Kristjan Saal

Preparation of smooth siloxane surfaces for AFM visualization of immobilized biomolecules

Development of scanning probe microscopy (SPM) techniques during past decade has made possible to study bioprocesses at a molecular level. Common protocols for immobilization of biomolecules for SPM studies are based on their adsorption to alkylsiloxane monolayers on hydroxylated surfaces. The same procedure is also widely used for DNA chip and biosensor fabrication. For SPM studies of immobilized biomolecules smooth carrier surfaces are mandatory. Several studies refer to the lack of reproducibility in formation of smooth silanized surfaces. In this work a new method based on carrier treatment with linearly polymerized 3-aminopropyltrimethoxysilane for preparation of reproducibly smooth silanized surfaces is proposed.

Characterization of glucose oxidase immobilization onto mica carrier by atomic force microscopy and kinetic studies

Glucose oxidase (E.C 1.1.3.4) immobilized onto activated surface of mica was analyzed by enzymatic kinetics and visualization with atomic force microscopy (AFM). The activity of the immobilized enzyme decreased with the decrease of concentration of gamma-aminopropyltrimethoxysilane used for the first step of activation of mica, while AFM analysis showed similar homogeneous filling of the surface with the enzyme. The comparison of enzyme activity with its surface filling revealed that there has to be additional vertical structures, which cannot be visualized by the methods of AFM. The simultaneous decrease of the silanizing agent and the concentration of the enzyme led to molecular resolution for the enzyme on the surface of mica. This allows to propose the described method also for analyzing other surfaces of solid materials with coupled biomolecules.

Pinching of alkoxide jets—a route for preparing nanometre level sharp oxide fibres

The pinching phenomenon is used to shape jets of Sn(OBu)4 based viscous oligomeric melts into nanometre range sharp oxide needles. The influence of viscosity of the liquid, humidity of surrounding environment and pulling speed on formation of the needles is investigated. Optimal conditions enable reproducible preparation of needles that have tip radii down to 15–25 nm, i.e. in the range that is of considerable interest for many nanotechnological applications.

A straightforward and “green” solvothermal synthesis of Al doped zinc oxide plasmonic nanocrystals and piezoresistive elastomer nanocomposite

Plasmonic oxide nanocrystals hold great promise in a wide range of applications, for which the availability of scalable and “green” synthesis methods is prerequisite, whereas until recently an excellent response has been demonstrated only for samples prepared through intricate synthesis paths. We report here a simple ethanol solvothermal synthesis route of Al doped ZnO plasmonic nanocrystals (Zn1−xAlxO) at doping levels of x up to 0.15. The obtained Al doped ZnO samples consisted of nanoparticles and short nanorods with a diameter of around 10 nm at x = 0.15 doping level while reaching aspect ratio levels of 50 for lower doping levels. Detailed structural studies using powder X-ray diffraction Rietveld refinement, X-ray absorption and photoelectron spectroscopies show that all samples maintain the structure of the phase-pure zincite with the space group P63mc. The resulting powders exhibit strong infrared absorption while remaining largely transparent for visible light, enabling the preparation of transparent colloidal dispersions. Furthermore, as a test of applicability in a practical device, the nanocrystals were used to prepare transparent piezoresistive Zn0.925Al0.075O–polydimethylsiloxane composites. The prepared sensor material exhibits excellent repeatable and reproducible piezoresistive behaviour.

TiO2 nanowire dispersions in viscous polymer matrix: electrophoretic alignment and optical properties

The changes in optical properties during TiO₂ nanowire orientation in polydimethylsiloxane (PDMS) matrix under the influence of an electric field are strongly influenced by nanowire (NW) diameter. It was demonstrated for the first time that either positive or negative change in transmittance can be induced by NW alignment parallel to the electric field depending on the NW diameter. These effects can be explained by the interplay between scattering and reflectance. Experimental findings reported could be important for smart window applications for the regulation of visible or even infrared transparency, thus reducing the energy consumption by air conditioning systems in buildings and automobiles in the future.

Micro- and nanoscale structures by sol-gel processing

An overview of the practical output of sol-gel chemistry is demonstrated from the viewpoint of its contribution to the design of 1D and 2D materials. Different structures like thin films, fibres, needles, microtubes, -patterns and -rolls are discussed. In most cases, the advantages of sol-gel processing feasibility and cost-effectiveness are clearly evident. Accompanied by flexibility of production and good quality of the formed structures, the method offers interesting possibilities for practical applications such as sensors, opto-electronic devices, scintillators, etc.

New Method for Synthesis of Methacrylate-Type Polymerizable Ionic Liquids

Abstract A new method for the synthesis of polymerizable ionic liquids bearing a methacrylate moiety was developed with the aim to avoid premature polymerization of synthesized compounds. Spacer length between the imidazolium cation and the polymerizable functional group varied from 2 to 10 carbon atoms. Different 1-(n-hydroxyalkyl)-3-methylimidazolium bromides and 1-[n-(methacryloyloxy)-alkyl]-3-methylimidazolium bromides were obtained with very good yields (more than 90%). [Supplementary materials are available for this article. Go to the publishers online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details.] GRAPHICAL ABSTRACT

Counterintuitive increase in optical scattering efficiency during negentropic orientational transition in dilute ZnO nanowire suspensions

We demonstrate experimentally that the electrophoretic manipulation of a ZnO nanowire (NW) suspension in polydimethylsiloxane (PDMS) causes a remarkable change in optical scattering. Counterintuitively, as an electric field is applied to the suspension and a negentropic orientational transition from a chaotically oriented state to a partially ordered (aligned) state is induced, the geometrical cross-section of the particles decreases whereas the scattering efficiency increases significantly, indicating an increase in the scattering cross-section. The alignment of the longer axis of oblong ZnO nanoparticles in the direction of incident light unexpectedly resulted in up to a 40% decrease in transmittance in the middle of the visible spectral range in the case of 150 μm thick composite films with below 0.1 vol% NW concentration. A prepared prototype smart window device exhibited spontaneous restoration of transmittance, persistent electro-optical performance (0% change in contrast after more than 10 cycles), and temporal stability against nanoparticle sedimentation and agglomeration.

Formation of thick dielectrophoretic carbon nanotube fibers.

The aim of this work was to study the formation process of dielectrophoretic (DEP) carbon nanotube fibers (CNT-fibers) and characterize the fiber properties relevant to their technological applications. The fiber diameter was shown to increase when applied voltage was increased (up to 350 V(pp)) and when retraction speed was decreased (down from 400 µm s(-1)) in accordance with theoretical expectations. This paper represents the first demonstration of the formation of thick DEP CNT-fibers (up to ∼ ∅0.4 mm). This is an intriguing result, as it expands the diversity of possible applications of the fibers and facilitates their characterization by analytical methods that require large quantities of the material. The performance of these thick fibers was as follows: a density of ∼ 0.35 g cm(-3), a tensile strength of ∼ 15 MPa, a Youngs modulus of ∼ 1 GPa, and an electrical resistivity of ∼ 70 mΩ cm.

A route towards a new hydrazino-ormosil

We have synthesized a new compound, 3-hydrazinopropyltrimethoxysilane, which can be applied in chemical modification of SiO2 surfaces. The synthesis route is rather simple, including only two major steps. The compound was analysed and confirmed by NMR and FTIR spectroscopy. The new silane can offer a sound alternative to aminosilanes, which are widely applied in several technologies as adhesion promoters.