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Search Results: 1 - 10 of 5539 matches for " Giovanni Dietler "
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The Use of Light Diffracted from Grating Etched onto the Backside Surface of an Atomic Force Microscope Cantilever Increases the Force Sensitivity  [PDF]
Sergey K. Sekatskii, Mounir Mensi, Andrey G. Mikhaylov, Giovanni Dietler
Journal of Surface Engineered Materials and Advanced Technology (JSEMAT) , 2013, DOI: 10.4236/jsemat.2013.34A1004

A reflecting diffraction grating has been etched onto the backside of a standard cantilever for atomic force microscopy, and the diffracted light has been used to monitor the angular position of the cantilever. It is shown experimentally that for small angles of incidence and for large reflection angles, the force sensitivity can be improved by few times when an appropriate detection scheme based on the position sensitive (duolateral) detector is used. The first demonstration was performed with a one micron period amplitude diffraction grating onto the backside of an Al-coated cantilever etched by a focused ion beam milling for the experiments in air and an analogous 600 nm-period grating for the experiments in air and in water.

Force spectroscopy on DNA by FM-AFM
Giovanni Di Santo,Susana Tobenas,Jozef Adamcik,Giovanni Dietler
Physics , 2007,
Abstract: We present imaging and force spectroscopy measurements of DNA molecules adsorbed on functionalized mica. By means of Non-Contact mode AFM (NC-AFM) in Ultra High Vacuum (UHV), the frequency shift (\Delta f) versus separation (z) curves were measured providing a quantitative measurement of both force and energy of the tip-DNA interaction. Similarly, topographic images of the adsorbed DNA molecules in constant frequency shift mode were collected. The high resolution force measurements confirm the imaging contrast difference between the substrate and DNA. The force curves measured along the DNA molecule can be divided into two classes showing marked differences in the minimum of the interaction force and energy, indicating that NC-AFM could deliver chemical contrast along the DNA molecule.
Excluded volume effects on semiflexible ring polymers
Fabian Drube,Karen Alim,Guillaume Witz,Giovanni Dietler,Erwin Frey
Quantitative Biology , 2009, DOI: 10.1021/nl1003575
Abstract: Two-dimensional semiflexible polymer rings are studied both by imaging circular DNA adsorbed on a mica surface and by Monte Carlo simulations of phantom polymers as well as of polymers with finite thickness. Comparison of size and shape of the different models over the full range of flexibilities shows that excluded volume caused by finite thickness induces an anisotropic increase of the main axes of the conformations, a change of shape, accomplished by an enhanced correlation along the contour.
Photonic Crystal Biosensor Based on Optical Surface Waves
Valery N. Konopsky,Tanya Karakouz,Elena V. Alieva,Chiara Vicario,Sergey K. Sekatskii,Giovanni Dietler
Sensors , 2013, DOI: 10.3390/s130202566
Abstract: A label-free biosensor device based on registration of photonic crystal surface waves is described. Angular interrogation of the optical surface wave resonance is used to detect changes in the thickness of an adsorbed layer, while an additional simultaneous detection of the critical angle of total internal reflection provides independent data of the liquid refractive index. The abilities of the device are demonstrated by measuring of biotin molecule binding to a streptavidin monolayer, and by measuring association and dissociation kinetics of immunoglobulin G proteins. Additionally, deposition of PSS / PAH polyelectrolytes is recorded in situ resulting calculation of PSS and PAH monolayer thicknesses separately.
Scaling exponents and probability distributions of DNA end-to-end distance
Francesco Valle,Melanie Favre,Paolo De Los Rios,Angelo Rosa,Giovanni Dietler
Physics , 2005, DOI: 10.1103/PhysRevLett.95.158105
Abstract: Correlation length exponent $\nu$ for long linear DNA molecules was determined by direct measurement of the average end-to-end distance as a function of the contour length $s$ by means of atomic force microscopy (AFM). Linear DNA, up to 48'502 base pairs (bp), was irreversibly deposited from a solution onto silanized mica and imaged in air. Under the adsorption conditions used, the DNA is trapped onto the surface without any two-dimensional equilibration. The measured exponent is $\nu = 0.589 \pm 0.006$, in agreement with the theoretical 3D value of $\nu = 0.5880 \pm 0.0010$. The persistence length $\ell_p$ of DNA was estimated to be 44$\pm$3 nm, in agreement with the literature values. The distribution of the end-to-end distances for a given contour length $s$ and the exponents characterizing the distribution were determined for different $s$. For $s$ smaller or comparable to $\ell_p$, a delta function like distribution was observed, while for larger $s$, a probability distribution of the type $x^{d-1}x^g e^{-bx^\delta}$ was observed with $g=0.33\pm0.22$ and $\delta=2.58\pm0.76$. These values are compared to the theoretical exponents for Self-Avoiding Walk (SAW): namely $g=\frac{\gamma-1}{\nu}$ and $\delta=(1-\nu)^{-1}$. So for $d=2$, $g\approx0.44$ and $\delta=4$, while for $d=3$, $g\approx0.33$ and $\delta\approx2.5$. The derived entropic exponent $\gamma$ is $\gamma=1.194\pm0.129$. The present data indicate that the DNA behaves on large length scales like a 3 dimensional SAW.
Functional Dynamics of PDZ Binding Domains: A Normal Mode Analysis
Paolo De Los Rios,Fabio Cecconi,Anna Pretre,Giovanni Dietler,Olivier Michielin,Francesco Piazza,Brice Juanico
Quantitative Biology , 2005,
Abstract: PDZ (Post-synaptic density-95/discs large/zonula occludens-1) domains are relatively small (80 to 120 residues) protein binding modules central in the organization of receptor clusters and in the association of cellular proteins. Their main function is to bind C-terminals of selected proteins that are recognized through specific amino-acids in their carboxyl end. Binding is associated with a deformation of the PDZ native structure and is responsible for dynamical changes in regions not in direct contact with the target. We investigate how this deformation is related to the harmonic dynamics of the PDZ structure and show that one low-frequency collective normal mode, characterized by the concerted movements of different secondary structures, is involved in the binding process. Our results suggest that even minimal structural changes are responsible of communication between distant regions of the protein, in agreement with recent Nuclear Magnetic Resonance (NMR) experiments. Thus PDZ domains are a very clear example of how collective normal modes are able to characterize the relation between function and dynamics of proteins, and to provide indications on the precursors of binding/unbonding events.
Nanoscale spatially resolved infrared spectra from single microdroplets
Thomas Müller,Francesco Simone Ruggeri,Andrzej J. Kulik,Ulyana Shimanovich,Thomas O. Mason,Tuomas P. J. Knowles,Giovanni Dietler
Physics , 2014, DOI: 10.1039/C3LC51219C
Abstract: Droplet microfluidics has emerged as a powerful platform allowing a large number of individual reactions to be carried out in spatially distinct microcompartments. Due to their small size, however, the spectroscopic characterisation of species encapsulated in such systems remains challenging. In this paper, we demonstrate the acquisition of infrared spectra from single microdroplets containing aggregation-prone proteins. To this effect, droplets are generated in a microfluidic flow-focussing device and subsequently deposited in a square array onto a ZnSe prism using a micro stamp. After drying, the solutes present in the droplets are illuminated locally by an infrared laser through the prism, and their thermal expansion upon absorption of infrared radiation is measured with an atomic force microscopy tip, granting nanoscale resolution. Using this approach, we resolve structural differences in the amide bands of the spectra of monomeric and aggregated lysozyme from single microdroplets with picolitre volume.
Fractal Dimension and Localization of DNA Knots
Erika Ercolini,Francesco Valle,Jozef Adamcik,Guillaume Witz,Ralf Metzler,Paolo De Los Rios,Joaquim Roca,Giovanni Dietler
Physics , 2006, DOI: 10.1103/PhysRevLett.98.058102
Abstract: The scaling properties of DNA knots of different complexities were studied by atomic force microscope. Following two different protocols DNA knots are adsorbed onto a mica surface in regimes of (i) strong binding, that induces a kinetic trapping of the three-dimensional (3D) configuration, and of (ii) weak binding, that permits (partial) relaxation on the surface. In (i) the gyration radius of the adsorbed DNA knot scales with the 3D Flory exponent $\nu\approx 0.58$ within error. In (ii), we find $\nu\approx 0.66$, a value between the 3D and 2D ($\nu=3/4$) exponents, indicating an incomplete 2D relaxation or a different polymer universality class. Compelling evidence is also presented for the localization of the knot crossings in 2D.
Spontaneous Rupture of an Adrenal Artery in Pregnancy: A Case Report
D. Bolla,V. Schyrba,G. Drack,S. Dietler
Case Reports in Obstetrics and Gynecology , 2012, DOI: 10.1155/2012/859068
Spontaneous Rupture of an Adrenal Artery in Pregnancy: A Case Report
D. Bolla,V. Schyrba,G. Drack,S. Dietler,R. Hornung
Case Reports in Obstetrics and Gynecology , 2012, DOI: 10.1155/2012/859068
Abstract: A spontaneous rupture of an adrenal artery is a rare cause of abdominal pain in pregnancy. We present a case of a pregnant woman who needed to be operated on because of a rupture of the right adrenal artery associated with a fetal bradycardia. An immediate caesarean section was performed. The intra-abdominal palpation identified an extensive retroperitoneal mass near the right kidney and a postoperative computer tomography confirmed an active bleeding near the kidney. For this reason our interventional radiology team, using a right femoral artery approach, performed a flush aortogram and identified the source of bleeding in the right adrenal artery. After two attempts, a coiling of the artery stopped the haemorrhage. The pathogenesis of arterial haemorrhage is still poorly understood although a possible cause could be the excess of hormones during pregnancy, which can lead to a significant arterial wall degeneration. In case of a retroperitoneal bleeding and if the patient is still haemodynamically stable, a transcatheter embolization using microcoils must be considered. This technique is nowadays safe and effective and can be performed within a short time with a lower risk of complications. 1. Introduction A spontaneous rupture of an adrenal artery is extremely rare in pregnancy. In the literature, only a few cases of rupture of an adrenal artery have been reported [1–3]. The frequency, in nonpregnant women, varies from 0.03% to 1.8% of all visceral aneurysms [2]. The most common localization of visceral aneurysms is the celiac followed by mesenteric, hepatic, and splenic arteries [4]. We present a further case of a spontaneous rupture of the right adrenal artery, which was detected after a caesarean delivery performed because of a fetal bradycardia. 2. Case A 28-year-old gravida 1 with an uneventful course of pregnancy and no history of a trauma was referred to our hospital because of an unclear retroperitoneal mass. This was diagnosed at a nearby hospital where the patient had presented with an acute right-sided abdominal pain at 32 1/7 weeks of gestation. By admission in the referral hospital, she had an unremarkable medical history without evidence of trauma. There was no vaginal bleeding or uterine activity, but fetal bradycardia was detected. An immediate caesarean section was performed under general anaesthesia. A female newborn, weighing 1970?g, was delivered with an Apgar score of 0 at 1 minute, 1 at 5 minutes, and 5 at 10 minutes, respectivly. The pH from the umbilical artery was 6.88. The placenta showed no signs of haemorrhage. The
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