Carbon Ionic Liquid Electrode Research Articles

Application of Multi‐walled Carbon Nanotube Modified Carbon Ionic Liquid Electrode for the Voltammetric Detection of Dopamine

AbstractIn this paper a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF6) as the binder. Then a Nafion and multi‐walled carbon nanotubes (MWCNTs) composite material was further cast on the CILE surface to get a modified electrode denoted as Nafion‐MWCNTs/CILE. The fabricated electrode showed strong electrocatalytic ability to the oxidation of dopamine (DA) with a pair of well‐defined redox peaks appeared. Compared with other electrodes the redox peak currents increased with the decrease of the peak‐to‐peak separation (Δ Ep), and the result was attributed to the specific properties of MWCNTs and its interaction with imidazolium ion present on the CILE surface. The electrochemical parameters of DA on the Nafion‐MWCNTs/CILE were calculated with the electron transfer coefficient (α) as 0.433, the electron transfer number (n) as 1.1, the apparent heterogeneous electron transfer rate constant (ks) as 0.774 s−1 and the diffusion coefficient (D) as 3.05 × 10−5 cm2/s. Under the selected conditions the oxidation peak current was in linear with DA concentration from 1.0 × 10−5 to 6.0 × 10−4 mol/L with the detection limit as 6.75 × 10−6 mol/L (3σ)by differential pulse voltammetry. The proposed method showed good selectivity and was further applied to the DA injection samples determination with satisfactory results.

Electrochemical horseradish peroxidase biosensor based on dextran–ionic liquid–V 2O 5 nanobelt composite material modified carbon ionic liquid electrode

Direct electrochemistry of horseradish peroxidase (HRP) was realized in a dextran (De), 1-ethyl-3-methylimidazolium ethylsulphate ([EMIM]EtOSO 3) and V 2O 5 nanobelt composite material modified carbon ionic liquid electrode (CILE). Spectroscopic results indicated that HRP retained its native structure in the composite. A pair of well-defined redox peaks of HRP appeared in pH 3.0 phosphate buffer solution with the formal potential of −0.213 V (vs. SCE), which was the characteristic of HRP heme Fe(III)/Fe(II) redox couple. The result was attributed to the specific characteristics of De–IL–V 2O 5 nanocomposite and CILE, which promoted the direct electron transfer rate of HRP with electrode. The electrochemical parameters of HRP on the composite modified electrode were calculated and the electrocatalysis of HRP to the reduction of trichloroacetic acid (TCA) was examined. Under the optimal conditions the reduction peak current increased with TCA concentration in the range from 0.4 to 16.0 mmol L −1. The proposed electrode is valuable for the third-generation electrochemical biosensor.

Copper oxide nanoparticles and ionic liquid modified carbon electrode for the non-enzymatic electrochemical sensing of hydrogen peroxide

The direct electrocatalytic reduction of hydrogen peroxide in alkaline medium at a carbon ionic liquid electrode modified with copper oxide nanoparticles was investigated. The electrode was prepared by mixing graphite particles, ionic liquid (n-octylpyridium hexafluorophosphate) and copper oxide nanoparticles. Unlike the film-modified electrode, the fabrication of this electrode is simple and highly reproducible. The combination of the good conductivity of the ionic liquid and the high catalytic activity of the nanoparticles resulted in an electrode with attractive properties for the determination of hydrogen peroxide. The concentration of NaOH and the loading of copper oxide nanoparticles were optimized. The linear range for the determination of hydrogen peroxide is from 1.0 μM to 2.5 mM, the detection limit is 0.5 μM. High stability, sensitivity, selectivity and reproducibility, fast response, the ease of preparation, and surface renewal made the electrode well suitable for the determination of hydrogen peroxide in real samples.

Label-free amperometric immunobiosensor based on a gold colloid and Prussian blue nanocomposite film modified carbon ionic liquid electrode

A novel experimental methodology based on a Prussian blue (PB) and gold nanoparticles (AuNPs) modified carbon ionic liquid electrode (CILE) was developed for use in a label-free amperometric immunosensor for the sensitive detection of human immunoglobulin G (HIgG) as a model protein. The CILE was fabricated by using the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate as binder. Controllable electrodeposition of PB on the surface of the CILE and coating with 3-aminopropyl triethylene silane (APS) formed a film with high electronic catalytic activity and large surface area for the assembly of AuNPs and further immobilization of HIgG antibody. The electrochemistry of the formed nanocomposite biofilm was investigated by electrochemical techniques including cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. The HIgG concentration was measured through the decrease of amperometric responses in the corresponding specific binding of antigen and antibody. The decreased differential pulse voltammetric values were proportional to the HIgG concentration in two ranges, 0.05-1.25 ng mL(-1) and 1.25-40 ng mL(-1), with a detection limit of 0.001 ng mL(-1) (S/N = 3). This electrochemical immunoassay combined the specificity of the immunological reaction with the sensitivity of the AuNPs, ionic liquid, and PB amplified electrochemical detection and would therefore be valuable for clinical immunoassays.

Development of a sensitive and selective Riboflavin sensor based on carbon ionic liquid electrode

The electrochemical properties of Riboflavin adsorbed on carbon ionic liquid electrode (CILE) were studied by cyclic voltammetry. A film with a surface coverage of up to 3.3 × 10 −9 mol cm −2 was formed after 10 min exposure time. Electron transfer coefficient and rate constant of electron transfer across the modified electrode were found to be 0.43 and 3.03 s −1, respectively. Differential pulse voltammetry was used for the determination of Riboflavin. Two linear working ranges of 0.8–110 nM and 0.11–1.0 μM were obtained with correlation coefficients of 0.998 and 0.996, respectively. The experimental detection limit was obtained as 0.1 nM. The relative standard deviation for five replicate analyses was 4.7%. Other soluble vitamins had no significant interferences and the electrode was used for the determination of Riboflavin in pharmaceutical products, nutrition and beverages.

Direct electrochemistry and electrocatalysis of hemoglobin with carbon nanotube-ionic liquid-chitosan composite materials modified carbon ionic liquid electrode

A novel composite biomaterial was prepared by combining chitosan, multi-walled carbon nanotubes (MWCNTs), hemoglobin (Hb) and ionic liquid (IL) 1-butyl-3-methyl-imidazolium bromide together, which was further modified on the surface of a carbon ionic liquid electrode (CILE) with another ionic liquid 1-ethyl-3-methylimidazolium ethylsulphate as the binder. Ultraviolet-visible and Fourier transform infrared spectroscopic results indicated that Hb molecules in the composite film retained the native structure. Cyclic voltammetric results showed that a pair of well-defined redox peaks appeared in 0.1 mol/L phosphate buffer solution, indicating that the direct electron transfer of Hb in the composite film with the underlying electrode was realized. The results were attributed to the synergistic effect of MWCNTs and IL in the composite film, which promoted the electron transfer rate of Hb. The composite material modified electrode showed excellent electrocatalytic ability towards the reduction of different substrates such as trichloroacetic acid and NaNO 2 with good stability and reproducibility.

Direct electrochemistry of hemoglobin in a nafion and CuS microsphere modified carbon ionic liquid electrode and its electrocatalytic behavior

Direct electrochemistry of hemoglobin (Hb) was realized on a Nafion and CuS microsphere composite film modified carbon ionic liquid electrode (CILE) with N-butylpyridinium hexafluorophosphate (BPPF6) as binder. Scanning electron microscopy (SEM), UV-Vis absorption spectroscopy and cyclic voltammetry were used to characterize the fabricated Nafion/CuS/Hb/CILE. Experimental results showed that a pair of well-defined quasi-reversible redox peaks appeared with the formal potential as -0.386 V (vs. SCE) in pH 7.0 Britton-Robinson (B-R) buffer solution, which was attributed to the Hb heme Fe(III)/Fe(II) redox couples. The electrochemical parameters of Hb in the composite film were carefully investigated with the charge transfer coefficient (α), the electron transfer number (n) and the electron transfer rate constant (ks) as 0.505, 1.196 and 0.610 s -1 , respectively. The composite film provided a favorable microenvironment for retaining the native structure of Hb. The presence of CuS microspheres showed great improvement on the electron transfer rate of Hb with the CILE, which maybe due to the contribution of specific characteristics of CuS microspheres and the inherent advantages of ionic liquid on the modified electrode. The fabricated Hb modified electrode showed good electrocatalytic ability in the reduction of H2O2. The proposed bioelectrode can be used as a new third generation H2O2 biosensor.

Electrochemical behavior and determination of L-tryptophan on carbon ionic liquid electrode

A carbon ionic liquid electrode (CILE) was fabricated by mixing N-butylpyridinium hexafluoro-phosphate (BPPF 6 ) with graphite powder and further used for the investigation on the electrochemical behavior of L-tryptophan (Trp). The fabricated CILE showed good conductivity, inherent electrocatalytic ability and strong promotion to the electron transfer of Trp. On the CILE, an irreversible oxidation peak appeared at 0.948 V (vs. saturated calomel reference electrode). For 5.0 × 10−5 M Trp the oxidation peak current increased about 5 times and the oxidation peak potential decreased on 0.092 V compared to carbon paste electrode. The results indicated that an electrocatalytic reaction occurred on CILE. The conditions for the electrochemical detection were optimized and the electrochemical parameters of Trp on CILE were carefully investigated. Under the selected conditions, the oxidation peak current showed linear relationship with Trp concentration in the range of 8.0 × 10−6 ∼1.0 × 10−3 M for cyclic voltammetry and the detection limit was estimated as 4.8 × 10−6 M (3σ). The interferences of other amino acids or metal ions on the determination were tested and the proposed method was successfully applied to the synthetic sample analysis.

Carbon electrode modified with ionic liquid and multi-walled carbon nanotubes for voltammetric sensing of adenine

A voltammetric sensor was fabricated by applying a Nafion and multi-walled carbon nanotubes (MWCNTs) composite film on the surface of a carbon ionic liquid electrode (CILE), which was prepared by mixing 1-butyl-3-methylimidazolium hexafluorophosphate with graphite powder. The electrochemical behavior of adenine on the Nafion-MWCNTs/CILE was investigated in pH 5.5 buffer solution. Adenine showed an irreversible adsorption-controlled oxidation reaction with enhanced electrochemical response, which was due to the presence of high conductive MWCNTs on the CILE surface. The electrochemical parameters of adenine electro-oxidation were determined, and the experimental conditions were optimized. Under the optimal conditions, the oxidation peak current was linear to the adenine concentration over the range of 1.0 × 10−7 to 7.0 × 10−5 mol L−1 with a detection limit of 3.3 × 10−8 mol L−1 (signal/noise = 3). The electrode showed good stability and selectivity, and was further applied to milk powder samples with satisfactory results.

Direct electrochemistry and electrocatalysis of horseradish peroxidase with hyaluronic acid–ionic liquid–cadmium sulfide nanorod composite material

A new composite material consisted of hyaluronic acid (HA), ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF 4) and cadmium sulfide (CdS) nanorod was fabricated and used for the immobilization of horseradish peroxidase (HRP) on the surface of a carbon ionic liquid electrode (CILE), which was prepared with 1-ethyl-3-methyl-imidazolium ethylsulphate ([EMIM]EtOSO 3) as modifier. Spectroscopic results indicated that HRP remained its native structure in the composite film. Based on the synergistic effect of the materials used, an obvious promotion to the direct electron transfer efficient between HRP and CILE was achieved with a pair of well-defined redox peaks appeared in 0.1 mol L −1 phosphate buffer solution, indicating the realization of the direct electrochemistry of HRP. The immobilized HRP showed good electrocatalytic activity towards the reduction of trichloroacetic acid and H 2O 2 with the electrochemical parameters calculated. Based on the fabricated electrode, a new third-generation electrochemical biosensor was constructed with good stability and reproducibility.

Amperometric glucose biosensor with remarkable acid stability based on glucose oxidase entrapped in colloidal gold-modified carbon ionic liquid electrode

A colloidal gold-modified carbon ionic liquid electrode was constructed by mixing colloidal gold-modified graphite powder with a solid room temperature ionic liquid n-octyl-pyridinium hexafluorophosphate (OPPF 6). Glucose oxidase (GOD) was entrapped in this composite matrix and maintained its bioactivity well and displayed excellent stability. The effect conditions of pH, applied potential and GOD loading were examined. Especially, the glucose oxidase entrapped in this carbon ionic liquid electrode fully retained its activity upon stressing in strongly acidic conditions (pH 2.0) for over one hour. The proposed biosensor responds to glucose linearly over concentration range of 5.0 × 10 −6 to 1.2 × 10 −3 and 2.6 × 10 −3 to 1.3 × 10 −2 M, and the detection limit is 3.5 × 10 −6 M. The response time of the biosensor is fast (within 10 s), and the life time is over two months. The effects of electroactive interferents, such as ascorbic acid, uric acid, can be significantly reduced by a Nafion film casting on the surface of resulting biosensor.

Simultaneous Determination of Dihydroxybenzene Isomers at MWCNTs/β‐Cyclodextrin Modified Carbon Ionic Liquid Electrode in the Presence of Cetylpyridinium Bromide

AbstractSimultaneous determination of dihydroxybenzene isomers was investigated at a multi‐wall carbon nanotubes (MWCNTs)/β‐cyclodextrin composite modified carbon ionic liquid electrode in phosphate buffer solution (pH 7.0, 1/15 mol/L) in the presence of cationic surfactant cetylpyridinium bromide (CPB). With the great enhancement of surfactant CPB, the voltammetric responses of dihydroxybenzene isomers were more sensitive and selective. The oxidation peak potential of hydroquinone was about 0.024 V, catechol was about 0.140 V and resorcinol 0.520 V in differential pulse voltammetric (DPV) measurements, which indicated that the dihydroxybenzene isomers could be separated entirely. The electrode showed wide linear behaviors in the range of 1.2×10−7–2.2×10−3, 7.0×10−7–1.0×10−3, 2.6×10−6–9.0×10−4 mol/L for hydroquinone, catechol and resorcinol, respectively. And the detection limits of the three dihydroxybenzene isomers were 4.0×10−8, 8.0×10−8, 9.0×10−7 mol/L, respectively. The proposed method could be applied to the determination of dihydroxybenzene isomers in artificial wastewater, and the recovery was from 97.4% to 104.2%.

Direct electrochemistry and electrocatalytic properties of hemoglobin immobilized on a carbon ionic liquid electrode modified with mesoporous molecular sieve MCM-41

The direct electron transfer and electrocatalysis of hemoglobin (Hb) entrapped in the MCM-41 modified carbon ionic liquid electrode (CILE) were investigated by using cyclic voltammetry in 0.10 M pH 7.0 phosphate buffer solution (PBS). Due to its uniform pore structure, high surface areas and good biocompatibility, the mesoporous silica sieve MCM-41 provided a suitable matrix for immobilization of biomolecule. The MCM-41 modified CILE showed significant promotion to the direct electron transfer of Hb, which exhibited a pair of well defined and quasi-reversible peaks for heme Fe(III)/Fe(II) with a formal potential of −0.284 V (vs. Ag/AgCl). Additionally, the Hb immobilized on the MCM-41 modified carbon ionic liquid electrode showed excellent electrocatalytic activity toward H 2O 2. The electrocatalytic current values were linear with increasing concentration of H 2O 2 in a wide range of 5–310 μM and the corresponding detection limit was calculated to be 5 × 10 −8 M (S/N = 3). The surface coverage of Hb immobilized on the MCM-41 modified carbon ionic liquid electrode was about 2.54 × 10 −9 mol cm −2. The Michaelis–Menten constant K m app of 214 μM indicated that the Hb immobilized on the modified electrode showed high affinity to H 2O 2. The proposed electrode had high stability and good reproducibility due to the protection effect of MCM-41 and ionic liquid, and it would have wide potential applications in direct electrochemistry, biosensors and biocatalysis.

Ordered mesoporous carbon modified carbon ionic liquid electrode for the electrochemical detection of double-stranded DNA

In this paper the direct electrochemistry of double-stranded DNA (dsDNA) was investigated on ordered mesoporous carbon (OMC) modified carbon ionic liquid electrode (CILE). CILE was prepared by mixing graphite powder with 1-ethyl-3-methylimidazolium ethylsulphate ([EMIM]EtOSO 3) and liquid paraffin. A stable OMC film was formed on the surface of CILE with the help of Nafion to get a modified electrode denoted as Nafion-OMC/CILE. Due to the specific characteristics of OMC and IL present on the electrode surface, the fabricated electrode showed good electrochemical performances to different electroactive molecules. The electrochemical responses of dsDNA were carefully investigated on this electrode with two irreversible oxidation peak appeared at +1.250 V and +0.921 V (vs. SCE), which was corresponding to the oxidation of adenine and guanine residues in dsDNA structure. The electrochemical behaviors of dsDNA were carefully investigated on the Nafion-OMC/CILE. Experimental results indicated that the electron transfer rate was promoted with the increase of the oxidation peak current and the decrease of the oxidation peak potential, which was due to the electrocatalytic ability of OMC on the electrode surface. Under the optimal conditions the oxidation peak current increased with dsDNA concentration in the range of 10.0–600.0 μg mL −1 by differential pulse voltammetry (DPV) with the detection limit of 1.2 μg mL −1 (3 σ).

Direct electrochemistry of hemoglobin entrapped in dextran film on carbon ionic liquid electrode

Direct electrochemistry of hemoglobin (Hb) entrapped in the dextran (De) film on the surface of a room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) modified carbon paste electrode (CILE) has been investigated. UV-Vis and FT-IR spectroscopy showed that Hb retained its native structure in the De film. Scanning electron microscopy (SEM) indicated an uniform film was formed on the electrode surface. Cyclic voltammetric experiments indicated that the electron transfer efficiency between Hb and the electrode was greatly improved due to the presence of the De film and ionic liquid, which provided a biocompatible and higher conductive interface. A pair of well-defined and quasi-reversible redox peak was obtained with the anodic and cathodic peaks located at −0·195 V and −0·355 V in pH 7·0 phosphate buffer solution, respectively. The electrochemical parameters were calculated by investigating the relationship of the peak potential with the scan rate. The fabricated De/Hb/CILE showed good electrocatalytic ability to the reduction of H2O2 with the linear concentration range from 4·0 × 10−6 to 1·5 × 10−5 mol/L and the apparent Michaelis-Menten constant (K M app) for the electrocatalytic reaction was calculated as 0·17 µM.

Direct electrochemistry and electrocatalysis of hemoglobin on carbon ionic liquid electrode

Hemoglobin in agarose was successfully immobilized on a carbon ionic liquid electrode and the direct electrochemical behavior of hemoglobin was investigated. Room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was used as the modifier. Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy and cyclic voltammetry were used to characterize the hemoglobin on the modified electrode. The results showed that the immobilized hemoglobin retained its bioelectrocatalytic activity. The electrochemistry of hemoglobin provided an opportunity to manufacture a third generation of biosensors. Experimental conditions influencing the biosensor performances such as pH, and potential were optimized and assessed. Under the optimal conditions, hydrogen peroxide was detected in the concentration range from 2 × 10 −6 to 1.2 × 10 −3 M with a detection limit of 0.2 μM at S/N = 3. The apparent Michaelis–Menten constant was 1.495 mM. The biosensor exhibited some advantages, such as short time respond, high sensitivity, good reproducibility and long-term stability.

Direct electrochemistry and electrocatalysis of myoglobin immobilized on Fe 2O 3 nanoparticle–sodium alginate–ionic liquid composite-modified electrode

A biocomposite material composed of sodium alginate (SA), Fe 2O 3 nanoparticles, and ionic liquid 1-decyl-3-methylimidazolium bromide ([DMIM]Br) was fabricated and used for the immobilization of myoglobin (Mb) on the surface of a carbon ionic liquid electrode (CILE). The CILE was fabricated by mixing graphite powder with ionic liquid N-butylpyridinium hexafluorophosphate (BPPF 6) together. UV–Vis absorption and FTIR spectroscopic results indicated that Mb retained its native structure in the composite material. A pair of well-defined redox peaks appeared on the cyclic voltammogram in pH 7.0 phosphate buffer solution (PBS) with the formal peak potential ( E 0′) at −0.256 V (versus SCE), which was the typical electrochemical behavior of Mb heme Fe(III)/Fe(II) redox couples. The Mb-modified electrode showed good electrocatalytic activity to the reduction of trichloroacetic acid (TCA) and NaNO 2 with wide linear range, good sensitivity, and reproducibility. The calibration range for TCA detection was between 0.6 and 12.0 mmol L −1 with the linear regression equation as Iss (μA) = 42.44 C (mmol L −1) + 50.57 and a detection limit of 0.4 mmol L −1 (3 σ). The Mb-modified electrode also applied to NaNO 2 determination in the concentration range from 4.0 to 100.0 mmol L −1 with a detection limit of 1.3 mmol L −1 (3 σ). So the proposed electrode has potential applications as third-generation biosensors.

Electrocatalytic oxidation of the reduced nicotinamide adenine dinucleotide at carbon ionic liquid electrode modified with polythionine/multi-walled carbon nanotubes composite

A carbon ionic liquid electrode (CILE) was modified with a polythionine (PTh)/multi-walled carbon nanotubes (MWCNTs) composite and used for the detection of reduced nicotinamide adenine dinucleotide (NADH). The electrode was prepared by electrochemical polymerization of thionine on the MWCNTs in neutral medium. Cyclic voltammetry indicated that the electrode was capable of mediating the oxidation of NADH at an overpotential as low as 0.03 V. Amperometric experiments showed that a sensitive and stable response towards NADH is obtained within 5 s. The linear range for the determination of NADH is from 0.8 μmol L−1 to 422 μmol L−1, with a detection limit of 0.26 μmol L−1 (S/N = 3). The wide linear range, lower detection limit and faster response towards NADH suggests that the new method potentially is useful for developing NAD+-dependent enzyme-based biosensors.

Electrochemistry and Voltammetric Determination of Adenosine with N‐Hexylpyridinium Hexafluorophosphate Modified Electrode

AbstractAn ionic liquid N‐hexylpyridinium hexafluorophosphate (HPPF6) modified carbon paste electrode was fabricated for the sensitive voltammetric determination of adenosine in this paper. Carbon ionic liquid electrode (CILE) was prepared by mixing graphite powder and HPPF6 together and the CILE was characterized by scanning electron microscopy (SEM) and electrochemical methods. The electrochemical behaviors of adenosine on the CILE were studied carefully. Compared with the traditional carbon paste electrode (CPE), a small negative shift of the oxidation peak potential appeared with greatly increase of the oxidation peak current, which indicated the presence of ionic liquid in the carbon paste not only as the binder but also as the modifier and promoter. Under the optimal conditions the oxidation peak current increased with the adenosine concentration in the range from 1.0×10−6 mol/L to 1.4×10−4 mol/L with the detection limit of 9.1×10−7 mol/L (S/N=3) by differential pulse voltammetry. The proposed method was applied to the human urine samples detection with satisfactory results.

Direct electrochemistry and electrocatalysis of hemoglobin on gold nanoparticle decorated carbon ionic liquid electrode

In this paper a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM]EtOSO(3)) as modifier and further gold nanoparticles were in situ electrodeposited on the surface of CILE. The fabricated Au/CILE was used as a new platform for the immobilization of hemoglobin (Hb) with the help of a Nafion film. Electrochemical experimental results indicated that direct electron transfer of Hb was realized on the surface of Au/CILE with a pair of well-defined quasi-reversible redox peaks appeared. The formal peak potential (E(0)') was obtained as -0.210 V (vs. SCE) in pH 7.0 phosphate buffer solution (PBS), which was the characteristic of Hb heme Fe(III)/Fe(II) redox couple. The fabricated Nafion/Hb/Au/CILE showed excellent electrocatalytic activity to the reduction of trichloroacetic acid (TCA) and the reduction peak current was in proportional to TCA concentration in the range from 0.2 to 18.0 mmol/L with the detection limit as 0.16 mmol/L (S/N=3). The proposed electrode showed good stability and reproducibility, and it had the potential application as a new third-generation electrochemical biosensor.