Publications

by Keyword: Field


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

Oliva, A. M., Homs-Corbera, A., Torrents, E., Juarez, A., Samitier, J., (2014). Synergystic effect of temperature and electric field intensity in Escherichia coli inactivation Micro and Nanosystems , 6, (2), 79-86

Electric Fields are increasingly used to manipulate bacteria. However, there is no systematic and definitive study on how the different electric parameters change bacteria viability. Here we present a study on the effects of electric field intensity and temperature to bacterial cultures. Escherichia coli colonies have been exposed to different electric field intensities at 1MHz during 5 minutes by means of a microfluidic device specially designed for the experiment. From the analysis of the results it is possible to see that Escherichia coli survival rate diminishes when applying field intensities as low as 220V during 5 minutes. Death rates also increase when stronger fields are applied. However, viability of survived bacteria is maintained. Additionally, temperature shows a synergistic effect with voltage. When temperature was increased, results showed a stronger sensitivity of cells to the electric field. Moreover, the expression patterns of Outer Membrane Protein A and Ribosomal Proteins differ in control and treated samples, suggesting changes in bacterial metabolism and structure.

Keywords: E. coli, Electric field, Temperature, Viability


Oliva, A. M., Homs, A., Torrents, E., Juarez, A., Samitier, J., (2014). Effect of electric field and temperature in E.Coli viability IFMBE Proceedings XIII Mediterranean Conference on Medical and Biological Engineering and Computing 2013 (ed. Roa Romero, Laura M.), Springer (Seville, Spain) 41, 1833-1836

Electromagnetic Fields are increasingly used to manipulate bacteria. However, there is no systematic and definitive study on how the different electric parameters change bacteria viability. Here we present preliminary data on the effect of electric field intensity and temperature applica- tion. E. Coli colonies have been exposed to different voltages at 1MHz during 5 minutes by means of a custom-made micro- fluidic device. Results show that E.Coli survival rate is already reduced by applying field intensities as low as 220V/cm during 5 minutes. The use of stronger fields resulted in death rates increase also. Viability of survived bacteria was maintained. On the other hand, temperature has shown a synergistic effect with voltage. When temperature is increased results seem to indicate stronger sensitivity of cells to the electric field. It is necessary to continue studying the contribution of other para- meters as intensity, time, frequency or concentration, to study further synergies.

Keywords: E. Coli, Electromagnetic Field, Temperature, Viability


Bueno, M., Paganetti, H., Duch, M. A., Schuemann, J., (2013). An algorithm to assess the need for clinical Monte Carlo dose calculation for small proton therapy fields based on quantification of tissue heterogeneity Medical Physics , 40, (8), 081704

Purpose: In proton therapy, complex density heterogeneities within the beam path constitute a challenge to dose calculation algorithms. This might question the reliability of dose distributions predicted by treatment planning systems based on analytical dose calculation. For cases in which substantial dose errors are expected, resorting to Monte Carlo dose calculations might be essential to ensure a successful treatment outcome and therefore the benefit is worth a presumably long computation time. The aim of this study was to define an indicator for the accuracy of dose delivery based on analytical dose calculations in treatment planning systems for small proton therapy fields to identify those patients for which Monte Carlo dose calculation is warranted. Methods: Fourteen patients treated at our facility with small passively scattered proton beams (apertures diameters below 7 cm) were selected. Plans were generated in the XiO treatment planning system in combination with a pencil beam algorithm developed at the Massachusetts General Hospital and compared to Monte Carlo dose calculations. Differences in the dose to the 50% of the gross tumor volume (D50, GTV) were assessed in a field-by-field basis. A simple and fast methodology was developed to quantify the inhomogeneity of the tissue traversed by a single small proton beam using a heterogeneity index (HI) - a concept presented by Plugfelder [Med. Phys. 34, 1506-1513 (2007)10.1118/1. 2710329] for scanned proton beams. Finally, the potential correlation between the error made by the pencil beam based treatment planning algorithm for each field and the level of tissue heterogeneity traversed by the proton beam given by the HI was evaluated. Results: Discrepancies up to 5.4% were found in D50 for single fields, although dose differences were within clinical tolerance levels (<3%) when combining all of the fields involved in the treatment. The discrepancies found for each field exhibited a strong correlation to their associated HI-values (Spearman's ρ = 0.8, p < 0.0001); the higher the level of tissue inhomogeneities for a particular field, the larger the error by the analytical algorithm. With the established correlation a threshold for HI can be set by choosing a tolerance level of 2-3% - commonly accepted in radiotherapy. Conclusions: The HI is a good indicator for the accuracy of proton field delivery in terms of GTV prescription dose coverage when small fields are delivered. Each HI-value was obtained from the CT image in less than 3 min on a computer with 2 GHz CPU allowing implementation of this methodology in clinical routine. For HI-values exceeding the threshold, either a change in beam direction (if feasible) or a recalculation of the dose with Monte Carlo would be highly recommended.

Keywords: Heterogeneities, Heterogeneity index, Monte Carlo, Proton therapy, Small fields


Garcia-Parajo, M. F., (2012). The role of nanophotonics in regenerative medicine Nanotechnology in Regenerative Medicine - Methods and Protocols (Methods in Molecular Biology) (ed. Navarro, M., Planell, J. A.), Springer (New York, USA) 811, 267-284

Cells respond to biochemical and mechanical stimuli through a series of steps that begin at the molecular, nanometre level, and translate finally in global cell response. Defects in biochemical- and/or mechanical-sensing, transduction or cellular response are the cause of multiple diseases, including cancer and immune disorders among others. Within the booming field of regenerative medicine, there is an increasing need for developing and applying nanotechnology tools to bring understanding on the cellular machinery and molecular interactions at the nanoscale. Nanotechnology, nanophotonics and in particular, high-resolution-based fluorescence approaches are already delivering crucial information on the way that cells respond to their environment and how they organize their receptors to perform specialized functions. This chapter focuses on emerging super-resolution optical techniques, summarizing their principles, technical implementation, and reviewing some of the achievements reached so far.

Keywords: Cell membrane organization, Nanophotonics, Near-field optical microscopy, Super-resolution optical microscopy


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


Ivon Rodriguez-Villarreal, Angeles, Tarn, Mark D., Madden, Leigh A., Lutz, Julia B., Greenman, John, Samitier, Josep, Pamme, Nicole, (2011). Flow focussing of particles and cells based on their intrinsic properties using a simple diamagnetic repulsion setup Lab on a Chip 11, (7), 1240-1248

The continuous flow focussing and manipulation of particles and cells are important factors in microfluidic applications for performing accurate and reproducible procedures downstream. Many particle focussing methods require complex setups or channel designs that can limit the process and its applications. Here, we present diamagnetic repulsion as a simple means of focussing objects in continuous flow, based only on their intrinsic properties without the requirement of any label. Diamagnetic polystyrene particles were suspended in a paramagnetic medium and pumped through a capillary between a pair of permanent magnets, whereupon the particles were repelled by each magnet into the central axis of the capillary, thus achieving focussing. By investigating this effect, we found that the focussing was greatly enhanced with (i) increased magnetic susceptibility of the medium, (ii) reduced flow rate of the suspension, (iii) increased particle size, and (iv) increased residence time in the magnetic field. Furthermore, we applied diamagnetic repulsion to the flow focussing of living, label-free HaCaT cells.

Keywords: Feeble magnetic substances, On-chip, Blood-cells, Microfluidic device, Separation, Field, Levitation, Magnetophoresis, Fractionation, Nanoparticles


van Zanten, T. S., Gomez, J., Manzo, C., Cambi, A., Buceta, J., Reigada, R., Garcia-Parajo, M. F., (2010). Direct mapping of nanoscale compositional connectivity on intact cell membranes Proceedings of the National Academy of Sciences of the United States of America 107, (35), 15437-15442

Lateral segregation of cell membranes is accepted as a primary mechanism for cells to regulate a diversity of cellular functions. In this context, lipid rafts have been conceptualized as organizing principle of biological membranes where underlying cholesterol-mediated selective connectivity must exist even at the resting state. However, such a level of nanoscale compositional connectivity has been challenging to prove. Here we used single-molecule near-field scanning optical microscopy to visualize the nanolandscape of raft ganglioside GM1 after tightening by its ligand cholera toxin (CTxB) on intact cell membranes. We show that CTxB tightening of GM1 is sufficient to initiate a minimal raft coalescence unit, resulting in the formation of cholesterol-dependent GM1 nanodomains <120 nm in size. This particular arrangement appeared independent of cell type and GM1 expression level on the membrane. Simultaneous dual color high-resolution images revealed that GPI anchored and certain transmembrane proteins were recruited to regions proximal (<150 nm) to CTxB-GM1 nanodomains without physical intermixing. Together with in silico experiments, our high-resolution data conclusively demonstrate the existence of raft-based interconnectivity at the nanoscale. Such a linked state on resting cell membranes constitutes thus an obligatory step toward the hierarchical evolution of large-scale raft coalescence upon cell activation.

Keywords: Cholera toxin, Membrane heterogeneity, Near-field scanning optical microscopy, Raft ganglioside GM1, Single-molecule detection


Gil, Vanessa, Bichler, Zoe, Lee, Jae K., Seira, Oscar, Llorens, Franc, Bribian, Ana, Morales, Ricardo, Claverol-Tinture, Enric, Soriano, Eduardo, Sumoy, Lauro, Zheng, Binhai, del Rio, Jose A., (2010). Developmental expression of the oligodendrocyte myelin glycoprotein in the mouse telencephalon Cerebral Cortex , 20, (8), 1769-1779

The oligodendrocyte myelin glycoprotein is a glycosylphosphatidylinositol-anchored protein expressed by neurons and oligodendrocytes in the central nervous system. Attempts have been made to identify the functions of the myelin-associated inhibitory proteins (MAIPs) after axonal lesion or in neurodegeneration. However, the developmental roles of some of these proteins and their receptors remain elusive. Recent studies indicate that NgR1 and the recently discovered receptor PirB restrict cortical synaptic plasticity. However, the putative factors that trigger these effects are unknown. Because Nogo-A is mostly associated with the endoplasmic reticulum and myelin associated glycoprotein appears late during development, the putative participation of OMgp should be considered. Here, we examine the pattern of development of OMgp immunoreactive elements during mouse telencephalic development. OMgp immunoreactivity in the developing cortex follows the establishment of the thalamo-cortical barrel field. At the cellular level, we located OMgp neuronal membranes in dendrites and axons as well as in brain synaptosome fractions and axon varicosities. Lastly, the analysis of the barrel field in OMgp-deficient mice revealed that although thalamo-cortical connections were formed, their targeting in layer IV was altered, and numerous axons ectopically invaded layers II-III. Our data support the idea that early expressed MAIPs play an active role during development and point to OMgp participating in thalamo-cortical connections.

Keywords: Axon plasticity, Barrel-field specification, Cortical lamination, Myelin


van Zanten, T. S., Cambi, A., Garcia-Parajo, M. F., (2010). A nanometer scale optical view on the compartmentalization of cell membranes Biochimica et Biophysica Acta - Biomembranes , 1798, (4), 777-787

For many years, it was believed that the laws of diffraction set a fundamental limit to the spatial resolution of conventional light microscopy. Major developments, especially in the past few years, have demonstrated that the diffraction barrier can be overcome both in the near- and far-field regime. Together with dynamic measurements, a wealth of new information is now emerging regarding the compartmentalization of cell membranes. In this review we focus on optical methods designed to explore the nanoscale architecture of the cell membrane, with a focal point on near-field optical microscopy (NSOM) as the first developed technique to provide truly optical super-resolution beyond the diffraction limit of light. Several examples illustrate the unique capabilities offered by NSOM and highlight its usefulness on cell membrane studies, complementing the palette of biophysical techniques available nowadays.

Keywords: Membrane nanodomain, Lipid raft, Single molecule detection, Near-field scanning optical microscopy, Super-resolution optical microscopy


Tarzan-Lorente, M., Gutierrez-Galvez, A., Martinez, D., Marco, S., (2010). A biologically inspired associative memory for artificial olfaction Practica 2010 International Joint Conference on Neural Networks (IJCNN 2010) , IEEE, Piscataway, NJ, USA (Barcelona, Spain) , 6 pp.

In this paper, we propose a biologically inspired architecture for a Hopfield-like associative memory applied to artificial olfaction. The proposed algorithm captures the projection between two neural layers of the insect olfactory system (Antennal Lobe and Mushroom Body) with a kernel based projection. We have tested its classification performance as a function of the size of the training set and the time elapsed since training and compared it with that obtained with a Support Vector Machine.

Keywords: Biocomputing, Chemioception, Content-addressable storage, Hopfield neural nets, Support vector machines


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


van Zanten, T. S., Cambi, A., Koopman, M., Joosten, B., Figdor, Carl G., Garcia-Parajo, M. F., (2009). Hotspots of GPI-anchored proteins and integrin nanoclusters function as nucleation sites for cell adhesion Proceedings of the National Academy of Sciences of the United States of America 106, (44), 18557-18562

Recruitment of receptor proteins to lipid rafts has been proposed as an important mechanism to regulate their cellular function. In particular, rafts have been implicated in regulation of integrin-mediated cell adhesion, although the underlying mechanism remains elusive. We used single-molecule near-field optical microscopy (NSOM) with localization accuracy of approximately 3 nm, to capture the spatio-functional relationship between the integrin LFA-1 and raft components (GPI-APs) on immune cells. Dual color nanoscale imaging revealed the existence of a nanodomain GPI-AP subpopulation that further concentrated in regions smaller than 250 nm, suggesting a hierarchical prearrangement of GPI-APs on resting monocytes. We previously demonstrated that in quiescent monocytes, LFA-1 preorganizes in nanoclusters. We now show that integrin nanoclusters are spatially different but reside proximal to GPI-AP nanodomains, forming hotspots on the cell surface. Ligand-mediated integrin activation resulted in an interconversion from monomers to nanodomains of GPI-APs and the generation of nascent adhesion sites where integrin and GPI-APs colocalized at the nanoscale. Cholesterol depletion significantly affected the reciprocal distribution pattern of LFA-1 and GPI-APs in the resting state, and LFA-1 adhesion to its ligand. As such, our data demonstrate the existence of nanoplatforms as essential intermediates in nascent cell adhesion. Since raft association with a variety of membrane proteins other than LFA-1 has been documented, we propose that hotspots regions enriched with raft components and functional receptors may constitute a prototype of nanoscale inter-receptor assembly and correspond to a generic mechanism to offer cells with privileged areas for rapid cellular function and responses to the outside world.

Keywords: Integrin LFA-1, Membrane nanocompartments, Near-field scanning optical microscopy (NSOM), Single molecule detection


Mir, M., Homs, A., Samitier, J., (2009). Integrated electrochemical DNA biosensors for lab-on-a-chip devices Electrophoresis , 30, (19), 3386-3397

Analytical devices able to perform accurate and fast automatic DNA detection or sequencing procedures have many potential benefits in the biomedical and environmental fields. The conversion of biological or biochemical responses into quantifiable optical, mechanical or electronic signals is achieved by means of biosensors. Most of these transducing elements can be miniaturized and incorporated into lab-on-a-chip devices, also known as Micro Total Analysis Systems. The use of multiple DNA biosensors integrated in these miniaturized laboratories, which perform several analytical operations at the microscale, has many cost and efficiency advantages. Tiny amounts of reagents and samples are needed and highly sensitive, fast and parallel assays can be done at low cost. A particular type of DNA biosensors are the ones used based on electrochemical principles. These sensors offer several advantages over the popular fluorescence-based detection schemes. The resulting signal is electrical and can be processed by conventional electronics in a very cheap and fast manner. Furthermore, the integration and miniaturization of electrochemical transducers in a microsystem makes easier its fabrication in front of the most common currently used detection method. In this review, different electrochemical DNA biosensors integrated in analytical microfluidic devices are discussed and some early stage commercial products based on this strategy are presented.

Keywords: DNA, Electrochemical DNA biosensors, Electrochemistry, Lab-on-a-chip, Micro Total Analysis systems, Field-effect transistors, Sequence-specific detection, Chemical-analysis systems, Solid-state nanopores, Carbon nanotubes, Microfluidic device, Electrical detection, Hybridization, Molecules, Sensor


de Bakker, Barbel I., Bodnar, Andrea, van Dijk, Erik M. H. P., Vamosi, Gyorgy, Damjanovich, Sandor, Waldmann, Thomas A., van Hulst, Niek F., Jenei, Attila, Garcia-Parajo, M. F., (2008). Nanometer-scale organization of the alpha subunits of the receptors for IL2 and IL15 in human T lymphoma cells Journal of Cell Science 121, (5), 627-633

Interleukin 2 and interleukin 15 (IL2 and IL15, respectively) provide quite distinct contributions to T-cell-mediated immunity, despite having similar receptor composition and signaling machinery. As most of the proposed mechanisms underlying this apparent paradox attribute key significance to the individual {alpha}-chains of IL2 and IL15 receptors, we investigated the spatial organization of the receptors IL2R{alpha} and IL15R{alpha} at the nanometer scale expressed on a human CD4+ leukemia T cell line using single-molecule-sensitive near-field scanning optical microscopy (NSOM). In agreement with previous findings, we here confirm clustering of IL2R{alpha} and IL15R{alpha} at the submicron scale. In addition to clustering, our single-molecule data reveal that a non-negligible percentage of the receptors are organized as monomers. Only a minor fraction of IL2R{alpha} molecules reside outside the clustered domains, whereas [~]30% of IL15R{alpha} molecules organize as monomers or small clusters, excluded from the main domain regions. Interestingly, we also found that the packing densities per unit area of both IL2R{alpha} and IL15R{alpha} domains remained constant, suggesting a `building block' type of assembly involving repeated structures and composition. Finally, dual-color NSOM demonstrated co-clustering of the two {alpha}-chains. Our results should aid understanding the action of the IL2R-IL15R system in T cell function and also might contribute to the more rationale design of IL2R- or IL15R-targeted immunotherapy agents for treating human leukemia.

Keywords: Near-field scanning optical microscopy (NSOM), Interleukin receptors IL2R, IL15R, Single-molecule detection, Nanometer-scale membrane organization