Twisting and buckling: a new undulation mechanism for artificial swimmers

We present an artificial swimmer consisting in a long cylinder of ferrogel which is polarized transversely and in opposite directions at each extremity. When it is placed on a water film and submitted to a transverse oscillating magnetic field, this artificial worm undulates and swims. Whereas symmetry breaking is due to the field gradient, the undulations of the worm result from a torsional buckling instability as the polarized ends tend to align with the applied magnetic field. The critical magnetic field above which buckling and subsequent swimming is observed may be predicted using elasticity equations including the effect of a magnetic torque. As the length of the worm is varied, several undulation modes are observed which are in good agreement with the bending modes of an elastic rod with free ends

Nager grâce à un mécanisme de torsion/flexion

Nous présentons un nageur artificiel qui progresse grâce à un mécanisme original. Il consiste en un cylindre de ferrogel polarisé transversalement et en sens opposé à ses extrémités. Placé à la surface d'un film d'eau et soumis à un champ magnétique oscillant, le ver ondule et nage. Alors que la brisure de symétrie résulte de l'inhomogénéité du champ magnétique, les ondulations du ver sont dues à une instabilité de torsion/flexion liée à l'alignement des moments magnétiques des extrémités avec le champ appliqué. Les ondes de flexion ainsi excitées régissent alors les modes de nage du ver

Nanopore surface coating delivers nanopore size and shape through conductance-based sizing

The performance of nanopore single-molecule sensing elements depends intimately on their physical dimensions and surface chemical properties. These factors underpin the dependence of the nanopore ionic conductance on electrolyte concentration, yet the measured, or modeled, dependence only partially illuminates the details of geometry and surface chemistry. Using the electrolyte-dependent conductance data before and after selective surface functionalization of solid-state nanopores, however, introduces more degrees of freedom and improves the performance of conductance-based nanopore characterizations. Sets of representative nanopore profiles were used to generate conductance data, and the nanopore shape and exact dimensions were identified, through conductance alone, by orders-of-magnitude 3 reductions in the geometry optimization metrics. The optimization framework could similarly be used to evaluate the nanopore surface coating thickness

Dendrimers in Nanoscale Confinement: The Interplay between Conformational Change and Nanopore Entrance

Hyperbranched dendrimers are nanocarriers for drugs, imaging agents, and catalysts. Their nanoscale confinement is of fundamental interest and occurs when dendrimers with bioactive payload block or pass biological nanochannels or when catalysts are entrapped in inorganic nanoporous support scaffolds. The molecular process of confinement and its effect on dendrimer conformations are, however, poorly understood. Here, we use single-molecule nanopore measurements and molecular dynamics simulations to establish an atomically detailed model of pore dendrimer interactions. We discover and explain that electrophoretic migration of polycationic PAMAM dendrimers into confined space is not dictated by the diameter of the branched molecules but by their size and generation-dependent compressibility. Differences in structural flexibility also rationalize the apparent anomaly that the experimental nanopore current read-out depends in nonlinear fashion on dendrimer size. Nanoscale confinement is inferred to reduce the protonation of the polycationic structures. Our model can likely be expanded to other dendrimers and be applied to improve the analysis of biophysical experiments, rationally design functional materials such as nanoporous filtration devices or nanoscale drug carriers that effectively pass biological pores

Transport de macromolécules à travers un pore nanométrique unique

Nous présentons dans ce travail une étude expérimentale du transport de différents polymères, neutres, chargés, et partiellement structurés à travers un pore protéique nanométique (l -Hémolysine du Staphylocoque doré). Dans un domaine où la taille des chaînes de polymères est comparable ou supérieure au diamètre du pore. Le pore est inséré dans une bicouche lipidique plane soumise à une différence de potentiel. Le passage de polymère est détecté électriquement en mesurant les fluctuations du courant électrique induite par la présence des chaînes dans le pore. Nous avons mis en évidence un seuil de concentration en régime semi-dilué permettant le passage de grandes chaînes neutres et flexibles de taille très supérieure devant le diamètre du pore. Le temps de passage de ces chaînes obtenu expérimentalement est en excellent accord avec celui décrit par le modèle de reptation. Cependant la dynamique des chaînes de taille comparable au diamètre du pore est anormalement ralentie comparée aux différentes prédictions théoriques. Nous avons prouvé expérimentalement l existence d un seuil en force ionique qui gouverne l entrée des chaînes chargées. Une chaîne chargée passe dans le pore seulement si l épaisseur du nuage de contre ions qui entour la chaîne est inférieure au diamètre du pore. Nous avons mis en évidence l existence d états intermédiaires correspondant à longue durée de vie dans des protéine partiellement repliées. De plus nous avons montré la coexistence de conformation dépliée et partiellement repliée pour une concentration donnée en agent dénaturant.An experimental study of the transport of various polymers chains, neutral, charged, and partially structured through a proteic nanopore ( -Hémolysin from Staphylococcus aureus) is presented in this work. In the domain where the size of the polymer chains is comparable or higher than the diameter of the pore. A proteinic pore is inserted in lipid bilayers subjected to an electrical tension. The passage of chains is detected electrically by measuring the electrical current fluctuation induced by the presence of chains in the pore. We observe a threshold of concentration in the semi-dilute regime allowing the passage of large neural flexible chains. The residence time of these chains obtained in experiments is in excellent agreement with that described by the model of reptation . However the dynamics of the chains of size comparable with the diameter of the pore is abnormally slowed down compared with the various theoretical predictions. We proved in experiments the existence of a threshold in ionic strength which controls the entry of the charged chains. A charged chain passes in the pore only if the thickness of the cloud of conter-ions around the chain is smaller than the diameter of the pore. We highlighted the existence of intermediate states corresponding to long life in protein partially folded. Moreover we showed the coexistence of conformation (unfolded and partially folded) for a given concentration of denaturing agent.EVRY-BU (912282101) / SudocSudocFranceF

Focus on Protein Unfolding Through Nanopores

International audienceIn this review, we focus only on the unfolding of proteins through nanopores. We introduce the principle of electrical detection with nanopores and how this technique provides information using an electric signal. We describe different pioneer studies on protein unfolding through protein channels and through solid-state nanopores. We discuss different methods to study protein unfolding at the single-molecule level and the advantages this new nanopore technique offers

Caractérisation de l'organisation moléculaire de polysaccharides par extrusion et confinement dans des Nanopores

Conférence du 15 au 18 Mai 2006. Communication par affiche