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The detection of trace fenthion using surface-enhanced Raman scattering (SERS) was proposed via the OH stretching band of water serving as an internal standard. The adsorption process of fenthion on the silver nanoparticle aggregates was characterized by UV-Visible absorption spectrometry and the optimal adsorption time was about 20 min. The OH stretching band of H2O molecule presented around 3100-3500 [cm.sup.-1] in SERS spectrum was identified by density functional theory and it was not interfered with other characteristic peaks of fenthion. The linearity was obtained from the concentrations divided by the ratio of the benzene ring stretching area around 1073 [cm.sup.-1] and the internal standard of OH stretching area from 3100 to 3500 [cm.sup.-1], while the detection limit was calculated as 0.46 pM. The proposed SERS detection method was used in analyzing lake water sample with the recovery of 94-99%. Keywords: fenthion, surface-enhanced Raman scattering, silver nanoparticle aggregates, internal standard, Fenthion is widely used as an organophosphorous pesticide by inhibiting the activities of acetyl cholinesterase, but the residue of fenthion has been reported a high mammalian toxicity [1]. The maximum [...]

We report recent observations of resonant inelastic X-ray scattering (RIXS) at the cerium [L.sub.3]-edge of CeP[O.sub.4], Ce[O.sub.2], and [Ce.sup.3+] ion in aqueous solution. The intensity of the emission spectrum, including the dispersive Raman below the edge and the emerging nondispersive fluorescence above the edge, was recorded with a solid-state detector with low-energy resolution and a WDX detector with modestly high-energy resolution. The yield of the emission was used to monitor the cerium [L.sub.3]-edge X-ray absorption near edge structures (XANES) in a constant initial state (CIS) mode as the photon energy sweeps across the cerium [L.sub.3]-edge. The CIS XANES is compared with the XANES recorded using the nondispersive fluorescence yield, [L.sub.α], in a constant final state (CFI) mode. It is found that the Raman yield dominates the total emission in the pre-edge region and diminishes rapidly at threshold. The RIXS of [Ce.sup.3+] in aqueous solution exhibits similar behavior as CeP[O.sub.4]. The post-whiteline RIXS intensity of CeP[O.sub.4] exhibits a correlation with excitation energy. Ce[O.sub.2] also exhibits a less intense whiteline in CIS XANES compared with the XANES detected with normal fluorescence. The implications of these observations with improved instrumental resolution are noted. Key words: resonant inelastic X-ray scattering (RIXS), X-ray emission (XES), cerium [L.sub.3]-edge, XANES, constant initial state (CIS), constant final state (CFS). Nous rendons compte de nos recentes observations en ce qui a trait a la diffusion inelastique resonante de rayons X au seuil d'energie [L.sub.3] du cerium des composes CeP[O.sub.4], Ce[O.sub.2] et de l'ion [Ce.sup.3+] en solution aqueuse. L'intensite du spectre d'emission, y compris celle de la diffusion dispersive Raman sous le seuil d'energie et de la fluorescence non dispersive emergente au-dessus du seuil d'energie, ont ete mesurees au moyen d'un detecteur transistorise a basse resolution energetique et d'un detecteur de rayons X a dispersion de longueurs d'onde a resolution energetique moderement elevee. On a employe le rendement de l'emission pour suivre l'evolution de la structure pres du front d'absorption de rayons X (XANES) du seuil d'energie [L.sub.3] du cerium a l'etat initial stationnaire alors que l'energie des photons balaie le seuil d'energie [L.sub.3] du cerium. On a compare le spectre XANES a l'etat stationnaire au spectre XANES enregistre en employant le rendement d'emission de fluorescence non dispersive, [L.sub.α], a l'etat initial stationnaire. On a observe que le rendement de l'emission Raman constitue la majeure partie de l'emission totale dans la region qui precede le seuil d'energie et qu'il diminue rapidement a partir du seuil. La diffusion inelastique resonante de rayons X du [Ce.sup.3+] en solution aqueuse se manifeste de facon analogue a celle du CeP[O.sub.4]. L'intensite de la diffusion inelastique resonante de rayons X apres la raie blanche du CeP[O.sub.4] presente une correlation avec l'energie d'excitation. Le spectre XANES a l'etat stationnaire du Ce[O.sub.2] montre egalement une raie blanche moins intense que le spectre XANES enregistre en employant la fluorescence normale. Nous faisons etat de la portee de ces observations obtenues grace a l'amelioration de la resolution des instruments. [Traduit par la Redaction] Mots-cles : diffusion inelastique resonante de rayons X, emission de rayons X, seuil d'energie [L.sub.3] du cerium, XANES, etat initial stationnaire, etat final stationnaire., Introduction As third-generation light sources become increasingly accessible, the photon brightness brought about by these undulators-based sources has made it possible to study more readily many low-cross-section X-ray events, such [...]

We present a rapid and straightforward procedure for the synthesis of core--shell surface-enhanced Raman scattering (SERS) tags. SERS tags are combinations of Raman active dyes with metallic nanoparticles inducing the enhancement. Because of their significantly higher stability to environmental conditions, the majority of SERS tags are designed in core--shell geometry. The main disadvantage of this approach up to now was the time-consuming (normally days) and complex preparation of these labeled core--shell particles. The presented approach can be performed within hours on a daily base. The main characteristics and the stability of the fabricated SERS tags m extreme pH values, high ion strength, or in organic solvent is demonstrated in this communication. Furthermore, the SERS tags are functionalized with anti-Salmonella antibody as a model to present a potential application of the core--shell particles in bioimaging. 10.1021/ac902573p

A low-cost Raman system was constructed and used to perform Raman scattering measurements on liquid carbon disulfide at different sample temperatures. The [v.sub.1] and [v.sub.3] bands are identified based on the frequencies calculated by the normal mode analysis. The ratio of the intensities of the anti-Stokes and Stokes bands can be used to illustrate the Boltzmann distribution of the molecules among the vibrational energy levels. [DOI: 10.1119/1.3226562]

A sensitive technique is introduced for the measurement of impulsively excited vibrational Raman modes and a linear sweep in the instantaneous frequency of the probe pulse has isolated Raman sidebands from noise, thus enhancing sensitivity. The temporal interference between two stretched, time-delayed pump pulses has helped in selectively exciting specific modes.

A numerical model of pulsed Raman fiber converters is developed in the near infrared around 2 [micro]m, where the theory is based on Feynman-like diagrams describing each possible interaction between photons and phonons in the Raman medium. The simulation has modeled single-pass or cavity configurations as it has included copropagating and counterpropagating waves, calculating the spectral power density and the temporal repartition of the pulse at the output of the fiber.

The design of a cladding-pumped silicon Raman amplifier is discussed. Results suggest the achievement of an enhanced total gain of 18 dB at a pump power of 300 mW.

The article discusses the analytical and numerical modeling of the two-photon photovoltaic effect in silicon devices. Results suggest the achievement of maximum Raman gain at pump intensities of 90-125 MW/[cm.sup.2] for optimum device lengths of 5-7 cm.

The importance of the substrate field inhomogeneities in the optical response of an adsorbate experiencing a resonant Raman scattering process is studied. The analysis reveals that the number of intermediate vibrational levels becomes very large for a strong substrate field.

The calculation for actively Q-switched intracavity Raman laser to investigate the use of curve and equations is presented. This helps in estimating the first stokes and increase the efficiency of Raman conversion.

The analysis presents the Raman scattering studies of [YBa.sub.2][Cu.sub.3][O.sub.7-x] (YBCO) films, which are grown by a high-rate electron-beam co-evaporation method. The study helps in the determination of the local chemical homogeneity of the film.

We describe a straightforward and highly visual experiment designed to demonstrate Raman scattering spectroscopy by measuring the vibrational energy spacing of nitrogen molecules in the liquid phase. Interpretation of the spectrum teaches the principles of elastic and inelastic light scattering and the intrinsic properties of molecules. The use of a pulsed Nd: YAG laser with high peak power leads to a plethora of nonlinear optical phenomena. The presence of highly visible stimulated Raman scattering greatly enhances the normal Raman-shifted signal, allowing for a more engaging laboratory experience in comparison to traditional Raman scattering experiments. [DOI: 10.1119/1.2721584]

A Raman shifter is optimized for generating high-energy laser pulses at a 1.54 [micro]m wavelength. A forward-scattering design is described, including details of the multiple pass and nonfocused optical design, Stokes injection seeding, and internal gas recirculation. First-Stokes conversion efficiencies up to 43%--equivalent to 62% photon conversion efficiency--were measured. Experimental results show output average power in excess of 17.5 W, pulse energies of 350 mJ at 50 Hz, with good beam quality ([M.sup.2] < 6). Narrow bandwidth and tunable output is produced when pumping with a single longitudinal mode Nd:YAG laser and seeding the process with a Stokes wavelength narrowband laser diode. OCIS codes: 010.3640, 280.3640, 140.3550, 280.1100, 280.1120.

Laser emission, consisting of three primary colors, is generated by frequency conversions of the second-harmonic emission of a picosecond (120 ps) Nd:YAG laser by means of stimulated Raman scattering and subsequent four-wave Raman mixing in molecular deuterium. In the double-pass configuration, the fundamental beam (532 nm, 14.16 mJ, 100%) is converted to blue (459 nm, 1.71 mJ, 12.1%), green (532 nm, 7.04 mJ, 49.7%), and red (632 nm, 4.90 mJ, 34.6%), resulting in a total conversion efficiency of 96.4%. OCIS codes: 140.0140, 140.3550, 330.1690.

A series of ketimide complexes possessing fluorinated aromatic groups are reported that have established trends in their respective electronic structures based on electron-withdrawing ability. The results show that the thorium bis(ketimide) species are rare examples of tetravalent actinide-containing complexes that exhibit luminescence, with measured emission lifetimes at 77 K in the range of 50-400 [mu]s, and also engender resonance-enhanced Raman spectra when exciting into the visible electronic transitions.

Raman spectroscopy is used to study the thermal relaxation kinetics of defects in single-wall carbon nanotubes irradiated with a 248 nm pulsed excimer laser. The two relaxation processes have demonstrated the strong temperature dependence, which have corresponded to vacancy-interstitial recombination and vacancy migration along the tube axis.

Raman scattering is used to investigate the oxygen-octahedral [A.sub.1g](O) phonons for both 1:2 ordered xBaTi[O.sub.3](1-x)Ba([Mg.sub.1/3][Ta.sub.2/3])[O.sub.3] and 1:1 xCa([Sc.sub.1/2][Nb.sub.1/2])[O.sub.3](1-x)Ba([Sc.sub.1/2][Nb.sub.1/2])[O.sub.3] ceramics. The size and the atomic polarizability of doped atoms and the substitution site have affected the phonon properties of the oxygen octahedral structure.

Here, it is demonstrated that similar chemical species within a multicomponent sample can be distinguished, down to the single-molecule level, by means of their surface-enhanced vibrational fingerprints. Surface-enhanced resonance Raman scattering spectra and 2D spatial intensity maps are recorded from thin Ag nanoparticle films coated with fatty acid Langmuir-Blodgett monolayers containing one-to-one binary mixtures, at varying concentrations, of two dye molecules of similar absorption and scattering cross section (n-pentyl-5-salicylimidoperylene and octadecylrhodamine B). The results reveal the change in the distribution of the two dyes within the monolayer, and the breakdown of ensemble spectral averaging, which occur as the single-molecule regime is approached. It is found that the unimolecular level is reached when 1-10 molecules of each dye occupy the 1-[micro][m.sup.2] scattering areas probed by the laser. These signals are attributed to the rare spatial coincidence of isolated target analyte molecules and localized electromagnetic hot spots in the nanostructured metal film. The bianalyte nature of the samples provides strong corroborative support for the attribution of spectra to single molecules at high dilution, while the effect of domain formation/aggregation is found to be important at higher concentrations.

Single-phase [Bi.sub.1-x][Nd.sub.x]Fe[O.sub.3] (x = 0-0.2) multiferroic ceramics were prepared to study the effects of Nd substitution on their crystal structures, Raman scattering spectra, and ferroelectric properties. The x-ray diffraction data showed a gradual change in crystal structure from rhombohedral to pseudotetragonal via triclinic with increasing x, and the increasing x value suggest that the structural change is accompanied by the weakening of long-range ferroelectric order.

Raman studies of the [A.sub.1](TO), [E.sub.1](TO) , [E.sub.2.sup.2], [A.sub.1](LO) and [E.sub.1] (LO) symmetry phonons of GaN are described. The [A.sub.1](TO) and [E.sub.1](TO) vibrations show symmetric two-phonon decay whereas [E.sub.2.sup.2] decays through the creation three phonons.

A combination of the scattering Raman spectra and density functional theory calculations are used to analyze the Raman dispersion and intermolecular interactions of several unsubstituted thiophene oligomers. The results demonstrate that the intensities, as well as the frequencies are highly affected by the intermolecular interactions, which also has a strong impact on the conjugation length of the oligomers.

A study was conducted to investigate the continuous-wave laser operation of Nd-doped tetragonal NaLa[(W[O.sub.4]).sub.2] crystal at room temperature by optical pumping in the special region overlapping AlGaAs diode laser emission. The findings were found to justify the better efficiency for laser operation of the [pi]-configuration and determined the optimum Nd concentration for this purpose in the 3 at.%- 5 at.% range.

Nonlinear response formalism is used to investigate Raman intensity of intramolecular and lattice modes of crystalline [alpha]-bithiophene ([alpha]-2T), within density functional theory. It is demonstrated that the first principle based on comparison of the calculated Raman spectrum and the experimental data, and bond polarizability model approaches are powerful complementary tools to calculate the nonresonant Raman spectrum of [alpha]-2T and predict on larger oligothiophenes.

Raman scattering is used to study structural relaxation in amorphous 1, 2-dichloroethane (DCE) samples prepared by vapor disposition on cold substrates. The structural relaxation in amorphous DCE occurs over a wide temperature range in contrast to glass states of benzene derivatives, which can be attributed to the characteristic molecular structure of DCE.

Steady-state variations and time-resolved blue-shifts in the surface-enhanced resonance Raman scattering background luminescence of single Ag nanoaggregates adsorbed with rhodamine 6G ( R6G) molecules are investigated. The origin of the background luminescence is attributed to luminescence from several kinds of aggregates after considering pioneering work that dealt with the affinity of R6G molecules to Ag surfaces and aggregation of R6G molecules.

Synthesis of four different sizes of citrate-protected silver nanoplates with the corresponding in-plane dipole resonance band at 530, 619, 778, and 858 nm, respectively is performed for surface-enhanced Raman scattering (SERS) study. Results reveal that a market red shift of the in-plane dipole resonance of silver nanoplates is observed, whereas their other resonance modes only have small alterations in the site or intensity during the aggregation process.

A new modeling method to describe the steady-state and transient regimes of a continuous-wave pumped Raman laser that emits both stokes and anti-stokes photons is described. The anti-stokes emission generated by a silicon-based Raman laser is numerically simulated for the first time to demonstrate the potentialities of the proposed method.

The ultrafast dynamics of the coherent phonons of single crystal Bi is investigated under moderate photoexcitation as a function of temperature, excitation density and optical polarization. Coherent [E.sub.g] phonon disappears more rapidly than [A.sub.1g] with rising temperature due to its larger coupling with lower-frequency phonons.

This work describes the development and demonstration of a non-scanning chemical imaging probe, capable of obtaining surface-enhanced Raman scattering (SERS) images of samples with which it is in direct contact. The SERS imaging arrays (i.e., nanoprobes) are used in a signal collection mode to obtain images by measuring as many as 30 000 individual sub-diffraction-limited locations on a sample's surface simultaneously. These SERS probes are fabricated from coherent fiber-optic imaging bundles, allowing for the formation of a highly ordered roughened metal surface, capable of providing uniform SERS enhancement (< 2.0% relative standard deviation) across the entire imaging surface. These optimized SERS nanoprobes have potential application to a wide range of research fields from materials science to cellular biology.

The structural characteristics and adsorption behavior of 4,4'-thiobenzenethiol (TBBT) self-assembled monolayers (SAMs) on Au is investigated by surface enhanced Raman scattering (SERS), electrochemical cyclic voltammetry (CV), ac impedance spectroscopy (EIS), and atomic force microscopy (AFM). A scanning electron microscopic image of Ag nanoparticles on TBBT/Au and the Raman spectrum of TBBT in smooth macroscopic Au/TBBT SAMs/Ag nanoparticle sandwich structure indicate that metal nanoparticles could be adsorbed on TBBT SAMs effectively through covalent linkage.

The praline zwitterions Raman and Raman optical activity (ROA) spectra were interpreted on the basis of ab initio computations. The results are found to be consistent with the presence of both conformers in the solution determined also on the basis of NMR spectra analysis.

The evaporative cooling rates of a droplet train of liquid water injected into vacuum was studied using Raman thermometry to test the hypothesis that states that on average, molecules in the higher-energy tail of the Boltzmann distribution are more readily transferred into the vapor during evaporation. The value of the evaporation coefficient of liquid water was determined to be 0.62 plusmn 0.09, confirming that a rate-liming barrier impedes the evaporation rate.

Depth and in-plane profiling of strain, Ge composition, and defects in strained-Si/[Si.sub.1-x][Ge.sub.x]/Si heterostructures using micro-Raman imaging is reported. For the top strained-Si layer, two-dimensional UV-Raman images of the frequency and bandwidth of the Si band reveal that film crystallinity is correlated with the magnitude of in-plane strain.

The changes in the composition and optical properties of Ag[O.sub.x] thin films induced by thermal annealing are studied. Results reveal that the Ag aggregation region work as precursors to Ag nanoparticles upon visible laser irradiation.

Phospholipase [A.sub.2] (PL[A.sub.2])-catalyzed hydrolysis at the sn-2 position of 1,2-dimyristoyl-sn-glycero-3-phosphocholine in optically trapped liposomes is monitored in situ using confocal Raman microscopy. Individual optically trapped liposomes (0.6 [micro]m in diameter) are exposed to PL[A.sub.2] isolated from cobra (Naja naja naja) venom at varying enzyme concentrations. The relative Raman scattering intensities of C-C stretching vibrations from the trans and gauche conformers of the acyl chains are correlated directly with the extent of hydrolysis, allowing the progress of the reaction to be monitored in situ on a single vesicle. In dilute vesicle dispersions, the technique allows the much higher local concentration of lipid molecules in a single vesicle to be detected free of interferences from the surrounding solution. Observing the local composition of an optically trapped vesicle also allows one to determine whether the products of enzyme-catalyzed hydrolysis remain associated with the vesicle or dissolve into solution. The observed reaction kinetics exhibited a time lag prior to the rapid hydrolysis. The lag time varied inversely with the enzyme concentration, which is consistent with the products of enzyme-catalyzed lipid hydrolysis reaching a critical concentration that allows the enzyme to react at a much faster rate. The turnover rate of membrane-bound enzyme determined by Raman microscopy during the rapid, burst-phase kinetics was 1200 [s.sup.-1]. Based on previous measurements of the equilibrium for PL[A.sub.2] binding to lipid membranes, the average number of enzyme molecules responsible for catalyzing the hydrolysis of lipid on a single optically trapped vesicle is quite small, only two PL[A.sub.2] molecules at the lowest enzyme concentration studied.

An efficient self-Raman laser is realized based on the multifunctional laser crystal Nd:YVO4 with the acoustooptic Q-switch. The theoretically calculated results suggest that Nd:YVO4 crystal is a good choice for the diode-laser end-pumped self-Raman laser to produce new spectrum lines due to its attractive features as the gain material and Raman-active medium at the same time.

Metal catalyzed, CVD-grown silicon nanowires decorated by chemical assembly of closely spaced Ag nanocrystals were modified with the well-known 'silver mirror' reaction and investigated as substrates for surface-enhanced Raman (SERS) and hyper-Raman (SEHRS) spectroscopy. Four chromophores were examined: Rhodamine 6G, crystal violet, a cyanine dye, and a cationic donor-acceptor substituted stilbene. After soaking the substrates overnight in [10.sup.-4] M aqueous chromophore solutions, all four chromophores gave good-quality SERS spectra in [less than or equal to] 60 s using < 1 [micro]W of 458-nm cw laser power, and SEHRS spectra are obtained in [less than or equal to] 120 s using < 1 mW of mode-locked 916-nm laser power. Results from this substrate are compared with those on colloidal silver nanoparticles deposited as a film, as well as surfaces grown by the silver mirror reaction.

Here we report in vitro and in vivo detection of self-assembled Au-imidazole by using near-infrared surface-enhanced Raman scattering (NIR-SERS). In vivo, the Auimidazole structures were administered into tumor-bearing mice and detected noninvasively. The self-assembled Au--imidazole complexes were generated by the adsorption of imidazole molecules onto Au nanoparticles (NP) and were then characterized as aqueous suspensions by using NIR-SERS, angle-dependent light scattering with fractal dimension analysis, and visible extinction spectroscopy. The structure and optical activity was sensitive to imidazole concentration and Au NP size. Specifically, the Au--imidazole assemblies formed at lower imidazole concentrations had the lowest fractal dimension ([D.sub.f] = 1.2) and the largest Raman enhancement factors for the dominant NIR-SERS feature, a ring-breathing vibrational mode at 954 [cm.sup.-1]. Changes in elastic scattering intensity, fractal dimension, and surface plasmon absorption were observed with increasing imidazole concentration. The Raman enhancement factor was also found to range between [10.sup.6] and [10.sub.9] with different primary Au nanoparticle sizes. For the higher enhancement factor systems, NIR-SERS detection of Au-imidazole was performed with data acquisitions time of only 5 s. The largest enhancement was observed for the 954-[cm.sup.-1] feature at an imidazole concentration of 1.9 [micro]M when coupled to 54-nm-diameter Au NPs (the largest NP tested). Finally, we show the first demonstration of in vivo, noninvasive, and real-time SERS detection.

Chemical imaging analysis holds great potential in probing the chemical heterogeneity of samples with high spatial resolution and molecular specificity. This paper demonstrates the implementation of Raman mapping for microscopic characterization of tablets containing chloramphenicol palmitate polymorphs with the aid of a new multivariate image segmentation approach based on spatial directed agglomeration clustering. This approach performs the agglomeration clustering by stepwise merging the pixels possessing both spatial closeness and spectral similarity into clusters that define the image segmentation. The incorporation of spatial closeness into the clustering process enables the approach to improve the robustness and avoid poorly defined image segmentation arising from clusters with highly separated pixels. Additionally, the stepwise merging of clusters offers an F-statistic-based procedure to automatically ascertain the number of image segments. Raman mapping analysis of tablets containing two polymorphs of chloramphenicol palmitate followed by multivariate image segmentation reveals that the proposed technique offers the identification of each polymorph and a quantitative visualization of the spatial distribution of the polymorphs identified. This technique holds promise in rapid, noninvasive, and quantitative polymorph analysis for pharmaceutical production processes.

Raman scattering in single-mode optical fibers is exploited to generate multispectral light from a green nanolaser with high pulse repetition rate. Each pulse triggers a picosecond camera and measures the distance by time-of-flight in each of the 0.5 Mpixels. Three-dimensional images are then constructed with submillimeter accuracy for all visible colors. The generation of a series of Stokes peaks by Raman scattering in a Si fiber is discussed in detail and the laser radar technique is demonstrated. The data recording takes only a few seconds, and the high accuracy 3D color imaging works at ranges up to ~200 m. Applications for optical tomography in highly scattering media such as water and human tissue are mentioned. OCIS codes: 010.3640, 060.4370, 110.6880, 140.3550, 170.6920, 280.3640.

A combined synchrotron X-ray diffraction (XRD), Raman scattering and infrared spectroscopy study of the pressure-induced changes in H3BO3 to 10 GPa has demonstrated a new high-pressure phase transition between 1 and 2 GPa followed by chemical decomposition into cubic HBO2, ice-VI and ice-VII. The results are used to propose a mechanism for pressure-induced dehydration of H3BO3 that implies a proton disorder in the system.

Optical-trapping confocal Raman microscopy is developed as a method to study the interactions of drugs or other compounds with the membranes of individual phospholipid vesicles. This technique allows membrane disorder, permeability, and drug localization to be assessed without the need for labeling of the membrane or the compounds of interest. We have applied this technique to study the interactions of two nonsteroidal antiinflammatory drugs, salicylate and ibuprofen, with vesicles prepared from 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The results show that both salicylate and ibuprofen increase membrane disorder, as determined from increases in the Raman scattering from gauche conformers in the phospholipid acyl chains. By monitoring the Raman scattering of the drug molecules in optically trapped DMPC vesicles, the membrane permeability and partitioning of the drugs could be determined; the spatial distributions of the drugs were also measured by scanning the laser focus through surface-adhered 1,2-dipalmitoyl-sn-glycero-3-phosphocholine vesicles, producing a profile of the vesicle and its contents. Though the membrane is permeable to both drugs, ibuprofen preferentially accumulates in the membrane, whereas salicylate does not. The measured ibuprofen accumulation agrees quantitatively with the water/ octanol partition coefficient of the drug and the estimated volume of the lipid membrane. The results suggest that ibuprofen localizes in the hydrophobic acyl chain region of the membrane, whereas salicylate weakly associates with the phospholipid headgroups.