Surface Characterization and in situ Protein Adsorption Studies on Carbene-Modified Polymers.

Polystyrene thin films were functionalized using a facile two-step chemical protocol involving carbene insertion followed by azo-coupling, permitting the introduction of a range of chemical functional groups, including aniline, hexyl, amine, carboxyl, phenyl, phosphonate diester, and ethylene glycol. X-ray photoelectron spectroscopy (XPS) confirmed the success of the two-step chemical modification with a grafting density of at least 1/10th of the typical loading density (10(14)-10(15)) of a self-assembled monolayer (SAM). In situ, real-time quartz crystal microbalance with dissipation (QCM-D) studies show that the dynamics of binding of bovine serum albumin (BSA) are different at each modified surface. Mass, viscoelastic, and kinetic data were analyzed, and compared to cheminformatic descriptors (i.e., c log P, polar surface area) typically used for drug discovery. Results show that functionalities may either resist or adsorb BSA, and uniquely influence its adsorption dynamics. It is concluded that carbene-based surface modification can usefully influence BSA binding dynamics in a manner consistent with, and more robust than, traditional systems based on SAM chemistry.

Amplified electron transfer at poly-ethylene-glycol (PEG) grafted electrodes.

"Amplified" electron transfer is observed purely based on electron transfer kinetic effects at modified carbon surfaces. An anodic attachment methodology is employed to modify the surface of glassy carbon or boron doped diamond electrodes with poly-ethylene glycols (PEGs) for polymerisation degrees of n = 4.5 to 9.1 (PEG200 to PEG400). Voltammetry and impedance data for aqueous Fe(CN)6(3-/4-) suggest systematic PEG structure-dependent effects on the standard rate constant for heterogeneous electron transfer as a function of PEG deposition conditions and average polymer chain length. Tunnel distance coefficients are polymerisation degree dependent and estimated for shorter PEG chains, ß = 0.17 Å(-1) for aqueous Fe(CN)6(3-/4-), consistent with a diffuse water-PEG interface. In contrast, electron transfer to 1,1'-ferrocene-dimethanol (at 1 mM concentration) appears un-impeded by PEG grafts. Mediated or "amplified" electron transfer to Fe(CN)6(3-/4-) based on the 1,1'-ferrocene-dimethanol redox shuttle is observed for both oxidation and reduction with estimated bimolecular rate constants for homogeneous electron transfer of kforward = 4 × 10(5) mol dm(3) s(-1) and kbackward = 1 × 10(5) mol dm(3) s(-1). Digital simulation analysis suggests an additional resistive component within the PEG graft double layer.

Hydrothermal conversion of one-photon-fluorescent poly(4-vinylpyridine) into two-photon-fluorescent carbon nanodots.

A novel two-photon-fluorescent N,O-heteroatom-rich carbon nanomaterial has been synthesized and characterized. The new carbon nanoparticles were produced by hydrothermal conversion from a one-photon-fluorescent poly(4-vinylpyridine) precursor (P4VP). The carbonized particles (cP4VP dots) with nonuniform particle diameter (ranging from sub-6 to 20 nm with some aggregates up to 200 nm) exhibit strong fluorescence properties in different solvents and have also been investigated for applications in cell culture media. The cP4VP dots retain their intrinsic fluorescence in a cellular environment and exhibit an average excited-state lifetime of 2.0 ± 0.9 ns in the cell. The cP4VP dots enter HeLa cells and do not cause significant damage to outer cell membranes. They provide one-photon or two-photon fluorescent synthetic scaffolds for imaging applications and/or drug delivery.

Enhanced TiO2 surface electrochemistry with carbonised layer-by-layer cellulose-PDDA composite films.

In this report we demonstrate a versatile (and potentially low-cost) cellulose nano-whisker-based surface carbonisation method that allows well-defined films of TiO(2) nanoparticles surface-modified with carbon to be obtained. In a layer-by-layer electrostatic deposition process based on TiO(2) nanoparticles, cellulose nano-whiskers, and poly(diallyl-dimethylammonium) or PDDA are employed to control the ratio of surface carbon to TiO(2). Characterisation based on optical, AFM, XRD, and XPS methods is reported. Electrochemical measurements suggest improved access to surface states, dopamine binding at the anatase surface, and surface redox cycling aided by the thin amorphous carbon film in mesoporous TiO(2). In future, the amorphous carbon layer method could be applied for surface processes for a wider range of semiconductor or insulator surfaces.

Carbon nanoparticle surface functionalisation: converting negatively charged sulfonate to positively charged sulfonamide.

The surface functionalities of commercial sulfonate-modified carbon nanoparticles (ca. 9-18 nm diameter, Emperor 2000) have been converted from negatively charged to positively charged via sulfonylchloride formation followed by reaction with amines to give suphonamides. With ethylenediamine, the resulting positively charged carbon nanoparticles exhibit water solubility (in the absence of added electrolyte), a positive zeta-potential, and the ability to assemble into insoluble porous carbon films via layer-by-layer deposition employing alternating positive and negative carbon nanoparticles. Sulfonamide-functionalised carbon nanoparticles are characterised by Raman, AFM, XPS, and voltammetric methods. Stable thin film deposits are formed on 3 mm diameter glassy carbon electrodes and cyclic voltammetry is used to characterise capacitive background currents and the adsorption of the negatively charged redox probe indigo carmine. The Langmuirian binding constant K = 4000 mol(-1)dm(3) is estimated and the number of positively charged binding sites per particle determined as a function of pH.

Novel Modifications to Carbon-Based Electrodes to Improve the Electrochemical Detection of Dopamine.

In this work, we describe three simple modifications to carbon electrodes that were found to improve the detection of an exemplar neurotransmitter (dopamine) in the presence of physiological interferents (ascorbic acid and/or uric acid). First, the electro-oxidation of ascorbic acid, as a pretreatment, at boron-doped diamond electrode (BDE) interfaces is studied. This treatment did suppress the detection of ascorbic acid oxidation signal, but only in a manner suitable for single-use detection of high concentrations of dopamine (i.e., > 1 µM). Second, the hydrogenation of BDE by electrochemical cathodic treatment and plasma hydrogenation was investigated. Large cathodic, applied potentials (i.e., > - 5 V) and hydrogen plasma pretreatment of BDE lead to the partial and complete oxidization of ascorbic acid before dopamine, respectively. The consequence at hydrogen-plasma treated BDE is the complete electrochemical separation of these two species without any typical catalytic reactions between the analytes. Third, the modification of glassy carbon electrodes with carbon black nanoparticles is explored. This modification enables the simultaneous detection of ascorbic acid, dopamine and uric acid, significantly enhancing the sensitivity of dopamine. Dopamine was best detected using the unconventional route of detecting 5,6-dihydroxyindole, which is made possible by use of carbon-black nanoparticles. The potential of all three studied modifications to be of electroanalytical use is highlighted throughout this work.

A conducting polymer with enhanced electronic stability applied in cardiac models.

Electrically active constructs can have a beneficial effect on electroresponsive tissues, such as the brain, heart, and nervous system. Conducting polymers (CPs) are being considered as components of these constructs because of their intrinsic electroactive and flexible nature. However, their clinical application has been largely hampered by their short operational time due to a decrease in their electronic properties. We show that, by immobilizing the dopant in the conductive scaffold, we can prevent its electric deterioration. We grew polyaniline (PANI) doped with phytic acid on the surface of a chitosan film. The strong chelation between phytic acid and chitosan led to a conductive patch with retained electroactivity, low surface resistivity (35.85 ± 9.40 kilohms per square), and oxidized form after 2 weeks of incubation in physiological medium. Ex vivo experiments revealed that the conductive nature of the patch has an immediate effect on the electrophysiology of the heart. Preliminary in vivo experiments showed that the conductive patch does not induce proarrhythmogenic activities in the heart. Our findings set the foundation for the design of electronically stable CP-based scaffolds. This provides a robust conductive system that could be used at the interface with electroresponsive tissue to better understand the interaction and effect of these materials on the electrophysiology of these tissues.

Cellulose-Derived Supercapacitors from the Carbonisation of Filter Paper.

Advanced carbon materials are important for the next-generation of energy storage apparatus, such as electrochemical capacitors. Here, the physical and electrochemical properties of carbonised filter paper (FP) were investigated. FP is comprised of pure cellulose and is a standardised material. After carbonisation at temperatures ranging from 600 to 1700 °C, FP was contaminant-free, containing only carbon and some oxygenated species, and its primary fibre structure was retained (diameter ≈20-40 µm). The observed enhancement in conductivity of the carbonised FP was correlated with the carbonisation temperature. Electrochemical capacitance in the range of ≈1.8-117 F g(-1) was achieved, with FP carbonised at 1500 °C showing the best performance. This high capacitance was stable with >87 % retained after 3000 charge-discharge cycles. These results show that carbonised FP, without the addition of composite materials, exhibits good supercapacitance performance, which competes well with existing electrodes made of carbon-based materials. Furthermore, given the lower cost and renewable source, cellulose-based materials are the more eco-friendly option for energy storage applications.

Interfacial electron-shuttling processes across KolliphorEL monolayer grafted electrodes.

Covalently grafted KolliphorEL (a poly(ethylene glycol)-based transporter molecule for hydrophobic water-insoluble drugs; MW, ca. 2486; diameter, ca. 3 nm) at the surface of a glassy-carbon electrode strongly affects the rate of electron transfer for aqueous redox systems such as Fe(CN)6(3-/4-). XPS data confirm monolayer grafting after electrochemical anodization in pure KolliphorEL. On the basis of voltammetry and impedance measurements, the charge transfer process for the Fe(CN)6(3-/4-) probe molecule is completely blocked after KolliphorEL grafting and in the absence of a "guest". However, in the presence of low concentrations of suitable ferrocene derivatives as guests, mediated electron transfer across the monolayer via a shuttle mechanism is observed. The resulting amplification of the ferrocene electroanalytical signal is investigated systematically and compared for five ferrocene derivatives. The low-concentration electron shuttle efficiency decreases in the following sequence: (dimethylaminomethyl)ferrocene > n-butyl ferrocene > ferrocene dimethanol > ferroceneacetonitrile > ferroceneacetic acid.

Characterization of covalently bonded proteins on poly(methyl methacrylate) by X-ray photoelectron spectroscopy.

X-ray photoelectron spectroscopy (XPS) has been used to characterize a poly(methyl methacrylate) (PMMA) surface with covalently attached proteins. The PMMA surfaces were first aminated using hexamethyldiamine; the resulting -NH(2) sites were reacted with the hetero-bifunctional cross-linker Sulfo-EMCS to form a maleimide-terminated surface. The N-hydroxysuccinimide ester terminal and maleimide terminal groups of Sulfo-EMCS reacts with amine and sulfhydryl groups, respectively, exposed on the surface of the proteins. This study characterizes Thermotoga maritima beta-glucosidase 1 (TmGH1), which belongs to a family of proteins that facilitate hydrolysis of glucose-related monomers with retention of conformation. The surfaces were characterized by XPS to monitor surface composition, and to elucidate protein orientation on the surface. Results suggest that a covalently bonded surface of TmGH1 on PMMA has been obtained. These results demonstrate the feasibility of using XPS to study protein surface chemistry and demonstrate a useful method to anchor cysteine-terminated proteins for the purposes of creating biosensors or platforms for mechanical force experiments to investigate protein structure.