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Background: At lipid interfaces, water plays a crucial role in carrying biological processes, so that there is a huge interest in unravelling the behaviour of water close to membranes. At charged bio-interfaces, water dipoles form an organized layer. Probing such an interfacial thin layer buried between macroscopic bulk environments is a real challenge. Vibrational sum frequency generation (SFG) spectroscopy is intrinsically specific to interfaces, and has already proven to be an ideal tool to investigate model membranes and their surrounding water. Objectives: The goal of this work is to measure the vibrational SFG response of interfacial water around different model membranes — from easiest synthetic lipids to more complex natural lipids, — in order to use it as diagnostic signal able to distinguish the lipid bilayer interface by its charge properties. Materials and methods: Lipid bilayers made either of synthetic or natural lipids (Avanti Polar Lipids) were physisorbed on CaF2 prisms (Crystran), by using the method of the spontaneous fusion of lipid vesicles, to form so called solid-supported lipid bilayers (SSLBs). The model membranes were investigated by SFG spectroscopy at the solid/water interface. Results: The SFG response was measured between 3600 cm-1 and 2800 cm-1, where OH stretching vibrations of water molecules show-up. The SFG intensity of the OH peak maximum at 3125 cm-1 was recorded during the adsorption of lipid vesicles on the surface, and provided knowledge of the changes of the charge properties of the interface due to the adsorption of the model membranes. The SFG signal indicated that the organization of water was larger at negatively charged than at positively lipid interfaces, and reached the highest value with natural E. сoli сardiolipin layers. Moreover, when the full composition of natural lipids was unknown, the behaviour of the SFG response enabled establishing the charge characteristics of the corresponding lipid interfaces. Conclusion: The SFG response of water enabled estimating average charge behaviour of synthetic and natural lipid bilayers in pure water, thus paving the way to use the SFG signal of water as new diagnostic tool to identify lipid interfaces.

In this work, we demonstrated for the first time that the nonlinear optical (NLO) response of interfacial water, as obtained from sum frequency generation (SFG) spectroscopy, can be used as a quantitative, sensitive and label-free probe for nanoparticle/membrane interactions. We probed water molecules that are organized close to the surface of solid-supported model membranes, which mimic the cell barrier and act as sensing platforms, and we measured the SFG response of OH stretching modes of the above interfacial water upon interaction with 5-nm positive gold nanoparticles (AuNPs) in real time. We analyzed three parameters, representing the SFG response of interfacial water: the signal gain, the detection time and the interaction time. A clear dependence on the concentration of AuNPs interacting with the sensing platforms was observed, providing quantitative data about these interactions. From this information, we evaluated the detection performance of this nonlinear optical tool with two sensing platforms, namely, solid-supported bilayers of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) or of DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine). With the DPPC sensing platform, the SFG response of water allowed for the detection of Au concentrations as low as 50 ng/mL. This sensitivity was achieved in less than 300 s. With the DOPC sensing platform, the sensitivity was even better, with a detection threshold of 0.8 ng/mL of gold. However, the required detection rate was approximately 4000 s. Quantifying biological interactions through the NLO response of interfacial water could be extended to many biological host-guest interactions; thus, SFG spectroscopy is a promising quantitative, sensitive and label-free biodetection system.

Vertically aligned MoS2 nanosheets (NSs) with exposed edges were successfully synthesized over a large area (∼2 cm2). The NSs were grown using an ambient pressure chemical vapor deposition technique via rapid sulfurization of sputter deposited thick molybdenum films. Extensive characterization of the grown MoS2 NSs has been carried out using high resolution scanning and transmission electron microscopy (SEM & TEM). A special care was given to the TEM lamella preparation process by means of a focused ion beam to preserve the NS growth direction. The cross-section TEM measurements revealed the growth of densely packed, vertically aligned and straight MoS2 NSs. Additional characterization techniques such as atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence (PL) were used to evaluate the MoS2 NSs. These studies revealed the high crystallinity and quality of the synthesized NSs. The MoS2 NSs show visible light emission similar to mechanically exfoliated monolayer MoS2 NSs. The striking PL signal comes from the exposed edges as shown by experimental and theoretical calculations. The vertical MoS2 NSs also exhibit a hydrophobic character with a contact angle of 114°. The as-grown MoS2 NSs would be highly useful in the development of catalysis, nano-optoelectronics, gas-sensing and bio-sensing device applications.

Structural changes of solid-supported lipid bilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and of their interfacial water surrounding have been probed with vibrational sum frequency generation (SFG) upon interaction with functionalized gold NPs, carrying negative or positive surface charges. Switching the substrate/DPPC zeta potential from strongly negative to weakly negative or positive values by using SiO2 or CaF2 supporting surfaces has enabled elucidating interfacial charge effects, intermolecular interactions, and interaction mechanisms regulating those nano-bio interfaces. At SiO2/DPPC surfaces (ζ = -30 mV), negative NPs have reinforced the average interfacial water alignment, while no interaction has occurred with DPPC bilayer. Oppositely, positive NPs interact with DPPC, with a probable two-step mechanism involving the formation of pores within the bilayer followed by a reorganization of a quasi-ordered DPPC bilayer around NPs. At CaF2/DPPC surfaces (ζ = ±15 mV), both negative and positive NPs have clearly damaged the lipid bilayer structure, together with a drastic disruption of the water organization at the interface. Importantly, all major interfacial structural changes have occurred within the first 15-90 min after exposure to NPs whatever the lipid is supported on SiO2 or CaF2.

Here, we demonstrate how sum frequency generation (SFG), a vibrational spectroscopy based on a nonlinear three-photon mixing process, may provide a direct and unique fingerprint of bio-recognition; This latter can be detected with an intrinsically discriminating unspecific adsorption, thanks to the high sensitivity of the second-order nonlinear optical (NLO) response to preferential molecular orientation and symmetry properties. As a proof of concept, we have detected the biological event at the solid/liquid interface of a model bio-active antigen platform, based on a solid-supported hybrid lipid bilayer (ss-HLB) of a 2,4-dinitrophenyl (DNP) lipid, towards a monoclonal mouse anti-DNP complementary antibody.

In this work, we investigated the interaction of cationic gold nanoparticles (AuNPs) with an anionic solid-supported lipid bilayer (SSLB) prepared via the spontaneous fusion of vesicles of phosphatidylserine (DPPS) and phosphatidylcholine (DPPC) on SiO 2. We combined sum frequency generation (SFG) spectroscopy at the SSLBs interfaces with electrophoretic light scattering at the vesicles/liquid interfaces, and we provided further insight into the formation of organized DPPS-DPPC films on SiO 2 and their interaction with NPs. We found that there is a critical threshold of the relative vesicles/substrate interfacial zeta potentials, beyond which the conformational organization of SSLBs failed. Moreover, we also demonstrated that the presence of anionic DPPS lipids in model mixed DPPS-DPPC membranes accelerated the interaction rate with cationic AuNPs.

Nonlinear second harmonic optical activity of graphene covering a gold photon sieve was determined for different polarizations. The photon sieve consists of a subwavelength gold nanohole array placed on glass. It combines the benefits of efficient light trapping and surface plasmon propagation in order to unravel different elements of graphene second-order susceptibility \chi(2). Those elements efficiently contribute to second harmonic generation. In fact, the graphene- coated photon sieve produces a second harmonic intensity at least two orders of magnitude higher compared with a bare, flat gold layer and an order of magnitude coming from the plasmonic effect of the photon sieve; the remaining enhancement arises from the graphene layer itself. The measured second harmonic generation yield, supplemented by semianalytical computations, provides an original method to constrain the graphene \chi(2) elements. The values obtained are |d_{31} + d_{33}| < 8.1 x 10^3 pm^2/V and |d_{15}| < 1.4 x 10^6 pm^2/V for a second harmonic signal at 780 nm. This original method can be applied to any kind of 2D materials covering such a plasmonic structure., Comment: 8 pages, 5 figures, 1 table, supplementary materials (7 pages, 4 figures, 1 table), accepted for publication in Nano Letters

The sum frequency generation (SFG) signatures of octadecyl-trichlorosilane (OTS) and dodecyl-dimethyl-chlorosilane (DDCS) monolayers on silica were simulated in the C–H stretching region for three polarization combinations (ppp, sps, and ssp), showing the impact of the additional Si-linked methyl groups of DDCS on its SFG signatures. These simulations are based on a two-step procedure where (i) the molecular properties (vibrational frequencies, IR and Raman intensities) are evaluated using first principles methods and (ii) the three-layer model is employed to calculate the macroscopic responses using these molecular responses, the geometry of the experimental setup, and the optical properties of the layers. These first principles calculations adopt the own N-layered integrated orbital molecular mechanics (ONIOM) approach, which divides the system and enables different levels of approximation to be applied to its different parts. Here, the same ωB97X-D exchange-correlation functional is used for all parts, while the underlying silica layers are described with a smaller atomic basis set (STO-3G, 3-21G, or 6-31G) than the alkylsilane and the top silica layer (6-311G*). Calculations show that for describing the lower layer the minimal STO-3G basis set already provides reliable spectral profiles. For OTS, the results are compared to the experiment, demonstrating a good agreement for ppp and sps configurations, provided the refractive index of the layer nl is set to 1.1. To highlight the origin of the SFG signatures, two chemical models were used, one that includes explicitly the SiO2 surface in the first principles calculations (adsorbed-model) and the other that only considers the silane chain (isolated-model). Simulations show that OTS and DDCS display similar spectral patterns where, for ppp and sps configurations, the r− CH3 stretching vibrations are dominant in comparison to the r+ stretching ones. Still, in the case of DDCS, the r− peak presents a shoulder, which is assigned to the vibrations of the Si-linked methyl groups. This shoulder vanishes when these CH3 groups are frozen. Then, using the isolated-model, the rotation angle (ξ) is gradually changed, showing that in the ppp SFG spectrum the r−/r+ intensity ratio decreases from 73.4 at 0° to 1.7 at 180°, The sum frequency generation (SFG) signatures of octadecyl-trichlorosilane (OTS) and dodecyl-dimethyl-chlorosilane (DDCS) monolayers on silica were simulated in the C–H stretching region for three polarization combinations (ppp, sps, and ssp), showing the impact of the additional Si-linked methyl groups of DDCS on its SFG signatures. These simulations are based on a two-step procedure where (i) the molecular properties (vibrational frequencies, IR and Raman intensities) are evaluated using first principles methods and (ii) the three-layer model is employed to calculate the macroscopic responses using these molecular responses, the geometry of the experimental setup, and the optical properties of the layers. These first principles calculations adopt the own N-layered integrated orbital molecular mechanics (ONIOM) approach, which divides the system and enables different levels of approximation to be applied to its different parts. Here, the same ωB97X-D exchange-correlation functional is used for all parts, while the underlying silica layers are described with a smaller atomic basis set (STO-3G, 3-21G, or 6-31G) than the alkylsilane and the top silica layer (6-311G*). Calculations show that for describing the lower layer the minimal STO-3G basis set already provides reliable spectral profiles. For OTS, the results are compared to the experiment, demonstrating a good agreement for ppp and sps configurations, provided the refractive index of the layer nl is set to 1.1. To highlight the origin of the SFG signatures, two chemical models were used, one that includes explicitly the SiO2 surface in the first principles calculations (adsorbed-model) and the other that only considers the silane chain (isolated-model). Simulations show that OTS and DDCS display similar spectral patterns where, for ppp and sps configurations, the r− CH3 stretching vibrations are dominant in comparison to the r+ stretching ones. Still, in the case of DDCS, the r− peak presents a shoulder, which is assigned to the vibrations of the Si-linked methyl groups. This shoulder vanishes when these CH3 groups are frozen. Then, using the isolated-model, the rotation angle (ξ) is gradually changed, showing that in the ppp SFG spectrum the r−/r+ intensity ratio decreases from 73.4 at 0° to 1.7 at 180°.

The enhancement of the vibrational sum-frequency generation (SFG) signal from molecules adsorbed on metallic nanopillars excited at a resonance frequency matching their localized surface plasmons is reported. The nanopillars stand vertically on a metal surface and possess two plasmon modes that can be selectively excited by either the incident visible laser beam, or the generated SFG beam itself. This nanostructured platform increases the molecular SFG signal of a monolayer by two orders of magnitude. The localization and the geometry of the two plasmon modes enables to probe the molecules adsorbed onto the vertical nanopillar wall, or on the top of it, or on the flat surface between the pillars, selectively. In practice, this spatial selectivity is set by switching the polarization of the visible and SFG beams at resonance. Owing to the largely improved sensitivity combined with a specific spatial selectivity, plasmon-enhanced SFG boosts the versatility of second-order vibrational SFG spectroscopy or microscopy. This makes them promising platforms in the development of analytical molecular devices. Molecules adsorbed on metallic nanopillars give an enhanced vibrational sum-frequency generation (SFG) signal when a localized surface plasmon resonance is excited. The nanopillars possess two plasmon modes that can be selectively excited by either the incident visible or the generated SFG polarized laser beams. Depending on which mode is excited, one can probe molecules adsorbed at different regions of the nanostructured surface selectively, i.e., the vertical pillar sidewall, the pillar top, or the flat surface between the pillars. Owing to the largely improved sensitivity combined with a specific spatial selectivity, a plasmon-enhanced SFG boosts the versatility of SFG spectroscopy with regard to specific chemical sensing.

We use doubly resonant, infrared-visible sum-frequency generation spectroscopy (DR-SFG) to probe vibrational and electronic properties of C 60 and K-doped C 60 monolayers adsorbed on Ag(111) single crystal under ultra-high vacuum (UHV). We recorded the interface SFG spectra for five visible wavelengths. We observe a strong dependence of the SFG intensity of the totally symmetric Ag(2) mode of the fullerene while scanning the visible wavelength, due to the DR-SFG phenomenon. The SFG intensity of the Ag(2) mode is the strongest at 488 nm and at 532 nm for the pure and fully doped monolayers, respectively. These results demonstrate the occurrence of electron-phonon couplings at the C 60 /Ag(111) and saturated K/C 60 /Ag(111) interfaces. They enable us to determine the energy of the coupled electronic transition and to link the electronic resonance to the h u (HOMO) to t 1g (LUMO + 1) transition of C 60 .

International audience; We have investigated a metal-supported lipid film by using a sum frequency generation (SFG) spectrometer coupled to a free electron laser (FEL). DFT calculations on a molecular model have enabled to assign the vibrational signatures. The SFG vibrations detected in the backbone region, between 1375 cm À1 and 1000 cm À1 , originate from the vibrational motions of the 2,4-dinitrophenyl polar head of the lipid, which holds antigenic properties, and can therefore be used to selectively study the biological interactions with complementary antibodies. Theses results strengthen the role of SFG spectroscopy as a highly sensitive tool for biological detection.

The vibrational response of p-nitrothiophenol (p-NTP) self-assembled monolayers (SAMs), on Pt and on Au, has been investigated by combining theoretical methods with vibrational spectroscopies. Experimentally, the vibrational signatures have been measured using infrared spectroscopy (IR), polarization-modulation reflection absorption infrared spectroscopy (RAIRS), and with sum frequency generation spectroscopy (SFG). Theoretically, density functional theory calculations (DFT) have predicted the molecular vibrations and have estimated their IR vectors and Raman tensors, necessary to simulate the spectra and therefore to interpret the vibrational signatures as well as to retrieve the molecular orientation. So, a tilt angle (v) of 60° for the molecular 1,4-axis of p-NTP has been directly estimated for both Pt and Au SAMs by the polarizationdependent SFG data. Then, combining these results with RAIRS measurements has allowed to determine rotation angles (ξ) of 56° and 66° for p-NTP SAMs on Pt and Au, respectively.

Polarisation-dependent sum frequency generation (SFG) spectroscopy is used to investigate the orientation of molecules on metallic surfaces. In particular, self-assembled monolayers (SAMs) of dodecanethiol (DDT) and of p-nitrothiophenol (p- NTP), grown on Pt and on Au, have been chosen as models to highlight the ability of combining ppp and ssp polarisations sets (representing the polarisation of the involved beams in the conventional order of SFG, Vis and IR beam) to infer orientational information at metallic interfaces. Indeed, using only the ppp set of data, as it is usually done for metallic surfaces, is not sufficient to determine the full molecular orientation. We show here that simply combining ppp and ssp polarisations enables both the tilt and rotation angles of methyl groups in DDT SAMs to be determined. Moreover, for p-NTP, while the SFG active vibrations detected with the ppp polarisation alone provide no orientational information, however, the combination with ssp spectra enables to retrieve the tilt angle of the p- NTP 1,4 axis. Though orientational information obtained by polarisation-dependent measurements has been extensively used at insulating interfaces, we report here their first application to metallic surfaces. © 2010 Wiley-VCH Verlag GmbH& Co. KGaA, Weinheim.

Self-assembled monolayers (SAMs) of n -dodecanethiol (C 12 H 25 SH) and n -dodecaneselenol (C 12 H 25 SeH) on polycrystalline copper have been elaborated with the purpose of achieving densely packed and crystalline-like assemblies. By combining the surface sensitivity of polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation spectroscopy (SFG), the effect of the self-assembly time (15 min, 30 min, 1 h, 2 h and 24 h) on the formation of n -dodecanethiol and n -dodecaneselenol monolayers on untreated and electrochemically reduced polycrystalline copper has been investigated. On electrochemically reduced copper, PM-IRRAS spectroscopy shows that both molecules are able to form well organized layers. SFG spectroscopy indicates that the C 12 H 25 SeH SAMs are slightly better ordered than those achieved with C 12 H 25 SH. On untreated copper, the two molecules lead to different film organizations. Both PM-IRRAS and SFG indicate that C 12 H 25 SH SAMs are of the same film quality as those obtained on electrochemically reduced copper. On the contrary, C 12 H 25 SeH monolayers are invariably poorly organized at the molecular level.

The ability of microcontact printing to build highly ordered alkanethiol self-assembled monolayers (SAMs) on Pt substrates within a short time is studied by sum frequency generation (SFG) spectroscopy and contact angle measurements. The deposition of ordered hexadecanethiol and dodecanethiol monolayers onto platinum substrates is achieved in less than 1 s. The film order and the alkane chain orientation are deduced from the SFG fingerprint acquired under different sets of laser polarization. Comparisons between the SAMs prepared by printing or by immersion demonstrate that both methods lead to the same high quality organization. Patterning effects within printed films are also investigated with respect to the layer conformation. Finally, wetting properties of printed layers are correlated with the printing duration, corroborating the spectroscopic results.

Titanium dioxide nanoparticles were prepared on glass substrates by reactive DC magnetron sputtering. As highlighted by the atomic force microscopy characterization, we were able to control the nanoparticles' surface coverage and diameter by varying the deposition time and the total pressure, respectively. The titanium dioxide energy band gap, determined by using ultraviolet-visible spectroscopy, depends on the total pressure but is quite independent on the deposition temperature. On the contrary, it is blue shifted when the pressure increases. Finally, the contact angles slightly decrease after ultraviolet illumination irrespective of the different deposition parameters, indicating an improvement of the hydrophilic properties of the adsorbed layer. After 21 h in dark, the contact angles are nearly identical to the ones before exposure to UV light: the samples do not keep their hydrophilic behaviour.

Self-assembly of p-benzenedimethanethiol (p-BDMT) on Pt(111) has been investigated by high-resolution electron energy loss spectroscopy and sum-frequency generation spectroscopy. The molecules adsorb on Pt(111) like on gold, attached through one single thiol, leaving the second thiol moiety unreacted and exposed to the outer surface. Yet, the order of the p-BDMT self-assembled film is poor in comparison to alkanethiol SAMs. Displacement in solution of a preadsorbed pentanethiol (PTT) SAM by p-BDMT molecules proved to be a successful approach to achieve films of higher quality, where the size of the dithiol molecular domains tends toward the size measured for PTT. Nearly complete exchange is accomplished after 42 h. However, no significant exchange is observed when dodecanethiol replaces PTT. Displacing the alkanethiols by benzenethiol leads to the same conclusions, suggesting that the exchange processes are lessened as compared to gold.

In this study, we use the selectivity and sensibility of sum-frequency generation spectroscopy (SFG) to interfacial media (Chen and Chen, Biochimica et biophysica acta 1758:1257–1273, 2006) in order to characterize the interactions, and their effects, between a cell membrane model, here made of a li-pid bilayer, and gold nanoparticles. With the aim of giving to this study a sound basis, we did first realize separately the SFG characterization of the membrane model and the gold nanoparticles. Here, the membrane model is a bilayer made of phosphatidylcholine – one of the major components of living membranes – adsorbed on a CaF2 or SiO2 prism. The gold nanoparticles have a diameter of 6, 12 or 38 nm and a negative surface state of charge. We highlighted that as long as it stays in water, the membrane model is SFG inactive, due to the globally centrosymmetric nature of the lipid bilayer and to the SFG selection rule, which forbids the emergence of a SFG signal from centrosymmetric media. On the other hand, once it has been exposed to air, the bilayer gives a SFG signal. This fact is explained by the folding (flip-flop) of a part of the bilayer on itself at the contact with the air, due to its hydrophobic nature. Concerning the nanoparticles, they generate a SFG signal coming from the surfactant giving them their state of charge while preventing them binding together. That signal has been measured at the interface with a CaF2 prism. On the other hand, in the case of a SiO2 prism, no signal coming from the nanoparticles has been detected. The same results have been observed when the lipid bilayer was present on the prisms. This is explained by the fact that at neutral pH, the SiO2 has a distinctly negative state of charge (Yeganeh et al. Phys Rev Lett 83:1179–1182, 1999), repelling so the nanoparticles beyond the SFG field of detection at the interface. As for CaF2, it has a positive state of charge at neutral pH (Schrodle et al. J Phys Chem C 111:10088–10094, 2007), which leads to an attractive interaction with the negatively charged nanoparticles and so allows their detection. Furthermore, since it has been shown (Lin et al. ACS Nano 4:5421–5429, 2010) that in pH-neutral water, phosphatidyl-choline bilayers have a negative state of charge, the positive nanoparticles are mostly expected to interact with these bilayers. To sum up, we have experimentally confirmed that negative nanoparticles weakly interact with phosphatidylcholine bilayer, even with a substrate taking on a positive state of charge in contact with water. On the basis of these results, the next step will be to confirm the interaction of positive nanoparticles with the bilayer, knowing that this interaction should be even more important if the substrate takes on a negative state of charge in water (Figs. 68.1 and 68.2).

As the greenhouse effect increases, the development of systems able to convert with high efficiency CO2 to energetically rich molecules owns a crucial weight in the technological and environmental domain. As catalyst, rhenium complexes, of the type fac-[Re(L)(CO)3Cl] (i.e. L = 2,2′-bipyridyl or 4,4′-bipyridyl), have attracted a large interest demonstrating promising catalytic properties. fac-[Re(v-bpy)(CO)3Cl]-based polymer deposited onto a solid support has been already investigated as heterogeneous catalyst in the reduction of CO2. Here, we deposited by electrochemical polymerization fac-[Re(v-bpy)(CO)3Cl] onto a nanocrystalline TiO2 film on glass and we investigated by cyclic voltammetry the properties of such heterogeneous catalyst in the electrochemical reduction of CO2. We demonstrated that the nanoporous nature of the substrate allows to increase the two-dimensional number of redox sites per surface area and hence to get a significant enhancement of the catalytic yield.

Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and digital simulation techniques were used to investigate quantitatively the mechanism of electron transfer (ET) through densely packed and well-ordered self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid on gold, either pristine or modified by physically adsorbed glucose oxidase (GOx). In the presence of ferrocenylmethanol (FcMeOH) as a redox mediator, ET kinetics involving either solution-phase hydrophilic redox probes such as [Fe(CN)(6)](3-/4-) or surface-immobilized GOx is greatly accelerated: [Fe(CN)(6)](3-/4-) undergoes diffusion-controlled ET, while the enzymatic electrochemical conversion of glucose to gluconolactone is efficiently sustained by FcMeOH. Analysis of the results, also including the digital simulation of CV and EIS data, showed the prevalence of an ET mechanism according to the so-called membrane model that comprises the permeation of the redox mediator within the SAM and the intermolecular ET to the redox probe located outside the monolayer. The analysis of the catalytic current generated at the GOx/SAM electrode in the presence of glucose and FcMeOH allowed the high surface protein coverage suggested by X-ray photoelectron spectroscopy (XPS) measurements to be confirmed.

The electrochemical behaviour and the electrochromic properties of a film of poly-bithiophene (PBT) deposited onto a mesoporous TiO2 surface layered on an optically transparent electrode (OTE) were investigated. The polymeric film was prepared by anodic polymerisation of 2,2'-bithiophene (BT) and, interestingly, a cyclic voltammetric (CV) behaviour very similar to that observed on platinum or other conducting substrates was obtained. Furthermore, both the CV pattern and the absorption properties of the film grown on TiO2 indicated that a significantly larger amount of PBT could be deposited onto the mesoporous TiO2 layer with respect to Pt or conducting SnO2 substrates having the same geometric area. This suggested that PBT growth, besides at the exposed SnO2 surface within the pores of the mesoporous network, might also occur onto the (very large) surface of the TiO2 nanocrystals. Finally, the PBT/TiO2 heterojunction was investigated for its electrochromic properties. Because of the very large specific surface concentrations of PBT and the high volume density of surface-related defects in the mesoporous TiO2 film, the hetrojunction was shown to undergo sharp optical transition upon either oxidation of the PBT film or intercalation of Li+ ions in the reduced TiO2 film. (C) 2005 Elsevier B.V. All rights reserved.

We compare two routes for creating protein adsorption-resistant self-assembled monolayers (SAMs) by chemical modification of silicon surfaces with poly(ethylene oxide) (PEO) oligomeric derivatives. The first route involves the assembly of 2-methyl[(polyethyleneoxy)propyl]trichlorosilane (Cl3SiMPEO) films onto oxidized silicon surfaces (OH-SiO(x)) either by a liquid-phase process at room temperature or by a gas-phase process at 423 K, producing Si-O-Si bonds between the substrate and the organic layer. The second pathway makes use of the assembly of poly(ethylene glycol methyl ether) (MPEG) films onto hydrogen-passivated silicon surfaces (H-Si) using a liquid-phase process at 353 or 423 K, leading to the formation of Si-O-C bonds between the substrate and the organic layer. Structural investigation by X-ray reflectometry (XRR) reveals that the thickness and surface densities of the grafted PEO monolayers strongly depend on experimental conditions such as temperature and grafting time. Atomic force microscopy (AFM) shows that very smooth and homogeneous monolayers can be obtained with average roughnesses close to those measured on the corresponding bare substrates. Finally, the antifouling properties of the modified silicon surfaces were evaluated by X-ray photoelectron spectroscopy (XPS), using a membrane protein (P.69 antigen) as model protein. Both types of PEO monolayers exhibit excellent protein repellency, as soon as the grafting density is equal to or higher than 1.7 chains/nm2.

The grafting of benzylic amide macrocycles, the basic units of more complex mechanically interlocked architectures such as catenanes and rotaxanes, was performed via the functionalization of an acid-terminated self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA). Both chemical and physical adsorption were investigated using macrocycles containing either a reactive hydroxyl functionality or an exo-pyridyl moiety, with characterization of the systems using X-ray photoelectron spectroscopy (XPS), contact angle measurements, and reflection absorption infrared spectroscopy (RAIRS). By comparing theoretical values with experimental data, it was found that up to 40% of the acid groups on the SAM surface were modified by the macrocycles and that the macrocycle coverage can be controlled by varying the reaction time. Stability tests demonstrated that the prepared films are stable in air, under ultrasound treatment and against chemical substitution. RAIRS measurements suggested a tilted orientation of the macrocycle with respect to the plane of the SAM surface.

Thin films of a benzylic amide macrocycle, the common component of a wide class of mechanically interlocked molecules, are prepared by vapor deposition on Au(111). The films are characterized by monochromated X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS). The relative amounts of carbon, nitrogen, and oxygen are consistent with the formation of intact molecular species. At monolayer coverage, the relative intensity of out-of-plane to in-plane phenyl ring vibrational modes indicates that the macrocycle adopts a nearly flat-lying conformation. The formation of a chemisorption bond is evidenced by the presence of a Au-O stretching vibration and a low binding energy component in the O 1s core level region assigned to interfacial bonding. A decrease in film order and the absence of a preferred molecular orientation is observed at higher coverages. Computer modeling of the adsorption of the macrocycle on the surface rationalizes the experimental observations.

The adsorption from the gas phase of a macrocyclic molecule composed of benzylic amide (–CONH–CH 2 –C 6 H 4 –) groups on Au(1 1 1) at 300 K has been studied using high resolution electron energy loss spectroscopy. The film order and vibrational properties were explored as a function of coverage, method of adlayer deposition and annealing. Beyond a critical coverage, a template effect strongly influences the macrocycle’s orientation with respect to the substrate. In the case of ordered films (domain size>80 A), the intensity of the out-of-plane C–H deformation mode relative to the in-plane C–H stretch indicates that an adsorption geometry with the plane of the phenyl rings largely parallel to the Au(1 1 1) surface is favoured in the submonolayer to monolayer coverage regime. Upon consideration of solid state X-ray diffraction data, this flat-lying molecular orientation, which is accompanied by chemisorption via the carbonyl function, must involve considerable distortion of the adsorbed macrocycle from its crystal structure.

The vibrational nonlinear activity of films of 2,4-dinitrophenyl phospholipid (DNP) at the solid interface is measured by sum-frequency generation spectroscopy (SFG). Hybrid bilayers are formed by a Langmuir-Schaefer approach in which the lipid layer is physisorbed on top of a self-assembled monolayer of dodecanethiol on Pt with the polar heads pointing out from the surface. The SFG response is investigated in two vibrational frequency domains, namely, 3050-2750 and 1375-1240 cm. The first region probes the CH stretching modes of DNP films, and the latter explores the vibrational nonlinear activity of the 2,4-dinitroaniline moiety of the polar head of the lipid. Analysis of the CH stretching vibrations suggests substantial conformational order of the aliphatic chains with only a few gauche defects. To reliably assign the detected SFG signals to specific molecular vibrations, DFT calculations of the IR and Raman activities of molecular models are performed and compared to experimental solid-state spectra. This allows unambiguous assignment of the observed SFG vibrations to molecular modes localized on the 2,4-dinitroaniline moiety of the polar head of DNP. Then, SFG spectra of DNP in the 1375-1240 cm frequency range are simulated and compared with experimental ones, and thus the 1,4-axis of the 2,4-dinitrophenyl head is estimated to have tilt and rotation angles of 45±5° and 0±30°, respectively. Nonlinear vibrational response of a hybrid bilayer of 2,4-dinitrophenyl phospholipid (DNP) supported on a Pt surface is interpreted qualitatively and quantitatively by sum-frequency generation spectroscopy and density functional theory calculations. Spectral simulations also reveal the orientation of the 2,4-dinitrophenyl polar head of DNP, which is estimated to have tilt and rotation angles of 45±5° and 0±30°, respectively (see picture).

Introduction: Patients with cancer have a 7- to 10-fold increased risk of developing venous thromboembolism. Circulating microvesicles could be a useful predictive biomarker for venous thromboembolism in cancer. Validated and standardised techniques that could be used to determine the complete microvesicle phenotype are required. Objectives: These were two-fold: a) to characterise tissue factor (TF)-bearing microvesicles released by cultured breast cancer cells MDA-MB-231 by flow cytometry (FCM), transmission electron microscopy (TEM) and thrombin generation assay (TGA); and b) to validate the sensitivity and variability intra/interassay of TGA as a useful method to study the procoagulant activity (PCA) of microvesicles. Methods: Cultured breast cancer cells MDA-MB-231 were incubated for 45 minutes at 37°C. Samples were then centrifuged or not at 4,500 g for 15 minutes, and cells and MVs or MV-containing supernatants were used for TEM, FCM and TGA. In activity assays, microvesicles (i.e. cell-depleted supernatants) were incubated with anti-TF antibodies or with annexin V to assess the contribution of TF and phospholipids to the PCA. Alternatively, supernatants were filtered through 0.1, 0.22, 0.45 or 0.65 µm membranes and subjected to TGA. Results: The majority of the PCA was associated with microvesicles smaller than 0.1 µm, and the mean microvesicle size estimated by TEM after 10,000 g centrifugation was 121±54 nm with a majority of vesicles between 100 and 200 nm. Microvesicles derived from 5,000 MDA-MB-231cells/ml were sufficient to significantly increase the thrombin generation of normal pooled plasma. Conclusions: TEM, FCM and filtration coupled to TGA represent a useful combination to study the PCA of TF-bearing microvesicles, whatever their size. And it will be interesting to implement these techniques in patients. Keywords: tissue factor; microvesicles; cancer; thrombin generation Access the supplementary material to this article: Refractive index estimation. Please see Supplementary files in the column to the right (under Article Tools online). (Published: 18 March 2013) Citation: Journal of Extracellular Vesicles 2013, 2 : 19728 - http://dx.doi.org/10.3402/jev.v2i0.19728

Introduction : Extracellular vesicles (EVs) are shed from cells and carry markers of the parent cells. Vesicles derived from cancer cells reach the bloodstream and locally influence important physiological processes. It has been previously shown that procoagulant vesicles are circulating in patients’ fluids. These EVs are therefore considered as promising biomarkers for the thrombotic risk. Because of their small size, classical methods such as flow cytometry suffer from limitation for their characterisation. Atomic force microscopy (AFM) has been proposed as a promising complementary method for the characterisation of EVs. Objectives : The objectives of this study are: (a) to develop and validate AFM with specific antibodies (anti-TF) and (b) to compare air and liquid modes for EVs’ size and number determination as potential biomarkers of the prothrombotic risk. Methods : AFM multimode nanoscope III was used for air tapping mode (TM). AFM catalyst was used for liquid Peak Force Tapping (PFT) mode. Vesicles are generated according to Davila et al.'s protocol. Substrates are coated with various concentrations of antibodies, thanks to ethanolamine and glutaraldehyde. Results : Vesicles were immobilised on antibody-coated surfaces to select tissue factor (TF)-positive vesicles. The size range of vesicles observed in liquid PFT mode is 6–10 times higher than in air mode. This corresponds to the data found in the literature. Conclusion : We recommend liquid PFT mode to analyse vesicles on 5 µg/ml antibody-coated substrates. Keywords: extracellular vesicles; tissue factor; atomic force microscopy; coagulation; biomarker (Published: 27 August 2013) Citation: Journal of Extracellular Vesicles 2013, 2 : 21045 - http://dx.doi.org/10.3402/jev.v2i0.21045 To access the supplementary material to this article, please see Supplementary files under Article Tools online.

The recently developed chalcopyrite CdSiP2 is employed in a picosecond, 90°-phase-matched synchronously pumped optical parametric oscillator pumped at 1064 nm, to produce quasi-steady-state idler pulses near 6.4 μm with an energy as high as 2.8 μJ at 100 MHz. The train of 2 μs long macropulses, each consisting of 200 (picosecond) pulses, follows at a repetition rate of 25 Hz. This corresponds to an average power of 14 mW. The pump depletion (conversion efficiency) exceeds 40%. Without intracavity etalon, the 12.6 ps long mid-IR micropulses have a spectral width of 240 GHz.

This paper presents a very simple, industrially scalable method for transferring a high-resolution, biologically active protein pattern from one substrate to another. We demonstrate the transfer of a protein pattern formed initially by microcontact printing from a silicon surface (to which this form of printing is applicable) onto a glass or polymer substrate, almost independently of the surface/bulk properties of the second substrate. A very thin, spin-coated layer of a sugar is used to preserve the structure and organization of proteins during the subsequent plasma deposition of a siloxane polymer, after which the protein pattern could simply be peeled off the silicon substrate and glued onto any other desired substrate. © 2009 Elsevier B.V. All rights reserved.

The molecular orientation of adsorbed molecules forming selfassembled monolayers can be determined by combining vibrational sum-frequency generation (SFG) measurements with quantum chemical calculations. Herein, we present a theoretical methodology used to simulate the SFG spectra for different combinations of polarizations. These simulations are based on calculations of the IR vectors and Raman tensors, which are obtained from density functional theory computations. The dependency of the SFG vibrational signature with respect to the molecular orientation is presented for the molecules p-nitrothiophenol and 2,4-dinitroaniline. It is found that a suitable choice of basis set as well as of exchange-correlation (XC) functional is mandatory to correctly simulate the SFG intensities and consequently provide an accurate estimation of the adsor bed molecule orientation. Comparison with experimental data shows that calculations performed at the B3LYP/6-311 + + G(d,p) level of approximation provide good agreement with experimental frequencies, and with IR and Raman intensities. In particular, it is demonstrated that polarization and diffuse functions are compulsory for reproducing the IR and Raman spectra, and consequently vibrational SFG spectra, of systems such as p-nitrothiophenol. Moreover, the investigated XC functional reveal their influence on the relative intensities, which show rather systematic variations with the amount of Hartree-Fock exchange. Finally, further aspects of the modeling are revealed by considering the frequency dependence of the Raman tensors.

The grafting of poly-N-succinimidyl acrylate from scanning probe microscopy tips is shown to be a robust platform for the very easy elaboration of versatile probes with sensor capabilities and tunable properties. The modified tips (see image) can be easily postfunctionalized for single-molecule recognition of host–guest and ligand–receptor systems and for the design of smart probes that are thermo- and pH-responsive.

With the purpose of developing biosensors, the reliable proof of the biological activity of two new sensor systems was obtained by atomic force microscopy (AFM) in both the imaging and the single-molecule force spectroscopy modes. Antigens or antibodies of pharmacological interest were grafted onto self-assembled monolayers of thiols on gold, and AFM imaging demonstrated that the grafting process produced homogeneous submonolayers of isolated proteins. The analysis of the morphology of the surfaces at the different functionalization steps allowed evaluating the protein grafting density and showed that the recognition of complementary species present in the surrounding solution occurred. Single-molecule force spectroscopy experiments between the sensing surfaces and AFM probes, onto which the complementary species were grafted, enabled a direct and rapid test of the biological activity of the sensors by investigating the interaction occurring at the level of one single ligand-receptor bond. Ellipsometry and surface plasmon resonance allowed further characterization of the sensor surfaces and confirmed that the biological recognition took place.

Single layers Of C-60 mono- and bis-adducts have been obtained by functionalizing an acid-terminated self-assembled monolayer (SAM) of thiols on gold. X-ray photoelectron spectroscopy demonstrated the grafting onto the SAM by covalent bonding, via the formation of an amide bond, while cyclic voltammetry and electrochemical impedance spectroscopy provided information on the redox properties of the C-60-films, as well as on structural characteristics. (c) 2006 Elsevier Ltd. All rights reserved.

Keratinocytes and fibroblasts have been grown onto a series of triblock copolymers based on 1,5-dioxepan-2-one (DXO) and L-lactide (LLA). The molar ratio of DXO and LLA were varied in the copolymers. This resulted in different degrees of hydrophilicity, which in turn influenced the cell growth. On these surfaces, the morphological appearance of the cells with their cell movements and growth were investigated by means of scanning electron microscopy, time-lapse videomicroscopy and immunohistochemistry. All results clearly showed that the keratinocytes and fibroblasts adhered best to the most hydrophilic copolymers. A majority of the keratinocytes seeded on the most hydrophilic copolymer also presented a polarized morphology indicating a migration tendency. The cell growth onto these materials are interesting since a possible application for these unique materials is as polymeric membranes for guided cutaneous and/or periodontal tissue generation.

Molecules adsorbed on metallic nanopillars give an enhanced vibrational sum-frequency generation (SFG) signal when a localized surface plasmon resonance is excited. The metallic nanopillars, created on page 244 by D. Lis et al., possess two plasmon modes that can be selectively excited by either incident visible or generated SFG polarized laser beams. Depending on which mode is excited, the molecules adsorb either onto the vertical nanopillar wall, on top of it, or on the flat substrate. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this work, we investigate the adsorption process of two carboxylic acids (stearic and undecylenic) on a H-Si(111) surface via the calculation of structural and energy changes as well as the simulation of their IR and Raman spectra. The two molecules adsorb differently at the surface since the stearic acid simply physisorbs while the undecylenic acid undergoes a chemical reaction with the hydrogen atoms of the surface. This difference is observed in the change of geometry during the adsorption. Indeed, the chemisorption of the undecylenic acid has a bigger impact on the structure than the physisorption of the stearic acid. Consistently, the former is also characterized by a larger value of adsorption energy and a smaller value of the tilting angle with respect to the normal plane. For both the IR and Raman signatures, the spectra of both molecules adsorbed at the surface are in a first approximation the superposition of the spectra of the Si cluster and of the carboxylic acid considered individually. The main deviation from this simple observation is the peak of the stretching Si-H (ν(Si-H)) mode, which is split into two peaks upon adsorption. As expected, the splitting is bigger for the chemisorption than the physisorption. The modes corresponding to atomic displacements close to the adsorption site display a frequency upshift by a dozen wavenumbers. One can also see the disappearance of the peaks associated with the C=C double bond when the undecylenic acid chemisorbs at the surface. The Raman and IR spectra are complementary and one can observe here that the most active Raman modes are generally IR inactive. Two exceptions to this are the two ν(Si-H) modes which are active in both spectroscopies. Finally, we compare our simulated spectra with some experimental measurements and we find an overall good agreement.

The recently developed chalcopyrite CdSiP2 is employed in a picosecond, 90°-phase-matched, synchronously pumped, optical parametric oscillator pumped at 1064 nm to produce steady-state idler pulses near 6.4 𝜇m with an energy as high as 2.8 𝜇J at 100 MHz, in a train of 2-𝜇s-long macropulses following at a repetition rate of 25 Hz. Without an intracavity etalon, the 12.6-ps-long micropulses have a spectral width of 240 GHz

The ongoing evolution from SiO 2 to insulator materials with lower dielectric constant, k, through the introduction of pores, brings new challenges in terms of processing and reliability. Porosity enhances penetration of undesired chemical species. A method of sealing microporous low-k dielectric chemical vapor deposited silicon oxycarbide films using UV-ozone induced oxidation has been investigated. The film thickness, refractive index, porosity, pore size, and sealing as a function of exposure time have been characterized by ellipsometry. The films are sealed without modification of the underlying porosity, an essential first step in integrating porous materials.