Stephanie Hiltl

Ordering and Printing Virus Arrays: A Straightforward Way to Functionalize Surfaces

The fabrication of small structures has attracted increasing interest in the past few decades. One widespread technique to achieve patterned surfaces is microcontact printing ( μ CP). The concept of μ CP is to transfer a solution of the desired substance (ink) onto a fl at surface via a structured, elastomeric stamp. It is a very fl exible method as the ink and the stamp can be varied. Therefore, it is possible to produce surface patterns that differ in geometry and in the printed substance itself. Initially used for printing self-assembled monolayers (SAMs) of organic components, [ 1 ] today the applications vary from small molecules to macromolecules, nanoparticles, and biological systems. [ 2–6 ] While the well established μ CP technique has a lot of advantages in terms of fl exibility, it has one signifi cant drawback: the elastomeric stamps are usually made by replica molding. [ 7 ] Although the molding process itself is simple and cost effective, the process relies on a lithographically manufactured master. [ 8 ] Therefore, it is a rather expensive method (in terms of operating costs), which reduces the accessibility for a wide range of operators. Recently, we established an alternative approach to generate stamps in a lithography-free way. The effort made use of controlled wrinkling of poly(dimethylsiloxane) (PDMS) to produce the elastomeric stamps for μ CP. [ 3 ] Using this technique, it was possible to generate arrays of bovine serum albumin (BSA) on a SiO x surface, where the width of the stripes is on the order of < 1 μ m. In particular, the alignment and assembly of biomacromolecules has attracted intense interest in recent years. [ 9–14 ]

Nanostructured wrinkled surfaces for templating bionanoparticles—controlling and quantifying the degree of order

We present a novel method to align the tobacco mosaic virus (TMV) on topographically structured surfaces. In order to gain defined patterns we use wrinkled polydimethlysiloxane (PDMS) sheets as templates. We aligned the virus with a simple spin-coating procedure on the PDMS sheet. The concentration of the virus solution and the spin speed are varied in order to identify ideal conditions for the arrangement of the viruses on the wrinkled templates. Here, we establish a simple analytical approach which allows quantifying the degree of order of the patterns, which is the basis for a quantitative discussion of templating efficiency. Furthermore, we discuss the role of dewetting processes for the particle assembly. TMVs can be used as reactive nanoparticles due to their well-defined surface chemistry. They can as well serve as a model system for alignment of anisotropic particles via spin coating from solution.

A one-step screening process for optimal alignment of (soft) colloidal particles

We developed nanostructured gradient wrinkle surfaces to establish a one-step screening process towards optimal assembly of soft and hard colloidal particles (microgel systems and silica particles). Thereby, we simplify studies on the influence of wrinkle dimensions (wavelength, amplitude) on particle properties and their alignment. In a combinatorial experiment, we optimize particle assembly regarding the ratio of particle diameter vs. wrinkle wavelength and packing density and point out differences between soft and hard particles. The preparation of wrinkle gradients in oxidized top layers on elastic poly(dimethylsiloxane) (PDMS) substrates is based on a controlled wrinkling approach. Partial shielding of the substrate during plasma oxidation is crucial to obtain two-dimensional gradients with amplitudes ranging from 7 to 230 nm and wavelengths between 250 and 900 nm.

A Fluorescent Hydrogel-Based Flow Cytometry High-Throughput Screening Platform for Hydrolytic Enzymes

Screening throughput is a key in directed evolution experiments and enzyme discovery. Here, we describe a high-throughput screening platform based on a coupled reaction of glucose oxidase and a hydrolase (Yersinia mollaretii phytase [YmPh]). The coupled reaction produces hydroxyl radicals through Fentons reaction, acting as initiator of poly(ethyleneglycol)-acrylate-based polymerization incorporating a fluorescent monomer. As a consequence, a fluorescent hydrogel is formed around Escherichia coli cells expressing active YmPh. We achieve five times enrichment of active cell population through flow cytometry analysis and sorting of mixed populations. Finally, we validate the performance of the fluorescent polymer shell (fur-shell) technology by directed phytase evolution that yielded improved variants starting from a library containing 10(7) phytase variants. Thus, fur-shell technology represents a rapid and nonlaborious way of identifying the most active variants from vast populations, as well as a platform for generation of polymer-hybrid cells for biobased interactive materials.

Piezoelectric Properties of Non-Polar Block Copolymers

Most polymers are typical dielectric materials, but recent research in our group has shown that nanostructured block copolymer morphologies exhibit new and unexpected electroactive behavior. We present herein the fi rst study of converse piezoelectric properties in non-crystalline polymer systems, consisting of non-polar monomers, and evaluate its evolution with temperature to yield detailed information on electric fi eld‐ polymer interaction on a molecular level. The observed properties should hold generally and suggest that block copolymers may provide a valuable new route to piezoelectric materials. So far, mostly inorganic, perovskite structured ceramics, many of them titanate derivatives such as lead zirconate titanate (PZT), dominate the fi eld of commercial piezoelectric applications. Nanogenerators, fi eld-effect transistors, strain, and optoelectronic sensors are only few of many applications for this interesting class of materials. [ 1 , 2 ] Whilst the piezoelectric properties of many of these crystals and ceramics are well

Wetting Phenomena on (Gradient) Wrinkle Substrates

We characterize the wetting behavior of nanostructured wrinkle and gradient wrinkle substrates. Different contact angles on both sides of a water droplet after deposition on a gradient sample induce the self-propelled motion of the liquid toward smaller wrinkle dimensions. The droplet motion is self-limited by the contact angles balancing out. Because of the correlation between droplet motion and contact angles, we investigate the wetting behavior of wrinkle substrates with constant dimensions (wavelengths of 400-1200 nm). Contact angles of water droplets on those substrates increase with increasing dimensions of the underlying substrate. The results are independent of the two measurement directions, parallel and perpendicular to the longitudinal axis of the nanostructure. The presented findings may be considered for designing microfluidic or related devices and initiate ideas for the development of further wrinkle applications.