Improved sensitivity gas detection by spontaneous Raman scattering

Accurate, real-time measurement of the dilute constituents of a gaseous mixture poses a significant challenge usually relegated to mass spectrometry. Here, spontaneous Raman backscattering is used to detect low pressure molecular gases. Rapid detection of gases in the ∼100 parts in 106 (ppm) range is described. Improved sensitivity is brought about by use of a hollow-core, photonic bandgap fiber gas cell in the back-scattering configuration to increase collection efficiency and an image-plane aperture to greatly reduce silica-Raman background noise. Spatial and spectral properties of the silica noise were examined with a two-dimensional CCD detector array. © 2009 Optical Society of America

Spatial Diffusivity and Availability of Intracellular Calmodulin

Calmodulin (CaM) is the major pathway that transduces intracellular Ca2+ increases to the activation of a wide variety of downstream signaling enzymes. CaM and its target proteins form an integrated signaling network believed to be tuned spatially and temporally to control CaM's ability to appropriately pass signaling events downstream. Here, we report the spatial diffusivity and availability of CaM labeled with enhanced green fluorescent protein (eGFP)-CaM, at basal and elevated Ca2+, quantified by the novel fluorescent techniques of raster image scanning spectroscopy and number and brightness analysis. Our results show that in basal Ca2+ conditions cytoplasmic eGFP-CaM diffuses at a rate of 10 μm2/s, twofold slower than the noninteracting tracer, eGFP, indicating that a significant fraction of CaM is diffusing bound to other partners. The diffusion rate of eGFP-CaM is reduced to 7 μm2/s when a large (646 kDa) target protein Ca2+/CaM-dependent protein kinase II is coexpressed in the cells. In addition, the presence of Ca2+/calmodulin-dependent protein kinase II, which can bind up to 12 CaM molecules per holoenzyme, increases the stoichiometry of binding to an average of 3 CaMs per diffusive molecule. Elevating intracellular Ca2+ did not have a major impact on the diffusion of CaM complexes. These results present us with a model whereby CaM is spatially modulated by target proteins and support the hypothesis that CaM availability is a limiting factor in the network of CaM-signaling enzymes

Identification and quantification of explosives in nanolitre solution volumes by Raman spectroscopy in suspended core optical fibers

A novel approach for identifying explosive species is reported, using Raman spectroscopy in suspended core optical fibers. Numerical simulations are presented that predict the strength of the observed signal as a function of fiber geometry, with the calculated trends verified experimentally and used to optimize the sensors. This technique is used to identify hydrogen peroxide in water solutions at volumes less than 60 nL and to quantify microgram amounts of material using the solvent’s Raman signature as an internal calibration standard. The same system, without further modifications, is also used to detect 1,4-dinitrobenzene, a model molecule for nitrobenzene-based explosives such as 2,4,6-trinitrotoluene (TNT).Georgios Tsiminis, Fenghong Chu, Stephen C. Warren-Smith, Nigel A. Spooner and Tanya M. Monr

Diffusion in Model Networks as Studied by NMR and Fluorescence Correlation Spectroscopy

We have studied the diffusion of small solvent molecules (octane) and larger hydrophobic dye probes in octane-swollen poly(dimethyl siloxane) linear-chain solutions and end-linked model networks, using pulsed-gradient nuclear magnetic resonance (NMR) and fluorescence correlation spectroscopy (FCS), respectively, focusing on diffusion in the bulk polymer up to the equilibrium degree of swelling of the networks, that is, 4.8 at most. The combination of these results allows for new conclusions on the feasibility of different theories describing probe diffusion in concentrated polymer systems. While octane diffusion shows no cross-link dependence, the larger dyes are increasingly restricted by fixed chemical meshes. The simple Fujita free-volume theory proved most feasible to describe probe diffusion in linear long-chain solutions with realistic parameters, while better fits were obtained assuming a stretched exponential dependence on concentration. Importantly, we have analyzed the cross-link specific effect on probe diffusion independently of any specific model by comparing the best-fit interpolation of the solution data with the diffusion in the networks. The most reasonable description is obtained by assuming that the cross-link effect is additive in the effective friction coefficient of the probes. The concentration dependences as well as the data compared at the equilibrium degrees of swelling indicate that swelling heterogeneities and diffusant shape have a substantial influence on small-molecule diffusion in networks.

Appendix E. Flat-top model: stability of the single-species stationary state given by Eqs. 24 and 26 in the text.

Flat-top model: stability of the single-species stationary state given by Eqs. 24 and 26 in the text

Appendix D. Flat-top model: equilibrium diameter distribution.

Flat-top model: equilibrium diameter distribution

Appendix A. Derivation of the von Foerster Equation from the individual based model with the PPA.

Derivation of the von Foerster Equation from the individual based model with the PPA