Fabrication and Characterization of Conductive Conjugated Polymer‐Coated Antheraea mylitta Silk Fibroin Fibers for Biomedical Applications

Conductive polymers are interesting materials for a number of biological and medical applications requiring electrical stimulation of cells or tissues. Highly conductive polymers (polypyrrole and polyaniline)/Antheraea mylitta silk fibroin coated fibers are fabricated successfully by in situ polymerization without any modification of the native silk fibroin. Coated fibers characterized by scanning electron microscopy confirm the silk fiber surface is covered by conductive polymers. Thermogravimetric analysis reveals preserved thermal stability of silk fiber after coating process. X‐ray diffraction of degummed fiber diffraction peaks at around 2θ = 20.4 and 16.5 confirms the preservation of the β‐sheet structure typical of degummed silk II fibers. This phenomenon implies that both polypyrrole and polyaniline chains form interactions with peptide linkages in degummed fiber macromolecules, without significantly disrupting protein assembly. Fourier transform infrared spectroscopy of coated fibers indicates hydrogen bonding and electrostatic interactions exist between silk fibroin macromolecules and conductive polymers. Resulting fibers display good conductive properties compared to corresponding conjugated polymers. In vitro analysis (live/dead assay) of the behavior of human immortalized keratinocytes (HaCaTs) on coated fibers demonstrates improved cell‐adhesive properties and viability after polymers coating. Hence, polypyrrole‐ and polyaniline‐coated A. mylitta silk fibers are suitable for application in cell culture and for tissue engineering, where electrical conduction properties are required.

     

Correlated atomic force microscopy and fluorescence lifetime imaging of live bacterial cells

We report on imaging living bacterial cells by using a correlated tapping-mode atomic force microscopy (AFM) and confocal fluorescence lifetime imaging microscopy (FLIM). For optimal imaging of Gram-negative Shewanella oneidensis MR-1 cells, we explored different methods of bacterial sample preparation, such as spreading the cells on poly-L-lysine coated surfaces or agarose gel coated surfaces. We have found that the agarose gel containing 99% ammonium acetate buffer can provide sufficient local aqueous environment for single bacterial cells. Furthermore, the cell surface topography can be characterized by tapping-mode in-air AFM imaging for the single bacterial cells that are partially embedded. Using in-air rather than under-water AFM imaging of the living cells significantly enhanced the contrast and signal-to-noise ratio of the AFM images. Near-field AFM-tip-enhanced fluorescence lifetime imaging (AFM-FLIM) holds high promise on obtaining fluorescence images beyond optical diffraction limited spatial resolution. We have previously demonstrated near-field AFM-FLIM imaging of polymer beads beyond diffraction limited spatial resolution. Here, as the first step of applying AFM-FLIM on imaging bacterial living cells, we demonstrated a correlated and consecutive AFM topographic imaging, fluorescence intensity imaging, and FLIM imaging of living bacterial cells to characterize cell polarity.     

Graphene/Fe3O4 Nanocomposites as Efficient Anodes to Boost the Lifetime and Current Output of Microbial Fuel Cells

The enhancement of microbial activity and electrocatalysis through the design of new anode materials is essential to develop microbial fuel cells (MFCs) with longer lifetimes and higher output. In this research, a novel anode material, graphene/Fe₃O₄ (G/Fe₃O₄) composite, has been designed for Shewanella ‐inoculated MFCs. Because the Shewanella species could bind to Fe₃O₄ with high affinity and their growth could be supported by Fe₃O₄, the bacterial cells attached quickly onto the anode surface and their long‐term activity improved. As a result, MFCs with reduced startup time and improved stability were obtained. Additionally, the introduction of graphene not only provided a large surface area for bacterial attachment, but also offered high electrical conductivity to facilitate extracellular electron transfer (EET). The results showed that the current and power densities of a G/Fe₃O₄ anode were much higher than those of each individual component as an anode.     

Proton Transport in the Outer‐Membrane Flavocytochrome Complex Limits the Rate of Extracellular Electron Transport

The microbial transfer of electrons to extracellularly located solid compounds, termed extracellular electron transport (EET), is critical for microbial electrode catalysis. Although the components of the EET pathway in the outer membrane (OM) have been identified, the role of electron/cation coupling in EET kinetics is poorly understood. We studied the dynamics of proton transport associated with EET in an OM flavocytochrome complex in Shewanella oneidensis MR‐1. Using a whole‐cell electrochemical assay, a significant kinetic isotope effect (KIE) was observed following the addition of deuterated water (D₂O). The removal of a flavin cofactor or key components of the OM flavocytochrome complex significantly increased the KIE in the presence of D₂O to values that were significantly larger than those reported for proton channels and ATP synthase, thus indicating that proton transport by OM flavocytochrome complexes limits the rate of EET.     

Peptide‐Coated Platinum Nanoparticles with Selective Toxicity against Liver Cancer Cells

Peptide‐stabilized platinum nanoparticles (PtNPs) were developed that have significantly greater toxicity against hepatic cancer cells (HepG2) than against other cancer cells and non‐cancerous liver cells. The peptide H‐Lys‐Pro‐Gly‐d Lys‐NH₂ was identified by a combinatorial screening and further optimized to enable the formation of water‐soluble, monodisperse PtNPs with average diameters of 2.5 nm that are stable for years. In comparison to cisplatin, the peptide‐coated PtNPs are not only more toxic against hepatic cancer cells but have a significantly higher tumor cell selectivity. Cell viability and uptake studies revealed that high cellular uptake and an oxidative environment are key for the selective cytotoxicity of the peptide‐coated PtNPs.     

Nanostructured Conjugated Polymers for Energy‐Related Applications beyond Solar Cells

To meet the ever‐increasing requirements for the next generation of sustainable and versatile energy‐related devices, conjugated polymers, which have potential advantages over small molecules and inorganic materials, are among the most promising types of green candidates. The properties of conjugated polymers can be tuned through modification of the structure and incorporation of different functional moieties. In addition, superior performances can be achieved as a result of the advantages of nanostructures, such as their large surface areas and the shortened pathways for charge transfer. Therefore, nanostructured conjugated polymers with different properties can be obtained to be applied in different energy‐related organic devices. This review focuses on the application and performance of the recently reported nanostructured conjugated polymers for high‐performance devices, including rechargeable lithium batteries, microbial fuel cells (MFCs), thermoelectric generators, and photocatalytic systems. The design strategies, reaction mechanisms, advantages, and limitations of nanostructured conjugated polymers are further discussed in each section. Finally, possible routes to improve the performances of the current systems are also included in the conclusion.     

Crystalline Cooperativity of Donor and Acceptor Segments in Double‐Cable Conjugated Polymers toward Efficient Single‐Component Organic Solar Cells

The crystalline cooperativity of the donor and acceptor segment in double‐cable conjugated polymers plays an important role in the nanophase separation and photovoltaic performance in single‐component organic solar cells (SCOSCs). Two double‐cable conjugated polymers with the same conjugated backbone and perylene bisimide (PBI) side units were designed in which PBIs were positioned symmetrically and perpendicularly ( P1 ) and asymmetrically and slantingly ( P2 ) along the conjugated backbones. After thermal annealing, both conjugated backbones and PBI side units in P1 tend to form ordered nanostructures, while PBI side units in P2 dominated the crystallization and hamper the crystallization of conjugated backbones. P1 showed good crystalline cooperativity between conjugated backbones and PBI side units, resulting in improved power conversion efficiencies (PCEs) up to 3.43 % in SCOSCs, while P2 with poor crystalline cooperativity exhibited PCEs below 2.42 %.     

Combined spectroscopic and topographic characterization of nanoscale domains and their distributions of a redox protein on bacterial cell surfaces

Redox protein nanoscale domains on the cell surface of a bacterium, Shewanella oneidensis MR1, grown in the absence and presence of electron acceptors, is topographically characterized using combined atomic force microscopy (AFM) and confocal surface enhanced Raman scattering (SERS) spectroscopy. The protruding nanoscale domains on the outer membrane of S. oneidensis were observed, as was their disappearance upon exposure to electron acceptors such as oxygen, nitrate, fumarate, and iron nitrilotriacetate (FeNTA). Using SERS spectroscopy, a redox heme protein was identified as a major component of the cell surface domains. This conclusion was further confirmed by the disappearance of Raman vibrational frequencies, characteristic of heme proteins, upon exposure of the cells to electron acceptors. Our experimental results from our AFM imaging and SERS spectroscopy, consistent with the literature, suggest the protruding nanoscale surface domains as heme-containing secretions. Our results on the distributions of redox proteins on microbial cell surfaces will be helpful for a mechanistic understanding of the behaviors of surface proteins and their interactions with redox environments.     

Artificial Spores: Cytocompatible Coating of Living Cells with Plant‐Derived Pyrogallol

Cell nanoencapsulation, generating cell‐in‐shell structures (“artificial spores“), provides a chemical toolbox for controlling the cellular behaviors and functional characteristics of individual cells. Among the shell materials studied so far, naturally occurring polyphenolic compounds, including polydopamine and tannic acid, have intensively been employed in cell‐surface engineering, because their material‐independent coating property eliminates an extra priming step for inducing subsequent shell formation. Albeit successful in generating cell‐in‐shell structures, the coating of polyphenolic compounds generally requires alkaline conditions and/or high salt conditions, which are not compatible with certain cell types. In this work, we demonstrate that the nanocoating of individual cells with a plant‐derived phenolic compound, pyrogallol (1,2,3‐trihydroxybenzene), occurs at mildly alkaline pH of 7.8 in an isotonic buffer. Three different cell types (anucleate, microbial, and mammalian cells) are coated with pyrogallol without noticeable decrease in cell viability. The protocol developed in this work could be applied to other polyphenolic compounds, and, considering the many polyphenols identified as a coating material, provides an advanced chemical tool in cell‐surface engineering.     

A Biomimetic Escape Strategy for Cytoplasm Invasion by Synthetic Particles

The translocation of nanomaterials or complex delivery systems into the cytosol is a major challenge in nanobiotechnology. After receptor‐mediated endocytosis, most nanomaterials are sequestered and undergo degradation, therapy inactivation, or exocytosis. Herein we explore a novel surface particle coating made of adsorbed carbon nanotubes that provides coated materials with new properties that reproduce the viral cell‐invasive mechanisms, namely, receptor‐mediated endocytosis, endolysosomal escape, and cytosolic particle release preserving cell viability. This novel biomimetic coating design will enable the intracytoplasmic delivery of many different functional materials endowed with therapeutic, magnetic, optical, or catalytic functionalities, thus opening the door to a wide array of chemical and physical processes within the cytosolic or nuclear domains, and supporting new developments in the biotechnological, pharmaceutical, and biomedical industries.     

ATR-FTIR spectroscopy reveals bond formation during bacterial adhesion to iron oxide

The contribution of various bacterial surface functional groups to adhesion at hematite and ZnSe surfaces was examined using attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. When live Shewanella oneidensis, Pseudomonas aeruginosa, and Bacillus subtilis cells were introduced to a horizontal hematite (alpha-Fe(2)O(3))-coated internal reflection element (IRE), FTIR peaks emerged corresponding to bacterial phosphate group binding. These IR peaks were not observed when bacteria were introduced to the uncoated ZnSe IRE. When cells were added to colloidal suspensions of alpha-Fe(2)O(3) at pH 7, spectra included peaks corresponding to P-OFe and nu(COOH), the latter being attributed to bridging of carboxylate at mineral surface OH groups. Selected model organic compounds with P-containing functionalities (phenylphosphonic acid [PPA], adenosine 5'-monophosphate [AMP], 2'-deoxyadenyl(3'-->5')-2'-deoxyadenosine [DADA], and deoxyribonucleic acid [DNA]) produce spectra with similar peaks corresponding to P-OFe when adsorbed to alpha-Fe(2)O(3). The data indicate that both terminal phosphate/phosphonate and phosphodiester groups, either exuded from the cell or present as surface biomolecules, are involved in bacterial adhesion to Fe-oxides through formation of innersphere Fe-phosphate/phosphonate complexes.     

Cytocompatible Polymer Grafting from Individual Living Cells by Atom‐Transfer Radical Polymerization

A cytocompatible method of surface‐initiated, activator regenerated by electron transfer, atom transfer radical polymerization (SI‐ARGET ATRP) is developed for engineering cell surfaces with synthetic polymers. Dopamine‐based ATRP initiators are used for both introducing the ATRP initiator onto chemically complex cell surfaces uniformly (by the material‐independent coating property of polydopamine) and protecting the cells from radical attack during polymerization (by the radical‐scavenging property of polydopamine). Synthetic polymers are grafted onto the surface of individual yeast cells without significant loss of cell viability, and the uniform and dense grafting is confirmed by various characterization methods including agglutination assay and cell‐division studies. This work will provide a strategic approach to the generation of living cell–polymer hybrid structures and open the door to their application in multitude of areas, such as sensor technology, catalysis, theranostics, and cell therapy.     

OCVD polymerization of PEDOT: effect of pre‐treatment steps on PEDOT‐coated conductive fibers and a morphological study of PEDOT distribution on textile yarns

The functionalization of textile fibers with intrinsically conductive polymers has become a prominent research area throughout the world. A number of coating techniques have already been utilized and optimized to get the uniform layers of conductive polymers on the surface of different substrates. In our previous study, we produced poly(3,4‐ethylenedioxythiophene) (PEDOT)‐coated conductive fibers by employing oxidative chemical vapor deposition (oCVD) technique. This paper describes the effects of pre‐treatment steps, such as surface treatment of textile fibers with organic solvents, drying of oxidant‐enriched fibers at variable temperatures and time, and oxidant type on the electrical, mechanical, and thermal properties of PEDOT‐coated conductive fibers. Two well‐known oxidants, ferric(III)chloride and ferric(III)p‐toluenesulfonate (FepTS), were studied, and then their results were compared. In order to verify the PEDOT‐coated layer and, to some extent, its impregnation inside the viscose yarns, a morphological study was carried out by using the attenuated total reflectance Fourier transform infrared spectroscopic imaging technique and computed tomography scanning across the obtained conductive fibers. Differential scanning calorimetric and thermogravimetric analysis were utilized to investigate the thermal properties and the contents of PEDOT in PEDOT‐coated fibers. The mechanical properties of conductive fibers were evaluated by tensile strength testing of produced fibers. Effects of all of these pre‐treatment steps on electrical properties were analyzed with Kiethly picoammeter. This study cannot only be exploited to improve the properties of conductive fibers but also to optimize the oCVD process for the production of conductive textile fibers by coating with different conjugated polymers. Copyright © 2012 John Wiley & Sons, Ltd.     

金纳米粒子与聚吡咯纳米管的复合及其SERS效应研究

通过柠檬酸盐与HAuCl4水溶液在微沸状态下反应制备的金纳米粒子因其特殊的表面与界面效应在光学、生物学和催化化学领域得到了广泛应用,而聚吡咯(PPy)具有环境稳定性好、电导率高且变化范围大、容易合成等优点,聚吡咯纳米管可用作导电材料、酶封装材料、抗静电材料,也可用于制备传感器、传动器、固体电解质电容器等。     

Distinct Electron Conductance Regimes in Bacterial Decaheme Cytochromes

Shewanella oneidensis MR‐1 gains energy by extracellular electron transfer to solid surfaces. They employ c‐type cytochromes in two Mtr transmembrane complexes, forming a multiheme wire for electron transport across the cellular outer membrane. We investigated electron‐ and hole‐transfer mechanisms in the external terminal of the two complexes, MtrC and MtrF. Comparison of computed redox potentials with previous voltammetry experiments in distinct environments (isolated and electrode‐bound conditions of PFV or in vivo) suggests that these systems function in different regimes depending on the environment. Analysis of redox potential shifts in different regimes indicates strong coupling between the hemes via an interplay between direct Coulomb and indirect interactions through local structural reorganization. The latter results in the screening of Coulomb interactions and explains poor correlation of the strength of the heme‐to‐heme interactions with the distance between the hemes.     

共轭聚合物复合材料的结构和性能

对聚苯胺、聚吡啶等共轭聚合物与非导电聚合物材料的复合体系的结构和性能进行了综述。不同方法制备的复合材料在结构和性能上各有特点。一般共轭聚合物与非导电高分子材料相容性差、尤其是低极性高分了。     

Electrical resistance and heat generation of polypyrrole‐coated polyacrylonitrile nanofibrous and regular fibrous mats

This article reports the effect of fiber diameter on the electrical resistance and heat generation of fibrous polyacrylonitrile (PAN) mats coated with polypyrrole during chemical in situ polymerization. Polypyrrole is one of the important intrinsically conducting polymers that perform similar to semiconductors. The electrical resistance of polypyrrole‐coated mats depends on the fiber diameter, the applied pressure on the surface of the mats, and the mat thickness. The electrical resistance of polypyrrole‐coated PAN fibrous mats decreases as fiber diameter decreases. Moreover, electrical resistance decreases considerably as the mat thickness as well as the applied pressure on it increases. It was also observed that the heat generated in polypyrrole‐coated PAN fibrous mats increases with voltage and duration of the applied voltage. Lower fiber diameter also leads to higher heat generation. Furthermore, electrical current increases rapidly in the initial stages of applying voltage and then shows a marginal increase. Considering their high specific surface area, nanofibers convey considerable improvement in the electrical conductivity as well as heat generation capacity of the mats made from them. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of Multishell Carbon Nanotube Composites via Template Method

Multishell nanotubes of polyaniline and carbon were synthesized via a template approach. A thin layer of MnO₂ coated on carbon nanotubes acts as a reactive template for the consequent formation of the polyaniline coating. The polyaniline-carbon nanotubes show enhanced dispersibility in water and can be possibly used as a functional material of electrochemical capacitors with improved performance. The general method operates by coating carbon nanotubes on functional materials such as poly (3,4-ethylenedioxythiophene), polypyrrole, silica, and carbon.     

Repartition effect of aromatic polyaniline coatings on the separation of bioactive peptides in capillary electrophoresis

The capillary walls of fused-silica capillary electrophoresis (CE) columns were modified with a thin film of polyaniline (PANI), providing open-tubular columns with a stable coating containing aromatic groups and amine functionalities. Fast and efficient separations were observed for small bioactive peptides under acidic conditions on PANI-coated columns. The mechanism of separation is based on hydrophobic interactions between the analytes and the polymeric matrix. Good reproducibility was observed from run-to-run. Due to the simple derivatization procedure, method flexibility, the uniformity of the coating and its stability, conjugated polymers could find practical application in capillary zone electrophoresis (CZE) separations.     

An Unexpected Role of Hyaluronic Acid in Trafficking siRNA Across the Cellular Barrier: The First Biomimetic,Anionic, Non‐Viral Transfection Method

Circulating nucleic acids, such as short interfering RNA (siRNA), regulate many biological processes; however, the mechanism by which these molecules enter the cell is poorly understood. The role of extracellular‐matrix‐derived polymers in binding siRNAs and trafficking them across the plasma membrane is reported. Thermal melting, dynamic light scattering, scanning electron microscopy, and computational analysis indicate that hyaluronic acid can stabilize siRNA via hydrogen bonding and Van der Waals interactions. This stabilization facilitated HA size‐ and concentration‐dependent gene silencing in a CD44‐positive human osteosarcoma cell line (MG‐63) and in human mesenchymal stromal cells (hMSCs). This native HA‐based siRNA transfection represents the first report on an anionic, non‐viral delivery method that resulted in approximately 60 % gene knockdown in both cell types tested, which correlated with a reduction in translation levels.