H2S sensing for breath analysis with Au functionalized ZnO nanowires.

This work presents a H2S selective resistive gas sensor design based on a chemical field effect transistor (ChemFET) with open gate formed by hundreds of high temperature chemical vapour deposition (CVD) grown zinc oxide nanowires (ZnO NW). The sensing ability of pristine ZnO NWs and surface functionalized ZnO NWs for H2S is analysed systematically. ZnO NWs are functionalized by deposition of discontinuous gold (Au) nanoparticle films of different thicknesses of catalyst layer ranging from 1 to 10 nm and are compared in their gas sensing properties. All experiments were performed in a temperature stabilized small volume compartment with adjustable gas mixture at room temperature. The results allow for a well-founded understanding of signal-to-noise ratio, enhanced response, and improved limit of detection due to the Au functionalisation. Comprehension and controlled application of the beneficial effects of Au catalyst on ZnO NWs allow for the detection of very low H2S concentrations down to 10 ppb, and a theoretically estimated 500 ppt in synthetic air at room temperature.

Impact of Surface Chemistry and Doping Concentrations on Biofunctionalization of GaN/Ga‒In‒N Quantum Wells.

The development of sensitive biosensors, such as gallium nitride (GaN)-based quantum wells, transistors, etc., often makes it necessary to functionalize GaN surfaces with small molecules or even biomolecules, such as proteins. As a first step in surface functionalization, we have investigated silane adsorption, as well as the formation of very thin silane layers. In the next step, the immobilization of the tetrameric protein streptavidin (as well as the attachment of chemically modified iron transport protein ferritin (ferritin-biotin-rhodamine complex)) was realized on these films. The degree of functionalization of the GaN surfaces was determined by fluorescence measurements with fluorescent-labeled proteins; silane film thickness and surface roughness were estimated, and also other surface sensitive techniques were applied. The formation of a monolayer consisting of adsorbed organosilanes was accomplished on Mg-doped GaN surfaces, and also functionalization with proteins was achieved. We found that very high Mg doping reduced the amount of surface functionalized proteins. Most likely, this finding was a consequence of the lower concentration of ionizable Mg atoms in highly Mg-doped layers as a consequence of self-compensation effects. In summary, we could demonstrate the necessity of Mg doping for achieving reasonable bio-functionalization of GaN surfaces.

Lasing dynamics in single ZnO nanorods.

We study the lasing dynamics of individual ZnO nanorods by time-resolved mu-photoluminescence. The distinct laser modes show gain competition and pronounced shifts as a function of excitation density. This behavior can be understood in terms of many-particle effects within an inverted electron-hole plasma and of the calculated mode spectra of the particular nanorod, whose geometry is known from electron microscope investigations.

Using paramagnetic particles as repulsive templates for the preparation of membranes of controlled porosity.

Using mixtures of repulsive superparamagnetic polystyrene particles and a photopolymerizable organic liquid (trimethylolpropane trimethacrylate) that are applied to a water surface, it is possible to prepare porous membranes with controlled porosity. The particles were polarized by applying a magnetic field H perpendicular to the interface and spread out over the interface making use of the induced repulsive magnetic dipole interactions. As a consequence, the organic liquid in which the particles were embedded covered the water surface uniformly. Subsequent photo cross linking of the organic liquid and dissolution of the embedded particles gave rise to membranes whose porosities were controlled mainly by the chosen areas per particle. The spatial distribution of the pores and the deviation from a crystalline arrangement were characterized in terms of the 2D pair-correlation function and the mean nearest-neighbor interpore distance.