High Stability of Rh Oxide-Based Thermoresistive Catalytic Combustion Sensors Proven by Operando X-ray Absorption Spectroscopy and X-ray Diffraction.

Thermoresistive catalytic combustion sensors based on noble metals are very stable stable and highly sensitive devices to monitor potentially explosive atmospheres. We studied and proved the high stability of rhodium oxide-based sensors under working conditions in different CH4/air mixtures (up to 3.5 vol % methane) with the help of operando X-ray-based characterization techniques, DC resistance measurements, and IR thermography using a specially designed in situ cell. Operando X-ray diffraction and X-ray absorption spectroscopy showed that the active Rh species are in the oxidized state and their chemical state is preserved during operation under realistic conditions. The resistance correlated with the surface temperature of the pellistor and is related to the combustion of CH4, confirming the catalytic nature of the observed sensing process. Only under harsh operation conditions such as an oxygen-free atmosphere or enhanced working current, a reduction in the active Rh2O3 phase was observed. Finally, the effect of poisoning causing the lowered activity on the catalytic combustion of methane was investigated. While stable rhodium sulfate might form in a sulfur-poisoned pellistor, silicon dioxide seems to additionally physically block the pores in the alumina ceramics of the pellistor poisoned by hexamethyldisiloxane.

Investigations of ion transport through nanoscale polymer membranes by fluorescence quenching of CdSe/CdS quantum dot/quantum rods.

Detailed steady-state and time-resolved fluorescence quenching measurements give deep insight into ion transport through nanometer thick diblock copolymer membranes, which were assembled as biocompatible shell material around CdSe/CdS quantum dot in quantum rods. We discuss the role of polymer chain length, intermolecular cross-linking and nanopore formation by analysing electron transfer processes from the photoexcited QDQRs to Cu(II) ions, which accumulate in the polymer membrane. Fluorescence investigations on single particle level additionally allow identifying ensemble inhomogeneities.

A universal approach to ultrasmall magneto-fluorescent nanohybrids.

Seeded emulsion polymerization is a powerful universal method to produce ultrasmall multifunctional magnetic nanohybrids. In a two-step procedure, iron oxide nanocrystals were initially encapsulated in a polystyrene (PS) shell and subsequently used as beads for a controlled assembly of elongated quantum dots/quantum rods (QDQRs). The synthesis of a continuous PS shell allows the whole construct to be fixed and the composition of the nanohybrid to be tuned. The fluorescence of the QDQRs and magnetism of iron oxide were perfectly preserved, as confirmed by single-particle investigation, fluorescence decay measurements, and relaxometry. Bio-functionalization of the hybrids was straightforward, involving copolymerization of appropriate affinity ligands as shown by immunoblot analysis. Additionally, the universality of this method was shown by the embedment of a broad scale of NPs.

Fluorescence spectroscopy of individual semiconductor nanoparticles in different ethylene glycols.

The optical properties of single colloidal semiconductor nanoparticles (NPs) are considerably influenced by the direct environment of the NPs. Here, the influence of different liquid and solid glycol matrices on CdSe-based NPs is investigated. Since the fluorescence of individual NPs varies from one NP to another, it is highly desirable to study the very same individual NPs in different matrices. This was accomplished by immobilizing NPs in a liquid cell sample holder or in microfluidic devices. The samples have been investigated by space-resolved wide-field fluorescence microscopy and energy- and time-resolved confocal scanning fluorescence microscopy with respect to fluorescence intensities, emission energies, blinking behavior, and fluorescence decay dynamics of individual NPs. During the measurements the NPs were exposed to air, to liquid ethylene glycols H(OCH2CH2)nOH (also called EGn) with different chain lengths (1 ≤ n ≤ 7), to liquid 2-methylpentane-2,3-diol, or to solid polyethylene oxide. It was found that EG6-7 (also known as PEG 300) is very well suited as a liquid matrix or solvent for experiments that correlate chemical and physical modifications of the surface and of the immediate environment of individual NPs to their fluorescence properties since it leads to intense and stable fluorescence emission of the NPs.

A general route towards well-defined magneto- or fluorescent-plasmonic nanohybrids.

Herein, we present a general route towards defined nanohybrids, comprised of a fluorescent quantum dot (QD) or superparamagnetic iron oxide (Fe2O3) nanocrystal core and a tuneable corona of plasmonic gold or silver nanoparticles (NPs), adhered by a cross-linked poly(isoprene)-b-poly(ethylene glycol) diblock copolymer (PI-b-PEG) matrix. To this end, the PEG-terminus of the amphiphilic polymer was acylated with lipoic acid (LA), which, as is known, forms quasi-covalent Au-thiol- or Ag-thiol-bonds. Surprisingly, by variation of the ratio of the different NPs, inverse core/satellite structures bearing QDs or Fe2O3 around a metallic NP core were obtained. Furthermore, gold NPs or even closed gold shells were grown by in situ reductive deposition of Au(3+) ions on Fe2O3 NP seeds. Finally, in order to demonstrate the scope of the method, ternary nanohybrids, composed of QDs, Fe2O3 and Au NPs, were accomplished. All magneto-plasmonic and fluorescent-plasmonic materials were thoroughly characterized by absorption and emission spectroscopy, TEM and TEM-EDX. Antibody conjugation to these novel nanohybrids proved their practical utility in a prototype immunoassay.

Controlling the physical and biological properties of highly fluorescent aqueous quantum dots using block copolymers of different size and shape.

The phase transfer of fluorescent CdSe based quantum dots (QDs) while retaining their properties and offering some advantages concerning the stability and functionalization characteristics is an important and intensively investigated field of research. Here we report how to tune and control the properties of CdSe/CdS/ZnS core-shell-shell QDs in water, using poly(isoprene-block-ethylene oxide) (PI-b-PEO) as a versatile system of amphiphilic diblock copolymers for the micellular encapsulation of nanoparticles (NPs). We show the synthesis of a novel PI-b-(PEO)2 miktoarm star polymer and how this different architecture besides the variation of the polymers' molecular weight gives us the opportunity to control the size of the built constructs in water between 24 and 53 nm. Because of this size control, an upper limit of the construct's diameter for the cellular uptake could be determined by a systemic study with human alveolar epithelial cells (A549) and murine macrophage leukemia cell (RAW-264.7). Furthermore, fluorescence quenching experiments with copper(II) and iron(III) ions show a strong influence of the used polymer on the shielding against these ions. This enables us to control the permeability of the polymer shell from very porous shells, which allow an almost complete cation exchange up to very dense shells. These even offer the possibility to perform copper(I) catalyzed click reactions while keeping the fluorescence of the QDs. All these results underline the huge variability and controllability of the PI-b-PEO diblock copolymer system for the encapsulation and functionalization of nanoparticles for biological applications. As a general trend, it can be stated that those coatings, which were most stable against quenchers, also showed the best resistivity with respect to unspecific cellular uptake.