Carboxylic Acid-functionalized Carbon Nanotubes Research Articles

Sensitive Electrochemical Prostate Specific Antigen Aptasensor: Effect of Carboxylic Acid Functionalized Carbon Nanotube and Glutaraldehyde Linker

AbstractThe performance of carboxylic acid functionalized carbon nanotubes (CNTs(COOH)), chitosan (Chit), carbon nanotubes‐chitosan (CNTs‐Chit and CNTs(COOH)‐Chit) for immobilizing of amino‐functionalized ssDNA and fabrication of electrochemical prostate specific antigen (PSA) aptasensor were studied in detail using X‐ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR) and electrochemical impedance spectroscopy (EIS). The assemblies of capture probe are formed on the surface via two approaches: EDC/NHS chemistry and glutaraldehyde linker. Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and EIS techniques were used to investigate the analytical performance of the PSA aptasensor. Under optimum conditions the sensitivity of 0.0026 µA/(ng/ml) and a limit of detection of 0.75 ng/ml (22 pM) were obtained for PSA detection. This protocol offers a new means for sensitive detection of PSA with some advantages in terms of simplicity, selectivity, ease of use and regenerability.

Chronic In Vivo Evaluation of PEDOT/CNT for Stable Neural Recordings.

Subcellular-sized chronically implanted recording electrodes have demonstrated significant improvement in single unit (SU) yield over larger recording probes. Additional work expands on this initial success by combining the subcellular fiber-like lattice structures with the design space versatility of silicon microfabrication to further improve the signal-to-noise ratio, density of electrodes, and stability of recorded units over months to years. However, ultrasmall microelectrodes present very high impedance, which must be lowered for SU recordings. While poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonate (PSS) coating have demonstrated great success in acute to early-chronic studies for lowering the electrode impedance, concern exists over long-term stability. Here, we demonstrate a new blend of PEDOT doped with carboxyl functionalized multiwalled carbon nanotubes (CNTs), which shows dramatic improvement over the traditional PEDOT/PSS formula. Lattice style subcellular electrode arrays were fabricated using previously established method. PEDOT was polymerized with carboxylic acid functionalized carbon nanotubes onto high-impedance (8.0±0.1MΩ: M±S.E.) 250-μm(2) gold recording sites. PEDOT/CNT-coated subcellular electrodes demonstrated significant improvement in chronic spike recording stability over four months compared to PEDOT/PSS recording sites. These results demonstrate great promise for subcellular-sized recording and stimulation electrodes and long-term stability. This project uses leading-edge biomaterials to develop chronic neural probes that are small (subcellular) with excellent electrical properties for stable long-term recordings. High-density ultrasmall electrodes combined with advanced electrode surface modification are likely to make significant contributions to the development of long-term (permanent), high quality, and selective neural interfaces.

Carbon nanotube-gelatin-hydroxyapatite nanohybrids with multilayer core–shell structure for mimicking natural bone

We attempted to mimic collagen fibrils bearing apatite crystals in natural bone, using gelatin, carboxylic acid functionalized carbon nanotubes (f-CNTs), and hydroxyapatite (HA). Gelatin molecules were covalently grafted on the surface of f-CNTs by the formation of amide linkages. HA crystals were then assembled onto the gelatin-grafted f-CNTs in a highly concentrated CaP solution, resulting a multilayered core–shell structure, consisting of a f-CNT core and gelatin-HA shells (as a fibrous multilayered f-CNT/Gel/HA nanohybrid), and in a similar formation to the collagen fibers of natural bone. The tensile strength, elastic modulus, and elongation rate of the new hybrid material were significantly improved compared to both pure (f-CNT free) gelatin and a mixture of f-CNT and gelatin, by 4.6–8.8, 9–10, and 28–42 times, respectively. Cell viability studies of the f-CNT/Gel/HA nanohybrid also suggest a higher degree of biocompatibility compared to pure gelatin.

Hybrid carbon nanotube—silica/ polyvinyl alcohol nanocomposites films: preparation and characterisation

Composites of carbon nanotubes (CNT) in polymeric matrices have attracted considerable attention in the research and industrial communities due to their interesting and unique properties. However, the main intrinsic problem of CNT is their insolubility or very poor solubility in either water or organic solvents. Therefore, the dispersion of CNT has become the focus of many researches. In this study, a simple method based on a chemical process was developed in order to improve the dispersion of CNT. Our method consists in grafting carboxylic acid-functionalized carbon nanotubes (CNT-COOH) onto an amino-functionalized silica particles (SiO2-NH2) surface. Prior to assembly, CNT-COOH were prepared by using a mixture of concentrated nitric and sulfuric acids, while SiO2-NH2 were prepared by a silanization with 3-aminopropyltriethoxysilane (APTES). The hybrid carbon nanotube-silica (CNT/SiO2) was dispersed in polyvinyl alcohol (PVA) with 1, 3 and 5 wt% (by weight). Techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) measurement have been employed to study the dispersion state in the polymer matrix. The results indicated a good and uniform dispersion of hybrid fillers. Indeed, it was shown that the silica particles play the role of dispersing agents. In addition, a decrease of the resistivity of the composite films was observed as the concentration of CNT-silica fillers in the PVA increases, reaching 3.4 × 103 Ω.m when the hybrid fillers concentration is equal to 5 %.

Synergistic effect of self-assembled carboxylic acid-functionalized carbon nanotubes and carbon fiber for improved electro-activated polymeric shape-memory nanocomposite

The present work studies the synergistic effect of self-assembled carboxylic acid-functionalized carbon nanotube (CNT) and carbon fiber on the electrical property and electro-activated recovery behavior of shape memory polymer (SMP) nanocomposites. The combination of CNT and carbon fiber results in improved electrical conductivity in the SMP nanocomposites. Carboxylic acid-functionalized CNTs are grafted onto the carbon fibers and then self-assembled by deposition to significantly enhance the reliability of the bonding between carbon fiber and SMP via van der Waals and covalent crosslink. Furthermore, the self-assembled carboxylic acid-functionalized CNTs and carbon fibers enable the SMP nanocomposites for Joule heating triggered shape recovery.

Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) composite electrode as sensing platform for the simultaneous electrochemical determination of dihydroxybenzene isomers

Dihydroxybenzene isomers catechol (CC), resorcinol (RC), and hydroquinone (HQ) were simultaneously determined using a simple, inexpensive, water-stable, and conducting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composite sensing electrode by linear sweep voltammetry. The sensing electrode was prepared by dip-coating a mixture of PEDOT:PSS, Nafion, and carboxylic acid-functionalized single-walled carbon nanotubes on a gold electrode, then modifying by electrochemical doping in a hydrophobic ionic liquid. Nafion was selected as a binding agent to improve the adhesion and binding force between films and electrode interface, and ionic liquid was employed to improve the conductivity and water resistance of the composite electrode. The as-proposed sensing electrode displayed excellent electrochemical catalytic activities towards CC, RC, and HQ. Large peak separations were obtained between HQ and CC as well as CC and RC, i.e., up to 109 and 496 mV, respectively. The calibration curves for CC, RC, and HQ were obtained in the ranges of 0.56–70, 0.18–50, and 0.56–50 μM, with detection limits (S/N = 3) of 0.19, 0.08, and 0.20 μM, respectively. Finally, the sensing electrode was applied to river water sample analysis with reliable recovery. Satisfactory results revealed that the PEDOT:PSS composite can provide a promising platform for the design and application of sensing devices.

Self-assembled carboxylic acid-functionalized carbon nanotubes grafting onto carbon fiber for significantly improving electrical actuation of shape memory polymers

This study presents an effective approach to significantly reduce the electrical resistivity of thermally responsive shape memory polymer (SMP) nanocomposites that show Joule heating triggered shape recovery. Carboxylic acid-functionalized carbon nanotubes (CNTs) self-assembled and grafted onto the carbon fibers, were used to enhance the reliability in bonding between the carbon fiber and the SMP via van der Waals and covalent crosslinking, respectively. It was found that the electrical properties of SMP nanocomposites have been improved by the synergistic effect of carboxylic acid-functionalized CNTs and carbon fibers. Furthermore, the electrically responsive recovery behavior and temperature distribution were monitored and characterized. Finally, the molecular structure and temperature dependent electrical behavior were studied, and verified the electro-activated recovery performance of the SMP nanocomposites.

Interfacial improvement of carbon fiber/epoxy composites using a simple process for depositing commercially functionalized carbon nanotubes on the fibers

An aqueous suspension deposition method was used to coat the sized carbon fibers T700SC and T300B with commercially carboxylic acid-functionalized and hydroxyl-functionalized carbon nanotubes (CNTs). The CNTs on the fiber surfaces were expected to improve the interfacial strength between the fibers and the epoxy. The factors affecting the deposition, especially the fiber sizing, were studied. According to single fiber-composite fragmentation tests, the deposition process results in improved fiber/matrix interfacial adhesion. Using carboxylic acid-functionalized CNTs, the interfacial shear strength was increased 43% for the T700SC composite and 12% for the T300B composite. The relationship between surface functional groups of the CNTs and the interfacial improvement was discussed. The interfacial reinforcing mechanism was explored by analyzing the surface morphology of the carbon fibers, the wettability between the carbon fibers and the epoxy resin, the chemical bonding between the fiber sizing and the CNTs, and fractographic observation of cross-sections of the composites. Results indicate that interfacial friction, chemical bonding and resin toughening are responsible for the interfacial improvement of nanostructured carbon fiber/epoxy composites. The mechanical properties of the CNT-deposited composite laminate were further measured to confirm the effectiveness of this strategy.

Experimental assessment on potential for processiblity of carbon nanotubes/epoxy system used as nanocomposites

In this study, carboxylic acid functionalized carbon nanotubes (CNTs) were used to modify epoxy with intent to develop a nanocomposite matrix for hybrid multiscale composites combining benefits of nanoscale reinforcement with well-established fibrous composites. CNTs were dispersed in epoxy by using high energy sonication, followed by the fabrication of epoxy/CNTs composites. The processibility of CNTs/epoxy systems was explored with respect to their dispersion state and viscosity. The dependences of viscosity, mechanical and thermomechanical properties of nanocomposite system on CNTs content were investigated. The dispersion quality and reagglomeration behavior of CNTs in epoxy and the capillary infiltration of continuous fiber with the epoxy/CNTs dispersion were characterized using optical microscope and capillary experiment. As compared with neat epoxy sample, the CNTs nanocomposites exhibit flexural strength of 126.5 MPa for 1 wt% CNTs content and impact strength of 28.9 kJ m−2 for 0.1 wt% CNTs content, respectively. A CNTs loading of 0.1 wt% significantly improved the glass transition temperatures, Tg, of the nanocomposites. Scanning electron microscopy (SEM) was used to examine the fracture surface of the failed specimens. It is demonstrated that the properties of CNTs/epoxy system are dispersion-dominated and interface sensitive. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Alcohol dehydrogenase immobilization on functionalized carbon nano-tubes modified electrode

A thin layer of poly methylen green (PMG) was covered on glassy carbon (GC) electrode surface by electrochemical polymerization method. In the next step by dropping a suspension of carboxylic acid functionalized carbon nano-tubes on the PMG/GC electrode a layer of CNTs was coated on the electrode. Thereafter, to immobilize the enzyme on electrode surface, three layers of PMG, alcohol dehydrogenase and PMG were added to the modified electrode, respectively. The Fourier transform infrared, scanning electron microscopy and cyclic voltammetry measurements clearly confirmed the successful immobilization of enzyme on the GC electrode.