453 research outputs found
Position and Mode Dependent Optical Detection Back-Action in Cantilever Beam Resonators
Optical detection back-action in cantilever resonant or static detection
presents a challenge when striving for state-of-the-art performance. The origin
and possible routes for minimizing optical back-action have received little
attention in literature. Here, we investigate the position and mode dependent
optical back-action on cantilever beam resonators. A high power heating laser
(100 {\mu}W) is scanned across a silicon nitride cantilever while its effect on
the first three resonance modes is detected via a low-power readout laser (1
{\mu}W) positioned at the cantilever tip. We find that the measured effect of
back-action is not only dependent on position but also the shape of the
resonance mode. Relevant silicon nitride material parameters are extracted by
fitting the temperature-dependent frequency response of the first three modes
to finite element (FE) simulations. In a second round of simulations, using the
extracted parameters, we successfully fit the FEM results with the measured
mode and position dependent back-action. Finally, different routes for
minimizing the effect of this optical detection back-action are described,
allowing further improvements of cantilever-based sensing in general
Non-linear optomechanical measurement of mechanical motion
Precision measurement of non-linear observables is an important goal in all
facets of quantum optics. This allows measurement-based non-classical state
preparation, which has been applied to great success in various physical
systems, and provides a route for quantum information processing with otherwise
linear interactions. In cavity optomechanics much progress has been made using
linear interactions and measurement, but observation of non-linear mechanical
degrees-of-freedom remains outstanding. Here we report the observation of
displacement-squared thermal motion of a micro-mechanical resonator by
exploiting the intrinsic non-linearity of the radiation pressure interaction.
Using this measurement we generate bimodal mechanical states of motion with
separations and feature sizes well below 100~pm. Future improvements to this
approach will allow the preparation of quantum superposition states, which can
be used to experimentally explore collapse models of the wavefunction and the
potential for mechanical-resonator-based quantum information and metrology
applications.Comment: 8 pages, 4 figures, extensive supplementary material available with
published versio
Procathepsin D cannot autoactivate to cathepsin D at acid pH
AbstractThe amino acid sequence of the propart of bovine procathepsin D was determined at the protein level. Incubation of the isolated procathepsin D at pH 3.5â5.0 for 30â120 min leads to a 2 kDa reduction in its molecular mass, as seen by SDS-PAGE. The activation product is pseudocathepsin D and is the result of a proteolytic cleavage between LeuP26 and IleP27 in the propart. Incubation at pH 5.0 for 20 h of either procathepsin D or pseudocathepsin D results in both cases in approximately equal amounts of pseudocathepsin D and a further processed intermediate, nine amino acids shorter than pseudocathepsin D. No reaction products corresponding to cathepsin D with a mature amino terminus were observed, showing that autoproteolysis alone cannot generate the mature form found in the lysosomes
Adsorption and Vibrational Study of Folic Acid on Gold Nanopillar Structures Using Surface-enhanced Raman Scattering Spectroscopy
This paper presents a study of adsorption and vibrational features of folic acid, using surface-enhanced Raman scattering (SERS). A gold-capped silicon nanopillar (Au NP) with a height of 600 nm and a width of 120 nm was utilized to study the vibrational features of FA molecules adsorbed on the nanopillars within the high electromagnetic field areas. The adsorption behaviour of folic acid and the band assignment of the main vibrations together with the optimized geometry of folic acid and folic acid in the presence of a cluster of 10 gold atoms were assessed using the density functional theory (B3LYP(6-31G(d))) and the scalar relativistic effective core potential with a double-zeta basis set (LANL2DZ). The vibrations obtained from the solid-state folic acid and the folic acid on a gold cluster were in accordance with those observed experimentally. The analysis of the main vibrations indicated that the interaction of folic acid with the Au NP occurred primarily through the nitrogen atoms, from their pteridine ring. Finally, the obtained adsorption isotherm for folic acid was deduced from the analysis of the SERS spectra and it followed a negative cooperative binding model
New Evidence for the Mechanism of Action of a Type-2 Diabetes Drug Using a Magnetic Bead-Based Automated Biosensing Platform
The mechanism of
action (MOA) of the first line type-2 diabetes
drug metformin remains unclear despite its widespread usage. However,
recent evidence suggests that the mitochondrial copper (Cu)-binding
action of metformin may contribute toward the drugâs MOA. Here,
we present a novel biosensing platform for investigating the MOA of
metformin using a magnetic microbead-based agglutination assay which
has allowed us to demonstrate for the first time the interaction between
Cu and metformin at clinically relevant low micromolar concentrations
of the drug, thus suggesting a potential pathway of metforminâs
blood-glucose lowering action. In this assay, cysteine-functionalized
magnetic beadswere agglutinated in the presence of Cu due to cysteineâs
Cu-chelation property. Addition of clinically relevant doses of metformin
resulted in disaggregation of Cu-bridged bead-clusters, whereas the
effect of adding a closely related but blood-glucose neutral drug
propanediimidamide (PDI) showed completely different responses to
the clusters. The entire assay was integrated in an automated microfluidics
platform with an advanced optical imaging unit by which we investigated
these aggregationâdisaggregation phenomena in a reliable, automated,
and user-friendly fashion with total assay time of 17 min requiring
a sample (metformin/PDI) volume of 30 ÎŒL. The marked difference
of Cu-binding action between the blood-glucose lowering drug metformin
and its inactive analogue PDI thus suggests that metforminâs
distinctive Cu-binding properties may be required for its effect on
glucose homeostasis. The novel automated platform demonstrating this
novel investigation thus holds the potential to be utilized for investigating
significant and sensitive molecular interactions via magnetic bead-based
agglutination assay
Temperature-Modulated Micromechanical Thermal Analysis with Microstring Resonators Detects Multiple Coherent Features of Small Molecule Glass Transition
Present and future of surface-enhanced Raman scattering
The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article
Orientation of Pterin-6-Carboxylic Acid on Gold Capped Silicon Nanopillars Platforms: Surface Enhanced Raman Spectroscopy and Density Functional Theory Studies
The orientation of pterin-6-carboxylic acid on gold nanopillars was investigated by surface enhanced Raman spectroscopy and density functional theory methods. The experimentally vibrations from pterin-6-COOH free and attached to the Au surface display vibration features indicating chemical interaction of the pterin with the metal surface. The spectral feature evidenced that the pterin would adsorb on gold surface with a "lying down" configuration through the high intensity vibration of NH scissoring and rocking OH modes. The orientation study of pterins on gold nanopillars presented herein is believed to lead to new applications in biosensing field for detecting pterins of physiological importance
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