Non aggregated colloidal silver nanoparticles for surface enhanced resonance Raman spectroscopy

Silver nanoparticles with a tuneable λ max were produced as colloids by heterogeneous nucleation. The synthesis process is both fast and repeatable, producing stable PVA capped nanoparticles. The colloid's effectiveness in the SERRS system was investigated using Rhodamine 6G, R6G, Crystal Violet, CV, and Malachite Green, MG, as probe molecules. A clear sensing trend was observed, where the Raman signal emitted was significantly enhanced by the addition of silver nanoparticles. A build up of signal intensity is observed until an optimum ratio is achieved, followed by a decline in signal intensity as the concentration of nanoparticles is further increased. The sensing trend appeared to be dependant on the structure of these model molecules with similarly structured compounds exhibiting similar trends. Thus a maximum enhancement with the Ag: analyte molar ratio of ～ 5.56: 1, was seen for CV and MG whereas R6G had a maximum enhancement at the Ag: analyte molar ratio of ～ 2.25: 1.     

Smart polymer nanoparticles designed for environmentally compliant coatings

We describe the synthesis, characterization, and film-forming properties of two-component nanoparticles that undergo a reversible morphology transformation in water as a function of pH. The particles consist of a high molecular weight acrylate copolymer and an acid-rich oligomer designed to be miscible with the polymer when its -COOH groups are protonated. Attaching a fluorescence resonance energy transfer (FRET) pair to components inside the nanoparticles enabled us to assess morphology at the molecular level. By inspecting changes in the donor fluorescence decay profile at different pH values, we established miscibility of the components in acidic solution but with charge-induced phase separation when the oligomers were neutralized to their carboxylate form. Complementary titration experiments revealed that the nanoparticles adopt a core-shell structure when the acid groups are deprotonated. We studied the effect of the acid-rich oligomer on the diffusion rate of the high molecular weight polymers following film formation. Our results show that the carboxylated oligomer enhanced the rate of diffusive mixing between high molecular weight molecules by more than 2 orders of magnitude. FRET measurements carried out on partially dried films using a low-resolution microscope showed that the carboxylate oligomer shell can delay coalescence for ca. 30 min after passage of the drying front. This delay is expected to help with increasing the 'open time' of latex paints, a desirable property of solvent-based paints that remains difficult to achieve with (environmentally compliant) waterborne paints. Use of ammonia as a volatile base resulted in synergistic effects: initial retardation of coalescence followed by acceleration of diffusive mixing as the ammonium salts dissociated and ammonia evaporated from the film.     

Guided quasicontinuous atom laser

We report the first realization of a guided quasicontinuous atom laser by rf outcoupling a Bose-Einstein condensate from a hybrid optomagnetic trap into a horizontal atomic waveguide. This configuration allows us to cancel the acceleration due to gravity and keep the de Broglie wavelength constant at 0.5 microm during 0.1 s of propagation. We also show that our configuration, equivalent to pigtailing an optical fiber to a (photon) semiconductor laser, ensures an intrinsically good transverse mode matching.     

Constraining new physics in with reparametrization invariance and QCD factorization

Usually, B⁰→π⁺π⁻ decays are expressed in terms of weak amplitudes explicitly dependent on the CKM weak phase α or γ. In this Letter, we show that the weak amplitudes can be rewritten such that a manifest dependence on β emerges instead. Based on this, we constrain new-physics contributions to the CP-violating phase _d in mixing. Further, we apply reparametrization invariance and use QCD factorization predictions to investigate the bounds on an additional new-physics amplitude in B⁰→π⁺π⁻.     

Alkali metal hydrides: New metallating reagents for germanium and tin

New procedures for the preparation of organogermyl- and stannyl-sodium or -potassium, which undergo coupling reactions with alkyl, allyl, and benzyl halides and α-enones, are reported.     

Emergence of constraint in self-organizing systems

Practitioners of agent-based modeling are often tasked to model or design self-organizing systems while the theoretical foundation of self-organization in science remains to be set. This paper explores self-organization in the context of an agent-based model of ant colony food foraging. We gather specific measures of order-creation and constraint construction particular to leading theories of nonequilibrium thermodynamics that purport to govern self-organizing dynamics. These measures are used to explore three claims: (a) Constraints are constructed from entropy-producing processes in the bootstrapping phase of self-organizing systems; (b) positive feedback loops are critical in the structure formation phase; and (c) constraints tend to decay. The continued presence of far-from-equilibrium boundary conditions are required to reinforce constraints in the maintenance phase.     

The Application and Validation of HybridSPE-Precipitation Cartridge Technology for the Rapid Clean-up of Serum Matrices (from Phospholipids) for the Clinical Analysis of Serotonin,Dopamine and Melatonin

Phospholipids have been shown to cause matrix effects particularly in liquid chromatography–mass spectrometry (LC–MS) analysis of small molecules. This results in suppression of the analyte signal. This study provides a versatile validated method for the analysis of serotonin in serum along with dopamine and melatonin using LC–MS/MS. It utilises HybridSPE-Precipitation cartridges for the clean-up of serum samples. This technology involves a simple protein precipitation step together with a fast and robust SPE method that is designed to remove phospholipids. Serotonin and dopamine are major neurotransmitters in the brain which affect various functions both in the brain and in the rest of the body. Melatonin plays an important role in the regulation of circadian sleep–wake cycle. Good linear calibrations were obtained for the multiplex assay of analytes in serum samples (0.021–3.268 μmol L⁻¹; R ² = 0.9983–0.9993). Acceptable intra- and inter-day repeatability was achieved for all analytes in serum. Excellent limits of detection (LOD) and limits of quantitation (LOQ) were achieved with LODs of 3.2–23.5 nmol L⁻¹ and the LOQs of 15.4–70.5 nmol L⁻¹ for these analytes in serum. The sample clean-up procedure that was developed provided efficient recovery and reproducibility while also decreasing preparation time and solvent use. A sample storage protocol was established, this was achieved by investigation of sample stability under different storage conditions. Evaluation of matrix effects was also carried out and the influence of ion suppression on analytical results reported. This clean-up protocol was then applied to the analysis of clinical serum samples.

     

Synthesis of novel graft polyhydroxyalkanoates

Graft copolymers were synthesized by direct condensation of methoxy-poly(ethylene glycol) (MePEG) or methoxy-poly(lactic acid) (MePLA) onto a reactive polyhydroxyalkanoate (PHA) backbone in organic solvent. Side carboxylic groups of the PHA were coupled with end hydroxyl groups of MePEG or MePLA in the presence of N,N′-dicylohexylcarbodiimide (DCC). Graft copolymers were characterized by ¹H NMR spectroscopy and size exclusion chromatography (SEC). NMR spectra of PHA-g-PEG and PHA-g-PLA showed the presence of significant amounts of PEG and PLA, respectively. No noticeable unreacted PEG or PLA were detected in SEC chromatograms. Grafting of hydrophilic polymers chains as PEG or biodegradable oligomers as PLA onto PHA backbone will generate polyesters with a more rapid water uptake and faster biodegradation rates. These PHA polymers conjugates could be interesting for bioactive agent delivery systems.     

Photophysical and novel charge-transfer properties of adducts between [RuII(bpy)3]2+ and [S2Mo18O62]4-

The photophysical properties of acetonitrile solutions of [Ru(bpy)(3)](2+) and [S(2)Mo(18)O(62)](4-) are described. We discuss evidence for ion cluster formation in solution and the observation that despite the strong donor ability of the excited state of [Ru(bpy)(3)](2+) and its inherent photolability, adducts with [S(2)Mo(18)O(62)](4-) were photostable. Photophysical studies suggest that the quenching of the [Ru(bpy)(3)](2+) excited state by [S(2)Mo(18)O(62)](4-) occurs via a static mechanism and that binding is largely electrostatic in nature. Evidence is provided from difference spectroscopy and luminescence excitation spectroscopy for good electronic communication between [Ru(bpy)(3)](2+) and [S(2)Mo(18)O(62)](4-) with the presence of a novel, luminescent, inter-ion charge-transfer transition. The identity of the transition is confirmed by resonance Raman spectroscopy.     

Orthogonal Detection of Nitroaromatic Explosives via Direct Voltammetry Coupled to Enzyme‐Mediated Biocatalysis

This article describes a rapid and reliable electrochemical/enzymatic method of verifying the presence of nitroaromatic explosives. The new technique leverages both conventional voltammetric analysis and biocatalytic conversion of TNT. The simultaneous use of independent measurement schemes, based on two distinct processes, dramatically increases the information content and offers substantially improved reliability while minimizing the occurrence of false alarms. This has been accomplished by coupling direct voltammetric analysis with the biocatalytic conversion of the TNT substrate via nitroreductase (NR), which reduces a nitro group of TNT using NADH as an electron donor. This chemical reduction (30 s timescale) can then be observed using square‐wave voltammetry by examination of the reductive and oxidative features. This novel protocol was found to be selective for TNT, not only when compared to DNT and NT, but also to other explosive species such as RDX and PETN. This unique dual‐mode detection strategy for measuring TNT at a single device holds considerable promise for improving the probability of explosive detection and hence for diverse security screening applications.