Strong response of multilayer polyelectrolyte films to cationic surfactants

The influence of common cationic surfactants on the physical properties of differently composed polyelectrolyte films prepared by the layer-by-layer (LbL) technology was investigated. Free-standing polyelectrolyte films as microcapsules showed a fast, strong response to the addition of less than 1 mM cationic surfactant cetyltrimethylammonium bromide (CeTAB). As a function of the polyelectrolyte composition, the behavior of the capsules varied from negligible changes to complete disintegration via strong swelling. The response of microcapsules consisting of (poly(allylamine hydrochloride)(PAH)/poly(styrene sulfonate)(PSS))(4) was associated with a 5-fold volume increase, a fast switch of permeability, and in the case of fluorescently labeled films a 4-fold increase in fluorescence intensity. The kinetics and strengths of the interaction process were investigated by confocal laser scanning microscopy (CLSM) and fluorescence spectroscopy. Also, the relative stabilities of the polycation/polyanion and surfactant/polyanion complexes were determined. A mechanism was suggested to explain the interactions between the cationic surfactants and polyelectrolyte capsules. The strong response can be exploited in potential applications such as the triggered release of drugs or other encapsulated materials, the fluorescence-based detection of cationic detergents, and a switchable stopper in microchannels. However, the high sensitivity of LbL films to traces of cationic surfactants can also limit their applicability to the encapsulation of drugs or other materials because pharmaceutical or technical formulations often contain cationic surfactants as preservatives such as benzalkonium salts (BAC). It was demonstrated that undesired capsule opening can be effectively prevented by cross-linking the polyelectrolyte multilayers.     

Biomimetic anchors for antifouling and antibacterial polymer brushes on stainless steel

Barnacle cement (BC) was beneficially applied on stainless steel (SS) to serve as the initiator anchor for surface-initiated polymerization. The amine and hydroxyl moieties of barnacle cement reacted with 2-bromoisobutyryl bromide to provide the alkyl halide initiator for the surface-initiated atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate (HEMA). The hydroxyl groups of HEMA polymer (PHEMA) were then converted to carboxyl groups for coupling of chitosan (CS) to impart the SS surface with both antifouling and antibacterial properties. The surface-functionalized SS reduced bovine serum albumin adsorption, bacterial adhesion, and exhibited antibacterial efficacy against Escherichia coli (E. coli). The effectiveness of barnacle cement as an initiator anchor was compared to that of dopamine, a marine mussel inspired biomimetic anchor previously used in surface-initiated polymerization. The results indicate that the barnacle cement is a stable and effective anchor for functional surface coatings and polymer brushes.     

Enzyme digestion of entrapped single-DNA molecules in nanopores

The real-time digestion of entrapped single-DNA molecules by λ-exonuclease in nanoporous alumina membranes was observed using an epifluorescence microscope. The alumina membrane provides pL (∼10⁻¹² L) containers for confining single-DNA molecules without immobilization. When one end of the DNA molecule was inserted into a nanopore, it was possible to monitor the digestion process outside, near and inside the pore, where the individual DNA molecules exhibited different characteristic digestion modes. The digestion rates calculated from the decrease in fluorescence intensity showed different values according to the location of the individual molecules. Entrapment rather than immobilization allows the DNA strand to be fully exposed to the enzyme and the reaction buffer. These results confirm that the enzymatic digestion of DNA molecules is affected by their three-dimensional (3D) environment.     

Production of Lactate in <Emphasis Type="Italic">Escherichia coli</Emphasis> by Redox Regulation Genetically and Physiologically

Escherichia coli grows fermentatively in glucose-containing medium under anaerobic condition with formation of a mixture of organic acids (lactate, acetate, formate, and succinate) and ethanol to accommodate reducing equivalents generated during glycolysis. In this paper, we tried to improve the lactate accumulation in E. coli by redox regulation genetically and physiologically. Our results indicated that genetic regulation of the host by reducing the reductive by-product may improve the lactate production. In addition, lactate accumulation was also improved under reduced and anaerobic cultivation conditions. Engineered E. coli SDU4 was able to accumulate lactate under strictly anaerobic conditions to 100 g/L with a yield of 1.97 mol/mol glucose.     

Synthesis and X-ray diffraction analysis/crystal structure of new germatranes containing methyl substituents in three five-membered chelating rings

Three monomeric germatranes, 1-isopropoxy-3,3,7,7,10,10-hexamethyl-2,8,9-trioxa-5-aza-1-germatricyclo[3.3.3.0^1,5]undecane (1), 1-isopropoxy-3,3,7,7-tetramethyl-2,8,9-trioxa-5-aza-1-germatricyclo[3.3.3.0^1,5]undecane (2), and 1-isopropoxy-3,3-dimethyl-2,8,9-trioxa-5-aza-1-germatricyclo[3.3.3.0^1,5]undecane (3) have been synthesized by the reaction of Ge(O-i-Pr)₄ in refluxing toluene with corresponding triethanolamines, (HOCH₂CH₂)_nN(CH₂CMe₂OH)_3−n (n = 0, L1H₃; n = 1, L2H₃; n = 2, L3H₃), where the number of CMe₂ groups adjacent to a OH functionality varied from 3 (L1H₃) to 2 (L2H₃), and to 1 (L3H₃). These germatranes 1-3 have been characterized by solution ¹H and ¹³C{¹H} NMR and the solid state structure of 2 has been determined by single crystal X-ray diffraction.     

Au nanowire-on-film SERRS sensor for ultrasensitive Hg2+ detection

We report an ultrasensitive and selective single nanowire-on-film (SNOF) surface-enhanced resonance Raman scattering (SERRS) sensor for Hg(2+) detection based on structure-switching double stranded DNAs (dsDNAs). Binding of Hg(2+) induces conformational changes of the dsDNAs and let a Raman reporter get close to the SNOF structure, thereby turning on SERRS signal. The well-defined SNOF structure provides a detection limit of 100 pM with improved accuracy in Hg(2+) detection. This sensor is stable over a considerable amount of time and reusable after simple treatment. Since this SNOF sensor is composed of a single Au NW on a film, development of a multiplex sensor would be possible by employing NWs modified by multiple kinds of aptamers.     

Simple and accurate quantitative analysis of seven prohibited threshold substances in human urine by liquid chromatography/tandem mass spectrometry in doping control

A simple and accurate liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for the quantitative determination of ephedrine, pseudoephedrine, methylephedrine, cathine, salbutamol, morphine and epitestosterone in human urine. Urine samples were spiked with internal standard and diluted with acetonitrile. After centrifugation, the supernatants were directly analyzed by LC/MS/MS using the selected reaction monitoring (SRM) mode. The linearity, intra- and inter-day precision, accuracy, limit of detection (LOD) and limit of quantification (LOQ) were evaluated and the method was found to be accurate and reproducible for the quantitation of threshold substances. When the method was applied to the analysis of blind urine samples for the proficiency test, the results were close to the nominal concentrations, within 87.7-106.6% of nominal values, suggesting that the developed methods can be successfully applied to routine doping analyses.