195 research outputs found
Synthesis of Curcumin Derivatives and Analysis of Their Antitumor Effects in Triple Negative Breast Cancer (TNBC) Cell Lines
We analyzed antitumor effects of a series of curcumin analogues. Some of them were obtained by reaction of substitution involving the two phenolic OH groups of curcumin while the analogues with a substituent at C-4 was prepared following an original procedure that regards the condensation of benzenesulfenic acid onto the nucleophilic central carbon of the curcumin skeleton. We analyzed cytotoxic effects of such derivatives on two TNBC (triple negative breast cancer) cell lines, SUM 149 and MDA-MB-231, but only three of them showed an IC50 in a lower micromolar range with respect to curcumin. We also focused on these three derivatives that in both cell lines exhibited a higher or at least equivalent pro-apoptotic effect than curcumin. The analysis of molecular mechanisms of action of the curcumin derivatives under study has highlighted that they decreased NF-κB transcriptional factor activity, and consequently the expression of some NF-κB targets. Our data confirmed once again that curcumin may represent a very good lead compound to design analogues with higher antitumor capacities and able to overcome drug resistance with respect to conventional ones, even in tumors difficult to treat as TNBC
Magnetic resonance imaging sequence evaluation of an MR Linac system; early clinical experience.
Objectives:To systematically identify the preferred magnetic resonance imaging (MRI) sequences following volunteer imaging on a 1.5 Tesla (T) MR-Linear Accelerator (MR Linac) for future protocol development. Methods:Non-patient volunteers were recruited to a Research and Ethics committee approved prospective MR-only imaging study on a 1.5T MR Linac system. Volunteers attended 1-3 imaging sessions that included a combination of mDixon, T1w, T2w sequences using 2-dimensional (2D) and 3-dimensional (3D) acquisitions. Each sequence was acquired over 2-7 minutes and reviewed by a panel of 3 observers to evaluate image quality using a visual grading analysis based on a 4-point Likert scale. Sequences were acquired and modified iteratively until deemed fit for purpose (online image matching or re-planning) and all observers agreed they were suitable in 3 volunteers. Results:26 volunteers underwent 31 imaging sessions of six general anatomical regions. Images were acquired in one or two of six general anatomical regions: male pelvis (n = 9), female pelvis (n = 4), chestwall/breast (n = 5), lung/oesophagus (n = 5), abdomen (n = 3) and head and neck (n = 5). Images were acquired using a pre-defined exam-card that on average, included six sequences (range 2-10), with a maximum scan time of approximately one hour. The majority of observers preferred T2-weighted sequences. The thorax teams were the only groups to prefer T1-weighted imaging. Conclusions:An iterative process identified sequence agreement in all anatomical regions. These sequences will now be evaluated in patient volunteers. Advances in knowledge:This manuscript is the first publication sharing the results of the first systematic selection of MRI sequences for use in on-board MRI-guided radiotherapy by end-users (therapeutic radiographers and clinical oncologists) in healthy volunteers
Uniaxial strain in graphene by Raman spectroscopy: G peak splitting, Grüneisen parameters, and sample orientation
Graphene is the two-dimensional building block for carbon allotropes of every
other dimensionality. Since its experimental discovery, graphene continues to
attract enormous interest, in particular as a new kind of matter, in which
electron transport is governed by a Dirac-like wave equation, and as a model
system for studying electronic and phonon properties of other, more complex,
graphitic materials[1-4]. Here, we uncover the constitutive relation of
graphene and probe new physics of its optical phonons, by studying its Raman
spectrum as a function of uniaxial strain. We find that the doubly degenerate
E2g optical mode splits in two components, one polarized along the strain and
the other perpendicular to it. This leads to the splitting of the G peak into
two bands, which we call G+ and G-, by analogy with the effect of curvature on
the nanotube G peak[5-7]. Both peaks red shift with increasing strain, and
their splitting increases, in excellent agreement with first-principles
calculations. Their relative intensities are found to depend on light
polarization, which provides a useful tool to probe the graphene
crystallographic orientation with respect to the strain. The singly degenerate
2D and 2D' bands also red shift, but do not split for small strains. We study
the Gruneisen parameters for the phonons responsible for the G, D and D' peaks.
These can be used to measure the amount of uniaxial or biaxial strain,
providing a fundamental tool for nanoelectronics, where strain monitoring is of
paramount importance[8, 9
Local Optical Probe of Motion and Stress in a multilayer graphene NEMS
Nanoelectromechanical systems (NEMSs) are emerging nanoscale elements at the
crossroads between mechanics, optics and electronics, with significant
potential for actuation and sensing applications. The reduction of dimensions
compared to their micronic counterparts brings new effects including
sensitivity to very low mass, resonant frequencies in the radiofrequency range,
mechanical non-linearities and observation of quantum mechanical effects. An
important issue of NEMS is the understanding of fundamental physical properties
conditioning dissipation mechanisms, known to limit mechanical quality factors
and to induce aging due to material degradation. There is a need for detection
methods tailored for these systems which allow probing motion and stress at the
nanometer scale. Here, we show a non-invasive local optical probe for the
quantitative measurement of motion and stress within a multilayer graphene NEMS
provided by a combination of Fizeau interferences, Raman spectroscopy and
electrostatically actuated mirror. Interferometry provides a calibrated
measurement of the motion, resulting from an actuation ranging from a
quasi-static load up to the mechanical resonance while Raman spectroscopy
allows a purely spectral detection of mechanical resonance at the nanoscale.
Such spectroscopic detection reveals the coupling between a strained
nano-resonator and the energy of an inelastically scattered photon, and thus
offers a new approach for optomechanics
Performance of Monolayer Graphene Nanomechanical Resonators with Electrical Readout
The enormous stiffness and low density of graphene make it an ideal material
for nanoelectromechanical (NEMS) applications. We demonstrate fabrication and
electrical readout of monolayer graphene resonators, and test their response to
changes in mass and temperature. The devices show resonances in the MHz range.
The strong dependence of the resonant frequency on applied gate voltage can be
fit to a membrane model, which yields the mass density and built-in strain.
Upon removal and addition of mass, we observe changes in both the density and
the strain, indicating that adsorbates impart tension to the graphene. Upon
cooling, the frequency increases; the shift rate can be used to measure the
unusual negative thermal expansion coefficient of graphene. The quality factor
increases with decreasing temperature, reaching ~10,000 at 5 K. By establishing
many of the basic attributes of monolayer graphene resonators, these studies
lay the groundwork for applications, including high-sensitivity mass detectors
Aharonov-Bohm interferences from local deformations in graphene
One of the most interesting aspects of graphene is the tied relation between
structural and electronic properties. The observation of ripples in the
graphene samples both free standing and on a substrate has given rise to a very
active investigation around the membrane-like properties of graphene and the
origin of the ripples remains as one of the most interesting open problems in
the system. The interplay of structural and electronic properties is
successfully described by the modelling of curvature and elastic deformations
by fictitious gauge fields that have become an ex- perimental reality after the
suggestion that Landau levels can form associated to strain in graphene and the
subsequent experimental confirmation. Here we propose a device to detect
microstresses in graphene based on a scanning-tunneling-microscopy setup able
to measure Aharonov-Bohm inter- ferences at the nanometer scale. The
interferences to be observed in the local density of states are created by the
fictitious magnetic field associated to elastic deformations of the sample.Comment: Some bugs fixe
Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapor Deposition
The strong interest in graphene has motivated the scalable production of high
quality graphene and graphene devices. Since large-scale graphene films
synthesized to date are typically polycrystalline, it is important to
characterize and control grain boundaries, generally believed to degrade
graphene quality. Here we study single-crystal graphene grains synthesized by
ambient CVD on polycrystalline Cu, and show how individual boundaries between
coalescing grains affect graphene's electronic properties. The graphene grains
show no definite epitaxial relationship with the Cu substrate, and can cross Cu
grain boundaries. The edges of these grains are found to be predominantly
parallel to zigzag directions. We show that grain boundaries give a significant
Raman "D" peak, impede electrical transport, and induce prominent weak
localization indicative of intervalley scattering in graphene. Finally, we
demonstrate an approach using pre-patterned growth seeds to control graphene
nucleation, opening a route towards scalable fabrication of single-crystal
graphene devices without grain boundaries.Comment: New version with additional data. Accepted by Nature Material
Etching and Narrowing of Graphene from the Edges
Large scale graphene electronics desires lithographic patterning of narrow
graphene nanoribbons (GNRs) for device integration. However, conventional
lithography can only reliably pattern ~20nm wide GNR arrays limited by
lithography resolution, while sub-5nm GNRs are desirable for high on/off ratio
field-effect transistors (FETs) at room temperature. Here, we devised a gas
phase chemical approach to etch graphene from the edges without damaging its
basal plane. The reaction involved high temperature oxidation of graphene in a
slightly reducing environment to afford controlled etch rate (\leq ~1nm/min).
We fabricated ~20-30nm wide GNR arrays lithographically, and used the gas phase
etching chemistry to narrow the ribbons down to <10nm. For the first time, high
on/off ratio up to ~10^4 was achieved at room temperature for FETs built with
sub-5nm wide GNR semiconductors derived from lithographic patterning and
narrowing. Our controlled etching method opens up a chemical way to control the
size of various graphene nano-structures beyond the capability of top-down
lithography.Comment: 18 pages, 4 figures, to appear in Nature Chemistr
Energy gaps, topological insulator state and zero-field quantum Hall effect in graphene by strain engineering
Among many remarkable qualities of graphene, its electronic properties
attract particular interest due to a massless chiral character of charge
carriers, which leads to such unusual phenomena as metallic conductivity in the
limit of no carriers and the half-integer quantum Hall effect (QHE) observable
even at room temperature [1-3]. Because graphene is only one atom thick, it is
also amenable to external influences including mechanical deformation. The
latter offers a tempting prospect of controlling graphene's properties by
strain and, recently, several reports have examined graphene under uniaxial
deformation [4-8]. Although the strain can induce additional Raman features
[7,8], no significant changes in graphene's band structure have been either
observed or expected for realistic strains of approx. 10% [9-11]. Here we show
that a designed strain aligned along three main crystallographic directions
induces strong gauge fields [12-14] that effectively act as a uniform magnetic
field exceeding 10 T. For a finite doping, the quantizing field results in an
insulating bulk and a pair of countercirculating edge states, similar to the
case of a topological insulator [15-20]. We suggest realistic ways of creating
this quantum state and observing the pseudo-magnetic QHE. We also show that
strained superlattices can be used to open significant energy gaps in
graphene's electronic spectrum
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