New buffer systems for photopainting of single biomolecules.

We present newly developed buffer systems that significantly improve the efficiency of a photochemically induced surface modification at the single molecule level. Buffers with paramagnetic cations and radical oxygen promoting species facilitate laser-assisted protein adsorption by photobleaching (LAPAP) of single fluorescently labelled oligonucleotides or biotin onto multi-photon-lithography-structured 2D and 3D acrylate scaffolds. Single molecule fluorescence microscopy has been used to quantify photopainting efficiency.

Stimulated Emission Depletion Inspired Sub-100 nm Structuring of Epoxides Using 2-Chlorothioxanthone as Photosensitizer.

Until very recently, the enhancement of multiphoton-based optical lithography by stimulated emission depletion (STED) inspired techniques was limited mostly to (meth)acrylates. Epoxides, which play an important role in semiconductor clean-room technology, were basically excluded from capitalizing on STED-inspired lithography, and if they were successfully used in STED-inspired lithography, the achievable structure sizes remained at 125 nm and above. We now found that using 2-chlorothioxanthone (CTX) as a sensitizer for a sulfonium salt acting as the photoinitiator allows for shrinking the structure size down to 83 nm.

Multiphoton lithography with protein photoresists.

Recently, 2D/3D direct laser writing has attracted increased attention due to its broad applications ranging from biomedical engineering to aerospace. 3D nanolithography of water-soluble protein-based scaffolds have been envisioned to provide a variety of tunable properties. In this paper, we present a functional protein-based photoresist with tunable mechanical properties that is suitable for multiphoton lithography (MPL).

STED-Inspired Cationic Photoinhibition Lithography.

Direct laser writing by two-photon lithography has been enhanced substantially during the past two decades by techniques borrowed from stimulated emission depletion (STED) microscopy. However, STED-inspired lithography was so far limited to radical polymerizations, mostly to acrylates and methacrylates. Cationic polymers did not derive benefits from this technique.

Low-Fluorescence Starter for Optical 3D Lithography of Sub-40 nm Structures.

Stimulated emission depletion (STED) has been used to break the diffraction limit in fluorescence microscopy. Inspired by this success, similar methods were used to reduce the structure size in three-dimensional, subdiffractional optical lithography. So far, only a very limited number of radical polymerization starters proved to be suitable for STED-inspired lithography.

[The effect of mobile air filter systems on aerosol concentrations in large volume scenarios against the background of the risk of infection of COVID-19. Can classroom teaching be resumed?].

Background: As a consequence of the corona pandemic, universities nationwide had stopped classroom teaching by the start of the summer semester 2020. As part of the second lockdown, in many states schools and day care centers were also closed or reduced to a minimum. In this context the effect of room air filters has already been discussed multiple times; however, mobile devices for air filtration are currently not recommended by the German Federal Environment Agency.

Dual Channel Microfluidics for Mimicking the Blood-Brain Barrier.

High-resolution imaging is essential for analysis of the steps and way stations of cargo transport in models of the endothelium. In this study, we demonstrate a microfluidic system consisting of two channels horizontally separated by a cell-growth-promoting membrane. Its design allows for high-resolution (down to single-molecule level) imaging using a high numerical aperture objective with a short working distance.

STED lithography in microfluidics for 3D thrombocyte aggregation testing.

Three-dimensional photopolymerization techniques such as multiphoton polymerization lithography (MPL) and stimulated emission depletion (STED) lithography are powerful tools for fabricating structures in the sub-µm range. Combining these techniques with microfluidics enables us to broaden the range of their applications. In this study, we show a microfluidic device enhanced with MPL structures carrying STED-lithographically written nanoanchors that promote binding of the von Willebrand factor (vWF).

Plasmon-Assisted Direction- and Polarization-Sensitive Organic Thin-Film Detector.

Utilizing Bragg surface plasmon polaritons (SPPs) on metal nanostructures for the use in optical devices has been intensively investigated in recent years. Here, we demonstrate the integration of nanostructured metal electrodes into an ITO-free thin film bulk heterojunction organic solar cell, by direct fabrication on a nanoimprinted substrate. The nanostructured device shows interesting optical and electrical behavior, depending on angle and polarization of incidence and the side of excitation.

3D multiphoton lithography using biocompatible polymers with specific mechanical properties.

The fabrication of two- and three-dimensional scaffolds mimicking the extracellular matrix and providing cell stimulation is of high importance in biology and material science. We show two new, biocompatible polymers, which can be 3D structured multiphoton lithography, and determine their mechanical properties. Atomic force microscopy analysis of structures with sub-micron feature sizes reveals Young's modulus values in the 100 MPa range.

Optical Coulomb blockade lifting in plasmonic nanoparticle dimers.

If two metal nanoparticles are ultimately approached, a tunneling current prevents both an infinite redshift of the bonding dipolar plasmon and an infinite increase of the electric field in the hot spot between the nanoparticles. We argue that a Coulomb blockade suppresses the tunneling current and sustains a redshift even for sub-nanometer approach up to moderate fields. Only for stronger optical fields, the Coulomb blockade is lifted and a charge transfer plasmon is formed.

Quantitative regulation of the dynamic steady state of actin networks.

Principles of regulation of actin network dimensions are fundamentally important for cell functions, yet remain unclear. Using both in vitro and in silico approaches, we studied the effect of key parameters, such as actin density, ADF/Cofilin concentration and network width on the network length. In the presence of ADF/Cofilin, networks reached equilibrium and became treadmilling.

Proteins on Supported Lipid Bilayers Diffusing around Proteins Fixed on Acrylate Anchors.

Mobility of proteins and lipids plays a major role in physiological processes. Platforms which were developed to study protein interaction between immobilized and mobile proteins suffer from shortcomings such as fluorescence quenching or complicated fabrication methods. Here we report a versatile platform comprising immobilized histidine-tagged proteins and biotinylated proteins in a mobile phase.

Power Balance and Temperature in Optically Pumped Spasers and Nanolasers.

Spasers and nanolasers produce a significant amount of heat, which impedes their realizability. We numerically investigate the farfield emission and thermal load in optically pumped spasers with a coupled electromagnetic/thermal model, including additional temperature discontinuities due to interfacial Kapitza resistance. This approach allows to explore multiple combinations of constitutive materials suitable for robust manufacturable spasers.

Biofunctionalization of Sub-Diffractionally Patterned Polymer Structures by Photobleaching.

Stimulated emission depletion (STED) nanolithography allows nanofabrication below the diffraction limit. Recently, it was applied to nanoanchors for protein fixation down to the single molecule level. We now combined STED nanolithography with laser-assisted protein adsorption by photobleaching (LAPAP) for optical and selective attachment of proteins to subdiffractional structures.

Plasmonic Horizon in Gold Nanosponges.

An electromagnetic wave impinging on a gold nanosponge coherently excites many electromagnetic hot-spots inside the nanosponge, yielding a polarization-dependent scattering spectrum. In contrast, a hole, recombining with an electron, can locally excite plasmonic hot-spots only within a horizon given by the lifetime of localized plasmons and the speed carrying the information that a plasmon has been created. This horizon is about 57 nm, decreasing with increasing size of the nanosponge.

Multiphoton-Polymerized 3D Protein Assay.

Multiphoton polymerization (MPP) enables 3D fabrication of micro- and nanoscale devices with complex geometries. Using MPP, we create a 3D platform for protein assays. Elevating the protein-binding sites above the substrate surface allows an optically sectioned readout, minimizing the inevitable background signal from nonspecific protein adsorption at the substrate surface.

Network heterogeneity regulates steering in actin-based motility.

The growth of branched actin networks powers cell-edge protrusions and motility. A heterogeneous density of actin, which yields to a tunable cellular response, characterizes these dynamic structures. We study how actin organization controls both the rate and the steering during lamellipodium growth.

Bioinspired polymer microstructures for directional transport of oily liquids.

Nature has always served as an inspiration for scientists, helping them to solve a large diversity of technical problems. In our case, we are interested in the directional transport of oily liquids and as a model for this application we used the flat bug . In this report, we present arrays of drops looking like polymer microstructures produced by the two-photon polymerization technique that mimic the micro-ornamentation from the bug's cuticle.

Raman and Luminescent Spectra of Sulfonated Zn Phthalocyanine Enhanced by Gold Nanoparticles.

Sulfonated Zn phthalocyanine, as a prospective photosensitizer in the photodynamic therapy of tumors, is investigated by means of Raman, infrared, and fluorescence spectroscopies. Conventional and surface-enhanced spectra from this photosensitizer are obtained and compared. Gold nano-islands attached to silica cores (Au-SiO) are proposed as nanostructures providing plasmonically enhanced signals.

Bone-forming cells with pronounced spread into the third dimension in polymer scaffolds fabricated by two-photon polymerization.

The main aim of this work was to stimulate bone-forming cells to produce three-dimensional networks of mineralized proteins such as those occurring in bones. This was achieved by a novel approach using a specific type of mesenchymal progenitor cells (i.e.

Hybrid Multilayered Plasmonic Nanostars for Coherent Random Lasing.

Here, we report that hybrid multilayered plasmonic nanostars can be universally used as feedback agents for coherent random lasing in polar or nonpolar solutions containing gain material. We show that silver-enhancement of gold nanostars reduces the pumping threshold for coherent random lasing substantially for both a typical dye (R6G) and a typical fluorescent polymer (MEH-PPV). Further, we reveal that the lasing intensity and pumping threshold of random lasers based on silver-enhanced gold nanostars are not influenced by the silica coating, in contrast to gold nanostar-based random lasers, where silica-coated gold nanostars support only amplified spontaneous emission but no coherent random lasing.

Anticorrelation of Photoluminescence from Gold Nanoparticle Dimers with Hot-Spot Intensity.

Bulk gold shows photoluminescence (PL) with a negligible quantum yield of ∼10, which can be increased by orders of magnitude in the case of gold nanoparticles. This bears huge potential to use noble metal nanoparticles as fluorescent and unbleachable stains in bioimaging or for optical data storage. Commonly, the enhancement of the PL yield is attributed to nanoparticle plasmons, specifically to the enhancements of scattering or absorption cross sections.