Chirality-preserving growth of helical filaments in the B4 phase of bent-core liquid crystals

The growth of helical filaments in the B4 liquid-crystal phase was investigated in mixtures of the bent-core and calamitic mesogens NOBOW and 8CB. Freezing-point depression led to nucleation of the NOBOW B4 phase directly from the isotropic phase in the mixtures, forming large left- and right-handed chiral domains that were easily observed in the microscope. We show that these domains are composed of homochiral helical filaments formed in a nucleation and growth process that starts from a nucleus of arbitrary chirality and continues with chirality-preserving growth of the filaments. A model that accounts for the observed local homochirality and phase coherence of the branched filaments is proposed. This model will help in providing a better understanding of the nature of the B4 phase and controlling its growth and morphology for applications, such as the use of the helical nanophase as a nanoheterogeneous medium.     

Gene silencing by siRNA microhydrogels via polymeric nanoscale condensation

The first attempt to prepare biologically active siRNA-based microhydrogels is reported. The self-assembled microhydrogels were fabricated using sense/antisense complementary hybridization between single-stranded linear and Y-shaped trimeric siRNAs. The siRNA microhydrogels were condensed using a popular cationic polymer such as LPEI to form compact, stable siRNA/polymeric nanoparticles that exhibited superb cellular uptake efficiency and gene silencing activity.     

Immunochemical analysis of 3-phenoxybenzoic acid,a biomarker of forestry worker exposure to pyrethroid insecticides

Pyrethroid insecticides widely used in forestry, agricultural, industrial, and residential applications have potential for human exposure. Short sample preparation time and sensitive, economical high-throughput assays are needed for biomonitoring studies that analyze a large number of samples. An enzyme-linked immunosorbent assay (ELISA) was used for determining 3-phenoxybenzoic acid (3-PBA), a general urinary biomarker of exposure to some pyrethroid insecticides. A mixed-mode solid-phase extraction reduced interferences from acid hydrolyzed urine and gave 110 ± 6% recoveries from spiked samples. The method limit of quantification was 2 μg/L. Urine samples were collected from forestry workers that harvest pine cone seeds where pyrethroid insecticides were applied at ten different orchards. At least four samples for each worker were collected in a 1-week period. The 3-PBA in workers classified as high, low, or no exposure based on job analysis over all sampling days was 6.40 ± 9.60 (n = 200), 5.27 ± 5.39 (n = 52), and 3.56 ± 2.64 ng/mL (n = 34), respectively. Pair-wise comparison of the differences in least squares means of 3-PBA concentrations among groups only showed a significant difference between high and no exposure. Although this difference was not significant when 3-PBA excretion was normalized by creatinine excretion, the general trend was still apparent. No significant differences were observed among days or orchards. This ELISA method using a 96-well plate was performed as a high-throughput tool for analyzing around 300 urine samples measured in triplicate to provide data for workers exposure assessment.     

Electrophilic Addition Reaction of Ethene with Hydrogen Chloride on Cold Molecular Films: Evidence of Ethyl Cationic Intermediate

We studied the initial‐stage mechanism of the electrophilic addition reaction of ethene with HCl by examining the interactions between ethene and HCl on water‐ice and frozen molecular films at temperatures of 80–140 K. Cs⁺ reactive ion scattering (RIS) and low‐energy sputtering (LES) techniques were used to probe the reaction intermediates that were kinetically trapped on the surface, in conjunction with temperature‐programmed desorption (TPD) mass spectrometry to monitor the desorbing species. The reaction initially produced the π complex of HCl and ethene at temperatures below about 93 K and an “ethyl cationic species” at temperatures below about 100 K. The ethyl cationic species was formed via direct proton transfer from the HCl molecule to ethene with the assistance of water solvation, rather than via the interaction of hydronium ions and ethene. At high temperatures, this species dissociated into ethene and hydronium and chloride ions. The reaction did not, however, complete the final transition state on the ice surface to produce ethyl chloride. The observation gives evidence that the electrophilic addition reaction of ethene occurs through an ethyl‐like intermediate with an ionic character.     

The Role of Water for the Phase‐Selective Preparation of Hexagonal and Cubic Cobalt Oxide Nanoparticles

A selective preparation and the formation mechanism of hexagonal and cubic CoO nanoparticles from the reaction of [Co(acac)₂] (acac=acetylacetonate) and amine have been investigated. CoO nanoparticles with a hexagonal pyramidal shape were yielded under decomposition conditions with amine. Importantly, the addition of water altered the final phase to cubic and comprehensively changed the reaction mechanism. The average sizes of the hexagonal and cubic CoO nanoparticles could be controlled either by changing the amine concentration or by using different reaction temperatures. Detailed formation mechanisms are proposed on the basis of gas chromatography–mass spectrometry data and color changes of the reaction mixture. The hexagonal CoO phase is obtained through two distinct pathways: solvolysis with C C bond cleavage and direct condensation by amine. On the other hand, the cubic CoO nanoparticles were synthesized by strong nucleophilic attack of hydroxide ions from water and subsequent C C bond breaking. The resulting caboxylate ligand can stabilize a cobalt hydroxide intermediate, leading to the generation of a thermodynamically stable CoO phase.     

Compressed-air flow control system

We present the construction and operation of a compressed-air driven flow system that can be used for a variety of microfluidic applications that require rapid dynamic response and precise control of multiple inlet streams. With the use of inexpensive and readily available parts, we describe how to assemble this versatile control system and further explore its utility in continuous- and pulsed-flow microfluidic procedures for the synthesis and analysis of microparticles.     

Surface activation of plasma-patterned carbon nanotube based DNA sensing electrodes

We have studied the effect of treatment of multiwalled carbon nanotubes (MWCNTs) for use in DNA-based biosensors with oxygen plasma. Well-patterned MWCNT electrodes were photolithographically fabricated on glass substrates. Pure oxygen was used for etching and functionalization of the MWCNT film in a lab-made plasma chamber. The resulting electrodes exhibited a dramatic change in the morphology of their surface, the chemical composition, and the electrochemical properties in terms of peak current and peak potential separation. The electrodes also showed increased DNA immobilization efficiency and much higher sensitivity in the detection of target DNA as compared to non-treated MWCNT electrodes. Plasma treatment was optimized and electrodes were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and differential pulse voltammetry.

Preparation of silica-encapsulated hollow gold nanosphere tags using layer-by-layer method for multiplex surface-enhanced raman scattering detection

The use of silica shells offers many advantages in surface-enhanced Raman scattering (SERS)-based biological sensing applications due to their optical transparency, remarkable stability in environmental media, and improved biocompatibility. Here, we report a novel layer-by-layer method for the preparation of silica-hollow gold nanosphere (HGN) SERS tags. Poly(acrylic acid) was used to stabilize Raman reporter-tagged HGNs prior to the adsorption of a coupling agent, after which a silica shell was deposited onto the particle surface using Sto?ber's method. Importantly, competitive adsorption of the Raman reporter molecules and coupling agents, which results in unbalanced loading of reporter molecules on individual nanoparticles, was avoided using this method. As a result, the loading density of reporter molecules could be maximized. In addition, HGNs exhibited strong enhancement effects from the individual particles because of their ability to localize the surface electromagnetic fields through pinholes in the hollow particle structures. The proposed layer-by-layer silica-encapsulated HGN tags showed strong SERS signals as well as excellent multiplexing capabilities.     

Voltammetric characterization of a fully integrated, patterned single walled carbon nanotube three-electrode system on a glass substrate

A single walled carbon nanotube (SWCNT)-based three-electrode system was fully integrated on glass substrates using a standard microfabrication process and electrochemically characterized using cyclic voltammetry. O(2) plasma functionalization of the SWCNT film working electrode for achieving high sensitivity was voltammetrically optimized with respect to the plasma power and treatment time. Chlorination of a Ag thin-film was done in an acidic solution for different dip times to form a thin-film Ag/AgCl reference electrode. The Nernstian behavior of as-prepared and seven-day-aged Ag/AgCl thin-film electrodes was investigated for seeking the optimum reference electrode with long-term stability and was compared to a commercial reference electrode. A quality control evaluation and a performance assessment of the fully integrated SWCNT-transferred sensing systems were performed using cyclic voltammetry. The proposed SWCNT-based three electrode device exhibited clear electrochemistry under voltammetric conditions, and is therefore a candidate for use in all electrochemical biosensors.     

Phosphidation of Li4Ti5O12 nanoparticles and their electrochemical and biocompatible superiority for lithium rechargeable batteries

Phosphidated-Li(4)Ti(5)O(12) shows high capacity with a significantly enhanced kinetics opening new possibilities for ultra-fast charge/discharge of lithium rechargeable batteries. The in vitro cytotoxicity test proves its fabulous cell viability, indicating that the toxicity problem of nanoparticles can be also solved by phosphidation.