Structure and chemical composition of mixed benzylguanine- and methoxy-terminated self-assembled monolayers for immobilization of biomolecules

Photo-cross-linked and pH-Switchable Soft Polymer Nanocapsules from Polyglycidyl Ethers

Soft polymer nanocapsules and microgels, which can adapt their shape and, at the same time, sequester and release molecular payloads in response to an external trigger, are a challenging complement to vesicular structures like polymersomes. In this work, we report the synthesis of such capsules by photo-cross-linking of coumarin-substituted polyglycidyl ethers, which we prepared by Williamson etherification of epichlorohydrin (ECH) repeating units with 7-hydroxycoumarin in copolymers with tert-butyl glycidyl ether (tBGE). To control capsule size, we employed the prepolymers in an o/w miniemulsion, where they formed a gel layer at the interface upon irradiation at 365 nm by [2π + 2π] photodimerization of the coumarin groups. Upon irradiation at 254 nm, the reaction could be reversed and the gel wall could be repeatedly disintegrated and rebuilt. We further demonstrated (i) reversible hydrophilization of the gels by hydrolysis of the lactone rings in coumarin dimers as a mechanism to manipulate the permeability of the capsules and (ii) binding functional molecules as amides. Thus, the presented nanogels are remarkably versatile and can be further used as a carrier system.

The Evolution of SNAP-Tag Labels

The conjugation of proteins with synthetic molecules can be conducted in many different ways. In this Perspective, we focus on tag-based techniques and specifically on the SNAP-tag technology. The SNAP-tag technology makes use of a fusion protein between a protein of interest and an enzyme tag that enables the actual conjugation reaction. The SNAP-tag is based on the O⁶-alkylguanine-DNA alkyltransferase (AGT) enzyme and is optimized to react selectively with O⁶-benzylguanine (BG) substrates. BG-containing dye derivatives have frequently been used to introduce a fluorescent tag to a specific protein. We believe that the site-specific conjugation of polymers to proteins can significantly benefit from the SNAP-tag technology. Especially, polymers synthesized via reversible deactivation radical polymerization allow for the facile introduction of a BG end group to enable SNAP-tag conjugation.

Photothermal catalytic properties of layered titanium chalcogenide nanomaterials

Titanium chalcogenides are valuable candidates for visible light photocatalysis at high efficiency levels. TiS₂/TiO₂ core shell heterostructures are able to increase this efficiency by an effective quenching of the exiton recombination.

Light-induced cross-linking and post-cross-linking modification of polyglycidol

The photoinduced radical generation process has received renewed interest due to its economic and ecological appeal. Herein the light-induced cross-linking of functional polyglycidol and its post-cross-linking modification are presented. Linear polyglycidol was first functionalized with a tertiary amine in a two-step reaction. Dimethylaminopropyl functional polyglycidol was cross-linked in a UV-light mediated reaction with camphorquinone as a type II photoinitiator. The cross-linked polyglycidol was further functionalized by quaternization with various organoiodine compounds. Aqueous dispersions of the cross-linked polymers were investigated by means of DLS and zeta potential measurements. Polymer films were evaluated by DSC and XPS.

Bombyx mori silk/titania/gold hybrid materials for photocatalytic water splitting: combining renewable raw materials with clean fuels

The synthesis, structure, and photocatalytic water splitting performance of two new titania (TiO2)/gold(Au)/Bombyx mori silk hybrid materials are reported. All materials are monoliths with diameters of up to ca. 4.5 cm. The materials are macroscopically homogeneous and porous with surface areas between 170 and 210 m2/g. The diameter of the TiO2 nanoparticles (NPs) - mainly anatase with a minor fraction of brookite - and the Au NPs are on the order of 5 and 7-18 nm, respectively. Addition of poly(ethylene oxide) to the reaction mixture enables pore size tuning, thus providing access to different materials with different photocatalytic activities. Water splitting experiments using a sunlight simulator and a Xe lamp show that the new hybrid materials are effective water splitting catalysts and produce up to 30 mmol of hydrogen per 24 h. Overall the article demonstrates that the combination of a renewable and robust scaffold such as B. mori silk with a photoactive material provides a promising approach to new monolithic photocatalysts that can easily be recycled and show great potential for application in lightweight devices for green fuel production.

An interpenetrating, microstructurable and covalently attached conducting polymer hydrogel for neural interfaces

This study presents a new conducting polymer hydrogel (CPH) system, consisting of the synthetic hydrogel P(DMAA-co-5%MABP-co-2,5%SSNa) and the conducting polymer (CP) poly(3,4-ethylenedioxythiophene) (PEDOT), intended as coating material for neural interfaces. The composite material can be covalently attached to the surface electrode, can be patterned by a photolithographic process to influence selected electrode sites only and forms an interpenetrating network. The hybrid material was characterized using cyclic voltammetry (CV), impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS), which confirmed a homogeneous distribution of PEDOT throughout all CPH layers. The CPH exhibited a 2,5 times higher charge storage capacity (CSC) and a reduced impedance when compared to the bare hydrogel. Electrochemical stability was proven over at least 1000 redox cycles. Non-toxicity was confirmed using an elution toxicity test together with a neuroblastoma cell-line. The described material shows great promise for surface modification of neural probes making it possible to combine the beneficial properties of the hydrogel with the excellent electronic properties necessary for high quality neural microelectrodes.

STATEMENT OF SIGNIFICANCE

Conductive polymer hydrogels have emerged as a promising new class of materials to functionalize electrode surfaces for enhanced neural interfaces and drug delivery. Common weaknesses of such systems are delamination from the connection surface, and the lack of suitable patterning methods for confining the gel to the selected electrode site. Various studies have reported on conductive polymer hydrogels addressing one of these challenges. In this study we present a new composite material which offers, for the first time, the unique combination of properties: it can be covalently attached to the substrate, forms an interpenetrating network, shows excellent electrical properties and can be patterned via UV-irradiation through a structured mask.

Covalent and density-controlled surface immobilization of E-cadherin for adhesion force spectroscopy

E-cadherin is a key cell-cell adhesion molecule but the impact of receptor density and the precise contribution of individual cadherin ectodomains in promoting cell adhesion are only incompletely understood. Investigating these mechanisms would benefit from artificial adhesion substrates carrying different cadherin ectodomains at defined surface density. We therefore developed a quantitative E-cadherin surface immobilization protocol based on the SNAP-tag technique. Extracellular (EC) fragments of E-cadherin fused to the SNAP-tag were covalently bound to self-assembled monolayers (SAM) of thiols carrying benzylguanine (BG) head groups. The adhesive functionality of the different E-cadherin surfaces was then assessed using cell spreading assays and single-cell (SCSF) and single-molecule (SMSF) force spectroscopy. We demonstrate that an E-cadherin construct containing only the first and second outmost EC domain (E1-2) is not sufficient for mediating cell adhesion and yields only low single cadherin-cadherin adhesion forces. In contrast, a construct containing all five EC domains (E1-5) efficiently promotes cell spreading and generates strong single cadherin and cell adhesion forces. By varying the concentration of BG head groups within the SAM we determined a lateral distance of 5–11 nm for optimal E-cadherin functionality. Integrating the results from SCMS and SMSF experiments furthermore demonstrated that the dissolution of E-cadherin adhesion contacts involves a sequential unbinding of individual cadherin receptors rather than the sudden rupture of larger cadherin receptor clusters. Our method of covalent, oriented and density-controlled E-cadherin immobilization thus provides a novel and versatile platform to study molecular mechanisms underlying cadherin-mediated cell adhesion under defined experimental conditions.