No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Computational, electrochemical, and spectroscopic, studies of acetycholinesterase covalently attached to carbon nanotubes
Abstract
This manuscript describes results related to the characterization of electrodes modified with a composite of acetylcholinesterase covalently bound to carbon nanotubes (CNT). The characterization was performed by computational methods and complemented by cyclic voltammetry, infrared spectroscopy, and electrochemical impedance spectroscopy. In-silico simulations enabled the identification of the binding site and the calculation of the interaction energy. Besides complementing the computational studies, experimental results obtained by cyclic voltammetry showed that the addition of CNT to the surface of electrodes yielded significant increases in effective area and greatly facilitated the electron transfer reactions. These results are also in agreement with impedance spectroscopy data, which indicated a high apparent rate constant, even after the immobilization of the enzyme. These results lend new information about the physical and chemical properties of biointerfaces at the molecular level, specifically about the mechanism and consequences of the interaction of a model enzyme with CNT.
... Considering these aspects, researchers currently have a variety of immobilization methods at their disposal [17][18][19], including covalent attachment, entrapment, encapsulation, and cross-linking. While covalent attachment can provide an avenue to form a permanent bond between the functional groups of the protein and those of the substrate, the reactions are typically slow, laborious, and the experimental conditions required for such reactions can be detrimental to both the protein and electronic properties of the substrate [20][21][22][23]. The use of bifunctional reagents can be a simple and fast method to promote covalent interactions between the substrate-protein and protein-protein interface [24][25][26], but the bioactivity of the layer can be compromised by the poor accessibility of active sites. ...
... The first case involves a docking calculation using AutoDock Vina 4.2 [55]. As recently described [20,56], these calculations can be used to identify the most probable binding sites and the energy involved in the adsorption process (Fig. 2). Dependent on the size of the system, these calculations can be completed in less than 8 h using a standard computer. ...
... Molecular docking studies were performed using AutoDock 4.2 tool to predict the preferred binding mode and binding sites of PCeGONC with GP (Cabral et al., 2013). The binding mode of RB 4 and HOBT with free and PCeGONC bound GP was also compared. ...
In the present study novel polypyrrole-cellulose-graphene oxide nanocomposite (PCeGONC) was
employed for the immobilization of ginger peroxidase (GP) via simple adsorption mechanism. Immobilization
of enzyme on the obtained support resulted in enhancement of the enzyme activity. The recovery
of activity was 128% of the initial activity. Consequently, in 3 h stirred batch treatment, PCeGONC
bound GP exhibited higher decolorization efficiency (99%) for Reactive Blue 4 (RB 4) dye as compared to
free GP (88%). The immobilized GP exhibited higher operational stability and retained approximately 72%
of its initial activity even after ten sequential cycles of dye decolorization in batch process. The kinetic
characterization of PCeGONC bound GP revealed slightly lower Km and 3.3 times higher Vmax compared
to free GP. Degraded products were identified on the basis of GC-MS analysis and degradation pathway
was proposed accordingly which confirms enzymatic breakdown of RB 4 into low molecular weight
compounds. Genotoxic assessment of GP treated RB 4 revealed significant reduction of its genotoxic
potential. In-silico analysis identified that binding site of PCeGONC on enzyme is distinct and lies far away
from the active site of the enzyme. Furthermore, it also revealed higher affinity of 1-
hydroxybenzotriazole (a redox mediator) and RB 4 for PCeGONC bound enzyme as compared to the
free enzyme. This is in consensus with the observed decrease in Km of the immobilized GP.
... Molecular docking studies were performed using AutoDock 4.2 tool to predict the preferred binding mode and binding sites of PCeGONC with GP (Cabral et al., 2013). The binding mode of RB 4 and HOBT with free and PCeGONC bound GP was also compared. ...
In the present study novel polypyrrole-cellulose-graphene oxide nanocomposite (PCeGONC) was employed for the immobilization of ginger peroxidase (GP) via simple adsorption mechanism. Immobilization of enzyme on the obtained support resulted in enhancement of the enzyme activity. The recovery of activity was 128% of the initial activity. Consequently, in 3 h stirred batch treatment, PCeGONC bound GP exhibited higher decolorization efficiency (99%) for Reactive Blue 4 (RB 4) dye as compared to free GP (88%). The immobilized GP exhibited higher operational stability and retained approximately 72% of its initial activity even after ten sequential cycles of dye decolorization in batch process. The kinetic characterization of PCeGONC bound GP revealed slightly lower Kmand 3.3 times higher Vmaxcompared to free GP. Degraded products were identified on the basis of GC-MS analysis and degradation pathway was proposed accordingly which confirms enzymatic breakdown of RB 4 into low molecular weight compounds. Genotoxic assessment of GP treated RB 4 revealed significant reduction of its genotoxic potential. In-silico analysis identified that binding site of PCeGONC on enzyme is distinct and lies far away from the active site of the enzyme. Furthermore, it also revealed higher affinity of 1-hydroxybenzotriazole (a redox mediator) and RB 4 for PCeGONC bound enzyme as compared to the free enzyme. This is in consensus with the observed decrease in Kmof the immobilized GP.
... It is important to note that the R film decreased around a 96% respect to the resistance value displayed by the blank (bare CE), in agreement with the hypothesis that the conductivity is favored by the metallic properties of the nanoparticles. It was also observed that the electric double-layer capacitance (fitted using a CPE dl to represent the deviation from the ideal comportment) showed a slight increase with respect to the bare electrodes, observation that can be attributed to heterogeneities and roughness in the electrode surface [47][48][49] and that correlate well to the presence of CuNPs on the surface of the carbon fibers. In agreement with features observed in the SEM micrograph (Fig. 2), the lower exponent values obtained for both substrates (˛C PEdl < 0.5) [45] suggest that they behave as porous electrodes. ...
... This finding was not surprising considering the potential composition, topography (Fig. 4), and limited response (Fig. 6) observed with electrodes fabricated from both imaging card paper and multipurpose printing paper. For the case of electrodes fabricated from 3MM chromatography paper, the obtained spectra was fitted with a Randles-type equivalent electrical circuit (see insert in Fig. 8B), containing elements representing the resistance of the solution (R sol = 46.6 ± 0.4 Ω), the internal resistance of the film (R film = 2.6 ± 0.1 Ω), the capacitance of the film (C film = 22 ± 1 μ F), the charge transfer resistance (R ct = 63 ± 2 kΩ), and surface constant phase element (CPE = 32 ± 2 μ F) with an exponent constant (α = 0.93, instead of the traditional C dl representing the capacitance of the double layer) to account for heterogeneities and roughness of the surface of the electrode [62][63][64]. These results that are in within the range reported for other carbon electrodes [37,41,65] suggest that the electrochemical process is limited by the R ct rather than the internal resistance of the films. ...
Electrochemical paper-based analytical devices represent an innovative and versatile platform for fluid handling and analysis. Nevertheless, the intrinsic structure of the paper can impose limitations to both the selection of the electrode material and the method selected to attach the electrodes to the device, potentially affecting the analytical performance of the device. To address these limitations, we herein propose carbon tape as a simple and low cost alternative to develop ePADs. The proposed material (in the form of tape or tabs) was first characterized using a combination of contact angle analysis, resistivity, Raman spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Upon this initial assessment, carbon tape was selected and modified with carbon nanotubes, to provide not only a better surface for proteins to adhere to, but also an enhanced electroactive surface. The analytical performance of the resulting device was assessed by integrating three enzymes that facilitate the oxidation of ethanol, glucose, and phenol, and by performing the detection of these analytes in beer samples. The resulting device, for which materials cost less than a dollar, represents a simple alternative material for ePADs, applied in this case to monitor three of the most important parameters during the production of beers.
Calcium carbide (CaC2), a carcinogen is widely used for artificial ripening of mangoes. Usage of CaC2 for mango ripening results in serious health issues like neurological disorders, ulcers, hypoxia, memory loss, etc. Identification of artificially ripened mangoes and quantification of CaC2 in such fruits help in prevention of related health problems. Instability of CaC2 in water makes its detection complex. In addition, diffusion of calcium hydroxide (Ca(OH)2) and acetylene (C2H2) into the mangoes make it more challenging. In this scenario, an electrochemical CaC2 biosensor with platinum (Pt) working electrode surface modified by ceria (CeO2) nano-interface and acetylcholinesterase (AChE) enzyme has been developed. The mechanism involves competitive inhibition of Pt/CeO2/AChE bioelectrode by the mixture of calcium peroxide (CaO2) and C2H2. Different aspects of electrode immobilization with nano-interface were probed using cyclic voltammetric and amperometric studies. The fabricated Pt/CeO2/AChE bioelectrode exhibited LOD of 0.6 nM with a linear range of 1-20 nM and %recovery in the range of 97.89-104.82.
In this work, we studied the attachment of active acetylcholinesterase (AChE) enzyme on silicon substrate as a potential biomarker for the detection of organophosphorous (OP) pesticides. A multi-step functionalization strategy was developed on crystalline silicon surface: a carboxylic acid-terminated monolayer was grafted on hydrogen-terminated silicon surface by a photochemical hydrosilylation, and then AChE was covalently attached through amide bonds using an activation EDC/NHS process. Each step of the modification was quantitatively characterized by ex-situ Fourier-transform infrared spectroscopy in attenuated-total-reflexion geometry (ATR-FTIR) and atomic force microscopy (AFM). The kinetic of the enzyme immobilization was investigated using in-situ real-time infrared spectroscopy. The enzymatic activity of immobilized acetylcholinesterase enzymes was determined with a colorimetric test. The surface concentration of active AChE was estimated to be Γ= 1.72 x 10 10</sup> cm -2</sup>.
The present paper describes the results related to the optical and electrochemical characterization of thin carbon films fabricated by spin coating and pyrolysis of AZ P4330-RS photoresist. The goal of this paper is to provide comprehensive information allowing for the rational the selection of the conditions to fabricate optically-transparent carbon electrodes (OTCE) with specific electro-optical properties. According to our results, these electrodes could be appropriate choices as electrochemical transducers to monitor electrophoretic separations. At the core of this manuscript is the development and critical evaluation of a new optical model to calculate the thickness of the OTCE by variable angle spectroscopic ellipsometry (VASE). Such data was complemented with topography and roughness (obtained by AFM), electrochemical properties (obtained by cyclic voltammetry), electrical properties (obtained by electrochemical impedance spectroscopy), and structural composition (obtained by Raman spectroscopy). Although the described OTCE were used as substrates to investigate the effect of electrode potential on the real-time adsorption of proteins by ellipsometry, these results could enable the development of other biosensors that can be then integrated into various CE platforms. This article is protected by copyright. All rights reserved.
The current state of research in polymer/carbon nanotubes (single wall and multiwall) composites has been reviewed in context to various types of pre-treatments presently employed. The fundamental aspects of carbon nanotubes are briefly discussed and various strategies designed to alter the dispersion stability and quality of nanotubes in the composites is highlighted. A complete survey of the published data is provided and both the opportunities and the limitations in the frame of covalent and non-covalent type of pre-treatments of carbon nanotubes are juxtaposed. In this context, diverse proposed mechanisms behind different molecular level interactions between nanotubes and the functional moieties are addressed. The effects of these pre-treatments on electrical and rheological percolation thresholds are assessed as they provide an alternative means to evaluate the state of dispersion of carbon nanotubes in the composites. In this regard, the influence of various pre-treatments on the nature of charge transfer mechanisms, system dimensions etc. deduced from different parameters of classical percolation theories are also discussed. These transport parameters offer a vital clue on the nature of the pre-treatment and the effects it has on the structure–property correlations.
Nanostructured materials gained great importance in the past decade on account of their wide range of potential applications in many areas. A large interest is devoted to carbon nanotubes that exhibit exceptional electrical and mechanical properties and can therefore be used for the development of a new generation of composite materials. Nevertheless, poor dispersion and poor interfacial bonding limit the full utilization of carbon nanotubes for reinforcing polymeric media.In this paper, recent advances on carbon nanotubes and their composites will be presented through results of the author's research, essentially based on filled elastomeric networks. The intrinsic potential of carbon nanotubes as reinforcing filler in elastomeric materials will be demonstrated. It will be shown that, despite a poor dispersion, small filler loadings improve substantially the mechanical and electrical behaviors of the soft matrix. With the addition of 1phr of multiwall carbon nanotubes in a styrene–butadiene copolymer, a 45% increase in modulus and a 70% increase in the tensile length are achieved. Straining effects investigated by atomic force microscopy and infrared and Raman spectroscopies, provide interesting results for the understanding of the mechanical behavior of these nanotube-based composites. All the experimental data lead to the belief that the orientation of the nanotubes plays a major role in the mechanical reinforcement. The strong restriction in equilibrium swelling in toluene with the MWNT content is not ascribed to filler–matrix interfacial interactions but to the occlusion of rubber into the aggregates. On the other hand, carbon nanotubes impart conductivity to the insulator matrix. Between 2 and 4phr, the conductivity increases by five orders of magnitude reflecting the formation of a percolating network. Changes in resistivity under uniaxial extension completed by AFM observations of stretched composites bring new insights into the properties of these composites by highlighting the contribution of orientational effects.
The paper describes a set of simple experiments performed to develop an optical model to describe Si/SiO(2) substrates coated with two transparent films of carbon nanotubes. The final goal is to use such optical model to investigate the interaction of proteins with carbon nanotubes. Experiments were performed to assess light reflection as a function of the wavelength or angle of incidence using two substrates (same material, different amounts) composed of oxidized carbon nanotubes. The experimental results indicate that the selected carbon nanotubes layers are anisotropic and significantly different from each other. Experiments performed by spectroscopic ellipsometry (as a function of the wavelength and incident angle) enabled the development of an Effective Medium Approximation model consisting in a two-fraction phase (arc-evaporated carbon and void space). Furthermore, the model enabled calculating the amount of protein adsorbed on the surface of the carbon nanotubes film.
Since carbon nanotubes (CNTs) display unique structures and remarkable physical properties, a variety of applications have emerged in both materials and life sciences. In terms of applications, the functionalisation of nanotubes is extremely important, as it increases their solubility and processability, and combines the unique properties of single-walled carbon nanotubes (SWCNTs) with those of other classes of materials. A number of methods have been developed, which can be divided into two major approaches: (1) non-covalent supramolecular modifications, and (2) covalent functionalisation. In this tutorial review, we survey the covalent modification of SWCNTs with organic moieties, and illustrate the major analytical techniques routinely used to characterise the functionalised materials.
AutoDock Vina, a new program for molecular docking and virtual screening, is presented. AutoDock Vina achieves an approximately two orders of magnitude speed-up compared with the molecular docking software previously developed in our lab (AutoDock 4), while also significantly improving the accuracy of the binding mode predictions, judging by our tests on the training set used in AutoDock 4 development. Further speed-up is achieved from parallelism, by using multithreading on multicore machines. AutoDock Vina automatically calculates the grid maps and clusters the results in a way transparent to the user.
Carbon nanotubes uniformly 50 nm in diameter were directly grown on graphite foil. Cyclic voltammetry (CV) shows that the carbon nanotube/graphite foil electrode has a high specific capacitance (115.7 F/g at a scan rate of 100 mV/s) and exhibits typical double-layer behavior. A rectangular-shaped CV curve persists even at a scan rate of 100 mV/s in 1.0 M H2SO4 aqueous solution, which suggests that the carbon nanotube electrode could be an excellent candidate as the electrode in electrochemical double-layer capacitors. In addition, the influence of the potential scan rate, aging, and the electrolyte solution on the specific capacitance of nanotube electrodes was also studied.
The electrochemical behaviour of multi-walled carbon nanotubes was compared with that of glassy carbon, and the differences were investigated by cyclic voltammetry and electrochemical impedance spectroscopy before and after acid pre-treatment. The electrochemical techniques showed that acid functionalisation significantly improves the electrocatalytic properties of carbon nanotubes. These electrocatalytic properties enhance the analytical signal, shift the oxidation peak potential to a less positive value, and the charge-transfers rate increase of both dopamine and K4[Fe(CN)6]. The functionalisation step and the resulting appearance of edge planes covered with different chemical groups were confirmed by FTIR measurements. Carbon nanotubes after acid pre-treatment are a potentially powerful analytical tool for sensor development.
The role of band structure of individual tubules from single-walled carbon nanotube paper in the electron transfer process was considered within Gerischer–Marcus theory using Raman scattering spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy data. A heterogeneous electron transfer rate of 1.06×10−3cms was observed for ferri/ferrocyanid. A position of the Raman radial breathing mode was used for determination of the chiral vectors of tubules being in resonance with excitation laser light of 1.17eV. For these tubules, the calculated electron transfer rates are similar. It has been shown that nanotube electronic states away from the Fermi level contribute to the electron transfer kinetics due to the broad distribution of the redox states in electrolyte.
The effect of solvent on adsorption of the multi-walled carbon nanotube (MWNT) onto poly(methyl methacrylate) (PMMA) microspheres is examined and then their electrorheological (ER) behavior under an applied electric field when dispersed in a silicone oil is observed, using the MWNT which was initially modified with carboxylic acid functional groups on its outside wall through an oxidation treatment (c-MWNT). The c-MWNT was successfully incorporated onto the PMMA microsphere surface in either Di-water or methanol, while the adsorption state of the c-MWNT is strongly dependent on the solvent used. The dense and well dispersed c-MWNT is found to be more strongly attached onto the surface of PMMA microspheres when prepared in Di-water than in methanol. It is believed that hydrogen bonding component in the Hansen solubility parameter is a principal factor determining dispersion state of the c-MWNT in the solvent, because the nanotubes used have carboxylic acid functional groups on their surface forming hydrogen bonding between c-MWNT and the solvent. Moreover, c-MWNT/PMMA microsphere as an ER material dispersed in a silicone oil is observed to exhibit typical ER characteristics of fibril structure under an applied electric field, and the ER characteristics are found to be influenced by the conductivity of c-MWNT/PMMA microspheres.
In this work we report for the first time the use of the enzyme glucose oxidase (GOx) to efficiently disperse multiwall carbon nanotubes (CNT) and to confer biorecognition properties to the dispersed nanotubes. The optimum dispersion was obtained by sonicating for 15min 1.0mg/mL CNT in 1.0mg/mL GOx solution prepared in 50:50 ethanol/water. The dispersion was evaluated by Scanning Electron Microscopy (SEM), Infrared (FT-IR) and Ultraviolet-visible (UV-vis) Spectroscopy. The electrochemical characterization of glassy carbon electrodes (GCE) modified with the dispersion (by dropping) the dispersion was performed by Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV), and Amperometry. The amount of electroactive GOx deposited on GCE (GCE/CNT-GOx) was 1.02×10−10 molcm−2 and the rate constant for the electron transfer between FAD center and the electrode was (2.9±0.1)s−1 according to Laviron and (9.2±1.3)s−1 considering the model proposed by Albery. The enzyme demonstrated to keep its biocatalytic activity even after dissolution in 50/50 v/v ethanol water solution and sonication for 15min using either ferrocene methanol or oxygen as redox mediators. The sensitivity to glucose at 0.700V obtained for seventeen electrodes prepared with 6 different dispersions was (3.2±0.2) x 102μAM−1, (r=0.997), with an R.S.D. of 6.0%. The sensitivity remained highly constant after 30 days at room temperature (25°C) and 4°C, the sensitivity remained highly constant, with average values of (3.21±0.07) x 102μAM−1, r=0.9992 and (3.59±0.08) x 102μAM−1, r=0.9990, respectively. The GCE/CNT-GOx can be used as platform to build supramolecular architectures for biosensing through for the self-assembling of polyelectrolytes to build supramolecular architectures for biosensing, opening the doors to new and exciting possibilities for the development of biosensors
The effect of acid treatment on multiwalled carbon nanotubes (MWCNTs) was investigated through analysis of their morphologies followed by atomic force microscopy (AFM). The chemical changes were monitored by Fourier transform infrared (FTIR) and ultraviolet (UV/Vis) spectrophotometries. Treatments with nitric acid as well as with a mixture of nitric and sulfuric acids (1:3 by volume) were analyzed. Both acid treatments applied during a short ultrasonication time do not show any relevant effect. However, an additional peak can be observed at 1200 cm−1 in the FTIR spectrum of the MWCNTs treated with the acid mixture after 2 h but their UV/Vis spectrum did not change. These results could indicate that new C–O groups appear in the open ends of the nanotubes without modifying the structure of their sidewalls. When the treatment with the acid mixture was prolonged, the sidewall of the nanotubes began to be destroyed up to their nearly complete destruction as observed by both UV/Vis and AFM. The results reported in this work show that three simple and quick techniques can help to control the carboxylation process often carried out before the functionalization of MWCNTs.
Thermally conductive polymer composites offer new possibilities for replacing metal parts in several applications, including power electronics, electric motors and generators, heat exchangers, etc., thanks to the polymer advantages such as light weight, corrosion resistance and ease of processing. Current interest to improve the thermal conductivity of polymers is focused on the selective addition of nanofillers with high thermal conductivity. Unusually high thermal conductivity makes carbon nanotube (CNT) the best promising candidate material for thermally conductive composites. However, the thermal conductivities of polymer/CNT nanocomposites are relatively low compared with expectations from the intrinsic thermal conductivity of CNTs. The challenge primarily comes from the large interfacial thermal resistance between the CNT and the surrounding polymer matrix, which hinders the transfer of phonon dominating heat conduction in polymer and CNT.This article reviews the status of worldwide research in the thermal conductivity of CNTs and their polymer nanocomposites. The dependence of thermal conductivity of nanotubes on the atomic structure, the tube size, the morphology, the defect and the purification is reviewed. The roles of particle/polymer and particle/particle interfaces on the thermal conductivity of polymer/CNT nanocomposites are discussed in detail, as well as the relationship between the thermal conductivity and the micro- and nano-structure of the composites.
Poly(methyl methacrylate) (PMMA) nanocomposites containing well-dispersed multiwalled carbon nanotubes (MWNTs) were prepared via an in-situ bulk polymerization of methyl methacrylate (MMA) in the presence of carbon nanotubes (CNTs). Electrical conductivities of the synthesized PMMA/MWNT nanocomposite films containing 1−5 wt % of MWNT were between 10-4 and 10-2 S/cm. When PMMA/MWNT nanocomposites with the same MWNT concentrations were electrospun in DMF into nanofibrous membrane, the conductivities were reduced to 10-10 S/cm, even though dispersion of the MWNTs in the electrospun nanofibers was superior to the conventional polymer composites with carbon nanotubes. The diameter of the electrospun fibers ranged between 120 ± 30 and 710 ± 20 nm. In addition, MWNTs in the electrospun nanofibers were found to be embedded in the polymer matix and to align along the fiber axis.
Organized monolayers were constructed on gold electrodes by self-assembly of octadecyl derivatives with trichlorosilane or mercaptan head groups. The monolayers, which are highly oriented and densely packed, provide effective blocking of electrochemical reactivity at coated electrodes. With fractional surface coverages θ close to unity, the remaining exposed electrode surface 1 - θ is distributed as an array of extremely small ultramicroelectrodes with an average diameter of 5-10 nm. It is shown that such electrodes provide distinct advantages in various types of fundamental electrochemical studies, including background suppression, electron-transfer mediation, and most notably, in the measurement of very large heterogeneous electron-transfer rate constants k0. Several such cases are demonstrated, including convenient determination of k0 values as high as 5.0 cm/s. Values of k0 measured in the present work are in good agreement with those calculated from known self-exchange rate constants by using the Marcus relationship.
This work reports the supercapacitive properties of electrochemically grown composite films of multiwalled carbon nanotubes (MWNT) and polypyrrole (PPy), a conducting polymer. Scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy revealed that the nanoporous three-dimensional arrangement of PPy-coated MWNTs in these films facilitated improved electron and ion transfer relative to pure PPy films. The low-frequency capacitance was measured for films of varying thickness, revealing specific capacitances per mass (Cmass) and geometric area (Carea) as high as 192 F g-1 and 1.0 F cm-2, respectively. Rates of charge and discharge about an order of magnitude faster than similarly prepared pure PPy films were also observed.
Despite the extraordinary promise of single-wall carbon nanotubes, their realistic application in materials and devices has been hindered by processing and manipulation difficulties. Now that this unique material is readily available in near kilogram quantities (albeit still at high cost), research into means of chemical alteration is in full swing. The covalent attachment of appropriate moieties is anticipated to facilitate applications development by improving solubility and ease of dispersion, and providing for chemical attachment to surfaces and polymer matrices. While it is clear that more investigation is needed to elucidate the nature and locality of covalently attached moieties, developments to date indicate that carbon nanotubes may indeed be considered a true segment of organic chemistry. In this contribution, we review the current state of carbon nanotube covalent chemistry, and convey our anxious expectation that further developments will follow.
In the present study, we report the systematic investigation of the effect of chemical oxidation on the structure of single-walled carbon nanotubes (SWNTs) by using different oxidants. The oxidation procedure was characterized by using infrared spectroscopy and transmission electron microscopy (TEM). The SWNTs were produced by chemical vapor deposition (CVD) and oxidized with three kinds of oxidants: (1) nitric acid (2.6 M), (2) a mixture of concentrated sulfuric acid (98 wt %) and concentrated nitric acid (16 M) (v/v) 3/1) and (3) KMnO 4 . The results reveal that the different functional groups can be introduced when the SWNTs are treated with different oxidants. Refluxing in dilute nitric acid can be considered as a mild oxidation for SWNTs, introducing the carboxylic acid groups only at those initial defects that already exist. The abundance of the carboxylic acid groups generated with this oxidant remained constant along with the treating time. In contrast, sonication of SWNTs in H 2 SO 4 /HNO 3 increased the incidence of carboxylic acid groups not only at initial defect sites but also at newly created defect sites along the walls of SWNTs. Compared to the two oxidants above, when KMnO 4 in alkali was used as the oxidant, which is relatively mild, different amounts of -OH, -CdO, and -COOH groups were introduced. The oxidation processes begin mainly with the oxidation of the initial defects that arise during the CVD growth of the SWNTs and are accompanied by processes that can be roughly divided into two steps: (1) the defect-generating step and (2) the defect-consuming step. Specifically, during the defect-generating step, the oxidants attack the graphene structure by electrophilic reactions and generate active sites such as -OH and -CdO. This step depends on the oxidant's ability to generate -C-OH groups and to transform them into -CdO groups. During the defect-consuming step, the graphene structure of the tube was destroyed by the oxidation of the generated active sites in step 1. The defect-consuming step mostly counts on the ability of the oxidant to etch/destroy the graphite-like structure around the already generated -CdO and their neighborhood groups.
The electrostatic adsorption of poly-L-lysine molecules onto a vapor-deposited gold film modified with a carboxylic acid-terminated alkanethiol monolayer is monitored with the spectroscopic techniques of polarization-modulation Fourier transform infrared (PM-FTIR) spectroscopy and surface plasmon resonance (SPR). The PIM-FTIR spectrum of a monolayer of poly-L-lysine (PL) adsorbed onto a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) indicates that the lysine residues and the MUA carboxylic acid moieties form ammonium - carboxylate ion pairs which electrostatically bind the polypeptide to the surface. The PL molecules can be desorbed from the surface by rinsing with a buffer solution at a pH that destroys the ion pairing (pH < 6.5 or pH > 12). Measurements of the shift in the SPR angle upon adsorption were used to determine the thicknesses of the adsorbed monolayers; the MUA and PL monolayers were found to be 17.0 and 10.5 Angstrom thick, respectively. These thickness results suggest that the poly-L-lysine monolayer adsorbs onto the packed MUA surface in an extended conformation with the PL backbone lying parallel to the surface. Subsequent exposure of the PL monolayer to a solution of iron phthalocyanine tetracarboxylic acid (FePc) resulted in the adsorption of a third layer onto the surface. The ability of the adsorbed PL molecules to interact with FePc indicates the presence of free lysine residues available for interaction with molecules other than the MUA monolayer.
This study is the first to focus on the potential use of carbon nanotube (CNT) scaffolds as enzyme immobilization substrates for analytical purposes. Besides all the well-known advantages of CNT, three-dimensional scaffolds can significantly increase the amount of enzymes adsorbed per unit area, preserve the catalytic activity of the adsorbed molecules, and allow effective exposure to substrates present in the adjacent medium. Additionally, our results indicate that the sensitivity of analytical probes based on enzyme-loaded CNT scaffolds is proportional to the thickness of the scaffold providing 3-fold sensitivity improvements with respect to the control surfaces.
In this review article, we explore covalent chemical strategies for the functionalization of carbon-nanotube surfaces. In recent years, nanotubes have been treated as chemical reagents (be it inorganic or organic) in their own right. Indeed, from their inherent structure, one can view nanotubes as sterically bulky, pi-conjugated ligands, or conversely as electron-deficient alkenes. Hence, herein we seek to understand, from a structural perspective, the breadth and types of reactions single-walled nanotubes (SWNTs) can undergo in solution phase, not only at the ends and defect sites but also along the sidewalls. Controllable chemical functionalization suggests that the unique electronic and mechanical properties of SWNTs can be tailored in a determinable manner. Moreover, prevailing themes in nanotube functionalization have been involved with dissolution of tubes.
The aim of this work was to address the problems associated with the synthesis and purification of carbon nanotubes, which are essential for the use of this material in various modern technologies. Carbon nanotubes and different nano-structured carbon phases were synthesized using the thermal decomposition of methane and o-xylene mixture and the ferrocene catalyst. The morphology of the samples (which were obtained in the form of powder and coatings) was examined by SEM. With an aim to remove the residual Fe catalyst, the batches of carbon nanotubes were treated with CCl4 at 700 °C, and analysed using gravimetric procedures, magnetic balance, EDX and contact angle measurements. It was found that treatment with CCl4 significantly affects on the surface state of carbon nanotubes and different carbon nanostructures. Elemental analysis results showed that CCl4 is an efficient reagent for removing of iron from the carbon phase (from ∼3 up to 1%). Concurrently, treatment with tetrachloromethane increases the amount of chlorine (up to 6.8%).
Graphite-epoxy resin composite (GrEC) electrodes were modified with chitosan (Chit) films and characterised using electrochemical impedance spectroscopy (EIS). Several film modifications were made using different crosslinking agents: glutaraldehyde (GA), glyoxal (GO), epichlorohydrin (ECH) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) together with N-hydroxysuccinimide (NHS) and the characteristics of each of them evaluated in the presence of model electroactive compounds potassium hexacyanoferrate(III) and hexaammineruthenium(III) chloride. Immobilisation of functionalised carbon nanotubes into chitosan matrices (Chit–CNT) using the same crosslinking agents was also investigated. The impedance of the electrode with the best performance (GrEC/Chit–CNT/EDC–NHS) was characterised as a sensor for dipyrone and hydroquinone and for a glucose biosensor by immobilisation of glucose oxidase (GOx) on top of Chit–CNT using GA. Modelling and equivalent circuit analysis was carried out, with emphasis on diffusion characteristics and the significant features of the spectra are discussed.
A photometric method for determining acetylcholinesterase activity of tissue extracts, homogenates, cell suspensions, etc., has been described. The enzyme activity is measured by following the increase of yellow color produced from thiocholine when it reacts with dithiobisnitrobenzoate ion. It is based on coupling of these reactions: The latter reaction is rapid and the assay is sensitive (i.e. a 10 μ1 sample of blood is adequate). The use of a recorder has been most helpful, but is not essential. The method has been used to study the enzyme in human erythrocytes and homogenates of rat brain, kidney, lungs, liver and muscle tissue. Kinetic constants determined by this system for erythrocyte eholinesterase are presented. The data obtained with acetylthiocholine as substrate are similar to those with acetylcholine.
CNT-electronics is a field involving synthesis of carbon nanotubes-based novel electronic circuits, comparable to the size of molecules, the practically fundamental size possible. It has brought a new paradigm in science as it has enabled scientists to increase the device integration density tremendously, hence achieving better efficiency and speed. Here we review the state-of-art current research on the applications of CNTs in electronics and present recent results outlining their potential along with illustrating some current concerns in the research field. Unconventional projects such as CNT-based biological sensors, transistors, field emitters, integrated circuits, etc. are taking CNT-based electronics to its extremes. The field holds a promise for mass production of high speed and efficient electronic devices. However, the chemical complexity, reproducibility and other factors make the field a challenging one, which need to be addressed before the field realizes its true potential.
Carbon nanotubes have begun to attract enormous interest in electrochemistry because of their small size and good electrochemical properties. The vast majority of studies thus far have used ensembles of carbon nanotubes to nanostructure macroscopic electrodes either with randomly dispersed nanotubes or with aligned carbon nanotubes. The resultant nanotube modified electrodes have most frequently been used for electro-analytical purposes such as the development of biosensors. This review introduces carbon nanotubes and approaches to nanostructuring electrodes with carbon nanotubes, discusses what is known of their electrochemical properties and briefly outlines some of the exciting applications to which they are being targeted for use.
Carbon nanotubes (CNTs) combine in a unique way high electrical conductivity, high chemical stability and extremely high mechanical strength. These special properties of both single-wall (SW) and multi-wall (MW) CNTs have attracted the interest of many researchers in the field of electrochemical sensors. This article demonstrates the latest advances and future trends in producing, modifying, characterizing and integrating CNTs into electrochemical sensing systems.CNTs can be either used as single probes after formation in situ or even individually attached onto a proper transducing surface after synthesis. Both SWCNTs and MWCNTs can be used to modify several electrode surfaces in either vertically oriented “nanotube forests” or even a non-oriented way. They can be also used in sensors after mixing them with a polymer matrix to form CNT composites.We discuss novel applications of CNTs in electrochemical sensors, including enzyme-based biosensors, DNA sensors and immunosensors, and propose future challenges and applications.
Suitable oxidative treatment of catalytically grown carbon nanotubes introduces oxygen containing surface groups. Infrared and titration studies indicate that they are predominately phenolic, carboxylic and lactonic groups. These groups stabilize dispersions of nanotubes at much higher concentrations than are possible with the raw material. Plots of the viscosity of dispersions as a function of their concentration show a dramatic increase in gradient above a critical concentration, leading to the formation of viscoelastic gels. During continued drying, the solvent mediates the formation of dense assemblies of nanotubes which then bond together through the surface groups. If the nanotubes are deposited from a dilute suspension by filtration they are able to maximize the number of intertube contacts by packing into a locally parallelized structure, reminiscent of liquid crystalline polymers.
Enzyme immobilizations on carbon nanotubes for fabrication of biosensors and biofuel cells and for preparation of biocatalysts are rapidly emerging as new research areas. Various immobilization methods have been developed, and in particular, specific attachment of enzymes on carbon nanotubes has been an important focus of attention. The method of immobilization has an effect on the preservation of the enzyme structure and retention of the native biological function of the enzyme. In this review, we focus on recent advances in methodology for enzyme immobilization on carbon nanotubes.
Protein conformational changes may be associated with particular properties such as function, transportation, assembly, tendency to aggregate, and potential cytotoxicity. Protein misfolding, in particular, has been intimately related to protein-mediated diseases. In this study, the conformational structure changes of hemoglobin (Hb) induced by the assembly on gold nanoparticles (AuNPs) surface were studied in detail by a combination of electrochemical method and various spectroscopic techniques including UV-vis absorption, fluorescence, circular dichroism (CD), and Fourier transform infrared (FTIR) spectroscopy. The results indicated that Hb in the Hb-AuNPs bioconjugate system that was prepared by the assembly of Hb on the surface of AuNPs underwent substantial conformational changes both at secondary and tertiary structure level. The assembly of Hb on the boundary surface of AuNPs could result a disturbance of the structure of Hb and induce the exposure of the heme group and tryptophan (Trp) residues to the solvent, leading to the enhancement in the electron transfer rate of the protein. The calculation from quantitative second-derivative infrared and CD spectra of the Hb-AuNPs bioconjugate system showed that AuNPs could induce the conversion of α-helix to β-sheet structures and unfolding of the protein. Moreover, the effects of the concentration and the size of AuNPs on the conformational structure changes of Hb in the bioconjugate system were also demonstrated. The results obtained here not only provide the detailed conformational behavior of Hb molecules on nanoparticles, but also create a framework for analyzing the biosafety of nanoparticles in terms of the biological behavior of biomacromolecules.
A glucose biosensor based on a nanocomposite made by layer-by-layer electrodeposition of the redox polymer into a multilayer containing glucose oxidase (GOx) and single-walled carbon nanotubes (SWCNT) on a screen-printed carbon electrode (SPCE) surface was developed. The objectives of the electrodeposition of redox polymer are to stabilize further the multilayer using a coordinative cross-linked redox polymer and to wire the GOx. The electrochemistry of the layer-by-layer assembly of the GOx/SWCNT/redox polymer nanocomposite was followed by cyclic voltammetry. The resultant biosensor provided stable and reproducible electrocatalytic responses to glucose, and the electrocatalytic current for glucose oxidation was enhanced with an increase in the number of layers. The biosensor displayed a linear range from 0.5 to 6.0mM, a sensitivity of 16.4μA/(mMcm(2)), and a response time of about 5s. It shows no response to 0.05mM of ascorbic acid, 0.32mM of uric acid and 0.20mM of acetaminophen using a Nafion membrane covering the nanocomposite-modified electrode surface.
The objective of this review is to provide a broad overview of the advantages and limitations of carbon-based nanomaterials with respect to analytical chemistry. Aiming to illustrate the impact of nanomaterials on the development of novel analytical applications, developments reported in the 2005-2010 period have been included and divided into sample preparation, separation, and detection. Within each section, fullerenes, carbon nanotubes, graphene, and composite materials will be addressed specifically. Although only briefly discussed, included is a section highlighting nanomaterials with interesting catalytic properties that can be used in the design of future devices for analytical chemistry.
A simple and versatile approach for covalent immobilization of redox protein on solid surface via self-assembled technique and click chemistry is reported. The alkynyl-terminated monolayers are obtained by self-assembled technique, then, azido-horseradish peroxidase (azido-HRP) was covalent immobilized onto the formed monolayers by click reaction. The modified process is characterized by reflection absorption infrared spectroscopy (RAIR), surface-enhanced Raman scattering spectroscopy (SERS) and electrochemical methods. All the experimental results suggest that HRP is immobilized onto the electrode surface successfully without denaturation. Furthermore, the immobilized HRP shows electrocatalytic reduction for H(2)O(2), and the linear range is from 5.0 to 700 μM. The heterogeneous electron transfer rate constant k(s) is 1.11 s(-1) and the apparent Michaelis-Menten constant is calculated to be 0.196 mM.
Electrochemical (EC) sensing approaches have exploited the use of carbon nanotubes (CNTs) as electrode materials owing to their unique structures and properties to provide strong electrocatalytic activity with minimal surface fouling. Nanofabrication and device integration technologies have emerged along with significant advances in the synthesis, purification, conjugation and biofunctionalization of CNTs. Such combined efforts have contributed towards the rapid development of CNT-based sensors for a plethora of important analytes with improved detection sensitivity and selectivity. The use of CNTs opens an opportunity for the direct electron transfer between the enzyme and the active electrode area. Of particular interest are also excellent electrocatalytic activities of CNTs on the redox reaction of hydrogen peroxide and nicotinamide adenine dinucleotide, two major by-products of enzymatic reactions. This excellent electrocatalysis holds a promising future for the simple design and implementation of on-site biosensors for oxidases and dehydrogenases with enhanced selectivity. To date, the use of an anti-interference layer or an artificial electron mediator is critically needed to circumvent unwanted endogenous electroactive species. Such interfering species are effectively suppressed by using CNT based electrodes since the oxidation of NADH, thiols, hydrogen peroxide, etc. by CNTs can be performed at low potentials. Nevertheless, the major future challenges for the development of CNT-EC sensors include miniaturization, optimization and simplification of the procedure for fabricating CNT based electrodes with minimal non-specific binding, high sensitivity and rapid response followed by their extensive validation using "real world" samples. A high resistance to electrode fouling and selectivity are the two key pending issues for the application of CNT-based biosensors in clinical chemistry, food quality and control, waste water treatment and bioprocessing.
In this work, a novel avenue to create a generic approach for the fabrication of biofunctional materials with magnetic capabilities to be used in the design of highly stable, magnetically separable enzyme-based systems was explored. As a model system, immobilization of acetylcholinesterase (AChE) was investigated using biomagnetic glasses composed of a magnetic core with a size tunable porous silica shell. The efficiency of the immobilization was determined by analyzing the biosensing capability of these biomagnetic glasses for the detection of the organophosphorous pesticide paraoxon. Screen printed electrodes with the AChE-biomagnetic glasses showed higher current response and stability than for the free enzyme. The detection limit of the paraoxon biosensor was in the nanomolar range.
The adsorption conditions used to immobilize catalase onto thin films of carbon nanotubes were investigated to elucidate the conditions that produced films with maximum amounts of active catalase. The adsorption kinetics were monitored by spectroscopic ellipsometry, and the immobilized catalase films were then assayed for catalytic activity. The development of a volumetric optical model used to interpret the ellipsometric data is discussed. According to the results herein discussed, not only the adsorbed amount but also the initial adsorption rates determine the final catalytic activity of the adsorbed layer. The results described in this paper have direct implications on the rational design and analytical performance of enzymatic biosensors.
Protein conformational changes may be associated with particular properties such as its function, transportation, assembly, tendency to aggregate, and potential cytotoxicity. In this study, the mechanism of the effects of thermal unfolding of proteins on their catalytic activities and conformational structures were studied by utilizing glucose oxidase (GOx) as a model protein. The characteristic kinetic constants for the enzymatic reaction were evaluated by the use of an electrochemical approach under a substrate-saturated condition. A combination of quantitative second-derivative infrared analysis, two-dimensional infrared correlation spectroscopy (2D IR), and theoretical calculation was used to elucidate the conformational structures that were responsible for inactivation and denaturation of GOx induced by heat. The IR analysis demonstrated that the conformational structures of GOx, especially the α-helix and unordered structures, were greatly dependent on the system temperature. Thermal treatment resulted in the increase of the unordered structure accompanied by the loss of the α-helical structure in GOx conformation. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations revealed that thermal treatment could significantly alter the electronic characteristics and the intramolecular electron transfer ability of FAD (flavin adenine dinucleotide), and hydrogen bond networks formed between FAD and the amino acid residues around the cofactor, leading to the change of the secondary structure and the catalytic activity of GOx. The study essentially paves an effective approach to investigation of the mechanism of protein unfolding.
A new type of conductometric probe based on a molecularly imprinted membrane (MIM) for the detection of salbutamol has been designed and fabricated. The probe consists of two parallel screen-printed electrodes (SPE). One of the SPEs was coated with a molecularly imprinted membrane using salbutamol as the template, and the other was modified with a non-molecularly imprinted membrane (N-MIM). Measurements of salbutamol were conducted after the conductometric probe had been connected to a commercial portable conductometer. Multi-sample or successive detections could be easily accomplished by replacing the one-off SPE coated with the salbutamol molecularly imprinted membrane with a new one. The conductometric response of the sensor to the concentration of salbutamol displayed a linear correlation over a range from 50 to 280 nM, with a detection limit of 13.5 nM. The recoveries reached 92.1-98.3% based on pig urine samples. In addition, the sensor based on this new type of probe demonstrated high sensitivity and selectivity for salbutamol.
A review of recent advances in carbon nanotube science and applications is presented in terms of what was learned at the NT10 11th International Conference on the Science and Application of Nanotubes held in Montreal, Canada, June 29-July 2, 2010.
A simple method to immobilize acetylcholinesterase (AChE) on polypyrrole (PPy) and polyaniline (PANI) copolymer doped with multi-walled carbon nanotubes (MWCNTs) was proposed. The synthesized PAn-PPy-MWCNTs copolymer presented a porous and homogeneous morphology which provided an ideal size to entrap enzyme molecules. Due to the biocompatible microenvironment provided by the copolymer network, the obtained composite was devised for AChE attachment, resulting in a stable AChE biosensor for screening of organophosphates (OPs) exposure. MWCNTs promoted electron-transfer reactions at a lower potential and catalyzed the electro-oxidation of thiocholine, thus increasing detection sensitivity. Based on the inhibition of OPs on the AChE activity, using malathion as a model compound, the inhibition of malathion was proportional to its concentration ranging from 0.01 to 0.5 microg/mL and from 1 to 25 microg/mL, with a detection limit of 1.0 ng/mL. The developed biosensor exhibited good reproducibility and acceptable stability, thus providing a new promising tool for analysis of enzyme inhibitors.
Incluye bibliografía e índice
A recognition layer formed by multiwalled carbon nanotubes (MWCNTs) covalently modified with a ferrocene-lysine conjugate deposited on the indium tin oxide (ITO) was investigated as a sensor for chemical warfare agent (CWA) mimics. Electrochemical impedance spectroscopy measurements showed that upon addition of CWA mimic dramatic changes occurred in the electrical properties of the recognition layer. These changes allowed the detection of nerve agent analogues at the micromolar level, and a limited sensitivity was observed toward a sulfur mustard mimic. Experimental parameters were optimized so as to allow the detection of CWAs at single frequency, thereby significantly reducing acquisition time and simplifying data treatment. A proposed method of detection represents a significant step toward the design of an affordable and "fieldable" electrochemical CWA sensor.
Carbon nanotubes (CNTs) have been incorporated in electrochemical sensors to decrease overpotential and improve sensitivity. In this review, we focus on recent literature that describes how CNT-based electrochemical sensors are being developed to detect neurotransmitters, proteins, small molecules such as glucose, and DNA. Different types of electrochemical methods are used in these sensors including direct electrochemical detection with amperometry or voltammetry, indirect detection of an oxidation product using enzyme sensors, and detection of conductivity changes using CNT-field effect transistors (FETs). Future challenges for the field include miniaturizing sensors, developing methods to use only a specific nanotube allotrope, and simplifying manufacturing.
In this paper we demonstrate that SWNTs and a covalent immobilization strategy enable very sensitive sensors with excellent long term stability. Organophosphorus hydrolase (OPH) functionalized single and multi-walled carbon nanotube (CNT) conjugates were exploited for direct amperometric detection of paraoxon, a model organophosphate. The catalytic hydrolysis of paraoxon produces equimoles of p-nitrophenol; oxidation was monitored amperometrically in real time under flow-injection (FIA) mode. OPH covalently immobilized on single-walled carbon nanotubes (SWNTs) demonstrated much higher activity than OPH conjugated to multi-walled carbon nanotubes (MWNTs). The dynamic concentration range for SWNT-OPH was 0.5-8.5 micromolL(-1) with a detection limit of 0.01 micromolL(-1) (S/N=3). In addition to this high sensitivity, the immobilized OPH retained a significant degree of enzymatic activity, and displayed remarkable stability with only 25% signal loss over 7 months. These results suggest that covalent immobilization of OPH on CNTs can be used for specific immobilization with advantages of long term stability, high sensitivity, and simplicity.
The relationship between the state of the surface of carbon nanotubes (CNTs) and their electrochemical activity was investigated using the enzyme cofactor dihydronicotinamide adenine dinucleotide (NADH) as a redox probe. The boiling of CNTs in water, while nondestructive, activated them toward the oxidation of NADH, as indicated by a shift in the anodic peak potential of NADH (E(NADH)) from 0.4 V to 0.0 V. The shift in E(NADH) was due to the redox mediation of NADH oxidation by traces of quinone species that were formed on the surface of treated CNTs. The harsher treatment that was comprised of microwaving CNTs in concentrated nitric acid had a similar effect on the E(NADH), and, additionally, it increased the anodic peak current of NADH. The latter correlated with the formation of defects on the surface of acid-microwaved CNTs, as indicated by their Raman spectra. The increase in current was discussed, considering the role of surface mediators on the buckled graphene sheets of acid-microwaved CNTs. The other carbon allotropes, including the edge-plane pyrolytic graphite, graphite powder, and glassy carbon, did not display a comparable activation toward the oxidation of NADH.
Carbon nanotube (CNT) adsorption technology has the potential to support point of use (POU) based treatment approach for removal of bacterial pathogens, natural organic matter (NOM), and cyanobacterial toxins from water systems. Unlike many microporous adsorbents, CNTs possess fibrous shape with high aspect ratio, large accessible external surface area, and well developed mesopores, all contribute to the superior removal capacities of these macromolecular biomolecules and microorganisms. This article provides a comprehensive review on application of CNTs as adsorbent media to concentrate and remove pathogens, NOM, and cyanobacterial (microcystin derivatives) toxins from water systems. The paper also surveys on consideration of CNT based adsorption filters for removal of these contaminants from cost, operational and safety standpoint. Based on the studied literature it appears that POU based CNT technology looks promising, that can possibly avoid difficulties of treating biological contaminants in conventional water treatment plants, and thereby remove the burden of maintaining the biostability of treated water in the distribution systems.
Carbon nanotubes and carbon nanofibers have long been investigated for applications in composite structural materials, semiconductor devices, and sensors. With the recent well-documented ability to chemically modify nanofibrous carbon materials to improve their solubility and biocompatibility properties: a whole new class of bioactive carbon nanostructures has been created for biological applications. This review focuses on the latest applications of carbon nanofibers and carbon nanotubes in regenerative medicine.
Other than concentrating the target molecules at the sensor location, we demonstrate two distinct new advantages of an open-flow impedance-sensing platform for DNA hybridization on carbon nanotube (CNT) surface in the presence of a high-frequency AC electric field. The shear-enhanced DNA and ion transport rate to the CNT surface decouples the parasitic double-layer AC impedance signal from the charge-transfer signal due to DNA hybridization. The flow field at high AC frequency also amplifies the charge-transfer rate across the hybridized CNT and provides shear-enhanced discrimination between DNA from targeted species and a closely related congeneric species with three nucleotide mismatches out of 26 bases in a targeted attachment region. This allows sensitive detection of hybridization events in less than 20 min with picomolar target DNA concentrations in a label-free CNT-based microfluidic detection platform.
We have investigated the interaction of d-amino acid oxidase (DAAO) with single-walled carbon nanotubes (CNT) by spectroscopic ellipsometry. Dynamic adsorption experiments were performed at different experimental conditions. In addition, the activity of the enzyme adsorbed at different conditions was studied. Our results indicate that DAAO can be adsorbed to CNT at different pH values and concentrations by a combination of hydrophobic and electrostatic interactions. Considering that the highest enzymatic activity was obtained by adsorbing the protein at pH 5.7 and 0.1 mg x mL(-1), our results indicate that DAAO can adopt multiple orientations on the surface, which are ultimately responsible for significant differences in catalytic activity.
We developed a simple strategy for designing a highly sensitive electrochemical biosensor for organophosphate pesticides (OPs) based on acetylcholinesterase (AChE) immobilized onto Au nanoparticles-polypyrrole nanowires composite film modifid glassy carbon electrode (labeled as AChE-Au-PPy/GCE). Where, the generated Au nanoparticles (AuNPs) were homogenously distributed onto the interlaced PPy nanowires (PPy NWs) matrix, constructing a three-dimensional porous network. This network-like nanocomposite not only provided a biocompatible microenvironment to keep the bioactivity of AChE, but also exhibited a strong synergetic effect on improving the sensing properties of OPs. The combination of AuNPs and PPyNWs greatly catalyzed the oxidation of the enzymatically generated thiocholine product, thus increasing the detection sensitivity. On the basis of the inhibition of OPs on the enzymatic activity of AChE, the conditions for OPs detection were optimized by using methyl parathion as a model OP compound. The inhibition of methyl parathion was proportional to its concentration ranging from 0.005 to 0.12 and 0.5 to 4.5 microgmL(-1). The detection limit was 2 ngmL(-1). The developed biosensor exhibited good reproducibility and acceptable stability. This study provides a new promise tool for analysis of organophosphate pesticides.