protected aminopropyltriethoxysilane (NPEOC-APTES). Exposure to near-UV irradiation removes the protein-resistant protecting group, and allows protein adsorption onto the resulting aminated surface. The protein resistance was tested using proteins with fluorescent labels and microspectroscopy of two-component structures formed by micro- and nanopatterning and deposition of yellow and green fluorescent proteins (YFP/GFP). Nonspecific adsorption onto regions where the protecting group remained intact was negligible. Multiple component patterns were also formed by near-field methods. Because reading and writing can be decoupled in a near-field microscope, it is possible to carry out sequential patterning steps at a single location involving different proteins. Up to four different proteins were formed into geometric patterns using near-field lithography. Interferometric lithography facilitates the organization of proteins over square cm areas. Two-component patterns consisting of 150 nm streptavidin dots formed within an orthogonal grid of bars of GFP at a period of ca. 500 nm could just be resolved by fluorescence microscopy.

Direct Imaging of Protein Organization in an Intact Bacterial Organelle Using High-Resolution Atomic Force Microscopy.

The function of bioenergetic membranes is strongly influenced by the spatial arrangement of their constituent membrane proteins. Atomic force microscopy (AFM) can be used to probe protein organization at high resolution, allowing individual proteins to be identified. However, previous AFM studies of biological membranes have typically required that curved membranes are ruptured and flattened during sample preparation, with the possibility of disruption of the native protein arrangement or loss of proteins. Imaging native, curved membranes requires minimal tip-sample interaction in both lateral and vertical directions. Here, long-range tip-sample interactions are reduced by optimizing the imaging buffer. Tapping mode AFM with high-resonance-frequency small and soft cantilevers, in combination with a high-speed AFM, reduces the forces due to feedback error and enables application of an average imaging force of tens of piconewtons. Using this approach, we have imaged the membrane organization of intact vesicular bacterial photosynthetic "organelles", chromatophores. Despite the highly curved nature of the chromatophore membrane and lack of direct support, the resolution was sufficient to identify the photosystem complexes and quantify their arrangement in the native state. Successive imaging showed the proteins remain surprisingly static, with minimal rotation or translation over several-minute time scales. High-order assemblies of RC-LH1-PufX complexes are observed, and intact ATPases are successfully imaged. The methods developed here are likely to be applicable to a broad range of protein-rich vesicles or curved membrane systems, which are an almost ubiquitous feature of native organelles.

Characterization of the spore surface and exosporium proteins of Clostridium sporogenes; implications for Clostridium botulinum group I strains.

Clostridium sporogenes is a non-pathogenic close relative and surrogate for Group I (proteolytic) neurotoxin-producing Clostridium botulinum strains. The exosporium, the sac-like outermost layer of spores of these species, is likely to contribute to adhesion, dissemination, and virulence. A paracrystalline array, hairy nap, and several appendages were detected in the exosporium of C. sporogenes strain NCIMB 701792 by EM and AFM. The protein composition of purified exosporium was explored by LC-MS/MS of tryptic peptides from major individual SDS-PAGE-separated protein bands, and from bulk exosporium. Two high molecular weight protein bands both contained the same protein with a collagen-like repeat domain, the probable constituent of the hairy nap, as well as cysteine-rich proteins CsxA and CsxB. A third cysteine-rich protein (CsxC) was also identified. These three proteins are also encoded in C. botulinum Prevot 594, and homologues (75-100% amino acid identity) are encoded in many other Group I strains. This work provides the first insight into the likely composition and organization of the exosporium of Group I C. botulinum spores.

The interplay between cell wall mechanical properties and the cell cycle in Staphylococcus aureus.

The nanoscale mechanical properties of live Staphylococcus aureus cells during different phases of growth were studied by atomic force microscopy. Indentation to different depths provided access to both local cell wall mechanical properties and whole-cell properties, including a component related to cell turgor pressure. Local cell wall properties were found to change in a characteristic manner throughout the division cycle. Splitting of the cell into two daughter cells followed a local softening of the cell wall along the division circumference, with the cell wall on either side of the division circumference becoming stiffer. Once exposed, the newly formed septum was found to be stiffer than the surrounding, older cell wall. Deeper indentations, which were affected by cell turgor pressure, did not show a change in stiffness throughout the division cycle, implying that enzymatic cell wall remodeling and local variations in wall properties are responsible for the evolution of cell shape through division.

A non-contact, thermal noise based method for the calibration of lateral deflection sensitivity in atomic force microscopy.

Calibration of lateral forces and displacements has been a long standing problem in lateral force microscopies. Recently, it was shown by Wagner et al. that the thermal noise spectrum of the first torsional mode may be used to calibrate the deflection sensitivity of the detector. This method is quick, non-destructive and may be performed in situ in air or liquid. Here we make a full quantitative comparison of the lateral inverse optical lever sensitivity obtained by the lateral thermal noise method and the shape independent method developed by Anderson et al. We find that the thermal method provides accurate results for a wide variety of rectangular cantilevers, provided that the geometry of the cantilever is suitable for torsional stiffness calibration by the torsional Sader method, in-plane bending of the cantilever may be eliminated or accounted for and that any scaling of the lateral deflection signal between the measurement of the lateral thermal noise and the measurement of the lateral deflection is eliminated or corrected for. We also demonstrate that the thermal method may be used to characterize the linearity of the detector signal as a function of position, and find a deviation of less than 8% for the instrument used.

The structure and formation of hydrogen-bonded molecular networks on Au(111) surfaces revealed by scanning tunnelling and torsional-tapping atomic force microscopy.

A comprehensive scanning probe microscopy study has been carried out to characterise 3,4,9,10-Perylenetetracarboxylic diimide (PTCDI)-melamine hydrogen-bonded networks deposited on Au(111)-surfaces. Both scanning tunnelling and atomic force microscopy were utilized. Such complementary analysis revealed a multilayered structure of the networks on the Au(111)-surface as opposed to a widely reported monolayer structure. Details of the network formation mechanism are presented. We have also demonstrated that despite the apparent network stability in ambient conditions it is unstable in aqueous solutions of pH 4.5 and 7.1.

Direct imaging of polyethylene films at single-chain resolution with torsional tapping atomic force microscopy.

The physical properties of semicrystalline polymers depend on the organisation of chains within the crystal and amorphous regions, on the interface between the two, and on the location and nature of defects. Here, torsional tapping atomic force microscopy has been used to image crystalline lamellae and the crystal-amorphous-region interface at the single-chain level with resolution down to 3.7 Å. Defects within the crystalline phase, such as buried folds and chain ends, are revealed. Imaging at the chain level also allows direct measurement of crystalline stem lengths, providing a potential route to test theories of crystal thickness selection.

Surface architecture of endospores of the Bacillus cereus/anthracis/thuringiensis family at the subnanometer scale.

Bacteria of the Bacillus cereus family form highly resistant spores, which in the case of the pathogen B. anthracis act as the agents of infection. The outermost layer, the exosporium, enveloping spores of the B. cereus family as well as a number of Clostridia, plays roles in spore adhesion, dissemination, targeting, and germination control. We have analyzed two naturally crystalline layers associated with the exosporium, one representing the "basal" layer to which the outermost spore layer ("hairy nap") is attached, and the other likely representing a subsurface ("parasporal") layer. We have used electron cryomicroscopy at a resolution of 0.8-0.6 nm and circular dichroism spectroscopic measurements to reveal a highly α-helical structure for both layers. The helices are assembled into 2D arrays of "cups" or "crowns." High-resolution atomic force microscopy of the outermost layer showed that the open ends of these cups face the external environment and the highly immunogenic collagen-like fibrils of the hairy nap (BclA) are attached to this surface. Based on our findings, we present a molecular model for the spore surface and propose how this surface can act as a semipermeable barrier and a matrix for binding of molecules involved in defense, germination control, and other interactions of the spore with the environment.