High-speed AFM with a light touch

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Uniform patchy and hollow rectangular platelet micelles from crystallizable polymer blends

Growing patterned rectangular objects The growth of patterned objects usually requires a template to aid the positioning of multiple materials. Qiu et al. used the seeded growth of a crystallizable block copolymer and a homopolymer to produce highly uniform rectangular structures (see the Perspective by Ballauff). Chemical etching, or dissolution, of uncross-linked regions of the rectangular structures produced perforated platelet micelles. The sequential addition of different blends and cross-linking/dissolution strategies allowed the formation of well-defined hollow rectangular micelles, which can be functionalized in a variety of ways. Science , this issue p. 697 ; see also p. 656 </jats:p

Estimation of the shear force in transverse dynamic force microscopy using a sliding mode observer

Open access journalIn this paper, the problem of estimating the shear force affecting the tip of the cantilever in a Transverse Dynamic Force Microscope (TDFM) using a real-time implementable sliding mode observer is addressed. The behaviour of a vertically oriented oscillated cantilever, in close proximity to a specimen surface, facilitates the imaging of the specimen at nano-metre scale. Distance changes between the cantilever tip and the specimen can be inferred from the oscillation amplitudes, but also from the shear force acting at the tip. Thus, the problem of accurately estimating the shear force is of significance when specimen images and mechanical properties need to be obtained at submolecular precision. A low order dynamic model of the cantilever is derived using the method of lines, for the purpose of estimating the shear force. Based on this model, an estimator using sliding mode techniques is presented to reconstruct the unknown shear force, from only tip position measurements and knowledge of the excitation signal applied to the top of the cantilever. Comparisons to methods assuming a quasi-static harmonic balance are made.Engineering and Physical Sciences Research Council (EPSRC

Real-Time Tracking of Metal Nucleation via Local Perturbation of Hydration Layers

The real-time visualization of stochastic nucleation events at electrode surfaces is one of the most complex challenges in electrochemical phase formation. The early stages of metal deposition on foreign substrates are characterized by a highly dynamic process in which nanoparticles nucleate and dissolve prior to reaching a critical size for deposition and growth. Here, high-speed non-contact lateral molecular force microscopy employing vertically oriented probes is utilized to explore the evolution of hydration layers at electrode surfaces with the unprecedented spatiotemporal resolution, and extremely low probe-surface interaction forces required to avoid disruption or shielding the critical nucleus formation. To the best of our knowledge, stochastic nucleation events of nanoscale copper deposits are visualized in real time for the first time and a highly dynamic topographic environment prior to the formation of critical nuclei is unveiled, featuring formation/re-dissolution of nuclei, two-dimensional aggregation and nuclei growth.Electrochemical deposition is important for industrial processes however, tracking the early stages of metallic phase nucleation is challenging. Here, the authors visualize the birth and growth of metal nuclei at electrode surfaces in real time via high-speed non-contact lateral molecular force microscopy

Structural features distinguishing infectious ex vivo mammalian prions from non-infectious fibrillar assemblies generated in vitro

Seeded polymerisation of proteins forming amyloid fibres and their spread in tissues has been implicated in the pathogenesis of multiple neurodegenerative diseases: so called "prion-like" mechanisms. While ex vivo mammalian prions, composed of multichain assemblies of misfolded host-encoded prion protein (PrP), act as lethal infectious agents, PrP amyloid fibrils produced in vitro generally do not. The high-resolution structure of authentic infectious prions and the structural basis of prion strain diversity remain unknown. Here we use cryo-electron microscopy and atomic force microscopy to examine the structure of highly infectious PrP rods isolated from mouse brain in comparison to non-infectious recombinant PrP fibrils generated in vitro. Non-infectious recombinant PrP fibrils are 10 nm wide single fibres, with a double helical repeating substructure displaying small variations in adhesive force interactions across their width. In contrast, infectious PrP rods are 20 nm wide and contain two fibres, each with a double helical repeating substructure, separated by a central gap of 8-10 nm in width. This gap contains an irregularly structured material whose adhesive force properties are strikingly different to that of the fibres, suggestive of a distinct composition. The structure of the infectious PrP rods, which cause lethal neurodegeneration, readily differentiates them from all other protein assemblies so far characterised in other neurodegenerative diseases