Investigation of dual-channel fiber-optic surface plasmon resonance sensing for biological applications

A dual-channel fiber-optic sensor based on surface plasmon resonance (SPR) for self-referencing refractive-index measurements has been proposed. Most applications of fiber-optic SPR sensors are designed to measure the refractive index of a liquid or gas sample by measuring the signal from a single surface, the sensitivity and stability of which is easily affected by the fluctuation of external environmental conditions. We have designed a dual-channel fiber-optic surface sensor with two independent SPR signals from two areas of the same probe. A prototype sensor was fabricated and characterized. The preliminary experimental results demonstrate the characteristic responses of both SPR signals from two channels that independently correspond to the refractive index changes in the liquid samples with which they are in contact. The design could be extended to a multichannel sensor with further developments. The experimental results confirmed that one channel can be used as a reference sensor that could compensate for unexpected changes in bulk refraction or temperature and develop this sensor as a practicable high-sensitivity biosensing device.     

Tapered fiber optic surface plasmon resonance sensor for analyses of vapor and liquid phases

We report a new approach to analyze both vapor and liquid phases by utilizing a tapered fiber optic surface plasmon resonance (SPR) probe. This technique employs a fiber optic SPR probe with a modified geometry to tune the SPR coupling wavelength-angle pair. The observed composite spectrum included two distinct SPR dips associated with surface plasmons excited in the gas and liquid active regions. This sensor is able to detect refractive index changes in both vapor and liquid phases individually by simultaneous monitoring SPR coupling wavelengths from the two sensing surfaces.     

Superbroadband 1310 nm emission from bismuth and tantalum codoped germanium oxide glasses

Near-infrared broadband emission from bismuth-tantalum-codoped germanium oxide glasses was observed at room temperature when the glasses were pumped by an 808 nm laser diode. The emission band covered the O, E, S, C, and L bands (1260-1625 nm), with a maximum peak at approximately 1310 nm, a FWHM broader than 400 nm, and a lifetime longer than 200 micros. The observed broadband luminescence was attributed to bismuth clusters in the glasses. Bismuth-tantalum-codoped germanium oxide glass might be promising as amplification media for broadly tunable lasers and wideband amplifiers in optical communications.     

Remarkable rate acceleration of imidazole-promoted Baylis-Hillman reaction involving cyclic enones in basic water solution

The Baylis-Hillman reaction of cyclic enones was greatly accelerated in basic water solution with imidazoles as catalysts, which resulted in short reaction time, high yields, and expanding substrate scopes. Bicarbonate solution was shown to be the optimal reaction medium for the reaction in this study. The apparent "enhanced basicity" of imidazoles accounted for the rate increase in alkaline solution.     

Oxygen activation by the noncoupled binuclear copper site in peptidylglycine alpha-hydroxylating monooxygenase. Reaction mechanism and role of the noncoupled nature of the active site

Reaction thermodynamics and potential energy surfaces are calculated using density functional methods to investigate possible reactive Cu/O(2) species for H-atom abstraction in peptidylglycine alpha-hydroxylating monooxygenase (PHM), which has a noncoupled binuclear Cu active site. Two possible mononuclear Cu/O(2) species have been evaluated, the 2-electron reduced Cu(II)(M)-OOH intermediate and the 1-electron reduced side-on Cu(II)(M)-superoxo intermediate, which could form with comparable thermodynamics at the catalytic Cu(M) site. The substrate H-atom abstraction reaction by the Cu(II)(M)-OOH intermediate is found to be thermodynamically accessible due to the contribution of the methionine ligand, but with a high activation barrier ( approximately 37 kcal/mol, at a 3.0-A active site/substrate distance), arguing against the Cu(II)(M)-OOH species as the reactive Cu/O(2) intermediate in PHM. In contrast, H-atom abstraction from substrate by the side-on Cu(II)(M)-superoxo intermediate is a nearly isoenergetic process with a low reaction barrier at a comparable active site/substrate distance ( approximately 14 kcal/mol), suggesting that side-on Cu(II)(M)-superoxo is the reactive species in PHM. The differential reactivities of the Cu(II)(M)-OOH and Cu(II)(M)-superoxo species correlate to their different frontier molecular orbitals involved in the H-atom abstraction reaction. After the H-atom abstraction, a reasonable pathway for substrate hydroxylation involves a "water-assisted" direct OH transfer to the substrate radical, which generates a high-energy Cu(II)(M)-oxyl species. This provides the necessary driving force for intramolecular electron transfer from the Cu(H) site to complete the reaction in PHM. The differential reactivity pattern between the Cu(II)(M)-OOH and Cu(II)(M)-superoxo intermediates provides insight into the role of the noncoupled nature of PHM and dopamine beta-monooxygenase active sites, as compared to the coupled binuclear Cu active sites in hemocyanin, tyrosinase, and catechol oxidase, in O(2) activation.     

Structure,transport and magnetic properties of the double perovskite (Ca<Subscript>2-2x</Subscript>Sr<Subscript>2x</Subscript>)FeMoO<Subscript>6</Subscript>

In this paper we report the results of a detailed investigation of the double perovskite (Ca_2-2xSr_2x)FeMoO₆ system. Chemical size effects on structural, electrical, and magnetic properties caused by the substitution of isovalent, larger Sr ions into the smaller Ca sites, resulting in (Ca_2-2xSr_2x)FeMoO₆, have been examined. The compounds crystallize in the monoclinic space group P2₁/n for 0.0x<0.2, the orthorhombic space group Pbnm for 0.2x<0.4, and the tetragonal space group I4/m and I4/mmm for x0.4. Examination of the resistivity of all compounds reveals a metallic behavior which is well described by a Tⁿ dependence except for x=1.0. These n values change from 1 to 2 as T decreases lower than T_c. This is indicative of a variation in the transport mechanism at T_c. The ferrimagnetic transition temperature T_c increases with increasing x from 318 (x=0.0) to 393 K (x=1.0). For all samples, the saturation magnetization at 82 K obeys M_s3.5_B/(formula unit), compared to a theoretical spin-only moment of 4_B/(formula unit) for a perfectly ordered compound. PACS 74.25.Fy; 74.25.Ha     

A new lubrication equation for ultra-thin gas film in hard disk drives

To overcome the complicated and time-consuming difficulties of current models, a new lubrication equation based on boundary velocity slip model for solving the ultra-thin film gas lubrication in hard disk drives is proposed by adopting the nanoscale effect function, N _p. The present model is easy to calculate and applicable at nanoscale. The results of numerical calculations indicate that the present model produces a close approximation to that of the exact Boltzmann model.     

Iron and copper complexes of tetraphenyl-m-benziporphyrin: reactivity of the internal C-H bond

Iron and copper complexes of tetraphenyl-m-benziporphyrin (TPmBPH)H have been prepared and structurally characterized. The iron system, (TPmBPH)Fe(II)Br, contains a high-spin Fe(II) center. In the solid state the complex forms dimeric units linked by weak CH.Br hydrogen bonds. The Cu complex contains a tetrameric copper cluster with a Cu(2)Cl(4)(2)(-) unit bridging two [(TPmBPCl)Cu(II)](+) fragments. The formation of (TPmBPCl)H represents an example of copper-catalyzed chlorination on the internal carbon atom of (TPmBPH)H.