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Fundamental costs in the production and destruction of persistent polymer copies
Get PDFProducing a polymer copy of a polymer template is central to biology, and effective copies must persist after template separation. We show that this separation has three fundamental thermodynamic effects. First, polymer-template interactions do not contribute to overall reaction thermodynamics and hence cannot drive the process. Second, the equilibrium state of the copied polymer is template independent and so additional work is required to provide specificity. Finally, the mixing of copies from distinct templates makes correlations between template and copy sequences unexploitable, combining with copying inaccuracy to reduce the free energy stored in a polymer ensemble. These basic principles set limits on the underlying costs and resource requirements, and suggest design principles, for autonomous copying and replication in biological and synthetic systems
Control of the electromagnetic field in a cavity by an external perturbation
Get PDFA prototypical experiment in cavity quantum electrodynamics involves controlling the light-matter interaction by tuning the frequency of a cavity mode in- and out-of resonance with the frequency of a quantum emitter,1-3 while the field amplitude is generally unaltered. The opposite situation, where one perturbs the spatial pattern of a cavity mode without changing its frequency, has been considered only recently in a few works.4, 5 Changing the amplitude of the field at the emitter's position has important applications, at it allows a real-time control of the light-matter coupling rate, and therefore a direct control of processes such as spontaneous emission and Rabi oscillations. In view of this large potential, in this paper we discuss general design principles that allow obtaining large variations of the electromagnetic field, without change of the frequency, upon an external perturbation of the cavity. We showcase the application of these rules to two photonic structures, a single Fabry-Perot cavity and a coupled three-cavity system. As showed by our analysis and by the examples provided, a small frequency spacing between the modes of the unperturbed cavity is an important requirement to obtain large field variations upon small perturbations. In this regard, a coupled-cavity system, where the frequency spacing is controlled by the interaction rates between the single cavities, constitutes the most promising system to achieve large modulations of the field amplitude
C-terminal truncated α-synuclein fibrils contain strongly twisted β-sheets
Get PDFC-terminal truncations of monomeric wild-type alpha synuclein (henceforth WT-αS) have been shown to enhance the formation of amyloid aggregates both in vivo and in vitro and have been associated with accelerated progression of Parkinson’s disease. The correlation with PD may not solely be influenced by faster aggregation, but also from the effect the deletion of C-terminal residues has on which fibril polymorphs are preferentially formed. Considering that different polymorphs are known to result in distinct pathologies, it is important to understand how these truncations affect the organization of αS into fibrils. Here we present high resolution microscopy and advanced vibrational spectroscopy studies that indicate that the C-terminal truncation variant of αS, lacking residues 109-140 (henceforth referred to as 1-108-αS), forms amyloid fibrils with a distinct structure and morphology. The 1-108-αS fibrils have a unique negative circular dichroism band at ∼230 nm, a feature that differs from the canonical ∼218 nm band usually observed for amyloid fibrils. We show that 1-108-αS fibrils consist of strongly twisted β-sheets with an increased inter-β-sheet distance and a higher solvent exposure than WT-αS fibrils, which is also indicated by the pronounced differences in the 1D-IR (FTIR), 2D-IR and vibrational circular dichroism spectra. As a result of their distinct β-sheet structure 1-108-αS fibrils resist incorporation of WT-αS monomers
Multi-chromatic silicon nanocrystals
Get PDFSilicon nanocrystals (SiNCs) have great potential to become environmental friendly alternatives to heavy-metal containing nanocrystals for applications including medical imaging, lighting and displays. SiNCs exhibit excellent photostability, non-toxicity and abundant resources, but their often reported inefficient and spectrally limited light emission seriously impair their applications.
Here we demonstrate a new method that converts SiNCs into an efficient and robust multi-chromatic phosphor. Using ~ 15 keV electron-beam irradiation of oxide-capped SiNCs, we introduce several types of color centers into the nanocrystal’s oxide shell with efficient blue, green and red emission bands, together yielding warm-white photoluminescence, even for a single SiNC.
Introduced centers are not native to the original system and we relate them to known defects in silica. Unlike in the silica host, however, here the centers are efficiently optically excitable. Provided further optimization and up-scaling of this method, e-beam irradiated SiNCs can be of great interest as white phosphors for applications such as LEDs
Core-shell plasmonic nanohelices
Get PDFWe introduce core-shell plasmonic nanohelices, highly tunable structures that have a different response in the visible for circularly polarized light of opposite handedness. The glass core of the helices is fabricated using electron beam induced deposition and the pure gold shell is subsequently sputter coated. Optical measurements allow us to explore the chiral nature of the nanohelices, where differences in the response to circularly polarized light of opposite handedness result in a dissymmetry factor of 0.86, more than twice of what has been previously reported. Both experiments and subsequent numerical simulations demonstrate the extreme tunability of the core-shell structures, where nanometer changes to the geometry can lead to drastic changes of the
optical responses. This tunability, combined with the large differential transmission, make core-shell plasmonic nanohelices a powerful nanophotonic tool for, for example, (bio-)sensing applications