Light on the interactions between nanoparticles and lipid membranes by interface-sensitive vibrational spectroscopy.

Nanoparticles are produced in natural phenomena or synthesized artificially for technological applications. Their frequent contact with humans has been judged potentially harmful for health, and numerous studies are ongoing to understand the mechanisms of the toxicity of nanoparticles. At the macroscopic level, the toxicity can be established in vitro or in vivo by measuring the survival of cells.

Probing alkylsilane molecular structure on amorphous silica surfaces by sum frequency generation vibrational spectroscopy: First-principles calculations.

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.

Interfacial charges drive the organization of supported lipid membranes and their interaction with nanoparticles.

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. 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 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.

Unique Vibrational Features as a Direct Probe of Specific Antigen-Antibody Recognition at the Surface of a Solid-Supported Hybrid Lipid Bilayer.

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.

Probing Graphene χ((2)) Using a Gold Photon Sieve.

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 to unravel different elements of graphene second-order susceptibility χ((2)).

Localized surface plasmon resonances in nanostructures to enhance nonlinear vibrational spectroscopies: towards an astonishing molecular sensitivity.

Vibrational transitions contain some of the richest fingerprints of molecules and materials, providing considerable physicochemical information. Vibrational transitions can be characterized by different spectroscopies, and alternatively by several imaging techniques enabling to reach sub-microscopic spatial resolution. In a quest to always push forward the detection limit and to lower the number of needed vibrational oscillators to get a reliable signal or imaging contrast, surface plasmon resonances (SPR) are extensively used to increase the local field close to the oscillators.

Characterisation of tissue factor-bearing extracellular vesicles with AFM: comparison of air-tapping-mode AFM and liquid Peak Force AFM.

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.

Thrombin generation assay and transmission electron microscopy: a useful combination to study tissue factor-bearing microvesicles.

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.

Vibrational sum-frequency generation activity of a 2,4-dinitrophenyl phospholipid hybrid bilayer: retrieving orientational parameters from a DFT analysis of experimental data.

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(-1).

Towards modelling the vibrational signatures of functionalized surfaces: carboxylic acids on H-Si(111) surfaces.

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.

Orientational analysis of dodecanethiol and p-nitrothiophenol SAMs on metals with polarisation-dependent SFG spectroscopy.

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.

Noncritical singly resonant synchronously pumped OPO for generation of picosecond pulses in the mid-infrared near 6.4 microm.

The recently developed chalcopyrite CdSiP(2) is employed in a picosecond, 90 degrees -phase-matched, synchronously pumped, optical parametric oscillator pumped at 1064 nm to produce steady-state idler pulses near 6.4 microm with an energy as high as 2.8 microJ at 100 MHz, in a train of 2-micros-long macropulses following at a repetition rate of 25 Hz.

Theoretical simulation of vibrational sum-frequency generation spectra from density functional theory: application to p-nitrothiophenol and 2,4-dinitroaniline.

The molecular orientation of adsorbed molecules forming self-assembled 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.

Atomic force microscopy investigation of the morphology and the biological activity of protein-modified surfaces for bio- and immunosensors.

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.

Electrode surface modification by a spirobifluorene derivative. An XPS and electrochemical investigation.

Ordered thin layers of a spirobifluorene derivative containing an amino group were formed by grafting them onto a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) on gold. Either physical (H-bonding) or chemical bonding (activated by EDCl) was investigated. X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy confirmed that both methods can be used to effectively graft 2-amino-9,9'-spirobifluorene molecules onto the SAM surface, giving high surface coverages, with a significantly higher packing in the case of chemisorbed films.

Redox mediation at 11-mercaptoundecanoic acid self-assembled monolayers on gold.

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.

One step growth of protein antifouling surfaces: monolayers of poly(ethylene oxide) (PEO) derivatives on oxidized and hydrogen-passivated silicon surfaces.

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.