by Keyword: Spectroscopy

By year:[ 2020 | 2019 | 2018 | 2017 | 2016 | 2015 | 2014 | 2013 | 2012 | 2011 | 2010 | 2009 | 2008 | 2007 | 2006 | 2005 ]

Pellequer, J. L., Parot, P., Navajas, D., Kumar, S., Svetli, Scheuring, S., Hu, J., Li, B., Engler, A., Sousa, S., Lekka, M., Szymo, Schillers, H., Odorico, M., Lafont, F., Janel, S., Rico, F., (2019). Fifteen years of Servitude et Grandeur to the application of a biophysical technique in medicine: The tale of AFMBioMed Journal of Molecular Recognition 32, (3), e2773

AFMBioMed is the founding name under which international conferences and summer schools are organized around the application of atomic force microscopy in life sciences and nanomedicine. From its inception at the Atomic Energy Commission in Marcoule near 2004 to its creation in 2007 and to its 10th anniversary conference in Krakow, a brief narrative history of its birth and rise will demonstrate how and what such an organization brings to laboratories and the AFM community. With the current planning of the next AFMBioMed conference in Münster in 2019, it will be 15 years of commitment to these events.

Keywords: Atomic Force Microscopy, Single molecules, Biomechanics, Force spectroscopy, High-speed AFM, Imaging, Nanoindentation, Nanomedicine, Nanotoxicology

Valenti, S., Diaz, A., Romanini, M., del Valle, L. J., Puiggalí, J., Tamarit, J. L., Macovez, R., (2019). Amorphous binary dispersions of chloramphenicol in enantiomeric pure and racemic poly-lactic acid: Morphology, molecular relaxations, and controlled drug release International Journal of Pharmaceutics 568, 118565

We characterize amorphous solid dispersions (ASDs) of the Chloramphenicol antibiotic in two biodegradable polylactic acid polymers, namely a commercial sample of enantiomeric pure PLLA and a home-synthesized PDLLA copolymer, investigating in particular the effect of polylactic acid in stabilizing the amorphous form of the drug and controlling its release (e.g. for antitumoral purposes). Broadband dielectric spectroscopy and differential scanning calorimetry are employed to study the homogeneity, glass transition temperature and relaxation dynamics of solvent-casted ASD membranes with different drug concentrations. We observe improved physical stability of the ASDs with respect to the pure drug, as well as a plasticizing effect of the antibiotic on the polymer, well described by the Gordon-Taylor equation. The release of the active pharmaceutical ingredient from the films in a simulated body fluid is studied by UV/vis spectroscopy at two different drug concentrations (5 and 20% in weight). The amount of released drug is found to be proportional to the square root of time, with proportionality constant that is almost the same in both dispersions, despite the fact that the relaxation time and thus the viscosity of the two samples differ by four orders of magnitude at body temperature. Since the drug release kinetics does not display a significant dependence on the drug content in the carrier, it may be expected to remain roughly constant during longer release times.

Keywords: Amorphous drug, Controlled liberation, Dielectric spectroscopy, Molecular mobility, Plasticizer, Polymer enantiomerism

Marti-Muñoz, Joan, Xuriguera, Elena, Layton, John W., Planell, Josep A., Rankin, Stephen E., Engel, Elisabeth, Castaño, Oscar, (2019). Feasible and pure P2O5-CaO nanoglasses: An in-depth NMR study of synthesis for the modulation of the bioactive ion release Acta Biomaterialia 94, 574-584

The use of bioactive glasses (e.g. silicates, phosphates, borates) has demonstrated to be an effective therapy for the restoration of bone fractures, wound healing and vascularization. Their partial dissolution towards the surrounding tissue has shown to trigger positive bioactive responses, without the necessity of using growth factors or cell therapy, which reduces money-costs, side effects and increases their translation to the clinics. However, bioactive glasses often need from stabilizers (e.g. SiO44−, Ti4+, Co2+, etc.) that are not highly abundant in the body and which metabolization is not fully understood. In this study, we were focused on synthesizing pure calcium phosphate glasses without the presence of such stabilizers. We combined a mixture of ethylphosphate and calcium 2-methoxyethoxide to synthesize nanoparticles with different compositions and degradability. Synthesis was followed by an in-depth nuclear magnetic resonance characterization, complemented with other techniques that helped us to correlate the chemical structure of the glasses with their physiochemical properties and reaction mechanism. After synthesis, the organically modified xerogel (i.e. calcium monoethylphosphate) was treated at 200 or 350 °C and its solubility was maintained and controlled due to the elimination of organics, increase of phosphate-calcium interactions and phosphate polycondensation. To the best of our knowledge, we are reporting the first sol-gel synthesis of binary (P2O5-CaO) calcium phosphate glass nanoparticles in terms of continuous polycondensated phosphate chains structure without the addition of extra ions. The main goal is to straightforward the synthesis, to get a safer metabolization and to modulate the bioactive ion release. Additionally, we shed light on the chemical structure, reaction mechanism and properties of calcium phosphate glasses with high calcium contents, which nowadays are poorly understood. Statement of Significance The use of bioactive inorganic materials (i.e. bioactive ceramics, glass-ceramics and glasses) for biomedical applications is attractive due to their good integration with the host tissue without the necessity of adding exogenous cells or growth factors. In particular, degradable calcium phosphate glasses are completely resorbable, avoiding the retention in the body of the highly stable silica network of silicate glasses, and inducing a more controllable degradability than bioactive ceramics. However, most calcium phosphate glasses include the presence of stabilizers (e.g. Ti4+, Na+, Co2+), which metabolization is not fully understood and complicates their synthesis. The development of binary calcium phosphate glasses with controlled degradability reduces these limitations, offering a simple and completely metabolizable material with higher transfer to the clinics.

Keywords: Calcium phosphate glasses, Sol-gel process, NMR spectroscopy, Ion release, Biomaterials

Gumí-Audenis, B., Giannotti, M. I., (2019). Structural and mechanical characterization of supported model membranes by AFM Biomimetic Lipid Membranes: Fundamentals, Applications, and Commercialization (ed. Kök, Fatma N., Arslan Yildiz, Ahu, Inci, Fatih), Springer International Publishing (Cham, Germany) , 1-27

Several cellular processes, including adhesion, signaling and transcription, endocytosis, and membrane resealing, among others, involve conformational changes such as bending, vesiculation, and tubulation. These mechanisms generally involve membrane separation from the cytoskeleton as well as strong bending, for which the membrane chemical composition and physicochemical properties, often highly localized and dynamic, are key players. The mechanical role of the lipid membrane in force triggered (or sensing) mechanisms in cells is important, and understanding the lipid bilayers’ physical and mechanical properties is essential to comprehend their contribution to the overall membrane. Atomic force microscopy (AFM)-based experimental approaches have been to date very valuable to deepen into these aspects. As a stand-alone, high-resolution imaging technique and force transducer with the possibility to operate in aqueous environment, it defies most other surface instrumentation in ease of use, sensitivity and versatility. In this chapter, we introduce the different AFM-based methods to assess topological and nanomechanical information on model membranes, specifically to supported lipid bilayers (SLBs), including several examples ranging from pure phospholipid homogeneous bilayers to multicomponent and phase-separated SLBs, increasing the bilayer complexity, in the direction of mimicking biological membranes.

Keywords: Atomic force microscopy, Force spectroscopy, Model membranes, Nanomechanics, Supported lipid bilayers

Peyman, Zirak, Clara, Gregori-Pla, Igor, Blanco, Ana, Fortuna, Gianluca, Cotta, Pau, Bramon, Isabel, Serra, Anna, Mola, Jordi, Solà-Soler, Beatriz, F. Giraldo-Giraldo, Turgut, Durduran, Mercedes, Mayos, (2018). Characterization of the microvascular cerebral blood flow response to obstructive apneic events during night sleep Neurophotonics 5, (4), 045003

Obstructive apnea causes periodic changes in cerebral and systemic hemodynamics, which may contribute to the increased risk of cerebrovascular disease of patients with obstructive sleep apnea (OSA) syndrome. The improved understanding of the consequences of an apneic event on the brain perfusion may improve our knowledge of these consequences and then allow for the development of preventive strategies. Our aim was to characterize the typical microvascular, cortical cerebral blood flow (CBF) changes in an OSA population during an apneic event. Sixteen patients (age 58  ±  8  years, 75% male) with a high risk of severe OSA were measured with a polysomnography device and with diffuse correlation spectroscopy (DCS) during one night of sleep with 1365 obstructive apneic events detected. All patients were later confirmed to suffer from severe OSA syndrome with a mean of 83  ±  15 apneas and hypopneas per hour. DCS has been shown to be able to characterize the microvascular CBF response to each event with a sufficient contrast-to-noise ratio to reveal its dynamics. It has also revealed that an apnea causes a peak increase of microvascular CBF (30  ±  17  %  ) at the end of the event followed by a drop (−20  ±  12  %  ) similar to what was observed in macrovascular CBF velocity of the middle cerebral artery. This study paves the way for the utilization of DCS for further studies on these populations.

Keywords: Sleep disorder breathing, Cerebral blood flow, Brain perfusion, Diffuse correlation spectroscopy

Wang, Y., van Merwyk, L., Tönsing, K., Walhorn, V., Anselmetti, D., Fernàndez-Busquets, X., (2017). Biophysical characterization of the association of histones with single-stranded DNA Biochimica et Biophysica Acta (BBA) - General Subjects , 1861, (11), 2739-2749

Background: Despite the profound current knowledge of the architecture and dynamics of nucleosomes, little is known about the structures generated by the interaction of histones with single-stranded DNA (ssDNA), which is widely present during replication and transcription. Methods: Non-denaturing gel electrophoresis, transmission electron microscopy, atomic force microscopy, magnetic tweezers. Results: Histones have a high affinity for ssDNA in 0.15 M NaCl ionic strength, with an apparent binding constant similar to that calculated for their association with double-stranded DNA (dsDNA). The length of DNA (number of nucleotides in ssDNA or base pairs in dsDNA) associated with a fixed core histone mass is the same for both ssDNA and dsDNA. Although histone-ssDNA complexes show a high tendency to aggregate, nucleosome-like structures are formed at physiological salt concentrations. Core histones are able to protect ssDNA from digestion by micrococcal nuclease, and a shortening of ssDNA occurs upon its interaction with histones. The purified (+) strand of a cloned DNA fragment of nucleosomal origin has a higher affinity for histones than the purified complementary (−) strand. Conclusions: At physiological ionic strength histones have high affinity for ssDNA, possibly associating with it into nucleosome-like structures. General significance: In the cell nucleus histones may spontaneously interact with ssDNA to facilitate their participation in the replication and transcription of chromatin.

Keywords: Electrophoresis, Force spectroscopy, Histones, Magnetic tweezers, Nucleosome, Single-stranded DNA

Gumí-Audenis, Berta, Costa, Luca, Carlá, Francesco, Comin, Fabio, Sanz, Fausto, Giannotti, M. I., (2016). Structure and nanomechanics of model membranes by atomic force microscopy and spectroscopy: Insights into the role of cholesterol and sphingolipids Membranes , 6, (4), 58

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information

Keywords: Atomic force microscopy, Force spectroscopy, Lipid membranes, Supported lipid bilayers, Nanomechanics, Cholesterol, Sphingolipids, Membrane structure, XR-AFM combination

Barreiros dos Santos, M., Azevedo, S., Agusil, J. P., Prieto-Simón, B., Sporer, C., Torrents, E., Juárez, A., Teixeira, V., Samitier, J., (2015). Label-free ITO-based immunosensor for the detection of very low concentrations of pathogenic bacteria Bioelectrochemistry , 101, 146-152

Abstract Here we describe the fabrication of a highly sensitive and label-free ITO-based impedimetric immunosensor for the detection of pathogenic bacteria Escherichia coli O157:H7. Anti-E. coli antibodies were immobilized onto ITO electrodes using a simple, robust and direct methodology. First, the covalent attachment of epoxysilane on the ITO surface was demonstrated by Atomic Force Microscopy and cyclic voltammetry. The immobilization of antibody on the epoxysilane layer was quantified by Optical Waveguide Lightmode Spectroscopy, obtaining a mass variation of 12 ng cm− 2 (0.08 pmol cm− 2). Microcontact printing and fluorescence microscopy were used to demonstrate the specific binding of E. coli O157:H7 to the antibody-patterned surface. We achieved a ratio of 1:500 Salmonella typhimurium/E. coli O157:H7, thus confirming the selectivity of the antibodies and efficiency of the functionalization procedure. Finally, the detection capacity of the ITO-based immunosensor was evaluated by Electrochemical Impedance Spectroscopy. A very low limit of detection was obtained (1 CFU mL− 1) over a large linear working range (10–106 CFU mL− 1). The specificity of the impedimetric immunosensor was also examined. Less than 20% of non-specific bacteria (S. typhimurium and E. coli K12) was observed. Our results reveal the applicability of ITO for the development of highly sensitive and selective impedimetric immunosensors.

Keywords: E. coli O157:H7, Electrochemical Impedance Spectroscopy, Immunosensor, Indium tin oxide, Label-free detection

Cuervo, A., Dans, P. D., Carrascosa, J. L., Orozco, M., Gomila, G., Fumagalli, L., (2014). Direct measurement of the dielectric polarization properties of DNA Proceedings of the National Academy of Sciences of the United States of America 111, (35), E3624-E3630

The electric polarizability of DNA, represented by the dielectric constant, is a key intrinsic property that modulates DNA interaction with effector proteins. Surprisingly, it has so far remained unknown owing to the lack of experimental tools able to access it. Here, we experimentally resolved it by detecting the ultraweak polarization forces of DNA inside single T7 bacteriophages particles using electrostatic force microscopy. In contrast to the common assumption of low-polarizable behavior like proteins (εr ~ 2–4), we found that the DNA dielectric constant is ~ 8, considerably higher than the value of ~ 3 found for capsid proteins. State-of-the-art molecular dynamic simulations confirm the experimental findings, which result in sensibly decreased DNA interaction free energy than normally predicted by Poisson–Boltzmann methods. Our findings reveal a property at the basis of DNA structure and functions that is needed for realistic theoretical descriptions, and illustrate the synergetic power of scanning probe microscopy and theoretical computation techniques.

Keywords: Atomic force microscopy, Atomistic simulations, DNA packaging, DNA-ligand binding, Poisson-Boltzmann equation, capsid protein, DNA, double stranded DNA, amino acid composition, article, atomic force microscopy, bacteriophage, bacteriophage T7, dielectric constant, dipole, DNA binding, DNA packaging, DNA structure, electron microscopy, ligand binding, nonhuman, polarization, priority journal, protein analysis, protein DNA interaction, scanning probe microscopy, static electricity, virion, virus capsid, virus particle, atomic force microscopy, atomistic simulations, DNA packaging, DNA-ligand binding, Poisson-Boltzmann equation, Bacteriophage T7, Capsid, Cations, Dielectric Spectroscopy, DNA, DNA, Viral, DNA-Binding Proteins, Electrochemical Techniques, Ligands, Microscopy, Atomic Force, Models, Chemical, Nuclear Proteins

Dols-Perez, A., Fumagalli, L., Gomila, G., (2014). Structural and nanomechanical effects of cholesterol in binary and ternary spin-coated single lipid bilayers in dry conditions Colloids and Surfaces B: Biointerfaces 116, 295-302

We investigate the effects of Cholesterol (Chol) in the structural and nanomechanical properties of binary and ternary spin-coated single lipid bilayers made of Dioleoylphosphatidylcholine (DOPC) and Sphingomyelin (SM) in dry conditions. We show that for the DOPC/Chol bilayers, Chol induces an initial increase of the bilayer thickness, followed by decrease for concentrations above 30% Chol. The mechanical properties, instead, appear practically insensitive to the Chol content. For the SM/Chol bilayers we have observed both the thinning of the bilayer and the decrease of the force necessary to break it for Chol content above 40. mol%. In both binary mixtures phase separation is not observed. For ternary single bilayers of DOPC/SM/Chol, Chol induces phase segregation and the formation of domains resembling lipid rafts. The domains show a thickness and mechanical response clearly distinct from the surrounding phase and dependent on the relative Chol content. Based on the results obtained for the binary mixtures, DOPC- and SM-enriched domains can be identified. We highlight that many of the effects of Chol reported here for the dry multicomponent single lipid bilayers resemble closely those observed in hydrated bilayers, thus offering an additional insight into their properties.

Keywords: AFM, Air-stable lipid layer, Force spectroscopy, Lipid raft, Spin-coating

Rajzer, I., Menaszek, E., Kwiatkowski, R., Planell, J. A., Castaño, O., (2014). Electrospun gelatin/poly(ε-caprolactone) fibrous scaffold modified with calcium phosphate for bone tissue engineering Materials Science and Engineering: C 44, 183-190

In this study gelatin (Gel) modified with calcium phosphate nanoparticles (SG5) and polycaprolactone (PCL) were used to prepare a 3D bi-layer scaffold by collecting electrospun PCL and gelatin/SG5 fibers separately in the same collector. The objective of this study was to combine the desired properties of PCL and Gel/SG5 in the same scaffold in order to enhance mineralization, thus improving the ability of the scaffold to bond to the bone tissue. The scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the wide angle X-ray diffraction (WAXD) measurements confirmed that SG5 nanoparticles were successfully incorporated into the fibrous gelatin matrix. The composite Gel/SG5/PCL scaffold exhibited more enhanced mechanical properties than individual Gel and Gel/SG5 scaffolds. The presence of SG5 nanoparticles accelerated the nucleation and growth of apatite crystals on the surface of the composite Gel/SG5/PCL scaffold in simulated body fluid (SBF). The osteoblast response in vitro to developed electrospun scaffolds (PCL and Gel/SG5/PCL) was investigated by using normal human primary NHOst cell lines. NHOst cell culture studies showed that higher alkaline phosphatase (ALP) activity and better mineralization were obtained in the case of composite materials than in pure PCL scaffolds. The mechanically strong PCL scaffold served as a skeleton, while the Gel/SG5 fibers facilitated cell spreading and mineralization of the scaffold.

Keywords: Bilayer fibrous scaffold, Ceramic nanoparticles, Electrospinning, Gelatin, Polycaprolactone, Biomechanics, Bone, Calcium phosphate, Cell culture, Electrospinning, Fourier transform infrared spectroscopy, Mechanical properties, Mineralogy, Nanoparticles, Phosphatases, Polycaprolactone, Scanning electron microscopy, X ray diffraction, Polycaprolactone, Alkaline phosphatase activity, Bone tissue engineering, Calcium phosphate nanoparticles, Ceramic nanoparticles, Fibrous scaffolds, Gelatin, Simulated body fluids, Wide-angle x-ray diffraction, Electrospuns, Scaffolds (biology), Electrospinning

Torrent-Burgués, J., Cea, P., Giner, I., Guaus, E., (2014). Characterization of Langmuir and Langmuir-Blodgett films of an octasubstituted zinc phthalocyanine Thin Solid Films , 556, 485-494

In this work we report the fabrication of Langmuir and Langmuir-Blodgett (LB) films of a substituted ZnPc (octakis(oxyoctyl)phthalocyanine of zinc), and their characterization by means of several techniques. These characterization techniques include surface pressure (π-A) and surface potential (ΔV-A) isotherms as well as UV-vis Reflection spectroscopy and Brewster Angle Microscopy (BAM) for the films at the air-water interface together with UV-vis absorption and IR spectroscopies and Atomic Force Microscopy (AFM) for the LB films. The π-A and ΔV-A isotherms and BAM images indicate a phase transition at a surface pressure of ca. 9 mN/m and a multilayer formation at surface pressures around 19-20 mN/m; at a surface pressure around 27 mN/m a disordered collapse of the film occurs. In addition, AFM images of LB films at π = 10 mN/m and π = 20 mN/m show a monomolecular and a multilayered film, respectively. The comparison of the UV-vis spectrum of ZnPc in solution, the reflection spectra of the Langmuir films and UV-vis spectra of LB films reveals a significant reduction in the Q band intensity for the films, indicative of an organization of ZnPc in the Langmuir and LB films versus the random distribution in solution. The UV-vis Reflection spectra are also consistent with multilayer formation at surface pressures around 19-20 mN/m. The relative intensities of the IR spectrum bands change from the KBr pellet to the LB film which is also attributable to orientation effects in the film. Cyclic voltammetric experiments of LB films incorporating the ZnPc derivative show peaks that can be correlated with redox processes occurring in the phthalocyanine ring. A small but significant influence of the surface pressure and the number of deposited layers in the electrochemical behaviour is observed. The electrochemical response of cast films exhibits some differences with respect to that of LB films which have been attributed to their different molecular organizations.

Keywords: Atomic Force Microscopy, Electrochemistry, Langmuir-Blodgett, Multilayers, Optical spectroscopy techniques, Zinc phthalocyanine, Atomic force microscopy, Electrochemistry, Interfaces (materials), Isotherms, Multilayers, Nitrogen compounds, Optical multilayers, Organic polymers, Zinc compounds, Brewster angle microscopy, Characterization techniques, Electrochemical behaviour, Langmuir and langmuir-blodgett films, Langmuir-blodgett, Optical spectroscopy techniques, UV-Vis Reflection Spectroscopy, Zinc phthalocyanines, Langmuir Blodgett films

Redondo-Morata, L., Giannotti, M. I., Sanz, F., (2014). Structural impact of cations on lipid bilayer models: Nanomechanical properties by AFM-force spectroscopy Molecular Membrane Biology , 31, (1), 17-28

Atomic Force Microscopy (AFM) has become an invaluable tool for studying the micro-and nanoworlds. As a stand-alone, high-resolution imaging technique and force transducer, it defies most other surface instrumentation in ease of use, sensitivity and versatility. The main strength of AFM relies on the possibility to operate in an aqueous environment on a wide variety of biological samples, from single molecules-DNA or proteins-to macromolecular assemblies like biological membranes. Understanding the effect of mechanical stress on membranes is of primary importance in biophysics, since cells are known to perform their function under a complex combination of forces. In the later years, AFM-based Force-Spectroscopy (AFM-FS) has provided a new vista on membrane mechanics in a confined area within the nanometer realm, where most of the specific molecular interactions take place. Lipid membranes are electrostatically charged entities that physiologically coexist with electrolyte solutions. Thus, specific interactions with ions are a matter of considerable interest. The distribution of ions in the solution and their interaction with the membranes are factors that substantially modify the structure and dynamics of the cell membranes. Furthermore, signaling processes are modified by the membrane capability of retaining ions. Supported Lipid Bilayers (SLBs) are a versatile tool to investigate phospholipid membranes mimicking biological surfaces. In the present contribution, we review selected experiments on the mechanical stability of SLBs as models of lipid membranes by means of AFM-FS, with special focus on the effect of cations and ionic strength in the overall nanomechanical stability.

Keywords: Atomic force microscopy, Cations, Force spectroscopy, Lipid bilayer, Mechanical stability

Caballero, D., Martinez, E., Bausells, J., Errachid, A., Samitier, J., (2012). Impedimetric immunosensor for human serum albumin detection on a direct aldehyde-functionalized silicon nitride surface Analytica Chimica Acta 720, 43-48

In this work we report the fabrication and characterization of a label-free impedimetric immunosensor based on a silicon nitride (Si 3N 4) surface for the specific detection of human serum albumin (HSA) proteins. Silicon nitride provides several advantages compared with other materials commonly used, such as gold, and in particular in solid-state physics for electronic-based biosensors. However, few Si 3N 4-based biosensors have been developed; the lack of an efficient and direct protocol for the integration of biological elements with silicon-based substrates is still one of its the main drawbacks. Here, we use a direct functionalization method for the direct covalent binding of monoclonal anti-HSA antibodies on an aldehyde-functionalized Si-p/SiO 2/Si 3N 4 structure. This methodology, in contrast with most of the protocols reported in literature, requires less chemical reagents, it is less time-consuming and it does not need any chemical activation. The detection capability of the immunosensor was tested by performing non-faradaic electrochemical impedance spectroscopy (EIS) measurements for the specific detection of HSA proteins. Protein concentrations within the linear range of 10 -13-10 -7M were detected, showing a sensitivity of 0.128ΩμM -1 and a limit of detection of 10 -14M. The specificity of the sensor was also addressed by studying the interferences with a similar protein, bovine serum albumin. The results obtained show that the antibodies were efficiently immobilized and the proteins detected specifically, thus, establishing the basis and the potential applicability of the developed silicon nitride-based immunosensor for the detection of proteins in real and more complex samples.

Keywords: Aldehyde, Electrochemical impedance spectroscopy, Human serum albumin, Immunosensor, Silicon nitride, Bovine serum albumins, Chemical reagents, Complex samples, Covalent binding, Detection capability, Electrochemical impedance, Electrochemical impedance spectroscopy measurements, Functionalizations, Human serum albumins, Impedimetric immunosensors, Label free, Limit of detection, Linear range, Protein concentrations, Silicon-based, Specific detection, Aldehydes

Redondo-Morata, L., Giannotti, M. I., Sanz, F., (2012). AFM-based force-clamp monitors lipid bilayer failure kinetics Langmuir 28, (15), 6403-6410

The lipid bilayer rupture phenomenon is here explored by means of atomic force microscopy (AFM)-based force clamp, for the first time to our knowledge, to evaluate how lipid membranes respond when compressed under an external constant force, in the range of nanonewtons. Using this method, we were able to directly quantify the kinetics of the membrane rupture event and the associated energy barriers, for both single supported bilayers and multibilayers, in contradistinction to the classic studies performed at constant velocity. Moreover, the affected area of the membrane during the rupture process was calculated using an elastic deformation model. The elucidated information not only contributes to a better understanding of such relevant process, but also proves the suitability of AFM-based force clamp to study model structures as lipid bilayers. These findings on the kinetics of lipid bilayers rupture could be extended and applied to the study of other molecular thin films. Furthermore, systems of higher complexity such as models mimicking cell membranes could be studied by means of AFM-based force-clamp technique.

Keywords: Chain-Length, Spectroscopy, Nanomechanics, Microscopy, Elasticity, Stability, Membranes, Reveals, Fusion, Ions

Valle-Delgado, J. J., Liepina, I., Lapidus, D., Sabaté, R., Ventura, S., Samitier, J., Fernàndez-Busquets, X., (2012). Self-assembly of human amylin-derived peptides studied by atomic force microscopy and single molecule force spectroscopy Soft Matter 8, (4), 1234-1242

The self-assembly of peptides and proteins into amyloid fibrils of nanometric thickness and up to several micrometres in length, a phenomenon widely observed in biological systems, has recently aroused a growing interest in nanotechnology and nanomedicine. Here we have applied atomic force microscopy and single molecule force spectroscopy to study the amyloidogenesis of a peptide derived from human amylin and of its reverse sequence. The spontaneous formation of protofibrils and their orientation along well-defined directions on graphite and DMSO-coated graphite substrates make the studied peptides interesting candidates for nanotechnological applications. The measured binding forces between peptides correlate with the number of hydrogen bonds between individual peptides inside the fibril structure according to molecular dynamics simulations.

Keywords: Amyloid fibril, Amyloidogenesis, Binding forces, Fibril structure, Graphite substrate, Molecular dynamics simulations, Nanometrics, Protofibrils, Single molecule force spectroscopy, Spontaneous formation, Atomic force microscopy, Atomic spectroscopy, Graphite, Hydrogen bonds, Medical nanotechnology, Molecular dynamics, Molecular physics, Self assembly, Thickness measurement, Peptides

Redondo, L., Giannotti, M. I., Sanz, F., (2012). Stability of lipid bilayers as model membranes: Atomic force microscopy and spectroscopy approach Atomic force microscopy in liquid (ed. Baró, A. M., Reifenberger, R. G.), Wiley-VCH Verlag GmbH & Co.KGaA (Weinheim, Germany) Part I: General Atomic Force Microscopy, 259-284

van Zanten, T. S., Garcia-Parajo, M. F., (2012). Super-resolution near-field optical microscopy Comprehensive Biophysics (ed. Egelman, E. H.), Elsevier (Desdren, Germany) Volume 2: Biophysical Techniques for Characterization of Cells, 144-164

Near-field optical microscopy is a technique not limited by the laws of diffraction that enables simultaneous high-resolution fluorescence and topographic measurements at the nanometer scale. This chapter highlights the intrinsic advantages of near-field optics in the study of cellular structures. The first part of the chapter lays the foundations of the near-field concept and technical implementation of near-field scanning optical microscopy (NSOM), whereas the second part of the chapter focuses on applications of NSOM to the study of model membranes and cellular structures on the plasma membrane. The last part of the chapter discusses further directions of near-field optics, including optical antennas and fluorescence correlation spectroscopy approaches in the near-field regime.

Keywords: Biological membranes, Cell membrane nanoscale compartmentalization, Cellular nanodomains, Fluorescence correlation spectroscopy in reduced volumes, Immunoreceptor imaging, Lipid rafts, Near-field scanning optical microscopy, Optical nano-antennas, Shear force imaging, Single molecule detection, Super-resolution microscopy

Artés, Juan M., Díez-Pérez, Ismael, Sanz, Fausto, Gorostiza, Pau, (2011). Direct measurement of electron transfer distance decay constants of single redox proteins by electrochemical tunneling spectroscopy ACS Nano 5, (3), 2060-2066

We present a method to measure directly and at the single-molecule level the distance decay constant that characterizes the rate of electron transfer (ET) in redox proteins. Using an electrochemical tunneling microscope under bipotentiostatic control, we obtained current-distance spectroscopic recordings of individual redox proteins confined within a nanometric tunneling gap at a well-defined molecular orientation. The tunneling current decays exponentially, and the corresponding decay constant (β) strongly supports a two-step tunneling ET mechanism. Statistical analysis of decay constant measurements reveals differences between the reduced and oxidized states that may be relevant to the control of ET rates in enzymes and biological electron transport chains.

Keywords: Long-range electron transfer (LRET), Distance decay constant, Single-molecule electrochemistry, Redox enzyme, Metalloprotein, Blue copper protein, Azurin, Electrochemical scanning tunneling microscopy and spectroscopy, Nanoelectrodes, Debye length, Electrochemical charge screening

Garcia-Manyes, S., Sanz, F., (2010). Nanomechanics of lipid bilayers by force spectroscopy with AFM: A perspective Biochimica et Biophysica Acta - Biomembranes , 1798, (4), 741-749

Lipid bilayers determine the architecture of cell membranes and regulate a myriad of distinct processes that are highly dependent on the lateral organization of the phospholipid molecules that compose the membrane. Indeed, the mechanochemical properties of the membrane are strongly correlated with the function of several membrane proteins, which demand a very specific, highly localized physicochemical environment to perform their function. Several mesoscopic techniques have been used in the past to investigate the mechanical properties of lipid membranes. However, they were restricted to the study of the ensemble properties of giant bilayers. Force spectroscopy with AFM has emerged as a powerful technique able to provide valuable insights into the nanomechanical properties of supported lipid membranes at the nanometer/nanonewton scale in a wide variety of systems. In particular, these measurements have allowed direct measurement of the molecular interactions arising between neighboring phospholipid molecules and between the lipid molecules and the surrounding solvent environment. The goal of this review is to illustrate how these novel experiments have provided a new vista on membrane mechanics in a confined area within the nanometer realm, where most of the specific molecular interactions take place. Here we report in detail the main discoveries achieved by force spectroscopy with AFM on supported lipid bilayers, and we also discuss on the exciting future perspectives offered by this growing research field.

Keywords: Force spectroscopy, Atomic force microscopy, Lipid bilayer, Nanomechanics

Almendros, I., Montserrat, J. M., Torres, M., Gonzalez, C., Navajas, D., Farre, R., (2010). Changes in oxygen partial pressure of brain tissue in an animal model of obstructive apnea Respiratory Research , 11, (3), 1-6

Cognitive impairment is one of the main consequences of obstructive sleep apnea (OSA) and is usually attributed in part to the oxidative stress caused by intermittent hypoxia in cerebral tissues. The presence of oxygen-reactive species in the brain tissue should be produced by the deoxygenation-reoxygenation cycles which occur at tissue level during recurrent apneic events. However, how changes in arterial blood oxygen saturation (SpO(2)) during repetitive apneas translate into oxygen partial pressure (PtO2) in brain tissue has not been studied. The objective of this study was to assess whether brain tissue is partially protected from intermittently occurring interruption of O-2 supply during recurrent swings in arterial SpO(2) in an animal model of OSA. Methods: Twenty-four male Sprague-Dawley rats (300-350 g) were used. Sixteen rats were anesthetized and noninvasively subjected to recurrent obstructive apneas: 60 apneas/h, 15 s each, for 1 h. A control group of 8 rats was instrumented but not subjected to obstructive apneas. PtO2 in the cerebral cortex was measured using a fast-response oxygen microelectrode. SpO(2) was measured by pulse oximetry. The time dependence of arterial SpO(2) and brain tissue PtO2 was carried out by Friedman repeated measures ANOVA. Results: Arterial SpO(2) showed a stable periodic pattern (no significant changes in maximum [95.5 +/- 0.5%; m +/- SE] and minimum values [83.9 +/- 1.3%]). By contrast, brain tissue PtO2 exhibited a different pattern from that of arterial SpO(2). The minimum cerebral cortex PtO2 computed during the first apnea (29.6 +/- 2.4 mmHg) was significantly lower than baseline PtO2 (39.7 +/- 2.9 mmHg; p = 0.011). In contrast to SpO(2), the minimum and maximum values of PtO2 gradually increased (p < 0.001) over the course of the 60 min studied. After 60 min, the maximum (51.9 +/- 3.9 mmHg) and minimum (43.7 +/- 3.8 mmHg) values of PtO2 were significantly greater relative to baseline and the first apnea dip, respectively. Conclusions: These data suggest that the cerebral cortex is partially protected from intermittently occurring interruption of O-2 supply induced by obstructive apneas mimicking OSA.

Keywords: Near-infrared spectroscopy, Sleep-apnea, Iintermittent hypoxia, Cerebral oxygenation, Oxidative stress, Blood-flow, Rat, Apoptosis, Inflammation, Hypercapnia

de Oliveira, I. A. M., Vocanson, F., Uttaro, J. P., Asfari, Z., Mills, C. A., Samitier, J., Errachid, A., (2010). Characterization of a self-assembled monolayer based on a calix[4]crown-5 derivate: fabrication of a chemical sensor sensitive to calcium Journal of Nanoscience and Nanotechnology , 10, (1), 413-420

The synthesis and self-assembled monolayer (SAM) formation of a calix[4]crown-5 derivative are reported. Several techniques, including electrochemistry, atomic force microscopy (AFM), Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and contact angle measurements have been applied to characterise the monolayer film designed for chemical sensor applications. The recognition properties of this SAM for metal cations has been investigated using impedance spectroscopy (IS) showing an electrochemical response proportional to calcium ion concentration in the range from 10(-7) M to 10(-2) M. This response is related to microscopic changes at the gold surface induced by selective binding by the immobilised calixarene.

Keywords: Calixarenes, Self assembled monolayer, Micro-contact printing, Atomic force microscopy, Impedance spectroscopy

Fumagalli, L., Ferrari, G., Sampietro, M., Gomila, G., (2009). Quantitative nanoscale dielectric microscopy of single-layer supported biomembranes Nano Letters 9, (4), 1604-1608

We present the experimental demonstration of low-frequency dielectric constant imaging of single-layer supported biomembranes at the nanoscale. The dielectric constant image has been quantitatively reconstructed by combining the thickness and local capacitance obtained using a scanning force microscope equipped with a sub-attofarad low-frequency capacitance detector. This work opens new possibilities for studying bioelectric phenomena and the dielectric properties of biological membranes at the nanoscale.

Keywords: Atomic-force microscopy, Nnear-field microscopy, Purple membrane, Scanning capacitance, Biological-systems, Fluid, Spectroscopy, Resolution, Proteins, Dynamics

Caballero-Briones, F., Artes, J. M., Diez-Perez, I., Gorostiza, P., Sanz, F., (2009). Direct observation of the valence band edge by in situ ECSTM-ECTS in p-type Cu2O layers prepared by copper anodization Journal of Physical Chemistry C 113, (3), 1028-1036

Polycrystalline Cu2O layers have been selectively grown by electrochemical anodization of polycrystalline Cu electrodes in an alkaline medium (pH 12.85). Uniform layers with thicknesses around 100 nm have been obtained. Using electrochemical impedance spectroscopy, it was concluded that the Cu2O films behave as a p-type semiconductor. The Mott-Schottky plot gives a value for the flat band potential of U-FB = -255 mV vs silver/silver chloride electrode (SSC), an estimated carrier density N-A = 6.1 x 10(17) cm(-3), and the space charge layer width was calculated to be W-SCL = 9 nm at a band bending of 120 mV. The electronic structure of the Cu vertical bar Cu2O vertical bar electrolyte interface was for the first time probed by in situ electrochemical tunneling spectroscopy. The use of in situ electrochemical scanning tunneling microscopy allows us to directly observed the valence band edge and determine its position against the absolute energy scale to be E-VB = -4.9 eV. Finally, we constructed a quantitative electronic diagram of the Cu vertical bar Cu2O vertical bar electrolyte interface, where the positions of the valence and conduction band edges are depicted, as well as the edge of the previously reported electronic subband.

Keywords: 0.1 m NaOH, Electrochemical tunneling spectroscopy, Cuprous-oxide films, Anodic-oxidation, Electronic-structure, Alkaline-solution, Aqueous-solution, Initial-stages, Passive film, Thin-films

Barreiros dos Santos, M., Sporer, C., Sanvicens, N., Pascual, N., Errachid, A., Martinez, E., Marco, M. P., Teixeira, V., Samiter, J., (2009). Detection of pathogenic Bacteria by Electrochemical Impedance Spectroscopy: Influence of the immobilization strategies on the sensor performance Procedia Chemistry 23rd Eurosensors Conference (ed. Brugger, J., Briand, D.), Elsevier Science, BV (Lausanne, Switzerland) 1, 1291-1294

Electrochemical impedance spectroscopy (EIS) is applied to detect pathogenic E. coli O157:H7 bacteria via a label free immunoassay-based detection method. Polyclonal anti-E.coli antibodies (PAb) are immobilized onto gold electrodes following two different strategies, via chemical bond formation between antibody amino groups and a carboxylic acid containing self-assembled molecular monolayer (SAM) and alternatively by linking a biotinylated anti-E. coli to Neutravidin on a mixed-SAM. Impedance spectra for sensors of both designs for increasing concentrations of E. coli are recorded in phosphate buffered saline (PBS). The Nyquist plots can be modeled with a Randle equivalent circuit, identifying the charge transfer resistance RCT as the relevant concentration dependent parameter. Sensors fabricated from both designs are able to detect very low concentration of E. coli with limits of detection as low as 10-100 cfu/ml. The influence of the different immobilization protocols on the sensor performance is evaluated in terms of sensitivity, dynamic range and resistance against nonspecific absorption.

Keywords: Bacteria detection, Biosensors, E-coli, Impedance spectroscopy

Guaus, E., Torrent-Burgues, J., Zine, N., Errachid, A., (2009). Glassy carbon electrode modified with a langmuir-blodgett film of a thiomacrocyclic ionophore for Cu(II) recognition Sensor Letters 6th Maghreb-Europe Meeting on Materials and Their Applications for Devices and Physical, Chemical and Biological Sensors , AMER SCIENTIFIC PUBLISHERS (Rabat, Morocco) 7, (5), 1006-1011

Nanometric films of a thiomacrocyclic ionophore, 4-phenyl-4-sulfide-11(1- oxodecyl)-1,7-dithia-11-aza-4-phosphacyclotetradecane (ThM), have been deposited on the surface of a Glassy Carbon Electrode (GCE) by the Langmuir-Blodgett (LB) technique. The films have been characterised by using AFM. The influence of these modified electrodes (GCE-ThM) on the reduction of Cu(II) ions has been investigated by using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS), and its sensor response has been checked. The CV and EIS responses of LB films on GCE indicate that these ThM films are sensitive to Cu(II) ions. The analysis by EIS of the interference of some other cations, as Mg(II) and Co(II), shows that LB films of ThM can be used for specific Cu(II) sensing applications.

Keywords: Cu(II) sensor, Cyclic voltammetry, Electrochemical impedance spectroscopy, Langmuir-blodgett films

Oncins, G., Torrent-Burgues, J., Sanz, F., (2008). Nanomechanical properties of arachidic acid Langmuir-Blodgett films Journal of Physical Chemistry C 112, (6), 1967-1974

The nanomechanical properties of Langmuir-Blodgett monolayers of arachidic acid extracted at surface pressures of 1, 15, and 35 mN/m and deposited on mica were investigated by atomic force microscopy, force spectroscopy, and lateral force microscopy. It was experimentally demonstrated that the arachidic acid molecular orientation depends on the extraction pressure. According to this, tilting angles of 50, 34, and 22 degrees with respect to the surface perpendicular were detected and identified as conformations that maximize van der Waals interactions between the arachidic acid alkyl chains. The vertical force needed to puncture the monolayers with the AFM tip strongly depends on the molecular tilting angles attained at different monolayer extraction surface pressures, obtaining values that range from 13.07 +/- 3.24 nN for 50 degrees to 22.94 +/- 5.49 nN for 22 degrees tilting angles. The different molecular interactions involved in the monolayer cohesion are discussed and quantitatively related to the experimental monolayer breakthrough forces. The friction measurements performed from low vertical forces up to monolayer disruption reveal the existence of three well-defined regimes: first, a low friction response due to the elastic deformation of the monolayer, which is followed by a sharp increase in the friction force due to the onset of a sudden plastic deformation. The last regime corresponds to the monolayer rupture and the contact between tip and substrate. The friction coefficient of the substrate is seen to depend on the monolayer extraction pressure, a fact that is discussed in terms of the relationship between the sample compactness and its rupture mechanism.

Keywords: AFM, SAM, Reflection-absortion spectroscopy, Lipid-bilayers, Frictional-properies, Molecular-structure, Thermal behavior, Nanometer-scale, Chain-length, LB films

Manara, S., Paolucci, F., Palazzo, B., Marcaccio, M., Foresti, E., Tosi, G., Sabbatini, S., Sabatino, P., Altankov, G., Roveri, N., (2008). Electrochemically-assisted deposition of biomimetic hydroxyapatite-collagen coatings on titanium plate Inorganica Chimica Acta 361, (6), 1634-1645

A biomimetic bone-like composite, made of self-assembled collagen fibrils and carbonate hydroxyapatite nanocrystals, has been performed by an electrochemically-assisted deposition on titanium plate. The electrolytic processes have been carried out using a single type I collagen molecules suspension in a diluted Ca(NO3)(2) and NH4H2PO4 solution at room temperature and applying a constant current for different periods of time. Using the same electrochemical conditions, carbonate hydroxyapatite nanocrystals or reconstituted collagen. brils coatings were obtained. The reconstituted collagen. brils, hydroxyapatite nanocrystals and collagen fibrils/apatite nanocrystals coatings have been characterized chemically, structurally and morphologically, as well as for their ability to bind fibronectin (FN). Fourier Transform Infrared microscopy has been used to map the topographic distribution of the coating components at different times of electrochemical deposition, allowing to single out the individual deposition steps. Moreover, roughness of Ti plate has been found to affect appreciably the nucleation region of the inorganic nanocrystals. Laser scanning confocal microscopy has been used to characterize the FN adsorption pattern on a synthetic biomimetic apatitic phase, which exhibits a higher affinity when it is inter-grown with the collagen fibrils. The results offer auspicious applications in the preparation of medical devices such as biomimetic bone-like composite-coated metallic implants.

Keywords: Hydroxyapatite-collagen coating, Electrochemically-assisted deposition, Micro-imaging FTIR spectroscopy, Laser scanning confocal microscopy, Biomimetic crystal growth, Fibronectin binding

Cho, S., Castellarnau, M., Samitier, J., Thielecke, H., (2008). Dependence of impedance of embedded single cells on cellular behaviour Sensors 8, (2), 1198-1211

Non-invasive single cell analyses are increasingly required for the medical diagnostics of test substances or the development of drugs and therapies on the single cell level. For the non-invasive characterisation of cells, impedance spectroscopy which provides the frequency dependent electrical properties has been used. Recently, microfludic systems have been investigated to manipulate the single cells and to characterise the electrical properties of embedded cells. In this article, the impedance of partially embedded single cells dependent on the cellular behaviour was investigated by using the microcapillary. An analytical equation was derived to relate the impedance of embedded cells with respect to the morphological and physiological change of extracellular interface. The capillary system with impedance measurement showed a feasibility to monitor the impedance change of embedded single cells caused by morphological and physiological change of cell during the addition of DMSO. By fitting the derived equation to the measured impedance of cell embedded at different negative pressure levels, it was able to extrapolate the equivalent gap and gap conductivity between the cell and capillary wall representing the cellular behaviour.

Keywords: Frequency-domain, Spectroscopy, Erythrocytes, Biosensor, Membrane, System

Torrent-Burgues, J., Oncins, G., Sanz, F., (2008). Study of mixed Langmuir and Langmuir-Blodgett films of dissimilar components by AFM and force spectroscopy Colloids and Surfaces a-Physicochemical and Engineering Aspects 12th International Conference on Organized Molecular Films , Elsevier Science (Krakow, Poland) 321, (1-3), 70-75

In this study the structure of mixed Langmuir-Blodgett (LB) monolayers has been investigated using atomic force microscopy, lateral force microscopy and force spectroscopy, as well as the characteristics of the Langmuir monolayers by surface pressure-area isotherms and Brewster angle microscopy. Mixed films were of dissimilar compounds, a fatty acid such as arachidic acid and a macrocyclic compound. The mixture forms separated phases, but some degree of partial miscibility occurs, with domains at the micro-scale that have different nanomechanical and nanotribological properties. LB films transferred at the same surface pressure show different characteristics depending on the composition. The higher domains correspond to arachidic acid and some of these domains show the presence of two phases, which have been identified as phases with discrete molecular tilting angles.

Keywords: Mixed monolayers, Pressure-area isotherm, Langmuir-Blodgett, AFM, Force spectroscopy

Díez-Pérez, Ismael, Sanz, Fausto, Gorostiza, Pau, (2006). Electronic barriers in the iron oxide film govern its passivity and redox behavior: Effect of electrode potential and solution pH Electrochemistry Communications , 8, (10), 1595-1602

We have measured in situ the electronic conductance spectra of the passive film formed on an Fe electrode immersed in a borate buffer solution using electrochemical tunneling spectroscopy (ECTS) and electrochemical impedance spectroscopy (EIS) techniques, and we have followed their changes as the electrode is electrochemically oxidized and reduced. We demonstrate that pre-passive Fe(II) oxide and the passive Fe(II)/Fe(III) film, behave as p- and n-type semiconductors, respectively and that their reversible inter-conversion is mediated by the availability of free charge carriers on the electrode surface. ECTS spectra have been also modeled to obtain the main electrochemical kinetic parameters of the electron transfer through both p-Fe(II) and n-Fe(III) oxides at different sample potentials and pHs values. We find that the electronic energy barrier in the oxide and its dependence with electrode potential and solution pH, determine the reactivity and passivity of iron.

Keywords: Electrochemical tunneling spectroscopy, Fe passivity Electronic energy barriers, pH effect on passivity

Díez-Pérez, Ismael, Vericat, Carolina, Gorostiza, Pau, Sanz, Fausto, (2006). The iron passive film breakdown in chloride media may be mediated by transient chloride-induced surface states located within the band gap Electrochemistry Communications , 8, (4), 627-632

Despite its tremendous scientific and economic impact, the mechanism that triggers metal passive film breakdown in the presence of aggressive ions remains under discussion. We have studied the iron passive film in chloride media using X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy and electrochemical tunneling spectroscopy (ECTS). Ex situ XPS reveal that the film consists exclusively of an Fe(III) oxide without chloride content. In situ ECTS has been used to build up conductance maps of the Fe electrode during its electrochemical oxidation in a borate buffer solution and its breakdown when the film is grown in the presence of chloride. This conductograms provide direct and in situ experimental evidence of chloride-induced surface states within the band gap of the oxide film (~3.3eV). These states enable new charge exchange pathways that allow hole capture at the surface of the n-type Fe(III) oxide. The blocking of VB processes that occurs in the iron passive film is no longer present in chloride media, and electrode corrosion can proceed through these new states. We propose a simple 3-step mechanism for the process, in which chloride anions form an oxidizing Fe(II) surface intermediate but do not participate directly in the reaction.

Keywords: Electrochemical tunneling spectroscopy, Electronic band structure, Fe passive film, Aqueous chloride corrosion, Semiconductor decomposition, Interface states