90 research outputs found
Light-Triggered Electron Transfer between a Conjugated Polymer and Cytochrome C for Optical Modulation of Redox Signaling
Protein reduction/oxidation processes trigger and finely regulate a myriad of physiological and pathological cellular functions. Many biochemical and biophysical stimuli have been recently explored to precisely and effectively modulate intracellular redox signaling, due to the considerable therapeutic potential. Here, we propose a first step toward an approach based on visible light excitation of a thiophene-based semiconducting polymer (P3HT), demonstrating the realization of a hybrid interface with the Cytochrome c protein (CytC), in an extracellular environment. By means of scanning electrochemical microscopy and spectro-electrochemistry measurements, we demonstrate that, upon optical stimulation, a functional interaction between P3HT and CytC is established. Polymer optical excitation locally triggers photoelectrochemical reactions, leading to modulation of CytC redox activity, either through an intermediate step, involving reactive oxygen species formation, or via a direct photoreduction process. Both processes are triggered by light, thus allowing excellent spatiotemporal resolution, paving the way to precise modulation of protein redox signaling
Micro- and Nanopatterned Silk Substrates for Antifouling Applications
A major problem of current biomedical implants is the bacterial colonization and subsequent biofilm formation, which seriously affects their functioning and can lead to serious post-surgical complications. Intensive efforts have been directed toward the development of novel technologies that can prevent bacterial colonization while requiring minimal antibiotics doses. To this end, biocompatible materials with intrinsic antifouling capabilities are in high demand. Silk fibroin, widely employed in biotechnology, represents an interesting candidate. Here, we employ a soft-lithography approach to realize micro- and nanostructured silk fibroin substrates, with different geometries. We show that patterned silk film substrates support mammal cells (HEK-293) adhesion and proliferation, and at the same time, they intrinsically display remarkable antifouling properties. We employ Escherichia coli as representative Gram-negative bacteria, and we observe an up to 66% decrease in the number of bacteria that adhere to patterned silk surfaces as compared to control, flat silk samples. The mechanism leading to the inhibition of biofilm formation critically depends on the microstructure geometry, involving both a steric and a hydrophobic effect. We also couple silk fibroin patterned films to a biocompatible, optically responsive organic semiconductor, and we verify that the antifouling properties are very well preserved. The technology described here is of interest for the next generation of biomedical implants, involving the use of materials with enhanced antibacterial capability, easy processability, high biocompatibility, and prompt availability for coupling with photoimaging and photodetection techniques
Role of Interfaces in the Proximity Effect in Anisotropic Superconductors
We report measurements of the critical temperature of YBCO-Co doped YBCO
Superconductor-Normal bilayer films. Depending on the morphology of the S-N
interface, the coupling between S and N layers can be turned on to depress the
critical temperature of S by tens of degrees, or turned down so the layers
appear almost totally decoupled. This novel effect can be explained by the
mechanism of quasiparticle transmission into an anisotropic superconductor.Comment: 13 pages, 3 figure
Vicariance in a generalist fish parasite driven by climate and salinity tolerance of hosts
Acanthocephalans are parasites with complex lifecycles that are important components of
aquatic systems and are often model species for parasite-mediated host manipulation.
Genetic characterization has recently resurrected Pomphorhynchus tereticollis as a distinct species from Pomphorhynchus laevis, with potential implications for fisheries management and
host manipulation research. Morphological and molecular examinations of parasites from 7
English rivers across 9 fish species revealed that P. tereticollis was the only Pomphorhynchus
parasite present in Britain, rather than P. laevis as previously recorded. Molecular analyses
included two non-overlapping regions of the mitochondrial gene â cytochrome oxidase
and generated 62 sequences for the shorter fragment (295 bp) and 74 for the larger fragment
(583 bp). These were combined with 61 and 13 sequences respectively, from Genbank. A
phylogenetic analysis using the two genetic regions and all the DNA sequences available
for P. tereticollis identified two distinct genetic lineages in Britain. One lineage, possibly associated with cold water tolerant fish, potentially spread to the northern parts of Britain from
the Baltic region via a northern route across the estuarine area of what is now the North
Sea during the last Glaciation. The other lineage, associated with temperate freshwater fish,
may have arrived later via the Rhine/Thames fluvial connection during the last glaciation
or early Holocene when sea levels were low. These results raise important questions on this
generalist parasite and its variously environmentally adapted hosts, and especially in relation
to the consequences for parasite vicariance
Normal-superconducting transition induced by high current densities in YBa2Cu3O7-d melt-textured samples and thin films: Similarities and differences
Current-voltage characteristics of top seeded melt-textured YBa2Cu3O7-d are
presented. The samples were cut out of centimetric monoliths. Films
characteristics were also measured on microbridges patterned on thin films
grown by dc sputtering. For both types of samples, a quasi-discontinuity or
quenching was observed for a current density J* several times the critical
current density Jc. Though films and bulks much differ in their magnitude of
both Jc and J*, a proposal is made as to a common intrinsic origin of the
quenching phenomenon. The unique temperature dependence observed for the ratio
J*/Jc, as well as the explanation of the pre-quenching regime in terms of a
single dissipation model lend support to our proposal.Comment: 10 pages, 10 figures, submitted to Physical Review
Field-effect and capacitive properties of water-gated transistors based on polythiophene derivatives
Recently, water-gated organic field-effect transistors (WGOFET) have been intensively studied for their application in the biological field. Surprisingly, a very limited
number of conjugated polymers have been reported so far. Here, we systematically explore a series of polythiophene derivatives, presenting different alkyl side chains
lengths and orientation, and characterized by various morphologies: comparative evaluation of their performances allows highlighting the critical role played by alkyl side chains, which significantly affects the polymer/water interface capacitance. Reported results provide useful guidelines towards further development of WGOFETs and represent a step forward in the understanding of the polymer/water interface phenomena
Current-induced highly dissipative domains in high Tc thin films
We have investigated the resistive response of high Tc thin films submitted
to a high density of current. For this purpose, current pulses were applied
into bridges made of Nd(1.15)Ba(1.85)Cu3O7 and Bi2Sr2CaCu2O8. By recording the
time dependent voltage, we observe that at a certain critical current j*, a
highly dissipative domain develops somewhere along the bridge. The successive
formation of these domains produces stepped I-V characteristics. We present
evidences that these domains are not regions with a temperature above Tc, as
for hot spots. In fact this phenomenon appears to be analog to the nucleation
of phase-slip centers observed in conventional superconductors near Tc, but
here in contrast they appear in a wide temperature range. Under some
conditions, these domains will propagate and destroy the superconductivity
within the whole sample. We have measured the temperature dependence of j* and
found a similar behavior in the two investigated compounds. This temperature
dependence is just the one expected for the depairing current, but the
amplitude is about 100 times smaller.Comment: 9 pages, 9 figures, Revtex, to appear in Phys. Rev.
Environmental DNA as a nonâinvasive sampling tool to detect the spawning distribution of European anadromous shads (Alosa spp.)
1. Populations of the European shads Alosa alosa (Linnaeus, 1758) and Alosa fallax LacĂ©pĂšde, 1800 (Alosa spp.) are protected under legislation because of their vulnerability to human disturbances. In particular, river impoundments block their upstream migration, preventing access to spawning areas. Knowledge on the spatial extent of their spawning is important for informing conservation and river management plans. 2. Determining the spatial extent of Alosa spp. spawning is challenging. They enter rivers over a 2â3âmonth period and the species potentially migrate different distances upstream. Capture and handling can be problematic, spawning events generally occur at night, and kickâsampling for eggs is limited to shallow water. Assessing their spatial extent of spawning could, however, incorporate nonâinvasive sampling tools, such as environmental DNA (eDNA). 3. An eDNA assay for Alosa spp. was successfully developed, based on the cytochrome c oxidase subunit I gene segment and quantitative polymerase chain reaction (qPCR). Application in spring 2017 to the River Teme (River Severn catchment, western England) revealed high sensitivity in both laboratory and field trials. Field data indicated Alosa spp. spawning between May and June, with migrants mainly restricted to areas downstream of the final impoundment. 4. eDNA can thus be used as a nonâinvasive sampling tool to determine the freshwater distribution of these fishes in Europe, enhancing their conservation at local and regional scales
Teleology and Realism in Leibniz's Philosophy of Science
This paper argues for an interpretation of Leibnizâs claim that physics requires both mechanical and teleological principles as a view regarding the interpretation of physical theories. Granting that Leibnizâs fundamental ontology remains non-physical, or mentalistic, it argues that teleological principles nevertheless ground a realist commitment about mechanical descriptions of phenomena. The empirical results of the new sciences, according to Leibniz, have genuine truth conditions: there is a fact of the matter about the regularities observed in experience. Taking this stance, however, requires bringing non-empirical reasons to bear upon mechanical causal claims. This paper first evaluates extant interpretations of Leibnizâs thesis that there are two realms in physics as describing parallel, self-sufficient sets of laws. It then examines Leibnizâs use of teleological principles to interpret scientific results in the context of his interventions in debates in seventeenth-century kinematic theory, and in the teaching of Copernicanism. Leibnizâs use of the principle of continuity and the principle of simplicity, for instance, reveal an underlying commitment to the truth-aptness, or approximate truth-aptness, of the new natural sciences. The paper concludes with a brief remark on the relation between metaphysics, theology, and physics in Leibniz
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