Block Copolymer-Templated Au@CdSe Core-Satellite Nanostructures with Solvent-Dependent Optical Properties.

In the present work, we report the fabrication and characterization of well-defined core-satellite nanostructures. These nanostructures comprise block copolymer (BCP) micelles, containing a single gold nanoparticle (AuNP) in the core and multiple photoluminescent cadmium selenide (CdSe) quantum dots (QDs) attached to the micelle's coronal chains. The asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) BCP was employed to develop these core-satellite nanostructures in a series of P4VP-selective alcoholic solvents. The BCP micelles were first prepared in 1-propanol and subsequently mixed with AuNPs, followed by gradual addition of CdSe QDs. This method resulted in the development of spherical micelles that contained a PS/Au core and a P4VP/CdSe shell. These core-satellite nanostructures, developed in different alcoholic solvents, were further employed for the time-resolved photoluminescence analysis. It was found that solvent-selective swelling of the core-satellite nanostructures tunes the distance between the QDs and AuNPs and modulates their Förster resonance energy transfer (FRET) behavior. The average lifetime of the donor emission varied from 12.3 to 10.3 nanoseconds (ns) with the change in the P4VP-selective solvent within the core-satellite nanostructures. Furthermore, the distances between the donor and acceptor were also calculated using efficiency measurements and corresponding Förster distances. The resulting core-satellite nanostructures hold promising potential in various fields, such as photonics, optoelectronics, and sensors that utilize the FRET process.

Directional Amplified Photoluminescence through Large-Area Perovskite-Based Metasurfaces.

Perovskite nanocrystals are high-performance, solution-processed materials with a high photoluminescence quantum yield. Due to these exceptional properties, perovskites can serve as building blocks for metasurfaces and are of broad interest for photonic applications. Here, we use a simple grating configuration to direct and amplify the perovskite nanocrystals' original omnidirectional emission. Thus far, controlling these radiation properties was only possible over small areas and at a high expense, including the risks of material degradation. Using a soft lithographic printing process, we can now reliably structure perovskite nanocrystals from the organic solution into light-emitting metasurfaces with high contrast on a large area. We demonstrate the 13-fold amplified directional radiation with an angle-resolved Fourier spectroscopy, which is the highest observed amplification factor for the perovskite-based metasurfaces. Our self-assembly process allows for scalable fabrication of gratings with predefined periodicities and tunable optical properties. We further show the influence of solution concentration on structural geometry. By increasing the perovskite concentration 10-fold, we can produce waveguide structures with a grating coupler in one printing process. We analyze our approach with numerical modeling, considering the physiochemical properties to obtain the desired geometry. This strategy makes the tunable radiative properties of such perovskite-based metasurfaces usable for nonlinear light-emitting devices and directional light sources.

Disentangling the Orientations of Spectrally Overlapping Transition Dipoles in Dense Dye Layers.

The transition dipole orientations of dye assemblies in heterostructures have a crucial impact on the efficiency of novel optoelectronic devices such as organic thin-film transistors and light-emitting diodes. These devices are frequently based on heterojunctions and tandem structures featuring multiple optical transitions. Precise knowledge of preferred orientations, spatial order, and spatial variations is highly relevant. We present a fast and universal large-area screening method to determine the transition dipole orientations in dye assemblies with diffraction-limited spatial resolution. Moreover, our hyperspectral imaging approach disentangles the orientations of different chromophores. As a demonstration, we apply our technique to dye monolayers with two optical transitions sandwiched between two ultrathin silicate nanosheets. A comprehensive model for dipole orientation distributions in monolayers reveals a long-range orientational order and a strong correlation between the two transitions.

Understanding Beta-Lactam-Induced Lysis at the Single-Cell Level.

Mechanical rupture, or lysis, of the cytoplasmic membrane is a common cell death pathway in bacteria occurring in response to ß-lactam antibiotics. A better understanding of the cellular design principles governing the susceptibility and response of individual cells to lysis could indicate methods of potentiating ß-lactam antibiotics and clarify relevant aspects of cellular physiology. Here, we take a single-cell approach to bacterial cell lysis to examine three cellular features-turgor pressure, mechanosensitive channels, and cell shape changes-that are expected to modulate lysis. We develop a mechanical model of bacterial cell lysis and experimentally analyze the dynamics of lysis in hundreds of single Escherichia coli cells. We find that turgor pressure is the only factor, of these three cellular features, which robustly modulates lysis. We show that mechanosensitive channels do not modulate lysis due to insufficiently fast solute outflow, and that cell shape changes result in more severe cellular lesions but do not influence the dynamics of lysis. These results inform a single-cell view of bacterial cell lysis and underscore approaches of combatting antibiotic tolerance to ß-lactams aimed at targeting cellular turgor.

Complex Metal Nanostructures with Programmable Shapes from Simple DNA Building Blocks.

Advances in DNA nanotechnology allow the design and fabrication of highly complex DNA structures, uisng specific programmable interactions between smaller nucleic acid building blocks. To convey this concept to the fabrication of metallic nanoparticles, an assembly platform is developed based on a few basic DNA structures that can serve as molds. Programming specific interactions between these elements allows the assembly of mold superstructures with a range of different geometries. Subsequent seeded growth of gold within the mold cavities enables the synthesis of complex metal structures including tightly DNA-caged particles, rolling-pin- and dumbbell-shaped particles, as well as T-shaped and loop particles with high continuity. The method further supports the formation of higher-order assemblies of the obtained metal geometries. Based on electrical and optical characterizations, it is expected that the developed platform is a valuable tool for a self-assembly-based fabrication of nanoelectronic and nanooptic devices.