Polarization nano-tomography of tightly focused light landscapes by self-assembled monolayers

Recently, four-dimensional (4D) functional nano-materials have attracted considerable attention due to their impact in cutting-edge fields such as nano-(opto)electronics, -biotechnology or -biomedicine. Prominent optical functionalizations, representing the fourth dimension, require precisely tailored light fields for its optimal implementation. These fields need to be like-wise 4D, i.e., nano-structured in three-dimensional (3D) space while polarization embeds additional longitudinal components. Though a couple of approaches to realize 4D fields have been suggested, their breakthrough is impeded by a lack of appropriate analysis techniques. Combining molecular self-assembly, i.e., nano-chemistry, and nano-optics, we propose a polarization nano-tomography of respective fields using the functional material itself as a sensor. Our method allows a single-shot identification of non-paraxial light fields at nano-scale resolution without any data post-processing. We prove its functionality numerically and experimentally, elucidating its amplitude, phase and 3D polarization sensitivity. We analyze non-paraxial field properties, demonstrating our method’s capability and potential for next generation 4D materials.

The realisation of 4D light fields, where longitudinal polarisation represents the fourth dimension, has been limited by the lack of appropriate analysis techniques. Here, the authors use interaction with self-assembled monolayers of fluorescent molecules, which allow for identification of non-paraxial light fields based on a single image frame.

Functionalization and Patterning of Self-Assembled Monolayers and Polymer Brushes Using Microcontact Chemistry

Because the surface connects a material to its environment, the functionalization, modification, and patterning of surfaces is key to a wide range of materials applied in microelectronics, displays, sensing, microarrays, photovoltaics, catalysis, and other fields. Self-assembled monolayers (SAMs), which can be deposited on a wide range of inorganic materials, are only a few nanometers thick, yet they can radically change the properties of the resulting interface. Alternatively, thin polymer films composed of polymer brushes grown from the surface provide a more robust molecular modification of inorganic materials. For many applications, patterned SAMs or polymer brushes are desired. Over the past decade, our group has shown that both SAMs as well as polymer brushes can be patterned very efficiently using microcontact printing. In microcontact printing, a molecular "ink" is deposited on a suitable substrate using a microstructured elastomer stamp, which delivers the ink exclusively in the area of contact between stamp and substrate. In contrast to most types of lithography, microcontact printing does not require expensive equipment. Our work has shown that "microcontact chemistry" is a powerful additive surface patterning method, in which molecular inks react with a precursor SAM during printing so that surfaces can be modified with various orthogonal functional groups or molecular recognition sites in microscale patterns. Functional groups include reactive groups for click chemistry or photochemistry and initiators for radical polymerization. Molecular recognition sites include host-guest chemistry as well as biochemical ligands such as carbohydrates and biotin. In this Account, we present an overview of our research in this area including selected examples of work by other groups. In the first part, we review our work on the patterning of SAMs using microcontact chemistry, with a focus on click chemistry and photochemistry. We will show how cycloadditions, thiol-ene reactions, and tetrazole chemistry can be used to obtain versatile surface patterns. In the second part, we demonstrate that microcontact chemistry can be used to pattern polymer brushes. Among others, initiators for surface-induced nitroxide-mediated polymerization and atom transfer polymerization were printed and used to grow patterned polymer brushes with molecular recognition groups suitable for responsive surface adhesion. In the third part, we describe how SAMs and polymer brushes can be printed on microparticles instead of flat substrates so that Janus particles with functional patches can be obtained. Finally, we present a brief outlook on further developments expected in this field.

Functionalization of Clinically Approved MRI Contrast Agents for the Delivery of VEGF

In combining the two clinically approved substances ferumoxytol and VEGF-165 via peptide coupling, we propose a straightforward approach to obtain a potentially ready-to-use theranostic contrast agent for specific cardiovascular diseases. Clinical and preclinical magnetic resonance imaging (MRI) studies have shown that intravenously applied superparamagnetic ferumoxytol nanoparticles accumulate in acute ischemic myocardial tissue. On the other hand, growth factors such as VEGF-165 (vascular endothelial growth factor) play a major role during angiogenesis and vasculogenesis. Promising clinical studies with systemic application of VEGF-165 have been performed in the past. However, following untargeted systemic application, the biological half-life of VEGF-165 was too short to develop its full effect. Therefore, we hypothesized that ferumoxytol particles functionalized with VEGF-165 will accumulate in ischemic myocardial regions and can be detected by MRI, while the prolonged retention of VEGF-165 due to ferumoxytol-coupling will help to prevent adverse tissue remodeling. In addition, strategies such as magnetic targeting can be used to enhance targeted local accumulation. As a precondition for further preclinical research, we confirmed the successful coupling between ferumoxytol and VEGF-165 in detail (TEM, XPS, and IR spectroscopy), characterized the functionalized ferumoxytol particles (DLS, TEM, and MRI) and performed in vitro tests that showed their superior effect on cell growth and survival.

Responsive surface adhesion based on host–guest interaction of polymer brushes with cyclodextrins and arylazopyrazoles

Polymer brushes functionalized with cyclodextrin host and arylazopyrazole guest monomers provide strong surface adhesion that is water resistent but can be deactivated by UV irradiation.

Carbohydrate-Responsive Surface Adhesion Based on the Dynamic Covalent Chemistry of Phenylboronic Acid- and Catechol-Containing Polymer Brushes

A glue, based on dynamic covalent chemistry, with a strong adhesion (2.38 kg cm^-2 ), water resistance and carbohydrate responsive reversibility is presented. Using surface initiated atom transfer radical polymerization (SI-ATRP), glass and silicon surfaces were coated with copolymers functionalized with phenylboronic acids and catechols. In combination with microcontact printing (μCP) these polymer brushes give access to a carbohydrate responsive "supramolecular Velcro".

Surface Functionalization with Carboxylic Acids by Photochemical Microcontact Printing and Tetrazole Chemistry

In this paper, we show that carboxylic acid-functionalized molecules can be patterned by photochemical microcontact printing on tetrazole-terminated self-assembled monolayers. Upon irradiation, tetrazoles eliminate nitrogen to form highly reactive nitrile imines, which can be ligated with several different nucleophiles, carboxylic acids being the most reactive. As a proof of concept, we immobilized trifluoroacetic acid to monitor the reaction with X-ray photoelectron spectroscopy. Moreover, we also immobilized peptides and fabricated carbohydrate-lectin as well as biotin-streptavidin microarrays using this method. Surface-patterning was demonstrated by fluorescence microscopy and time-of-flight secondary ion mass spectrometry.

Solid state electrochemiluminescence from homogeneous and patterned monolayers of bifunctional spirobifluorene

Electrochemiluminescence (ECL) from self-assembled monolayers of a spirobifluorene dye covalently linked to a transparent ITO surface is reported.

Metal vapor synthesis of ultrasmall Pd nanoparticles functionalized with N-heterocyclic carbenes

The synthesis of N-heterocyclic carbene (NHC)-stabilized palladium nanoparticles (PdNPs) by an entirely new strategy comprising the NHC functionalization of ligand-free PdNPs obtained by metal vapor synthesis is described.

Patterning of Nanoclays on Positively Charged Self-Assembled Monolayers via Micromolding in Capillaries

Nanoclays are nanomaterials with versatile adsorptive properties. This contribution describes the generation of micropatterns of a nanoclay ("laponite") on ammonium-terminated, self-assembled monolayers (SAMs) on glass and silicon. Microstructured immobilization of the laponite was performed using micromolding in capillaries (MIMIC). The immobilization was verified using contact angle goniometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and fluorescence microscopy. Furthermore, laponite was modified with Nile red to generate a fluorescence enhancement-based surface sensor for the vitamin choline.

Stabilization of High Oxidation State Upconversion Nanoparticles by N-Heterocyclic Carbenes

The stabilization of high oxidation state nanoparticles by N-heterocyclic carbenes is reported. Such nanoparticles represent an important subset in the field of nanoparticles, with different and more challenging requirements for suitable ligands compared to elemental metal nanoparticles. N-Heterocyclic carbene coated NaYF₄ :Yb,Tm upconversion nanoparticles were synthesized by a ligand-exchange reaction from a well-defined precursor. This new photoactive material was characterized in detail and employed in the activation of photoresponsive molecules by low-intensity near-infrared light (λ=980 nm).

On surface O-glycosylation by catalytic microcontact printing

Carbohydrate microarrays are made by microcontact printing of glycosyl donors on hydroxyl terminated substrates.

Preparation of Functional Alternating Polymer Brushes and Their Orthogonal Surface Modification through Microcontact Printing

This paper reports microcontact printing (μCP) to immobilize an alkoxyamine initiator (regulator) on glass and silicon substrates and subsequent surface-initiated alternating nitroxide-mediated copolymerization (siNMP) of hexafluoroisopropyl acrylate (HFIPA) and 7-octenylvinyl ether (OVE). The resulting patterned polymer brushes are analyzed by using atomic force microscopy (AFM). In addition, site-specific post-functionalization of the alternating polymer brushes by applying two orthogonal surface reactions is achieved with thiols and amines through μCP. The versatility of this post-polymerization modification approach is demonstrated by site-selective immobilization of small organic molecules, fluorophores, and ligands providing a binary bioactive surface. The successful side-by-side orthogonal immobilization is verified by using X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy.

[Elective and acute procedures in trauma surgery. Complications requiring revision]

BACKGROUND

Using data between 2010 and 31 March 2012, a cohort study concerning complications of all discharged patients who had undergone surgery was performed.

PATIENTS AND METHODS

In our detailed analysis, we defined two groups out of the 5,248 cases: an acute trauma patient group (n = 3,942) and an elective patient group (n = 1,306). Complications were divided into the following groups: (1) technical complications (failure of the implant, poor indication, instability or non-union), (2) local complication (hematoma or delayed wound healing), and (3) infection.

RESULTS

In 4.4% of patients (n = 233), treatment was delayed because of a complication. In 2.3% (n = 123), a technical complication was observed, followed by local complications in 1.3% [e.g., hematoma 0.6%, other wound healing disturbance (0.6%)]. In the elective surgery group, the percentage of complications needing revision (3.1%) was significantly lower compared to the trauma surgery group (4.9%). The patient's age for the non-complicated surgery group was significantly lower (54 vs. 63 years) and length of hospital stay (6.7 days longer) was significantly higher in patients with complications. Risk factors such as smoking were significantly more frequent in patients with complications (9% vs. 18.5%).

CONCLUSION

Recording and evaluating of complications in surgery plays a major role for quality control. Certain factors (e.g., comorbidity and the age of the patient) cannot be influenced, but complications caused by technical problems could theoretically be avoided. Especially these cases must be analyzed in detail to reduce the percentage of complications requiring revision.

Supramolecular surface adhesion mediated by azobenzene polymer brushes

Surface immobilised polymer brushes containing azobenzenes were prepared using microcontact chemistry and surface-initiated atom transfer radical polymerisation. Two surfaces bearing brushes can be glued together in the presence of a β-cyclodextrin polymer.

Surface patterning with natural and synthetic polymers via an inverse electron demand Diels–Alder reaction employing microcontact chemistry

Bioorthogonal ligation methods are the focus of current research due to their versatile applications in biotechnology and materials science for post-functionalization and immobilization of biomolecules.