Svetlana Erokhina

Electrochemical control of the conductivity in an organic memristor: a time-resolved X-ray fluorescence study of ionic drift as a function of the applied voltage.

Grazing-incidence X-ray fluorescence measurements were applied for a time-resolved study of an organic memristor conductivity variation mechanism. A comparison of these results with electrical measurements has allowed us to conclude that the variation of the fluorescence intensity of Rb ions is directly connected to the ionic charge transferred between the conducting polymer and the solid electrolyte, which made up the device. In addition, the conductivity of the memristor was shown to be a function of the transferred ionic charge.

Light-Driven Release from Polymeric Microcapsules Functionalized with Bacteriorhodopsin

Bacteriorhodopsin was incorporated into the shell of polymeric capsules. Light-driven variation of intercapsule volume pH with successive pore opening was demonstrated by scanning electron microscopy. Release of the encapsulated dye molecules was studied by confocal fluorescence microscopy.

Collagen containing microcapsules: smart containers for disease controlled therapy.

The protein collagen is the major component of connective tissue and it is involved in many biological functions. Its degradation is at the basis of different pathological processes. The up-regulated expression of matrix metalloproteinases and the down-regulated expression of their inhibitors are the causes for such degradation. The aim of this work was to evaluate the possibility to fabricate collagen based containers for drug encapsulation and release by cellular demand by the action of matrix metalloproteinases. In present work collagen type I based microcapsules were fabricated by means of the layer-by-layer assembly of oppositely charged collagen and poly (stirene sulfonate) onto colloidal particles, followed by removal of the cores to obtain hollow microcapsules. The process of shell growth on planar supports was monitored by quartz crystal microbalance. X-ray reflectivity measurements were carried out at the solid/water interface to study the interaction of matrix metalloproteinase 1 with LbL films of collagen. The morphology of hollow capsules was characterized by scanning electron microscopy, and compared to that of capsules exposed to the matrix metalloproteinase 1. Finally the matrix metalloproteinase 1 mediated permeability of capsules variation was studied by Confocal Laser Scanning Microscopy. The results demonstrated the possibility to fabricate a drug delivery system where the release of the drug is dependent on the biochemistry of the pathological state.

X-Ray Reflectivity Measurements of Layer-by-Layer Films at the Solid/Liquid Interface

In this Letter, we present a method for the decoration of layer-by-layer (LbL) structures by heavy metal ions, which allows X-ray reflectivity (XRR) measurements at the solid/water interface. The improved contrast has allowed us to obtain well-structured X-ray reflectivity curves from samples at the liquid/solid interface that can be used for the film structure modeling. The developed technique was also used to follow the formation of complexes between DNA and the LbL multilayer. The XRR data are confirmed by independent null-ellipsometric measurements at the solid/liquid interface on the very same architectures.

Electrical properties of thin copper sulfide films produced by the aggregation of nanoparticles formed in LB precursor

Abstract The present work is dedicated to the formation and characterization of copper sulfide layers. Nanoparticles of CuS were formed by exposing the deposited LB films of copper stearate to the H2S atmosphere for at least 12 h. The aggregation of the nanoparticles into thin layers was performed by washing the sample with chloroform after the reaction for removing stearic acid molecules. Electrical properties of CuS layers of different thickness were examined. The dependence of an electrical conductivity upon the frequency was observed. The electrical conductivity is strongly dependent upon the frequency when the thickness of the precursor copper stearate LB films is less than 30 bilayers. For such thickness the resultant aggregated layer is not continuous one and can be considered as a film of ‘islands’ separated one from the other. This fact is responsible for the increase of conductivity with frequency. Linear voltage–current characteristics with practically no dependence of the conductivity on frequency were measured for the films, obtained from more than 30 bilayers of the precursor. Typical resistivity of such layers was less than 1.0 Ω cm.

Polyaniline-based organic memristive device fabricated by layer-by-layer deposition technique

Memristors and memristive devices represent a splendid area of research due to the unique possibilities for the realization of new types of computer hardware elements and mimicking several essential properties of the nervous system of living beings. The organic memristive device was developed as an electronic single-device analogue of the synapse, suitable for the realization of circuits allowing Hebbian type of learning. This work is dedicated to the realization of the active channel of organic memristive devices by polyelectrolyte self-assembling (layer-by-layer technique). Stable and reproducible electrical characteristics of the device were obtained when the thickness of the active channel was more than seven bilayers. The device revealed rectifying behaviour and the presence of hysteresis—important properties for the realization of neuromorphic systems with synapse-like properties of the individual elements. Compared to previously reported results on organic memristive devices fabricated using other methods, the present device does not require any additional doping that is usually performed through acid treatment. Such a behaviour is extremely important for the cases in which biological systems (nervous cells, slime mould, etc.) must be interfaced with the system of organic memristive devices, since acid treatment can kill living beings.

Organic Memristors and Adaptive Networks

We describe the organic memristor – an element which varies its conductance according to the history of its previous involvement into the signal transfer processes. After the presentation of basic principles and fundamental properties, we present the architecture of the organization of model networks, capabale to learning. Finally, we discuss the possible ways, alternative to the currently existing lithography-based technologies, that would result in the fabrication of statistically organized fiber networks of such elements.

Skeleton-supported stochastic networks of organic memristive devices: Adaptations and learning

Stochastic networks of memristive devices were fabricated using a sponge as a skeleton material. Cyclic voltage-current characteristics, measured on the network, revealed properties, similar to the organic memristive device with deterministic architecture. Application of the external training resulted in the adaptation of the network electrical properties. The system revealed an improved stability with respect to the networks, composed from polymer fibers.

Layer-by-layer technique for the fabrication of organic memristors and neuromorphic systems

Layer-by-layer polyelectrolyte self assembling is a very promising techniques for the realization of organic films with nm resolution in thickness. We report here the application of the technique for the realization of active layers of organic memristors and for the realization of stochastic systems with learning properties. In particular, active channels of the memristive devices were fabricated by the deposition of alternating layers of polyaniline and polystyrene sulfonate. The advantage of the method is connected to the fact that additional doping is not required. Stochastic networks were formed on porous supports and revealed the adaptation of properties according to the applied external training procedures.

Nanoengineered polymeric capsules for bio-computing

Nanoengineered polymeric capsules are currently widely used in the drug design sector. In this paper, we present data, allowing to consider this objects as important elements of bio-computers, allowing, in particular, targeted delivery and smart release of the “main program” (special molecular preparations) to zones, where the adequate functioning of the system can be affected by undesirable events.