Anderson localization, the absence of diffusive transport in disordered systems, has been manifested as hopping transport in numerous electronic systems, whereas in recently discovered topological insulators it has not been directly observed. Here we report experimental demonstration of a crossover from diffusive transport in the weak antilocalization regime to variable range hopping transport in the Anderson localization regime with ultrathin (Bi1−xSbx)2Te3 films. As disorder becomes stronger, negative magnetoconductivity due to the weak antilocalization is gradually suppressed, and eventually positive magnetoconductivity emerges when the electron system becomes strongly localized. This works reveals the critical role of disorder in the quantum transport properties of ultrathin topological insulator films, in which theories have predicted rich physics related to topological phase transitions.The concept of Anderson localization has profoundly influenced our understanding of electron conductivity [1]. While examples for disorder driven metal-insulator transition are abundant in three-dimensions (3D), the question of whether Anderson transitions exist in 2D has posed a lot of theoretical and experimental challenges. Scaling theory proposed by Abrahams et al. predicts that there are no truly metallic states in non-interacting 2D electron systems [2,3]. It was, however, discovered later that extended electron states may exist when electronelectron (e-e) interaction, spin-orbit coupling (SOC) or magnetic field comes in to play [4,5]. The 3D topological insulators (TIs) discovered in recent years [6,7] provide novel types of 2D electron systems that are of particular interest for study of the localization-delocalization problem. The Dirac surface states of 3D TIs are believed to be topologically protected from localization due to its special symmetry class [8][9][10][11][12]. Moreover, when a 3D TI thin film is sufficiently thin, the hybridization between the top and the bottom surface states opens an energy gap near the Dirac point [13], and it is suggested theoretically that the hybridization gap would drive the electron system to topologically different phase, such as a quantum spin Hall insulator or a trivial band insulator [14][15][16]. Even though a lot of work has been carried out on electron transport properties of TI thin films [17][18][19][20], the fate of such electron systems under the condition of strong disorder (or in other words, whether Anderson localization could take place), still remains unclear.In this work, we have studied electron transport in a large number of highly gate-tunable TI thin films with various thicknesses and chemical compositions. We found that only in ultrathin TI films in which surface hybridization and disorder effects are significant, hopping transport, a hallmark of strong localization [21][22][23], can be observed. The observed temperature and magnetic field dependences of conductivity suggest that electron transport can be driven from the diffusive transport governed by we...

The in vivo aggregation of proteins into amyloid fibrils suggests that cellular mechanisms that normally prevent or reverse this aggregation have failed. The small heat-shock molecular chaperone protein αB-crystallin (αB-c) inhibits amyloid formation and colocalizes with amyloid plaques; however, the physiological reason for this localization remains unexplored. Here, using apolipoprotein C-II (apoC-II) as a model fibril-forming system, we show that αB-c binds directly to mature amyloid fibrils (Kd 5.4 ± 0.5 μM). In doing so, αB-c stabilized the fibrils from dilution-induced fragmentation, halted elongation of partially formed fibrils, and promoted the dissociation of mature fibrils into soluble monomers. Moreover, in the absence of dilution, the association of αB-c with apoC-II fibrils induced a 14-fold increase in average aggregate size, resulting in large fibrillar tangles reminiscent of protein inclusions. We propose that the binding of αB-c to fibrils prevents fragmentation and mediates the lateral association of fibrils into large inclusions. We further postulate that transient interactions of apoC-II with αB-c induce a fibril-incompetent monomeric apoC-II form, preventing oligomerization and promoting fibril dissociation. This work reveals previously unrecognized mechanisms of αB-c chaperone action in amyloid assembly and fibril dynamics, and provides a rationale for the in vivo colocalization of small heat-shock proteins with amyloid deposits.-Binger, K. J., Ecroyd, H., Yang, S., Carver, J. A., Howlett, G. J., Griffin, M. D. W. Avoiding the oligomeric state: αB-crystallin inhibits fragmentation and induces dissociation of apolipoprotein C-II amyloid fibrils.

Understanding the cytoarchitecture and wiring of the brain requires improved methods to record and stimulate large groups of neurons with cellular specificity. This requires miniaturized neural interfaces that integrate into brain tissue without altering its properties. Existing neural interface technologies have been shown to provide high-resolution electrophysiological recording with high signal-to-noise ratio. However, with single implantation, the physical properties of these devices limit their access to one, small brain region. To overcome this limitation, we developed a platform that provides three-dimensional coverage of brain tissue through multisite multifunctional fiber-based neural probes guided in a helical scaffold. Chronic recordings from the spatially expandable fiber probes demonstrate the ability of these fiber probes capturing brain activities with a single-unit resolution for long observation times. Furthermore, using Thy1-ChR2-YFP mice we demonstrate the application of our probes in simultaneous recording and optical/chemical modulation of brain activities across distant regions. Similarly, varying electrographic brain activities from different brain regions were detected by our customizable probes in a mouse model of epilepsy, suggesting the potential of using these probes for the investigation of brain disorders such as epilepsy. Ultimately, this technique enables three-dimensional manipulation and mapping of brain activities across distant regions in the deep brain with minimal tissue damage, which can bring new insights for deciphering complex brain functions and dynamics in the near future.

Ionotronic skin (i-skin) has drawn considerable attention, because it can interface with different systems to sense and respond to external stimuli, such as force and temperature. However, safety issues, such as biosecurity, sustainability, and safety in use, are rarely considered in i-skin designs. In this study, a flame-retardant and biosafe i-skin was developed by using silk fibroin and Ca 2+ ions as starting materials. The structures, performance, and safety issues of the i-skins were well-balanced. The resultant i-skins not only maintained the advantages of conventional i-skins, such as conductivity, transparency, high stretchability, and self-healing ability, but also featured outstanding flame retardancy and temperature sensibility. With these features, an automated fire alarm system was designed to detect possible fire conditions. Benefiting from their low cost, stretchability, and sustainability, these i-skins are expected to be employed in a range of emerging fields, such as flame-retardant materials, fire alarms, temperature sensors, and human/machine interfaces.