Chemical doping with foreign atoms is an effective method to intrinsically modify the properties of host materials. Among them, nitrogen doping plays a critical role in regulating the electronic properties of carbon materials. Recently, graphene, as a true two-dimensional carbon material, has shown fascinating applications in bioelectronics and biosensors. In this paper, we report a facile strategy to prepare N-doped graphene by using nitrogen plasma treatment of graphene synthesized via a chemical method. Meanwhile, a possible schematic diagram has been proposed to detail the structure of N-doped graphene. By controlling the exposure time, the N percentage in host graphene can be regulated, ranging from 0.11 to 1.35%. Moreover, the as-prepared N-doped graphene has displayed high electrocatalytic activity for reduction of hydrogen peroxide and fast direct electron transfer kinetics for glucose oxidase. The N-doped graphene has further been used for glucose biosensing with concentrations as low as 0.01 mM ...

Nitrogen-Doped Graphene and Its Application in Electrochemical Biosensing

Polymer surface modification by plasmas and photons

This review surveys methods for the fabrication, by plasma surface treatments or plasma polymerization, of polymeric surfaces and thin plasma polymer coatings that contain reactive chemical groups useful for the subsequent covalent immobilization, by solution chemical reactions or vapor phase grafting, of molecules or polymers that can exert bio-specific interfacial responses. Surfaces containing amine, carboxy, hydroxy, and aldehyde groups are the subject of this review. Aminated surfaces have been fabricated using various plasma vapors or mixtures and have found wide use for bio-interface applications. However, in many cases the amine surfaces have a rather limited shelf life, with post-plasma oxidation reactions and surface adaptation leading to the disappearance of amine groups from the surface. Aging is a widespread phenomenon that often has not been recognized, particularly in some of the earlier studies on the use of plasma-fabricated surfaces for bio-interfacial applications, and can markedly alter the surface chemistry. Plasma-fabricated surfaces that contain carboxy groups have also been well documented. Fewer reports exist on hydroxy and aldehyde surfaces prepared by plasma methods. Hydroxy surfaces can be prepared by water plasma treatment or the plasma polymerization of alkyl alcohol vapors. Water plasma treatment on many polymer substrates suffers from aging, with surface adaptation leading to the movement of surface modification effects into the polymer. Both hydroxy and aldehyde surfaces have been used for the covalent immobilization of biologically active molecules. Aging effects are less well documented than for amine surfaces. This review also surveys studies using such surfaces for cell colonization assays. Generally, these surface chemistries show good ability to support cell colonization, though the effectiveness seems to depend on the process vapor and the plasma conditions. Carboxylate co-polymer surfaces have shown excellent ability to support the colonization of some human cell lines of clinical interest. Immobilization of proteins onto plasma-carboxylated surfaces is also well established.

Plasma Methods for the Generation of Chemically Reactive Surfaces for Biomolecule Immobilization and Cell Colonization ‐ A Review

Electrochemical surface oxidation of Vulcan XC-72, a carbon black commonly used in proton exchange membrane (PEM) fuel cells, was studied following potentiostatic treatments up to 120 h at potentials from 0.6 to 1.2 V at room temperature and 65°C. Surface oxidation was followed using cyclic voltammetry (CV), thermal gravimetric analysis coupled to on-line mass spectrum-etry (TGA-MS), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. The analytical techniques all indicate significant surface oxidation occurred during the first 16 h of 1.2 V potential holds at room temperature and a slow increase in surface oxide formation thereafter. An identification of ether, carbonyl, and carboxyl surface oxide species was made by deconvolution of XPS spectra and assigning these functional groups to the observed TGA-MS CO 2 evolution peaks (150-750°C). An increase in CO evolution (>800°C) determined by TGA-MS was consistent with electrochemical CV data, which detected electroactive hydroquinone/quinone species; these electrochemically detected species were a minor fraction of the electrochemically generated surface oxides. Potential holds at 1.0 V at room temperature only resulted in slight oxidation of Vulcan XC-72. However, experiments at 65°C showed clear signs of surface oxidation after only 16 h at potentials ≥0.8 V, verifying that surface oxides can be generated under simulated PEM fuel cell conditions. Overall, these results suggest that changes in component hydrophobicity, driven by carbon surface oxidation, are an important factor in determining long-term PEM performance instability and decay.

Characterization of Vulcan Electrochemically Oxidized under Simulated PEM Fuel Cell Conditions

Surface characterization of carbon fibers using angle-resolved XPS and ISS

XPS study of the carbon fiber matrix interface

Gas phase chemical modification (GCM) is found to be more preferable as a pretreatment for the XPS surface analysis of polymer materials than the conventional liquid phase treatment because it can circumvent problems such as solvent contamination and swelling. We have tried the quantification of the surface composition successfully by estimating the yield of the reaction from model samples. GCM was then applied to correlate the surface composition of NH3 plasma-treated polystyrene films with their cell-affinity. The amount of primary-amine and that of carboxylic acid were directly determined by GCM. Although the amount of primary-amine, 15–20% of total nitrogen, did not depend on the treatment intensity, the total amine content for the treated samples increased with the plasma treatment intensity. The quantity of carboxylic acid generated was found to be very small. All treated samples had better cell-affinity than the control. The sample N2 (of medium treatment) showed the best cell-affinity. The most strongly treated sample N3, with larger amine content than N2, showed worse cell-affinity because of the interference by the sputtered SiO2 on the surface.

Youichi Nakayama

Papers

XPS study of the carbon fiber matrix interface

XPS analysis of NH3 plasma‐treated polystyrene films utilizing gas phase chemical modification

XPS study of oriented organic molecules: Vesicles of azobenzene-containing alkyl ammonium amphiphiles

XPS study of oriented organic molecules: The single crystal of an azobenzene-containing alkyl ammonium amphiphile

XPS study of oriented organic molecules: III. Langmuir-Blodgett membrane of a fatty acid