Electrochemical properties of carbon nanotube (CNT) film electrodes prepared by controllable adsorption of CNTs onto an alkanethiol monolayer self-assembled on gold electrodes

This paper describes electrochemical properties, such as electrode reactivity, electrode dimensions, and interfacial capacitance, of multiwalled carbon nanotube (MWNT) film electrodes prepared by controllable adsorption of the MWNTs onto the self-assembled monolayer (SAM) of n-octadecyl mercaptan (C18H37SH) deposited onto Au electrodes. The adsorption of the MWNTs onto the SAM-modified Au electrode substantially restores heterogeneous electron transfer between bare Au electrode and redox species in solution phase that is almost totally blocked by the SAM of C18H37SH, and as a result, the prepared MWNT/SAM-modified electrode possesses good electrode reactivity without a remarkable barrier to heterogeneous electron transfer. In addition, the surface coverage of the MWNTs is readily controlled by adjusting the immersion time for the adsorption of the MWNTs onto the SAM of C18H37SH, which essentially endows the prepared MWNT/SAM-modified electrodes with tunable electrode dimensions ranging from a nanoelectrode array to a macro-sized conventional electrode. On the other hand, the MWNT/SAM-modified electrode is found to possess a largely reduced interfacial capacitance, as compared with the MWNT film electrodes prepared with existing methods by directly confining the MWNTs onto electrode surface. This demonstration offers a new approach to fabrication of stable MWNT film electrodes with excellent electrochemical properties that are believed to be very attractive for electrochemical studies and electroanalytical applications.     

Cell chip with nano-scale peptide layer to detect dopamine secretion from neuronal cells

A cell chip with a nano-scaled thin film of cysteine modified synthetic oligopeptide C(RGD)4 was fabricated to detect dopamine secretion from neuronal cells. Thin C(RGD)4 peptide layer was fabricated on chip surface for increasing the binding affinity of cells to gold electrode surface, which is essential for the electrochemical detection of dopamine released from PC12 cells. The structural formation of the peptide thin film was confirmed by both atomic force microscopy (AFM) and scanning electron microscopy (SEM). Redox characteristics of chemical dopamine were firstly characterized by voltammetric tool to compare the dopamine released from PC12 cells. Cells grown on the chip were then subjected to cyclic voltammetric (CV) analysis after 48 hours of incubation. The intensities of reduction peaks were found to be increased with increasing the concentrations of PC12 cells. In addition, the electrochemical redox signal increased more in the cells treated with glucose and potassium compared to the control group. Hence, the developed cell chip can be used to determine the effects of drugs on living cells electrochemically.     

Cell chip to detect effects of graphene oxide nanopellet on human neural stem cell

The graphene oxide (GO) nanopellet, a potentially useful carbon-based material, recently started being applied in cell-based research areas. Its toxicity assessment using the neural-stem-cell-based chip has not been thoroughly reported yet, though. Herein, a cell chip was fabricated to electrochemically detect the toxic effects of GO nanopellets on HBl.F3 cells. The RGD peptide was immobilized on the gold electrode surface to enhance the binding affinity of the HBl.F3 cells to the electrode surface. A clear redox peak appeared when the HB1.F3 cells were analyzed via cyclic voltammetry. The GO nanopellet was analyzed via Raman spectroscopy to confirm its distinct structural characteristics that normally differ from those of graphite oxide. After GO was added to the HB1.F3 cells, differential pulse voltammetry was performed to discover the toxic effects of GO nanopellets on HB1.F3 cells. A negative correlation was achieved between the concentration of the GO nanopellets and the cell viability, which was verified via both MTT assay and a microscopic imaging tool. Thus, these electrochemical tools can be usefully applied to the toxicity assessment of various kinds of carbon-based materials.     

Self-assembled diphenylalanine nanowires for cellular studies and sensor applications

In this paper we present a series of experiments showing that vertical self-assembled diphenylalanine peptide nanowires (PNWs) are a suitable candidate material for cellular biosensing. We grew HeLa and PC12 cells onto PNW modified gold surfaces and observed no hindrance of cell growth caused by the peptide nanostructures; furthermore we studied the properties of PNWs by investigating their influence on the electrochemical behavior of gold electrodes. The PNWs were functionalized with polypyrrole (PPy) by chemical polymerization, therefore creating conducting peptide/polymer nanowire structures vertically attached to a metal electrode. The electroactivity of such structures was characterized by cyclic voltammetry. The PNW/PPy modified electrodes were finally used as amperometric dopamine sensors, yielding a detection limit of 3,1 microM.     

Nanofabrication of bio-self assembled monolayer and its electrochemical property for toxicant detection

Cyclic voltammetry (CV) has been used to investigate the electrochemical behavior of a glutathione (GSH) self assembled monolayer on modified gold electrodes (Bio-SAM). The GSH monolayer exhibits an influence on electrode surface activity. Electrochemically immobilized dsDNA onto a Cyt c/GSH-SAM/Au electrode, which is useful for the fabrication of a nanobiosensing device. The immobilized Cyt c followed by dsDNA immobilized films maintained its surface activity and finally dsDNA/Cyt c/GSH-SAM/Au electrode, targeted for the detection of toxicants. The films were characterized by CV, DPV, and AFM. The differential pulse voltammetry (DPV) technique was applied to detect three kinds of common toxins, 2-aminoanthracene (2-AA), 3-bromobenzanthrone (3-BBA) and bisphenol A (BPhA). The electrochemical signals showed good inverse relationship with the increase of concentrations of toxicants. Our proposed system based on electrochemical method with nanoscale film technology can be applied at highly sensitive biosensor for detecting various toxic chemicals.     

Electrochemical fabrication of polyaniline films containing gold nanoparticles deposited on titanium electrode for electro-oxidation of ascorbic acid

Polyaniline films prepared on titanium were employed as substrate for the electrodeposition of gold. The modified electrode was used as anode for the electro-oxidation of ascorbic acid. The electrochemical behavior and electro-catalytic activity of Au/PAni/Ti electrode were characterized by cyclic voltammetry. The morphology of the polyaniline film and gold coating on PAni/Ti electrode were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) techniques, respectively. Results indicated that gold nanoparticles were homogeneously dispersed on the surface of polyaniline film. The electro-oxidation of ascorbic acid is found to proceed more facile on Au/PAni/Ti electrode than on bare gold electrode. The irreversible oxidation current of ascorbic acid exhibits a linear dependence on the ascorbic acid concentration in the range of 1–5 mM.     

Electrochemical impedance measurement of prostate cancer cells using carbon nanotube array electrodes in a microfluidic channel

Highly aligned multi-wall carbon nanotubes were synthesized in the shape of towers and embedded into fluidic channels as electrodes for impedance measurement of LNCaP human prostate cancer cells. Tower electrodes up to 8 mm high were grown and easily peeled off a silicon substrate. The nanotube electrodes were then successfully soldered onto patterned printed circuit boards and cast into epoxy under pressure. After polishing the top of the tower electrodes, RF plasma was used to enhance the electrocatalytic effect by removing excess epoxy and activating the open end of the nanotubes. Electrodeposition of Au particles on the plasma-treated tower electrodes was done at a controlled density. Finally, the nanotube electrodes were embedded into a polydimethylsiloxane (PDMS) channel and electrochemical impedance spectroscopy was carried out with different conditions. Preliminary electrochemical impedance spectroscopy results using deionized water, buffer solution, and LNCaP prostate cancer cells showed that nanotube electrodes can distinguish the different solutions and could be used in future cell-based biosensor development.     

A cholesterol biosensor based on gold nanoparticles decorated functionalized graphene nanoplatelets

The fabrication of a cholesterol biosensor using gold nanoparticles decorated graphene nanoplatelets has been reported. Thermally exfoliated graphene nanoplatelets act as a suitable support for the deposition of Au nanoparticles. Cholesterol biosensor electrodes have been constructed with nafion solubilized functionalized graphene nanoplatelets (f-G) as well as Au nanoparticles decorated f-G, immobilized over glassy carbon electrode. f-G and Au/f-G thin film deposited glassy carbon electrodes were further functionalized with cholesterol oxidase by physical adsorption. Au nanoparticles dispersed over f-G demonstrate the ability to substantially raise the response current. The fabricated electrodes have been tested for their electrochemical performance at a potential of 0.2 V. The fabricated Au/f-G based cholesterol biosensor exhibits sensitivity of 314 nA/μM cm² for the detection of cholesterol with a linear response up to 135 μM. Furthermore, it has been observed that the biosensor exhibits a good anti-interference ability and favorable stability over a month's period.     

Electrochemical sensing of sulphur dioxide: a comparison using dodecanethiol and citrate capped gold nanoclusters

A comparison of cyclic voltammograms of dodecanethiol (DDT) capped Au nanoclusters (5.0 0.5 nm) and trisodium citrate (Cit) capped Au nanoclusters (approximately 10-15 nm) modified glassy carbon electrode shows a dramatic variation in the current when exposed to a small amount of sulphur dioxide. This is explained using the electrocatalytic properties of Au nanoclusters towards the oxidation of SO2, thus facilitating the fabrication of electrochemical sensors for the detection of SO2. The intrinsic redox changes observed for gold nanocluster-modified glassy carbon electrodes disappear on passing SO2, despite a dramatic current increase, which indeed scales up with the amount of dissolved SO2. Interestingly, a complete rejuvenation of the redox behavior of gold is also observed on subsequent removal of SO2 from the solution by passing pure nitrogen for 15 minutes. Further, these nanoclusters when characterized with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) after SO2 passage reveal a variety of SO2 adsorption modes on gold surface. XP spectra also show a shift of 1.03 eV towards higher binding energy indicating a strong adsorption of SO2 gas, while FTIR gives conclusive evidence for the interaction of SO2 with gold nanoparticles.     

Rapid, Sensitive Detection of Neurotransmitters at Microelectrodes Modified with Self-assembled SWCNT Forests

Carbon nanotube (CNT) modification of microelectrodes can result in increased sensitivity without compromising time response. However, dip coating CNTs is not very reproducible and the CNTs tend to lay flat on the electrode surface which limits access to the electroactive sites on the ends. In this study, aligned CNT forests were formed using a chemical self-assembly method, which resulted in more exposed CNT ends to the analyte. Shortened, carboxylic acid functionalized single-walled CNTs were assembled from a dimethylformamide (DMF) suspension onto a carbon-fiber disk microelectrode modified with a thin iron hydroxide-decorated Nafion film. The modified electrodes were highly sensitive, with 36-fold higher oxidation currents for dopamine using fast-scan cyclic voltammetry than bare electrodes and 34-fold more current than electrodes dipped in CNTs. The limit of detection (LOD) for dopamine was 17 ± 3 nM at a 10 Hz repetition rate and 65 ± 7 nM at 90 Hz. The LOD at 90 Hz was the same as a bare electrode at 10 Hz, allowing a 9-fold increase in temporal resolution without a decrease in sensitivity. Similar increases were observed for other cationic catecholamine neurotransmitters, and the increases in current were greater than for anionic interferents such as ascorbic acid and 3,4-dihydroxyphenylacetic acid (DOPAC). The CNT forest electrodes had high sensitivity at 90 Hz repetition rate when stimulated dopamine release was measured in Drosophila . The sensitivity, temporal resolution, and spatial resolution of these CNT forest modified disk electrodes facilitate enhanced electrochemical measurements of neurotransmitter release in vivo.     

Multiwalled carbon nanotube-based bi-enzyme electrode for total cholesterol estimation in human serum

This study aims at fabricating multiwalled carbon nanotubes (MWCNTs) based enzymatic bioelectrode for total cholesterol estimation in human serum. For this purpose, a gold (Au) electrode was modified with MWCNTs uniformly dispersed in nafion (Nf) matrix. Cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) were immobilised onto this Nf–MWCNTs film-modified Au electrode using layer-by-layer technique to fabricate the final bioelectrodes. The immobilisation of ChOx and ChEt onto the electrodes was demonstrated by scanning electron microscopy. The fabricated bioelectrodes were electrochemically characterised using cyclic voltammetry. The bioelectrodes offer reliable response characteristics towards cholesterol and stable electrochemical properties in terms of extended linear response range of 0.080–0.950?mM, detection limit up to 0.01?mM and optimum storage stability up to three weeks. Experimental results reveal that the fabricated bioelectrode offer optimum repeatability and reproducibility towards the cholesterol estimation and can also efficiently exclude interference by the commonly coexisting ascorbic acid, uric acid, lactic acid, glucose and urea, which is favourable for its efficient use in the highly selective analysis of total cholesterol in serum samples.     

Microfluidic electrochemical aptameric assay integrated on-chip: a potentially convenient sensing platform for the amplified and multiplex analysis of small molecules

Aptamers are artificial oligonucleotides that have been widely employed to design biosensors (i.e., aptasensors). In this work, we report a microfluidic electrochemical aptamer-based sensor (MECAS) by constructing Au-Ag dual-metal array three-electrode on-chip for multiplex detection of small molecules. In combination with the microfluidic channels covering on the glass chip, different targets are transported to the Au electrodes integrated on different positions of the chip. These electrodes are premodified by different kinds of aptamers, respectively, to fabricate different sensing interfaces which can selectively capture the corresponding target. It is an address-dependent sensing platform; thus, with the use of only one electrochemical probe, multitargets can be recognized and detected according to the readout on a corresponding aptamer-modified electrode. In the sensing strategy, the electrochemical probe, [Ru(NH(3))(6)](3+) (RuHex), which can quantitatively bind to surface-confined DNA via electrostatic interaction, was used to produce chronocoulometric signal; Au nanoparticles (AuNPs) were used to improve the sensitivity of the sensor by amplifying the detection signals. Moreover, the sensing interface fabrication, sample incubation, and electrochemical detection were all performed in microfluidic channels. By using this detection chip, we achieved the multianalysis of two model small molecules, ATP, and cocaine, in mixed samples within 40 min. The detection limit of ATP was 3 × 10(-10) M, whereas the detection limit of cocaine was 7 × 10(-8) M. This Au-Ag dual metal electrochemical chip detector integrated MECAS was simple, sensitive, and selective. Also it is similar to a dosimeter which accumulates signal upon exposure. It held promising potential for designing electrochemical devices with high throughput, high automation, and high integration in multianalysis.     

Fabrication of stem cell chip with peptide nanopatterned layer to detect cytotoxicity of environmental toxicants

A stem cell chip with peptide nanopatterned layer was fabricated to detect the effects of environmental toxins on human neural stem cells (HB1 x F3) electrochemically. The cell chip was recently developed as in vitro monitoring tool for determining the cell viability simply and rapidly compared to the conventional methods. However, cell chip composed of neural stem cells have not been reported due to the difficulties for maintaining its stemness and cell attachment on the artificial electrode surface, which is critical for sensitive detection of cell viability electrochemically. In this study, we fabricated peptide nanopatterned layer on gold electrode for increasing the affinity between the stem cell and an artificial electrode surface by self-assembly technique. After the confirmation of fabricated nanopatterned surface, neural stem cells were immobilized on chip surface and the viability was measured by electrochemical method. Thereafter, neural stem cells were treated with two kinds of common environmental toxins, and the intensities of reduction peak obtained by cyclic voltammetry (CV) were decreased with the increase of concentrations of environmental toxins. These electrochemical results were validated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Our newly developed stem cell chip can be used as useful label-free analysis tool for detecting drug effects or for assessing the toxicity electrochemically.     

Fabrication of gold nanodot arrays on a transparent substrate as a nanobioplatform for label-free visualization of living cells

Two-dimensional gold (Au) nanodot arrays on a transparent substrate were fabricated for imaging of living cells. A nanoporous alumina mask with large-area coverage capability was prepared by a two-step chemical wet etching process after a second anodization. Highly ordered Au nanodot arrays were formed on indium-tin-oxide (ITO) glass using very thin nanoporous alumina of approximately 200 nm thickness as an evaporation mask. The large-area Au nanodot arrays on ITO glass were modified with RGD peptide (arginine; glycine; aspartic acid) containing a cysteine (Cys) residue and then used to immobilize human cancer HeLa cells, the morphology of which was observed by confocal microscopy. The confocal micrographs of living HeLa cells on Au nanodot arrays revealed enhanced contrast and resolution, which enabled discernment of cytoplasmic organelles more clearly. These results suggest that two-dimensional Au nanodot arrays modified with RGD peptide on ITO glass have potential as a biocompatible nanobioplatform for the label-free visualization and adhesion of living cells.     

A Joint Experimental and Computational Search for Authentic Nano‐electrocatalytic Effects: Electrooxidation of Nitrite and L‐Ascorbate on Gold Nanoparticle‐Modified Glassy Carbon Electrodes

The investigation of electrocatalytic nanoeffects is tackled via joint electrochemical measurements and computational simulations. The cyclic voltammetry of electrodes modified with metal nanoparticles is modeled considering the kinetics of the electrochemical process on the bulk materials of the different regions of the electrode, that is, the substrate (glassy carbon) and the nanoparticles (gold). Comparison of experimental and theoretical results enables the detection of changes in the electrode kinetics at the nanoscale due to structural and/or electronic effects. This approach is applied to the experimental assessment of electrocatalytic effects by gold nanoparticles (Au NPs) in the electrooxidation of nitrite and L‐ascorbate. Glassy carbon electrode is modified with Au NPs via seed‐mediated growth method. Divergence between the kinetics of these processes on gold macroelectrodes and gold nanoparticles is examined. Whereas claimed catalytic effects are not observed in the electrooxidation of nitrite, electrocatalytic nanoeffects are verified in the case of L‐ascorbate. This is probably due to that the electron transfer process follows an adsorptive mechanism. The combination of simulation with experiments is commended as a general strategy of authentification, or not, of nanoelectrocatalytic effects.     

Electrogenerated chemiluminescence. 66. The role of direct coreactant oxidation in the ruthenium tris(2,2')bipyridyl/tripropylamine system and the effect of halide ions on the emission intensity

We describe the electrogenerated chemiluminescence (ECL) processes of the Ru(bpy)3(2+) (bpy = 2,2'-bipyridyl)/ tripropylamine (TPrA) system at glassy carbon, platinum, and gold electrodes. The electrochemical behavior of TPrA on different electrode materials and its influence on the ECL process are demonstrated. At glassy carbon electrodes, the direct oxidation of TPrA began at approximately 0.6 V vs SCE and exhibited a broad irreversible anodic peak. Two ECL waves were observed, one in the potential region more negative than 1.0 V vs SCE and one at more positive potentials. The first ECL process apparently occurs without the electrogeneration of Ru(bpy)3(3+), in contrast to that of the second ECL wave. At Pt and Au electrodes, however, the formation of surface oxides significantly blocked the direct oxidation of TPrA. An ECL wave below 1.0 V did not appear at Pt and was very weak at gold. The ECL peaks at potentials of 1.1-1.2 V were also much weaker than those observed at the glassy carbon electrode. These results showed that the direct oxidation of TPrA played an important role in the ECL processes. Therefore, the enhancement of the TPrA oxidation current might lead to an increase in the ECL intensity. Small amounts of halide species were found to inhibit the growth of surface oxides on Pt and gold electrodes and led to an obvious increase of TPrA oxidation current. The anodic dissolution of gold in halide-containing solution was also important in activating the gold electrode surface. The electrochemical catalytic effect of bromide further promoted the oxidation of TPrA. A halide effect on ECL at Pt and Au electrodes was also evident. The most effective enhancement of ECL was observed at Au electrode in a bromide-containing solution. This effect was also found in an commercial flow-through instrument (IGEN) and provided a simple way to improve the detection sensitivity at low concentrations of Ru(bpy)3(2+).     

Cell chip-based monitoring of toxic effects of cosmetic compounds on skin fibroblast cells

The present study estimated the efficacy of electrochemical detection of imidazolidinyl urea-induced cell toxicity in skin human fibroblast cells (HFF cells). The gold nanopunct structures were fabricated through a nanoporous alumina mask, and the structural formations were confirmed via scanning electron microscopy. The HFF cells were allowed to attach to RGD (Arg-Gly-Asp) peptide nanopatterned surfaces, and electrochemical tools were applied to skin cells attached to the chip surface. The HFF cells evidenced inflammation responses to allergens such as imidazolidinyl urea. The cells were subsequently treated with different concentrations of imidazolidinyl urea for 24 h in culture, which induced a change in the cyclic voltammetry (CV) current peak. Treatment with imidazolidinyl urea induced a loss of cell viability and accelerated inflammation in a concentration-dependent manner. The expression level of inflammation-related proteins such as IL-1 beta were increased in imidazolidinyl urea-treated cells. The CV results demonstrated that imidazolidinyl urea significantly reduced the current peaks in a dose-dependent manner. The results showed that the current peak was reduced in accordance with the increases in imidazolidinyl urea-induced inflammation. In conclusion, the results of this study suggest that the electrochemical-based chip provides crucial information for improvements to a cell chip system for drug screening applications.     

Rationally Designed Peptide Interface for Potential Modulated Cell Adhesion and Migration

Conformational changes of peptides are critically important in the control of their biological activities. Here, a quaternary ammonium group‐terminated RGD‐containing peptide (RGD‐NMe₃) is designed, which may undergo reversible conformational switch upon different electrochemical potentials. Potential responsive peptide interfaces are constructed on gold substrates with RGD‐NMe₃ in a tetra (ethylene glycol) background. It is demonstrated that by applying positive and negative potentials, the RGD peptide can be reversibly switched between linear and cyclic conformation, which can be used in reversible controlling of cell adhesion/migration on the interface. Furthermore, by combining microfluidics, adhesion of the cells in specific areas on the surface and subsequent directional migration of the cells can be controlled. It is believed that this straightforward potential modulation mechanism for peptide conformation control may find a wide use in design responsive peptide interfaces.     

RF-sputtering preparation of gold-nanoparticle-modified ITO electrodes for electrocatalytic applications

The preparation of gold-nanoparticle (AuNPs)-modified indium tin oxide (ITO) electrodes (AuNPs/ITO) was performed by radio-frequency (RF) sputtering from Ar plasmas at temperatures as low as 60?°C, tailoring the AuNP morphology and content as a function of the sole sputtering time. The latter parameter was varied from 5 to 20 min in order to investigate the influence of gold amount and distribution on the electrochemical performances of the resulting AuNPs/ITO systems. The electrodes were characterized using field emission-scanning electron microscopy (FE-SEM), UV-vis absorption and x-ray photoelectron spectroscopies (XPS); moreover variable scan rate cyclic voltammetry (CV) studies were performed to examine their electrochemical behavior. The electrocatalytic activity of the nanostructured AuNPs/ITO electrodes toward methanol oxidation was investigated and compared with a continuous gold film (Aufilm/ITO). The catalytic efficiency of the AuNPs/ITO systems was found to increase with the gold content and the AuNPs-support boundary region in the corresponding samples. For the longest sputtering time (i.e. 20 min) the performances of the nanostructured electrode were better than the Aufilm/ITO reference, despite the much lower catalyst amount. Furthermore, conversely from the AuNPs/ITO samples, in the Au(film)/ITO case the gold film displayed a poor adhesion to the substrate and the electrode could be used only for a limited number of electrochemical cycles.     

Direct electrochemistry of Shewanella loihica PV-4 on gold nanoparticles-modified boron-doped diamond electrodes fabricated by layer-by-layer technique

Microbial Fuel Cells (MFCs) are robust devices capable of taping biological energy, converting pollutants into electricity through renewable biomass. The fabrication of nanostructured electrodes with good bio- and electrochemical activity, play a profound role in promoting power generation of MFCs. Au nanoparticles (AuNPs)-modified Boron-Doped Diamond (BDD) electrodes are fabricated by layer-by-layer (LBL) self-assembly technique and used for the direct electrochemistry of Shewanella loihica PV-4 in an electrochemical cell. Experimental results show that the peak current densities generated on the Au/PAH multilayer-modified BDD electrodes increased from 1.25 to 2.93 microA/cm(-2) as the layer increased from 0 to 6. Different cell morphologies of S. loihica PV-4 were also observed on the electrodes and the highest density of cells was attached on the (Au/PAH)6/BDD electrode with well-formed three-dimensional nanostructure. The electrochemistry of S. loihica PV-4 was enhanced on the (Au/PAH)4/BDD electrode due to the appropriate amount of AuNPsand thickness of PAH layer.