Core-Shell Fe@SiO2 Nanoparticles Synthesized via Modified Stober Method for High Activity in Cr(VI) Reduction.

In this paper, Fe@SiO2 nanoparticles (α-Fe nanoparticles coated with SiO2 shell) were synthesized at room temperature using the modified Stöber method combined with potassium borohydride (KBH4) reduction process. The present study depicts the facile synthesis of Fe@SiO2 without the presence of surfactants and stabilizers. In this experiment, KBH4 acted both as a reducing agent for iron salt and a catalyst for hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The Fe@SiO2 nanoparticles were characterized using X-ray diffraction method, specific surface area (BET) technique, transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The optimal mass ratio of Fe in the form of anhydrous ferric chloride (FeCl3) and SiO2) in the form of TEOS was 4:1. α-Fe-Fe nanoparticles (size of about 45 nm) were coated with approximately 10 nm thick SiO2 shells. Moreover, Fe/SiO2 (Fe0 nanoparticles supported by silica nanoparticles) was synthesized to compare the results. Due to the silica shells, Fe cores cannot be oxidized when dipped in the concentrated sulfuric acid, and hence, the removal of Cr(VI) was not weakened in the acidic environment.

Single Interdigital Transducer Approach for Gravimetrical SAW Sensor Applications in Liquid Environments.

Surface acoustic wave (SAW) devices are well known for mass-sensitive sensor applications. In biosensing applications, chemical and biochemically evoked binding processes on surfaces are detected in liquid environments using delay line or resonator sensor configurations, preferably in combination with the appropriate microfluidic devices. All configurations share the common feature of analyzing the transmission characteristic of the propagating SAW. In this paper, a novel SAW-based impedance sensor type is introduced which uses only one interdigital transducer (IDT), simultaneously as the SAW generator and the sensor element. Here, the input port reflection coefficient S11 is measured at the IDT instead of the commonly used S21 transmission forward gain parameter. Thus, a sharp and distinct peak of the S11 spectrum is obtained, enabling a comfortable direct readout of the sensor signal. Proof of the concept was gained by analyzing the specific binding of the 4-mercaptophenylacetic acid gold nanoparticles (MPA-AuNP) directly to the IDT surface. The corresponding binding kinetic of the MPA-AuNP on the functionalized gold surface has been analyzed and a sensitivity of 7.4 mΩ nM-1 has been determined.

Lectin binding studies on a glycopolymer brush flow-through biosensor by localized surface plasmon resonance.

A localized surface plasmon resonance biosensor in a flow-through configuration was applied for investigating kinetics of lectin binding to surface-grafted glycopolymer brushes. Polycarbonate filter membranes with pore sizes of 400 nm were coated with a 114-nm thick gold layer and used as substrate for surface-initiated atom-transfer radical polymerization of a glycomonomer. These grafted from glycopolymer brushes were further modified with two subsequent enzymatic reactions on the surface to yield an immobilized trisaccharide presenting brush. Specific binding of lectins including Clostridium difficile toxin A receptor domain to the glycopolymer brush surface could be investigated in a microfluidic setup with flow-through of the analytes and transmission surface plasmon resonance spectroscopy. Graphical abstract Glycopolymer brushes serve as high affinity ligands for lectin and toxin interactions in a sensitive, disposable flow-through LSPR biosensor.

Surface enhanced infrared spectroscopy with gold strip gratings.

We investigate surface enhanced infrared absorption (SEIRA) spectroscopy with gold strip gratings made by standard optical lithography. By exciting surface plasmon polaritons on both air-gold and gold-substrate interfaces, the resonance of the 1D gratings is linearly tunable with the grating period. With the field enhancement at the edge of the gold strips, a SEIRA enhancement factor more than 6000 for PMMA molecules is achieved. The strong SEIRA enhancement together with the easy fabrication makes the gold strip grating a promising candidate for SEIRA experiments.

Surface topography enhances differentiation of mesenchymal stem cells towards osteogenic and adipogenic lineages.

Surface topography impacts on cell growth and differentiation, but it is not trivial to generate defined surface structures and to assess the relevance of specific topographic parameters. In this study, we have systematically compared in vitro differentiation of mesenchymal stem cells (MSCs) on a variety of groove/ridge structures. Micro- and nano-patterns were generated in polyimide using reactive ion etching or multi beam laser interference, respectively. These structures affected cell spreading and orientation of human MSCs, which was also reflected in focal adhesions morphology and size. Time-lapse demonstrated directed migration parallel to the nano-patterns. Overall, surface patterns clearly enhanced differentiation of MSCs towards specific lineages: 15 µm ridges increased adipogenic differentiation whereas 2 µm ridges enhanced osteogenic differentiation. Notably, nano-patterns with a periodicity of 650 nm increased differentiation towards both osteogenic and adipogenic lineages. However, in absence of differentiation media surface structures did neither induce differentiation, nor lineage-specific gene expression changes. Furthermore, nanostructures did not affect the YAP/TAZ complex, which is activated by substrate stiffness. Our results provide further insight into how structuring of tailored biomaterials and implant interfaces - e.g. by multi beam laser interference in sub-micrometer scale - do not induce differentiation of MSCs per se, but support their directed differentiation.