Temporal fluctuations in the SERRS spectra of single iron–protoporphyrin IX molecule

Surface enhanced resonance Raman spectra of Fe–protoporphyrin IX, adsorbed on silver colloidal nanoparticles immobilized onto a polymer-coated glass slide have been investigated at very low concentrations. The spectra exhibit drastic temporal fluctuations on a time scale of seconds in both line frequency and intensity; such a trend suggesting that the single molecule limit is approached. Sequences of spectra have been analyzed in terms of an underlying continuum and of Raman peaks superimposed on this continuum. A statistical analysis of the spectrum intensity has allowed us to put into evidence that main contribution to the intensity fluctuations arises from the continuum. In addition, a high correlation between the total integrated intensity and the intensity detected at different Raman peaks has been revealed. Furthermore, the ratio between the intensity detected in correspondence of different FePP vibrational modes shows a temporal variability likely reflecting the intrinsic dynamics of the molecule. All these findings have been ascribed to a desorption–adsorption mechanism of the molecules at the silver surface.     

Application of AXAFS spectroscopy to transition-metal oxides: influence of the nearest and next nearest neighbour shells in vanadium oxides

The influence of changes in coordination number, interatomic distances, and oxidation state on the intensity and centroid position of the Fourier transform (FT) of the atomic X-ray absorption fine structure (AXAFS) peak of vanadium oxide bulk model compounds and alumina-supported vanadium oxide clusters has been investigated. Using Na3VO4 and V2O5 as model compounds, it has been shown that the nearest neighbour shells have a pronounced influence on the AXAFS intensity; specifically, a 40 % decrease in intensity was observed between these two compounds. Secondly, the influence of partial reduction of the vanadium oxide species has been determined; this led to a 50 % decrease in the AXAFS intensity and to an increase in the centroid position. Furthermore, the influence of the vanadium oxide loading has been assessed. A non-linear relationship between the vanadium oxide loading and the AXAFS intensity has been found, indicating that the AXAFS intensity is sensitive to the formation of V-O-V bridging bonds between the vanadium VO4 clusters. The results show that AXAFS can be used to probe the relative energy level of the vanadium valence orbitals.     

Effect of surfactants on the fluorescence intensity of organic reagents

The effect of 45 surfactants on the fluorescence intensity of 12 organic reagents has been studied and discussed. It has been found that there is a marked enhancement in the fluorescence intensity of organic reagents with nonrigid structures and with phenyl groups closely located.     

Interaction of electromagnetic waves in planar waveguide with a nematic layer

This work is a theoretical study of energy exchange between two coupled TE-wave modes on director diffraction grating in a planar waveguide containing a layer of nematic liquid crystal. The diffraction grating is produced by an external electric field in the nematic layer with spatial periodic anchoring energy between director and waveguide surface. The intensity of a signal mode at the output of the nematic layer has been calculated in dependence of anchoring energy amplitude and modulation period, the size of nematic layer and electrical field value. The cases of co-propagating and oppositely propagating modes have been analysed. The analytical expressions that describe the maximum values of signal mode intensity have been derived. The maximum intensity value output from the nematic has been shown to depend monotonously on the anchoring energy parameters in the case of oppositely propagating wave modes and non-monotonously in the case of co-propagating wave modes. In both cases, the maximum value of signal mode intensity grows with the increase in electric field.     

Interference effects on the photoluminescence intensity of molecules near a dielectric surface

The photoluminescent intensity of a molecule near a dielectric interface has been investigated theoretically as a function of separation between the molecule and interface. The intensity is expressed by means of functions which have been derived previously. Numerical results have been calculated for the case of a luminescent coating near a semiconductor surface; these results are compared with recent experimental data on tetracene fluorescence near Si and GaAs surfaces.     

Fluorescence of indocyanine green in blood: intensity dependence on concentration and stabilization with sodium polyaspartate.

Indocyanine green (ICG) has been widely used in cardiovascular, hepatic, and ophthalmologic studies. Application of this fluorescent dye has been handicapped by its poor stability in solution and by the complex dependence of its fluorescence intensity on concentration. Noncovalent interactions between ICG and sodium polyaspartate (PASP) stabilize ICG fluorescence in aqueous solution, but the effect of PASP on ICG fluorescence in blood has not been described. The current study had two main goals: first, to characterize in vitro in blood the relationship between fluorescence intensity and concentration of ICG-PASP (ICG) and the stability of this relationship over time; second, to test a new phenomenological model describing the dependence of ICG fluorescence on concentration. Freshly-prepared ICG and ICG-PASP solutions produced the same fluorescence intensity over a wide range of concentrations (0.0005-0.1271 mg/ml). The peak fluorescence of ICG was reduced by 11% after 10 h and by 72% at 7 days. In contrast, the peak fluorescence intensity of ICG-PASP solutions was nearly unchanged for up to 14 days. The dependence of the fluorescence intensity on concentration was accurately represented by our model that accounted for the generation of fluorescence following light absorption, and for the reabsorption of the emitted fluorescence by ICG.     

The influence of acoustic power on multibubble sonoluminescence in aqueous solution containing organic solutes

The effect of varying the applied acoustic power on the extent to which the addition of water-soluble solutes affect the intensity of aqueous multibubble sonoluminescence (MBSL) has been investigated. Under most of the experimental conditions used, the addition of aliphatic alcohols to aqueous solutions was found to suppress the MBSL intensity, although an enhancement of the MBSL intensity was also observed under certain conditions. In contrast, the presence of an anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solutions generally enhanced the observed MBSL intensity. For a series of aliphatic alcohols and SDS, a strong dependence of the MBSL intensity on the applied acoustic power (in the range of 0.78-1.61 W/cm(2)) at 358 kHz was observed. The relative SL quenching was significantly higher at higher acoustic powers for the alcohol solutions, whereas the relative SL enhancement was lower at higher acoustic powers in SDS solutions. These observations have been interpreted in terms of a combination of material evaporation into the bubble, rectified diffusion, bubble clustering and bubble-bubble coalescence.     

四环素-Ca2+-CTMAB三元配合物体系荧光光谱的研究与应用

研究了Ca2+和阳离子表面活性剂CTMAB对四环素(TC)的荧光增敏作用,提出了一种利用Ca2+-TC-CTMAB三元配合物协同增敏体系来测定TC含量的新方法.在Ca2+-CTMAB及TC共存体系中,由于三元配合物的生成使TC的荧光强度急剧增加,其荧光强度与TC浓度在8.0×109-9～1.0×10-5 mol/L范围内具有良好的线性关系,方法检出限为5.97×10-9 mol/L.该法用于TC片剂、尿液及牛奶中残留TC的测定,加标回收率为82.4%～98.3%.同时对TC在不同介质中的荧光增敏作用机理进行了初步探讨.     

CPFX-Al3+-CTMAB体系的荧光特性及环丙沙星的测定

研究了不同表面活性剂对环丙沙星（ciprofloxacin,CPFX）-Al^3＋体系荧光特性的影响,发现十六烷基三甲基溴化铵（CTMAB）对该体系有显著的增敏作用,系统研究了CPFX—Al^3＋—CTMAB反应体系的荧光特性,利用这一反应体系,建立了简单、快速、灵敏的测定环丙沙星的荧光方法,选择了最佳实验条件,并用于环丙沙星片剂和软膏的测定。     

乙醇溶液电感耦合等离子体发射光谱研究 Ⅲ.关于背景和氰分子辐射的某些观察

乙醇导入ICP导致等离子体连续辐射(即复合辐射和轫致辐射)强度减小和分子带(主要是CN带)强度增大。分子带的影响随波长而异,所以在正常分析区不同波长处的总背景强度随乙醇浓度增大有三种变化趋势:单调增大、单调减小或在某个乙醇浓度时出现最小值。详细研究了CN带强度与ICP工作参数的关系以及CN带对稀土元素和钪灵敏线的干扰,指出适当增加炬管的外管长度可以有效地抑制CN带。     

Development and Certification of NIST Standard Reference Materials for Relative Raman Intensity Calibration

In analytical Raman spectroscopy it becomes increasingly important to employ a procedure for the correction of the relative intensity of Raman spectra. The determination of the intensity response function of a Raman instrument traditionally has been carried out through a white light source that has been calibrated for its relative spectral irradiance. While this method will furnish a correction curve to yield spectra corrected to relative Raman intensity, it is often cumbersome and fraught with experimental difficulties that can profoundly affect the reliability of the correction procedure. An alternate methodology that permits a simplified calibration of the Raman instrument response function is based on the use of luminescent glass standards that transfer a white light calibration onto the Raman measurement system. In this procedure, a measurement of the luminescence of an intensity standard, whose relative irradiance has been determined, provides a means to establish the instrument response function. Correction of measured spectra by this function furnishes spectra that are free of instrumental intensity artifacts. Based on this approach, NIST is developing a series of Standard Reference Materials (SRMs) for the calibration of Raman intensity. This process, and the results obtained thereby, is described for Raman spectroscopy measurements employing 785nm excitation. The procedure is valid for both macro-sampling and micro-sampling Raman work.     

Rotational isomerism and solvent effect on infrared intensities of ν(CO) stretching band in methyl alkyl ketones

A solvent-sensitive rotational equilibrium has been observed in several methyl alkyl keyones. This equilibrium arises from the rotational of the R group around thr R-(CO) bond. The variation in relative intensity of the two bands observed in methyl isobutyl ketone has been measured. Frequency and intensity of each band and the total intensity have been ralated to the solvent properties using the G parameter as a measure solvent polarity. From these relationships the stable conformer in gas phase has been determined.     

外加气体对碘的简并四波混频的影响

研究了入射激光能量密度,外加气体(N~2,CO~2,NO~2)对碘的简并四波混频(DFWM)光谱和信号强度的影响,测定了I~2的DFWM信号的饱和强度与外加气体压强之间的关系。结果表明外加气体对I~2的DFWM光谱结构的影响不大,但对信号强度的影响较大,而且与激光能量密度有关。I~2的DFWM信号的饱和强度(I~s~a~t)与N~2压强(p)之间的关系为I~s~a~t∝p^0^.^7。当激光能量密度足够大时,外加气体对信号的增强作用是热光栅所产生的。     

Effects of pressure and solvents on the infrared absorption intensity of the O-H stretching mode of phenol in solutions

Effects of pressure and solvents on the infrared spectrum of phenol in solutions have been investigated using a hydrostatic high-pressure cell with synthetic diamond windows. For the first time, we performed a quantitative investigation of the effect of pressure on the absolute intensity of O-H stretching mode up to 150 MPa (in CCl4) and 200 MPa (in CS2). For comparison, we measured the effect of solvents on the absorption intensity. The Polo-Wilson theory, which is the most traditional theory for medium effects on the intensity, was tested for present results. The pressure dependence was in sufficient agreement with their formula, while the solvent dependence is unsatisfactory. This suggests that the traditional intensity correction by Polo-Wilson's formula is practically valid for pressure-tuning infrared experiments.     

Generation and propagation of intense supersonic beams

Computer simulations and experiments have been performed to quantify the effects of nozzle shape and skimmer placement on high-density supersonic jets. It is shown that the on axis beam intensity achieved is much higher than intensity achieved using standard sonic nozzles. Changes in skimmer design and positioning are required to allow this intense jet to propagate in a typical supersonic beam setup.     

Ag|kCl|六氢吡啶体系表面增强喇曼散射效应的猝灭和恢复

在简述近年来电化学体系中表面增强喇曼散射(SERS)活性位置研究的实验结果和有关论述后, 着重报道作者在Ag/KCl/六氢吡啶体系中, Ag-Cl振动峰和六氢吡啶诸振动峰的强度, 在一定电位范围内电极被施加负脉冲电位后的同步下降, 以及采用氧化还原循环(ORC)处理得到同步恢复等新的实验结果, 并对上述体系中表面络合物的构成及其在SERS中的作用作了进一步的论证。     

A novel fluorescent sensor for metal cations and protons based of bis-1,8-naphthalimide

A newly synthesized bis-1,8-naphthalimide aimed to increase its fluorescence intensity in the presence of protons or metal cations has been investigated. Its spectral photophysical characteristics in acetonitrile and chloroform solutions are described. The influence of metal cations (Zn(2+), Ni(2+), Ce(3+), Co(2+), Cu(2+) and Ag(+)) and protons on the fluorescence intensity has been investigate with regard to obtain fluorescence sensors for this ions in the environment.     

Structure of glassy polymers. V. Small-angle x-ray scattering from polystyrene

Small-angle x-ray scattering (SAXS) from glassy atactic polystyrene has been measured using a Bonse–Hart system. After correcting for absorption, background, and beam divergence, the scattering has been placed on an absolute basis using a standard silica suspension as a reference.The desmeared absolute intensity decreases strongly with increasing scattering angle over the range between 20 sec and 20 min. At larger angles, the intensity decreases much more slowly with increasing angle and approaches the value expected for density fluctuations frozen-in at the glass transition. The angular variation of intensity is well described by the scattering from heterogeneities of various sizes and concentrations superimposed on the scattering from thermal density fluctuations. These heterogeneities range in radius from 10 to 4000 Å. The present SAXS results on glassy polystyrene seem inconsistent with the presence of nodular features as representative of the bulk polymer.     

Pre-electrohydrodynamic relaxation phenomenon in nematic liquid crystals

Study of electrohydrodynamic instabilities in thicker nematic liquid crystal samples (800–1200 μm) of MBBA is reported. An initial rise in the intensity of transmitted light immediately after the application of an electric field has been found to precede the attenuation of the transmitted beam due to the gradual development of hydrodynamic instability in the sample. The dependence of the relative dominance of the two relaxation phenomenon on the applied electric field intensity has been studied.     

ANS fluorescence as a tool to monitor cross-linking polymerization of acrylamide

A method based on monitoring the fluorescence intensity of 1-anilinonaphthalene-8-sulphonate (ANS) has been introduced to follow the cross-linking polymerization of acrylamide initiated by ammonium persulfate-TEMED redox initiator system. There is about a 20-fold increase in the fluorescence intensity of ANS accompanying polymerization. Preferential location of ANS molecules near the hydrophobic regions of the polymer surface appears to explain the fluorescence intensity enhancement. The method is found to be consistent with the conventional dilatometric method.