Patterning of conducting polymers using charged self-assembled monolayers

We introduce a new approach to pattern conducting polymers by combining oppositely charged conducting polymers on charged self-assembled monolayers (SAMs). The polymer resist pattern behaves as a physical barrier, preventing the formation of SAMs. The patterning processes were carried out using commercially available conducting polymers: a negatively charged PEDOT/PSS (poly(3,4-ethylene-dioxythiophene)/poly(4-stylenesulphonic acid)) and a positively charged polypyrrole (PPy). A bifunctional NH 2 (positively charged) or COOH (negatively charged) terminated alkane thiol or silane was directly self-assembled on a substrate (Au or SiO 2). A suspension of the conducting polymers (PEDOT/PSS and PPy) was then spin-coated on the top surface of the SAMs and allowed to adsorb on the oppositely charged SAMs via an electrostatic driving force. After lift-off of the polymer resist, i.e., poly(methyl methacrylate, PMMA), using acetone, the conducting polymers remained on the charged SAMs surface. Optical microscopy, Auger electron spectroscopy, and atomic force microscopy reveal that the prepared nanolines have low line edge roughness and high line width resolution. Thus, conducting polymer patterns with high resolution could be produced by simply employing charged bifunctional SAMs. It is anticipated that this versatile new method can be applied to device fabrication processes of various nano- and microelectronics.     

ELECTROACTIVE AND NANOSTRUCTURED POLYMERS AS SCAFFOLD MATERIALS FOR NEURONAL AND CARDIAC TISSUE ENGINEERING

Conducting polymer, polyaniline （PANI）, has been studied as a novel electroactive and electrically conductive material for tissue engineering applications. The biocompatibility of the conductive polymer can be improved by （i） covalently grafting various adhesive peptides onto the surface of prefabricated conducting polymer films or into the polymer structures during the synthesis, （ii） co-electrospinning or blending with natural proteins to form conducting nanofibers or films, and （iii） preparing conducting polymers using biopolymers, such as collagen, as templates. In this paper, we mainly describe and review the approaches of covalently attaching oligopeptides to PANI and electrospinning PANI-gelatin blend nanofibers. The employment of such modified conducting polymers as substrates for enhanced cell attachment, proliferation and differentiation has been investigated with neuronal PC-12 cells and H9c2 cardiac myoblasts. For the electrospun PANI- gelatin fibers, depending on the concentrations of PANI, H9c2 cells initially displayed different morphologies on the fibrous substrates, but after one week all cultures reached confluence of similar densities and morphologies. Furthermore, we observed, that conductive PANI, when maintained in an aqueous physiologic environment, retained a significant level of electrical conductivity for at least 100 h, even though this conductivity was decreasing over time. Preliminary data show that the application of micro-current stimulates the differentiation of PC-12 cells. All the results demonstrate the potential for using PANI as an electroactive polymer in the culture of excitable cells and open the possibility of using this material as an electroactive scaffold for cardiac and/or neuronal tissue engineering applications that require biocompatibility of conductive polymers.     

Photocurrent of purple membrane adsorbed onto a thin polymer film: action characteristics of the local anesthetics

The proton pumping activity of bacteriorhodopsin (bR) in the purple membrane adsorbed onto a thin polymer film as a solid support for electrical measurements has been examined in the presence of local anesthetics and 1-alcohols as an anesthetic model. This membrane adsorbed system provided high reproducibility of the photocurrents in bR due to the mechanical and the chemical stability and the electric properties of the thin polymer film. As the concentrations of the local anesthetics increased, the photocurrents generated by the proton pump of bR were cooperatively suppressed and the changes in the photocurrents were reversible. From the dose–response curves for the anesthetics, the concentration (EC₅₀) required for a 50% suppression showed a marked specificity in the order of lidocaine>bupivacaine>tetracaine>dibucaine. The suppression of the photocurrent in bR was more effective for the uncharged form of the local anesthetics than for the charged one. The absorption and fluorescence spectra suggested that the charged form of the anesthetics was bound to the purple membrane surface, while their uncharged form interacted with the hydrophobic portions of the purple membrane interior rather than with the membrane surface. From the dose–response curves for the 1-alcohols, an increase in hydrophobicity in their molecules effectively suppressed the photocurrent of bR. We found that the binding of hydrophobic organic cations such as tetracaine hydrochloride and bupivacaine hydrochloride to the blue membrane with loss of the proton pump, which was prepared by removal of the cations from the purple membrane, could regenerate the proton pumping activity. The photocurrent in bR in the purple membrane adsorbed onto a thin solid film sensitively responded to different local anesthetics.     

Polymer‐Based Surfaces Designed to Reduce Biofilm Formation: From Antimicrobial Polymers to Strategies for Long‐Term Applications

Contact‐active antimicrobial polymer surfaces bear cationic charges and kill or deactivate bacteria by interaction with the negatively charged parts of their cell envelope (lipopolysaccharides, peptidoglycan, and membrane lipids). The exact mechanism of this interaction is still under debate. While cationic antimicrobial polymer surfaces can be very useful for short‐term applications, they lose their activity once they are contaminated by a sufficiently thick layer of adhering biomolecules or bacterial cell debris. This layer shields incoming bacteria from the antimicrobially active cationic surface moieties. Besides discussing antimicrobial surfaces, this feature article focuses on recent strategies that were developed to overcome the contamination problem. This includes bifunctional materials with simultaneously presented antimicrobial and protein‐repellent moieties; polymer surfaces that can be switched from an antimicrobial, cell‐attractive to a cell‐repellent state; polymer surfaces that can be regenerated by enzyme action; degradable antimicrobial polymers; and antimicrobial polymer surfaces with removable top layers.     

In situ Raman spectroelectrochemical study of electrocatalytic processes at polyaniline modified electrodes: Redox vs. metal-like catalysis

Two processes of electrocatalytic oxidation of solution species at conducting polymer modified electrodes have been studied for the first time with in situ Resonance Raman spectroelectrochemical technique at a red laser excitation (λ = 632.8 nm), namely electrooxidation of hydroquinone at a sulfonated polyaniline modified electrode in an acidic solution and electrooxidation of ascorbic acid at polyaniline modified electrode in a pH-neutral solution. In both cases, characteristic Raman features have been identified for different redox forms of conducting polymers and changes in the net redox state of a polymer layer during electrooxidation of solution species have been studied. It has been shown that an increase in the concentration of oxidizable species causes an increase of the net content of a reduced form of polyaniline in the modifying layer. From this, the redox (vs. metal-like) mechanism of electrocatalysis at conducting polymer modified electrodes has been deduced.     

A ladder conjugated polymer transducer for solid-contact Cu2+-selective electrodes

In recent years, there has been a pronounced interest in solid-contact ion-selective electrodes （SC-ISEs）, with emphasis on the use of conducting polymers as ion-to-electron transducer. In this work, a ladder conjugated polymer, thieno[3,2-b]thiophene （LCPT）, was investigated in fabricating Cu2＋-selective electrodes for the first time. The resulting electrodes were characterized by electrochemical impedance spectroscopy （EIS）, chronopotentiometry, and the water layer test. Results proved that the active LCPT facilitates the ion-to-electron transduction, and avoids the detrimental aqueous layer formed at the interface of SC-ISEs.     

Adding Plasticizer Dispersible Conducting Polymer to the Ion-selective Membrane Composition – Revitalizing Single Piece Ion-selective Electrodes Concept

Typically, ion-selective electrodes used in current triggered electrochemical sensing apply a conducting polymer layer covered with an ion-selective membrane. In this work we propose an ion-selective membrane containing a dispersed conducting polymer. Thus obtained system allows elimination of the Achilles hell of heterogeneous ion-selective membranes containing solid particulates dispersed within the ion-selective polymeric membrane. The herein proposed system, even for high conducting polymer loading equal to 5 % w/w, is characterized with insensitivity towards redox interferences, as well as potentiometric detection limits, selectivity well comparable with that for other ion-selective electrodes constructions. Under voltammetric conditions, with increasing loading of the conducting polymer in the membrane cathodic peak potentials are shifted towards more negative values, yet the linear dependence of the peak potential on logarithm of concentration of the analyte in the solution is preserved.     

Chemical Reactivity of Polypyrrole and Its Relevance to Polypyrrole Based Electrochemical Sensors

One of the most frequently used conducting polymers, polypyrrole, can take part in chemical processes with typical components of ambient media: oxygen, acids, bases, redox reactants, water, and organic vapors; it can also incorporate nonreactive ions and surfactants from solutions. The influence of such processes on changes of the polymer structure, composition and on possible degradation is analyzed. The benefits and disadvantages of such processes for analytical characteristic of polypyrrole based electrochemical sensors are considered. This discussion is focused on potentiometric ion sensors, where polypyrrole is either a receptor membrane or an ion‐to‐electron transducer placed between a solid state electrode support and a typical ion‐selective membrane.     

Three-dimensional colloidal crystal-assisted lithography for two-dimensional patterned arrays

In this paper, we report our recent work on preparing two-dimensional patterned microstructure arrays using three-dimensional colloidal crystals as templates, namely, colloidal crystal-assisted lithography. Two alternative processes are described and involved in colloidal crystal-assisted lithography. One is based upon imprinting the polymer films with three-dimensional silica colloidal crystals, and the other is based upon chemically depositing Ag microstructures on Au substrates covered by polymer colloidal crystals. By varying the experimental conditions in the colloidal crystal-assisted lithography process, we can intentionally control the morphologies of the resulting microstructures. The resultant Ag-coated Au substrates can be used as surface-enhanced Raman scattering substrates, and they would provide an ideal system for the mechanism study of surface-enhanced Raman scattering. We expect that colloidal crystal-assisted lithography will be a versatile approach which can be applied to patterning other materials such as functional molecules, polymers, oxides, and metals.     

Characteristic noise features in light transmission across membrane protein undergoing photocycle

We demonstrate a technique based on noise measurements which can be utilized to study dynamical processes in protein assembly. Direct visualization of dynamics in membrane protein system such as bacteriorhodopsin (bR) upon photostimulation are quite challenging. bR represents a model system where the stimulus-triggered structural dynamics and biological functions are directly correlated. Our method utilizes a pump-probe near field microscopy method in the transmission mode and involves analyzing the transmittance fluctuations from a finite size of molecular assembly. Probability density distributions indicating the effects of finite size and statistical correlations appear as a characteristic frequency distribution in the noise spectra of bR whose origin can be traced to photocycle kinetics. Valuable insight into the molecular processes were obtained from the noise studies of bR and its mutant D96N as a function of external parameters such as temperature, humidity or presence of an additional pump source.     

Hybrid organic–inorganic materials: from child’s play to energy applications

The field of hybrids has boomed since its initial conception with silicones as structural materials to the wealth of different types of hybrid materials studied nowadays as functional materials. Hybrids based on conducting polymers and a great variety of inorganic species constitute a growing area of this field. We present a brief review of the intersection between conducting polymer hybrids and electrochemical applications to energy storage and conversion. But beyond examples of hybrids active in batteries, supercapacitors, solar or fuel cells, we have tried to convey the standing challenges concerning the design of chemically (and electrochemically) complex hybrid systems with components and building blocks ranging from extended oxides or nanoparticles to carbon or oxide nanotubes, to clusters and to molecules and the opportunities arising from their integration with conducting polymers.     

Physical properties of proton conducting membranes based on a protic ionic liquid

We have investigated the physical properties of proton conducting polymer membranes based on a protic ionic liquid (IL). Properties such as ionic conductivity, melting point of the polymer phase, and glass transition temperature of the liquid phase are studied as a function of IL/polymer ratio and temperature. We observe an increased thermomechanical stability of the membrane with increasing polymer content. However, there is a concomitant decrease in the conductivity with increasing polymer content. This decrease is larger than what can be expected from the dilution of the conducting IL by the insulating polymer matrix. The origin of this decrease can be caused both by the morphology of the membrane and by interactions between the polymer matrix and the ionic liquid. We find a change in the glass transition temperature and in the temperature dependence of the conductivity with increasing polymer content. Both effects can be related to the physical confinement of the IL in the polymer membrane.     

Preparation of composite membranes with bicontinuous structure

Composite membranes with a hierarchical structure comprising thin regions with a bicontinuous structure and thick regions providing mechanical strength have been prepared by casting inorganic zeolite particles and mixtures that yield organic polymers onto substrates that were decorated with sessile droplets of aqueous solutions. Analysis by scanning electron microscopy (SEM) showed a membrane structure with well-ordered imprints caused by the sessile template droplets. These imprints were open at the bottom and covered on the top with a thin sheet composed of particles and polymer. The particles protruded out of the polymer sheet at the top and bottom of the membrane in the thin regions. A significant number of the particles protruded out of both interfaces at the same time. Thus, these parts of the membrane can be considered to be bicontinuous. The imprints are surrounded by thick regions. These regions act as a supporting structure. Thus, the membranes are stable enough to be handled without special precautions and might be applicable to membrane separation processes.     

Monolayers and membranes from amphiphilic polymers

Nanometer thin, elastomeric membranes with considerable application potential in micro mechanics and materials science can be prepared by transferring monomolecular layers of polymers with ionic head groups from the water surface to solid substrates with holes. If monolayers of liquid polymers are transferred to substrates with openings they initially cover the openings, but finally rupture within a couple of minutes after transfer. However, if the polymer monolayers are stabilised by vitrification, chemical or physical cross-linking, they can be transferred to cover openings in solids substrates as stable membranes. Especially if monolayers of low glass transition polymers are cross-linked, elastomeric membranes are obtained, which might find application in micro mechanical devices like membrane valves and pumps. Incorporation of either a second, incompatible polymer or hydrophobised colloids leads to laterally structured and porous membranes.     

Impedance change induced by varying polymerization temperature of conducting polymer thin films

In this study, we use a conducting polymer precursor to build layer-by-layer (LbL) films. Thermal conversion of the polymer precursor to conducting polymer makes the LbL films intractable, so the LbL films can be used as protective layers in salt solution. The conducting polymer LbL film shows stabilizing effect on top of another LbL thin film that contains nanoparticles. The LbL film prepared in this study shows a 35-fold increase of conductivity than the literature values obtained from non-conducting polymer films. The stabilization of the films is the result of the polymerization of the conducting polymer, so other anionic polymers or nanoparticles may be used to afford additional functionalities.     

Metal-Catalyzed Coupling Reactions In The Synthesis Of New Conducting Polymers

The use of transition metal-catalyzed coupling reactions in the synthesis of conducting polymers is discussed. These reactions are of growing importance in polymer synthesis and are particularly important in the synthesis of highly functionalized conjugated (conducting) polymers. In this report we discuss applications of this methodology for the synthesis of conducting polymer sensory materials and polymers with reactive functional groups. In the sensory polymers we have incorporated crown ether groups which induce perturbations to the polymer's electronic structure when exposed to an alkali metal ion. Our interest in polymers with reactive functional groups is for the development of polymers which can be transformed into novel all-carbon ladder polymers.     

All‐Solid‐State Ion Selective and All‐Solid‐State Reference Electrodes

This paper is aiming to give a brief overview of recent research in the field of all‐solid‐state, internal solution free, ion‐selective electrodes and reference electrodes, employing conducting polymers or nano‐/microstructures as solid contacts beneath the polymeric, ion‐selective or reference membranes. The emphasis is on papers published in the last five years (after 2006). According to the papers published, poly(3‐octylthiophene) conducting polymer transducers offer highly reliable sensors for various applications, involving demanding analytical approaches and miniature sensors. On the other hand, the search for alternative materials continues: the sensors obtained by placing nano‐/microstructures (conducting polymers but also other materials, like, e.g., carbon nanotubes) underneath the receptor membrane are intensively tested. The recent years have also shown how useful the application of advanced instrumental methods is for the investigation of processes occurring within all‐solid‐state ion‐selective electrodes.     

The Research on Polymer Microcapsulation for Cell Technology

Microcapsulation is a technology that enwrapped the solid or liquid or some gas matter with membrane materials to form microparticles(i.e.microcapsules). The materials of microcapsule is composed of naturnal polymers or modified naturnal polymers or synthesized polymers. The water-soluble core matter can only use oil-soluble wall materials, and vice versa.Synthesized methods of polymer microcapsulesSynthesized methods with monomers as raw materialsThis kind of methods include suspension polymerization, emulsion polymerization, dispersal polymerization, precipitation polymerization,suspension condensation polymerization, dispersal condensation polymerization, deposition condensation polymerization, interface condensation polymerization, and so on.Synthesized methods with polymers as raw materialsThese methods are suspension cross-linked polymerization, coacervation phase separation,extraction with solvent evaporation, polymer deposition, polymer chelation, polymer gel,solidification of melting polymer, tray-painted ways, fluidized bed ways, and so forth.Polymer materials to synthesize microcapsules2.1. Naturnal polymer materialsThe characteristics of this kind of materials are easy to form membrane, good stability and no toxicity. The polymer materials include lipids(liposome), amyloses, proteins, plant gels, waxes, etc.2.2. Modified polymer materialsThe characteristics of these materials are little toxicity, high viscidity(viscosity), soluble salt materials. But they cannot be used in water, acidic environment and high temperature environment for a long time. The materials include all kind of derivants of celluloses.2.3. Synthesized polymer materialsThe characteristics of the materials are easy to form membrane, good stability and adjustment of membrane properties. The synthesized polymer materials include degradable polymers(PLA, PGA,PLGA, PCL, PHB, PHV, PHA, PEG, PPG and the like) and indegradable polymers(PA, PMMA,PAM, PS, PVC, PB, PE, PU, PUA, PVA and otherwise).The applications of polymer microcapsules in cell technologyThe "artificial cell" is the biological active microcapsule used in biological and medical fields.The applications of cells (including transgenic cells, the same as artificial cells) technology include several aspects as follows:3.1. Microcapsulation of artificial red cell3.2. Microcapsule of artificial cell of biological enzyme3.3. Microcapsule of artificial cell of magnetic material3.4. Microcapsule of artificial cell of active carbon3.5. Microcapsule of active biological cell     

Fluorescent Polypyrrole Nanospheres – Synthesis and Properties of “Wireless” Redox Probes

In this work a novel concept of monitoring of occurrence of redox reactions between conducting polymer nanospheres and redox species in a solution is proposed. The redox process is monitored in the emission mode (without wiring of the probe to an electrochemical measuring set‐up) as a change in emission spectrum of a dye (not participating in the redox process itself) but reporting the alteration of properties of highly sensitive conducting polymer nanoparticles. This approach is possible due to applied unique method of synthesis of conducting polymers nanospheres of highly active, unblocked surface. Thus the nanospheres redox state is affected by the solution redox potential, leading to change of their properties. If solvatochromic probe of sufficiently high brightness (pyrene) is present in nanospheres, a redox reaction between the conducting polymer and solution can be observed as change of emission spectrum of the probe. Thus a localized redox potential optical probe can be obtained. The emission properties of the dye incorporated were preserved in the nanospheres, moreover, the emission spectrum of the probe was affected by the change in redox potential of the solution, thus influencing the redox state and ultimately the properties of the conducting polymer. The emission changes observed were dependent on ion‐exchange properties of polypyrrole, i.e. depending on the dopant ions present in the polymer, the sensitivity of the optical probe can be tuned.     

Polypyrrole-calcion film as a membrane and solid-contact in an indicator electrode for potentiometric titrations

This paper shows the application of conducting polymers (CPs) for constructing potentiometric indicator electrodes. Two types of polypyrrole (PPy)-based calcium sensors are presented, one sensor with PPy-calcion film as the active part and the other sensor with PPy-calcion as a solid-state contact coated with a conventional membrane selective towards calcium ions. It is shown that the PPy-calcion film, due to the complexing properties of calcion ensuring high loading of the film with calcium, is sufficiently selective to be used as the active part or as a mediating layer of the indicator electrode. The electrode, with PPy-calcion film as the active part, was used as the indicator electrode in potentiometric titrations of calcium in mixed solvents, where conventional PVC-based electrode can not be used. For the first time, the practical applicability of PPy-based electrodes in titrations is demonstrated.