Carbon Nanotube Ionic Liquid Research Articles

Electrochemical determination of Sudan I in food products using a carbon nanotube-ionic liquid composite modified electrode

A sensitive and convenient electrochemical method was developed for the determination of Sudan I using a carbon nanotube-ionic liquid composite modified electrode with the enhancement effect of cetyltrimethyl ammonium bromide (CTAB). The modified electrode exhibited an obvious electrocatalytic activity towards the oxidation of Sudan I, and the oxidation peak current significantly increased in the presence of CTAB. The experimental parameters, such as solution pH, concentration of CTAB and accumulation time, were optimised for Sudan I determination. The oxidation peak current showed a linear relationship with the concentration of Sudan I in the range of 3.0 × 10−8 to 3.1 × 10−6 mol l−1, with a detection limit of 8.0 × 10−9 mol l−1. The proposed method was successfully applied for the determination of Sudan I in food products of ketchup and chilli sauce.

Different electrochemical behavior of adult and fetal hemoglobin at ionic liquid-carbon nanotube nanocomposite

The direct electrochemistry of human adult and fetal hemoglobin on the surface of nanocomposite containing the carboxylated multi-walled carbon nanotubes (MWCNTs) and a hydrophilic room temperature ionic liquid (RTIL) has been reported. The voltammetric results showed that both types of hemoglobins entrapped in RTIL-MWCNTs nanocomposite displayed a pair of well defined, quasi-reversible redox peaks, corresponding to the Fe(III)/Fe(II) redox couple of heme prosthetic group, with the formal potentials of −0.234 and −0.232 V (vs. Ag/AgCl) for human adult and fetal hemoglobin, respectively. Immobilized human fetal hemoglobin on RTIL-MWCNTs nanocomposite relative to immobilized human adult hemoglobin showed slight differences in reversibility, electron transfer rate and protein-substrate affinity toward hydrogen peroxide.

Improving Thermo-Electrochemical Cells Using Carbon Nanotubes

Thermo-electrochemical cells (TECs) allow us to recover the heat wasted from many sources directly, although the efficiency of the process is currently low. TECs are electrochemical devices that produce a steady electric voltage and current under an applied temperature difference between the electrodes. In order to improve the efficiency of TECs, it’s important to search for electrolytes with high electrical conductivities and low thermal conductivities. To this goal, we used impedance spectroscopy to study the effect of carbon nanotubes in ionic liquids used in TECs. Our research indicates that the addition of carbon nanotubes can result in a 3- to 5-fold increase of the mixture’s electrical conductivity. We further tested the power of coin sized-TECs using these novel mixtures. The results show that the addition of 0.06 wt% of carbon nanotubes to imidazolium-based ionic liquids with a modified cobalt redox couple improves the electrical power up to 80%, while there is no detectable change in the thermal conductivity of the mixture at this concentration of carbon nanotubes.

A chiral sensor for recognition of DOPA enantiomers based on immobilization of β-cyclodextrin onto the carbon nanotube-ionic liquid nanocomposite

A sensitive electrochemical method was explored for chiral recognition of 3,4-dihydroxyphenylalanine (DOPA) enantiomers based on immobilization of β-cyclodextrin (β-CD) onto the nanocomposite comprising multiwalled carbon nanotubes (MWCNTs) and ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (BIMIMPF6) modified glassy carbon electrode (β-CD/MWCNTs-IL/GCE). The combination of ionic liquid and carbon nanotubes could create unique nanomaterials which facilitated the electron transfer. In addition, β-CD was brought in to act as the chiral selector for DOPA enantiomers recognition. The immobilization process of β-CD/MWCNTs-IL/GCE was monitored by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The chiral interface (β-CD/MWCNTs-IL/GCE) was employed to discriminate DOPA enantiomers via differential pulse voltammetry. The results indicated that the proposed sensor exhibited a stronger electrochemical response toward D-DOPA over the linear range from 4.0 × 10−3 to 4.0 × 10−9 mol L−1 and the detection limit was 1.2 × 10−9 mol L−1 (S/N = 3). This work provided an available platform for enantioselective recognition of DOPA enantiomers based on the nanocomposite.

Bucky syntactic foam; multi-functional composite utilizing carbon nanotubes-ionic liquid hybrid

Syntactic foams are closed-cell foams made of hollow microballoons embedded in a polymeric matrix. Carbon nanotube-ionic liquid hybrid was used to develop the first “Bucky syntactic foam”. Improvement in the mechanical and electrical properties of syntactic foam was expected since ionic liquids (ILs) can act as a dispersing and binding agent between carbon nanotubes (CNTs) and the polymeric matrix. Several sets of bucky syntactic foam with various weight fractions of CNTs and IL were prepared. Thermal analysis was carried out by Differential Scanning Calorimetry to ensure samples were fully cured in the presence of IL. Mechanical and electrical properties were also characterized via compression and four-point-probe tests. Results showed that the yield strength, elastic modulus, and energy absorption were improved by choosing the optimized content and ratio of CNTs and IL. Electrical conductivity was also improved up to five orders of magnitude, turning traditionally insulator syntactic foam into a conductive nanocomposite. Bucky syntactic foam illustrated potential to be applied in electronic packaging, structure health monitoring, and EMI-shielding structural composites.

Determination of methyl parathion by solid-phase extraction on an ionic liquid–carbon nanotube composite electrode

A novel electrode made of carbon nanotube and ionic liquid (n-octylpyridinium hexafluorophosphate) was developed for the solid-phase extraction and detection of methyl parathion (MP). The electrode effectively accumulated MP and increased the cathodic peak current. Cyclic voltammetry was used to characterize the fabricated electrode and the electrochemical properties of MP on it. Linear sweep voltammetry was used for the quantitative detection of MP. A self-correcting algorithm was exploited to isolate the small peak of MP from the large background current, obtaining a remarkable peak for MP along with a flat baseline. With a preconcentration time of 3 minutes, the peak current was linear for MP concentrations in the range from 0.1 to 2.5 μg mL−1 with a detection limit of 0.008 μg mL−1 (S/N = 3). The electrode was applied to detect MP in soil and food samples. These results indicated that the proposed method was capable of monitoring MP, providing a simple approach for routine analysis.

Square wave voltammetric determination of diclofenac in liquid phase using a novel ionic liquid multiwall carbon nanotubes paste electrode

The direct electrochemistry of diclofenac (DCF) at a surface of modified carbon paste electrode (CPE) was described. The electrode was modified with multiwall carbon nanotubes (MWCNTs) and 1-butyl-3-methylimidazolium hexafluoro phosphate as a binder. The oxidation peak potential of the DCF at a surface of the ionic liquid carbon nanotubes paste electrode (IL/CNTPE) appeared at 750mV that was about 70mV lower than the oxidation peak potential at the surface of the traditional carbon paste electrode under similar condition. Under the optimized conditions at pH7.0, the peak current was linear to DCF concentrations over the concentration range of 0.3–750μmolL−1, using square wave voltammetry (SWV). The detection limit was 0.09μmolL−1. The proposed method was successfully applied to the determination of DCF in both pharmaceutical and patient urine samples.

Multiwall carbon nanotube-ionic liquid electrode modified with gold nanoparticles as a base for preparation of a novel impedimetric immunosensor for low level detection of human serum albumin in biological fluids

A highly sensitive ionic liquid-multiwall carbon nanotube based impedimetric immunosensor modified with gold nanoparticles (GNPs) was developed for the determination of human serum albumin (HSA). The antigen and antibody models used were HSA and activated anti-HSA, respectively. GNPs were electrodeposited on the multiwall based carbon ionic liquid electrode (MW-CILE) surface and then colloidal GNPs were coated through the thiol groups of 1,6-hexanedithiol (HDT) monolayer as a cross linker. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed for characterization of the various layers coated onto the electrode. The electron transfer resistance (Ret) of the antibody-modified electrode changed linearly with the concentration of HSA. The linear range and limit of detection were 0.1–100μgmL−1 and 15.4ngmL−1, respectively. The sensitivity and specificity of the immunosensor were validated using human urine and human serum samples. The results showed that the prepared immunosensor is a useful tool for screening trace amounts of HSA in the biological fluids of proteinuria and diabetics patients, in clinical laboratories.

A novel signal amplification strategy of an electrochemical immunosensor for human chorionic gonadotropin, based on nanocomposites of multi-walled carbon nanotubes–ionic liquid and nanoporous Pd

A novel electrochemical immunosensor using MWCNTs–BMIMPF6/NP-Pd as a sensor platform to sequentially immobilize antibodies was developed for hCG detection.

Functionalized carbon nanotube/ionic liquid-coated wire as a new fiber assembly for determination of methamphetamine and ephedrine by gas chromatography-mass spectrometry

Carbon nanotube–ionic liquid gel immobilized on a stainless steel wire as a novel fiber was successfully applied for headspace SPME of methamphetamine and ephedrine.

Electrochemical behavior of lansoprazole at a multiwalled carbon nanotubes-ionic liquid modified glassy carbon electrode and its electrochemical determination

The electrochemical behavior of lansoprazole (LNS) has been investigated at a glassy carbon electrode (GCE) and the electrode modified by a gel containing multiwalled carbon nanotubes (MWCNTs) and an room-temperature ionic liquid (RTIL) of 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) in 0.10 M phosphate buffer solution of pH 6.8. It was found that an irreversible anodic oxidation peak with Epa as 1.060 V appeared at MWCNTs-RTIL/GCE. Under the optimized experimental conditions a linear calibration curve were obtained over the concentration range from 5.0 ?M to 0.20 mM by differential pulse voltammetry with the limit of detection (LOD, S/N = 3) as 0.28 ?M. In addition, the novel MWCNTs-RTIL/GCE was also characterized by the electrochemical impedance spectroscopy and the proposed method has been successfully applied in the electrochemical quantitative determination of LNS content in commercial tablet samples and the determination results could meet the determination requirement.

Nitrite electrochemical sensor for food analysis based on direct immobilization of hemoglobin on multi-walled carbon nanotube ionic liquid electrode

A novel nitrite biosensor was constructed by simultaneous immobilization of hemoglobin (Hb) and a room temperature ionic liquid, octylpyridinium chloride ([OcPy][Cl]), on multi-walled carbon ionic liquid electrode (MWILE). The direct electron transfer of Hb showed a pair of redox peaks with a formal potential of −0.187 V vs. Ag/AgCl in pH 5.0 acetate buffer solution. Nitrite (NO2 −) catalysis on the modified electrode was investigated by cyclic voltammetry and amperometry. The biosensor exhibited a wide linear range for NO2 − detection from 0.01 to 15 mM, with a detection limit (3σ) of 1.46 μM. MWILE provided an excellent matrix for protein immobilization and biosensor fabrication which could be used for the determination of NO2 − with a low detection limit, fast response, long linearity, and excellent sensitivity.

Dispersing single-walled carbon nanotubes in ionic liquids: a quantitative analysis

The efficiency of various ionic liquids, specifically the 1-butyl-3-methylimidazolium tetrafluoroborate, hexafluorophosphate, chloride and dicyanamide salts, in dispersing single walled carbon nanotubes has been examined. The SWCNTs were dispersed in the ILs at varying concentrations by grinding. All of the ILs were found to be effective dispersants for nanotubes and quantitative evidences including X-ray scattering, Raman spectroscopy and UV-visible spectroscopy unambiguously showed that BMIM[BF4] is the most efficient IL while BMIM[DCA] is the least effective IL. A quantitative analysis of the interactions between SWCNTs and ionic liquids by analyzing their scattering and spectral features is put forth.

Ionic liquid–carbon nanotube composites as scaffolds in the determination of tetrachlorobenzene: electrochemical impedance technique

Room temperature ionic liquids (RTILs) and treated multi-walled carbon nanotubes (MWCNTs) have been innovatively integrated onto a screen-printed carbon electrode (SPCE) for the determination of chlorobenzene micropollutants, such as 1,2,4,5-tetrachlorobenzene (TeCB), based on the electrochemical impedance technique.

Carbon Nanotube–Ionic Liquid (CNT–IL) Nanocamposite Modified Sol-Gel Derived Carbon-Ceramic Electrode for Simultaneous Determination of Sunset Yellow and Tartrazine in Food Samples

Carbon-ceramic electrode modified with multi-walled carbon nanotubes–ionic liquid (MWCNTs–IL) nanocomposite was constructed. This electrode was used for electrochemical determination of food dyes Sunset Yellow (SY) and tartrazine (Tz). The modified electrode based on high surface area and high ionic conductivity of nanocomposite exhibited electrocatalytic effect for oxidation of SY and Tz; also, oxidation peak potentials of SY and Tz effectively separated on modified electrode, and their simultaneous determination was possible. Operational parameters, such as the amount of MWCNTs in suspension, IL volume, solution pH, and scan rate, which affect the analytical performance of determination, were optimized. The present electrode behaved linearly to Sunset Yellow and tartrazine in the concentration range of 4 × 10−7 to 1.1 × 10−4 M and 3 × 10−6 to 0.7 × 10−4 M with a detection limit of 10−7 M (0.045 mg L−1) and 1.1 × 10−6 M (0.59 mg L−1), respectively. The proposed method was successfully utilized for simultaneous determination of SY and Tz in different food samples, and the obtained results were in good agreement to those obtained by HPLC method.

Fast-moving bimorph actuator based on electrochemically treated millimeter-long carbon nanotube electrodes and ionic liquid gel

The development is described of an electromechanical bimorph actuator composed of ionic liquid gel sandwiched by electrochemically treated millimeter-long single-walled carbon nanotubes (SG-SWNT). Electrochemical doping of the SG-SWNT and electrochemical polymerization of polypyrrole on the surface of the SG-SWNT improved the performance of a previously reported actuator using non-treated SG-SWNTs. The conductivity of the SG-SWNT sheets treated at the anodic potential (doped) was found to be three times larger than that of the original film. The generated strain of the actuator prepared from the doped SG-SWNT sheets was increased compared to that prepared from non-doped sample. Moreover, the generated strain of the actuator from the doped SG-SWNT sheets swelled with ionic liquid (IL) was increased to twice that without ILs. The electropolymerization of pyrrole on the surface of the SG-SWNT sheet was carried out. The conductivity of the SG-SWNT was seven times larger after the electropolymerization. The generated strain of the SG-SWNT actuator prepared from the SG-SWNT sheets with electropolymerization was twice as large as that without the electropolymerization at low frequency. At higher frequency, both actuators provide almost the same performance. Both actuators exhibit mechanical resonance at about 100 Hz.

Highly sensitive immunosensing of prostate-specific antigen based on ionic liquid–carbon nanotubes modified electrode: Application as cancer biomarker for prostatebiopsies

A novel and highly sensitive electrochemical immunosensor was developed for detection of prostate specific antigen (PSA) based on immobilization of PSA-antibody (anti-PSA) onto robust nano composite containing multiwalled carbon nanotubes (MWCNTs) and ionic liquid (IL)1-buthyl-methylpyrolydinium bis (trifluromethyl sulfonyl) imide [C4mpyr][NTf2]. Thionine was used as redox system for electrochemical probe. The adsorbed thionine displayed a surface-controlled electrode process with electron transfer rate constant of 6.5s−1 and surface coverage of 3.1×10−11molcm−2. The PSA antibody (anti-PSA) was immobilized or entrapped in the nanocomposite and used in a sandwich type complex immunoassay with anti-PSA labeled with horseradish peroxidase (HRP) as secondary antibody and H2O2 as the substrate. Under optimal conditions, the DPV peak current of the immunosensor increased linearly with increasing PSA concentration in two concentration ranges, 0.2–1.0 and 1–40ngml−1 with detection limit 20pgml−1. The intra-assay and inter-assay coefficients of variation (CVs) for five replicate determinations were 2% and 1.35% at 5ngml−1 PSA. The immunosensor has been used for PSA detection in serum samples and the accuracy of the method was demonstrated by comparison to the standard ELISA assay. Furthermore, the immunosensor can be used for detection of PSA in prostate tissue samples. The simple one-step fabrication method, high sensitivity, good reproducibility and repeatability as well as acceptable accuracy for PSA detection in human serum samples are the main advantages of this immunosensor. Furthermore, the results indicate that differences in PSA concentration can be detected with the proposed immunosensor for cancer tissue samples which holds great promise in clinical screening of cancer biomarkers.

Electrochemical behaviors and determination of carbidopa on carbon nanotubes ionic liquid paste electrode

Electrochemical behaviors of carbidopa (CD) at the surface of the carbon nanotubes paste electrode modified with an ionic liquid of 1-methyl-3-butylimidazolium bromide (MBIDZBr) were studied. The oxidation peak potential of the CD at a surface of the ionic liquid carbon nanotubes paste electrode (IL/CNTPE) appeared at 555mV that was about 68mV lower than the oxidation peak potential at the surface of the traditional carbon paste electrode (CPE) under similar condition. On other hand, the oxidation peak current was increased for about three times at the surface of IL/CNTPE compared to CPE. The linear response range and detection limit were found to be 0.1–420μmolL−1 and 0.06μmolL−1, respectively. Another physiological species did not interfere for determination of CD at a surface of propose sensor in the optimum condition. The proposed sensor was successfully applied for the determination of CD in real samples such as human urine and serum.

Direct electrochemistry of adenine on multiwalled carbon nanotube–ionic liquid composite film modified carbon paste electrode and its determination in DNA

A novel, simple and reliable sensor based on multiwalled carbon nanotube–ionic liquid (1-ethyl-3-methylimidazolium hexafluorophosphate, EMIMPF6) composite film modified carbon paste electrode (MWCNT–IL/CPE) was proposed for direct electrooxidation behavior and determination of adenine. Compared with unmodified electrode, the modified electrode not only significantly enhanced the oxidation peak current but also lowered its oxidation peak potential. The electrochemical behavior of adenine on the modified electrode was carefully studied by cyclic voltammetry and the electrochemical parameters such as the electron transfer coefficient (α), the electrode reaction standard rate constant (ks), the area of the electrode (A), the electron transfer number (n) and the concentration of the electroactive adenine (ГT) were calculated with the results of 0.36, 3.65×10−6s−1, 1.4×10−3cm2, 2.04 and 7.43×10−9molcm−2 respectively. By using differential pulse voltammetry (DPV) as the detection method, a linear relationship was obtained between the oxidation peak current and the adenine concentration in the range from 5.0×10−7 to 7.5×10−5molL−1 with the detection limit of 1.089×10−9molL−1 (3σ) and the relative standard deviation (RSD) 6.5% (n=7) of 5×10−5molL−1 for adenine. The common coexisting substances showed no interferences to the adenine detection and the modified electrode showed good ability to distinguish the electrochemical response of adenine.

Determination of ascorbic acid levels in food samples by using an ionic liquid–carbon nanotube composite electrode

A novel carbon composite electrode consisted of ionic liquid n-octylpyridinum hexafluorophosphate (OPFP) and single-walled carbon nanotube (SWCNT) was fabricated and investigated. This electrode combined the advantages of ionic liquid and SWCNT together with the “bulk” composite electrode. Compared with other composite electrodes using graphite or paraffin oil, the ionic liquid–SWCNT (IL–SWCNT) composite electrode exhibited remarkable increase in the electron transfer rate for electroactive compound and significant decrease in the overpotential for ascorbic acid oxidation reaction. Based on the greatly enhanced electrocatalytic activity for the oxidation of ascorbic acid, a wide linear detection range from 3.0μM to 4.2mM with a low detection limit of 1.0μM was obtained. Furthermore, the IL–SWCNT electrode was applied to determine ascorbic acid levels in real food samples. Experimental results showed that the proposed electrode could be used as an effective and sensitive sensor for direct detection of ascorbic acid.