Confinement-guided shaping of semiconductor nanowires and nanoribbons: "writing with nanowires"

To fully exploit their full potential, new semiconductor nanowire building blocks with ab initio controlled shapes are desired. However, and despite the great synthetic advances achieved, the ability to control nanowire's geometry has been significantly limited. Here, we demonstrate a simple confinement-guided nanowire growth method that enables to predesign not only the chemical and physical attributes of the synthesized nanowires but also allows a perfect and unlimited control over their geometry. Our method allows the synthesis of semiconductor nanowires in a wide variety of two-dimensional shapes such as any kinked (different turning angles), sinusoidal, linear, and spiral shapes, so that practically any desired geometry can be defined. The shape-controlled nanowires can be grown on almost any substrate such as silicon wafer, quartz and glass slides, and even on plastic substrates (e.g., Kapton HN).     

Packaging and testing of a hydrogen safety sensor prototype

In this article, testing of an electrochemical, potentiometric hydrogen safety sensor is reported within a proposed packaging scheme. Device packaging under static and flow testing conditions are presented. During the static volume sensor testing, the sensors response is compared against a calibrated Gas Chromatography (GC) measurement. Also, a commercial H₂ sensor is incorporated into the test chamber to act as a benchmark for the sensor prototype. In the testing phase, H₂ selectivity is demonstrated using pulsed discharge technique.     

Fixed bed membrane reactors for WGSR-based hydrogen production: Optimisation of modelling approaches and reactor performance

The production of high-purity hydrogen using the water–gas-shift reaction in both conventional fixed bed reactor and hydrogen perm-selective membrane reactor at low to medium scale is studied in this work by developing and comparing models with different complexity levels. A two-dimensional rigorous reactor model considering radial and axial variations of properties (including bed porosity), setting mass, energy and momentum differential balances, and nesting a rigorous model for mass transfer within the porous catalyst was considered as reference for comparison. Different simplifications of this model for taking into account mass-transfer effects within the catalyst pellet (Thiele modulus, evaluation of apparent kinetic constants, empirical correlation for effectiveness factors or just neglecting these effects) were tested, being observed that these effects are not negligible and that the first two approaches are accurate enough for taking into account mass transfer within catalyst pellets. Regarding to the reactor model, it was observed that one-dimensional models are not adequate, especially for the membrane reactor. Analogously, neglecting the momentum balances in the reactor (as made is most simulations reported in the literature) leads to important misspredictions in the behaviour of the membrane reactor performance. Finally, the influence of the main operation parameters (inlet temperature, pressure, space velocity, etc.) was studied using the detailed reactor model, concluding that space velocity and pressure are the most important parameters affecting reactor performance for membrane reactors.     

Surface-Enhanced Raman Scattering Detection of pH with Silica-Encapsulated 4-Mercaptobenzoic Acid-Functionalized Silver Nanoparticles

Sensors based upon surface-enhanced Raman spectroscopy (SERS) are attractive because they have narrow, vibrationally specific spectral peaks that can be excited using red and near-infrared light which avoids photobleaching, penetrates tissue, and reduces autofluorescence. Several groups have fabricated pH nanosensors by functionalizing silver or gold nanoparticle surfaces with an acidic molecule and measuring the ratio of protonated to deprotonated Raman bands. However, a limitation of these sensors is that macromolecules in biological systems can adsorb onto the nanoparticle surface and interfere with measurements. To overcome this interference, we encapsulated pH SERS sensors in a 30 nm thick silica layer with small pores which prevented bovine serum albumin (BSA) molecules from interacting with the pH-indicating 4-mercaptobenzoic acid (4-MBA) on the silver surfaces but preserved the pH-sensitivity. Encapsulation also improved colloidal stability and sensor reliability. The noise level corresponded to less than 0.1 pH units from pH 3 to 6. The silica-encapsulated functionalized silver nanoparticles (Ag-MBA@SiO(2)) were taken up by J774A.1 macrophage cells and measured a decrease in local pH during endocytosis. This strategy could be extended for detecting other small molecules in situ.     

Engineering of gold surface work function by electrodeposition of spirobifluorene donor–acceptor bipolar systems

Charge separation in gold/spirobifluorene-based donor (triphenylamine)–acceptor (cyano) bipolar systems has been investigated by contact potential difference and surface photovoltage spectroscopy. Organic films were formed on gold electrode by electrochemical polymerization and by dipping in dye solution. The gold surface work function has been changed over more than 0.4 eV depending on the numbers of electrochemical deposition cycles. Photovoltage effects were analyzed in terms of internal photoemission from Au into organic film, and organic layer light absorption. The energetic differences between the Fermi-level of Au and HOMO levels of organic systems were obtained. The results showed that the electrodeposition is a versatile tool for electrode surface work function tuning.     

Carotenoid composition and vitamin A value in ají (Capsicum baccatum L.) and rocoto (C. pubescens R. & P.), 2 pepper species from the Andean region

The carotenoid patterns of fully ripe fruits from 12 Bolivian accessions of the Andean peppers Capsicum baccatum (ají) and C. pubescens (rocoto) were determined by high-performance liquid chromatography (HPLC)-photodiode array detector (PDA)-mass spectrometry (MS). We include 2 California Wonder cultivars as C. annuum controls. A total of 16 carotenoids were identified and differences among species were mostly found at the quantitative level. Among red-fruited genotypes, capsanthin was the main carotenoid in the 3 species (25% to 50% contribution to carotenoid fraction), although ajíes contained the lowest contribution of this carotenoid. In addition, the contribution of capsanthin 5,6-epoxide to total carotenoids in this species was high (11% to 27%) in comparison to rocotos and red C. annuum. Antheraxanthin and violaxanthin were, in general, the next most relevant carotenoids in the red Andean peppers (6.1% to 10.6%). Violaxanthin was the major carotenoid in yellow-/orange-fruited genotypes of the 3 species (37% to 68% total carotenoids), although yellow rocotos were characterized by lower levels (<45%). Cis-violaxanthin, antheraxanthin, and lutein were the next most relevant carotenoids in the yellow/orange Andean peppers (5% to 14%). As a whole, rocotos showed the highest contributions of provitamin A carotenoids to the carotenoid fraction. In terms of nutritional contribution, both ajíes and rocotos provide a remarkable provitamin A activity, with several accessions showing a content in retinol equivalents higher than California Wonder controls. Furthermore, levels of lutein in yellow/orange ajíes and rocotos were clearly higher than California Wonder pepper (≥1000 μg·100/g). Finally, the Andean peppers, particularly red ajíes, can be also considered as a noticeable source of capsanthin, the most powerful antioxidant compound among pepper carotenoids. Practical Application: Capsicum peppers are known for their content in carotenoids, although there is no information about 2 species with Andean origin: ajíes and rocotos. Due to their relevance for the Andean cuisine and increasing importance in ethnic restaurants in Europe, we studied their carotenoid pattern and vitamin A contribution.     

The p-nitroaniline test to asses the bacterial microbiota of raw ground meat aerobically stored

The previously developed p-nitroaniline test for assessing the microbial load of meat surfaces has been now adapted to determine the microbial quality of raw ground meat. A good correlation (r=0.91) between bacterial count determined by the pour plate method and the p-nitroaniline test was obtained. The sensitivity of the new method was of the order of magnitude of 10(4)cfu/g. This method allows the assay of ground meat in approximately 2.5h, it does not require expensive equipment and the results can be interpreted both spectrophotometrically and visually. Additionally, it has been proven that the method is useful in estimating the microbial quality of raw meat irrespective of the species of Gram-negative psychrotrophic bacteria prevailing in the meat during refrigerated storage.     

High flexibility of DNA on short length scales probed by atomic force microscopy

The mechanics of DNA bending on intermediate length scales (5-100 nm) plays a key role in many cellular processes, and is also important in the fabrication of artificial DNA structures, but previous experimental studies of DNA mechanics have focused on longer length scales than these. We use high-resolution atomic force microscopy on individual DNA molecules to obtain a direct measurement of the bending energy function appropriate for scales down to 5 nm. Our measurements imply that the elastic energy of highly bent DNA conformations is lower than predicted by classical elasticity models such as the worm-like chain (WLC) model. For example, we found that on short length scales, spontaneous large-angle bends are many times more prevalent than predicted by the WLC model. We test our data and model with an interlocking set of consistency checks. Our analysis also shows how our model is compatible with previous experiments, which have sometimes been viewed as confirming the WLC.