A novel biosensor based on electro-co-deposition of myoglobin (Mb), sodium alginate (SA), Fe3O4-graphene (Fe3O4-GR) composite on the carbon ionic liquid electrode (CILE) was fabricated using Nafion as the film forming material to improve the stability of protein immobilized on the electrode surface, and the modified electrode was abbreviated as Nafion/Mb-SA-Fe3O4-GR/CILE. FT-IR and UV–vis absorption spectra suggested that Mb could retain its native structure after being immobilized in the SA-Fe3O4-GR composite film. The electrochemical behavior of the modified electrode was studied by cyclic voltammetry, and a pair of symmetric redox peaks appeared in the cyclic voltammograms, indicating that direct electron transfer of Mb was realized on the modified electrode, which was ascribed to the good electrocatalytic capability of Fe3O4-GR composite, the good biocompatibility of SA and the synergistic effects of SA and Fe3O4-GR composite. The electrochemical parameters of the electron transfer number (n), the charge transfer coefficient (α) and the electron transfer rate constant (ks) were calculated as 0.982, 0.357 and 0.234 s−1, respectively. The modified electrode exhibited good electrocatalytic ability to the reduction of trichloroacetic acid (TCA) with wide linear range from 1.4 to 119.4 mmol/L, low detection limit as 0.174 mmol/L (3σ), good stability and reproducibility.

Palladium-graphene (Pd-GR) nanocomposite was acted as modifier for construction of the modified electrode with direct electrochemistry of hemoglobin (Hb) realized. By using Nafion as the immobilization film, Hb was fixed tightly on Pd-GR nanocomposite modified carbon ionic liquid electrode. Electrochemical behaviors of Hb modified electrode were checked by cyclic voltammetry and a pair of redox peaks originated from direct electron transfer of Hb was appeared. The Hb modified electrode had excellent electrocatalytic activity to the reduction of trichloroacetic acid and sodium nitrite in the concentration range from 0.6 to 13.0 mmol·L− 1 and from 0.04 to 0.5 mmol·L− 1. Therefore Pd-GR nanocomposite was proven to be a good candidate for the fabrication of third-generation electrochemical biosensor.Download high-res image (240KB)Download full-size image

A sensitive electrochemical method was proposed for the determination of adenosine-5′-diphosphate (ADP) on an ionic liquid (IL) 1-(3-chloro-2-hydroxy-propyl)-3-methylimidazole chloride modified carbon paste electrode (CPE) in a pH 4.5 Britton-Robinson (B-R) buffer solution. Compared with CPE, IL modified CPE (CILE) showed strong electrocatalytic ability to promote the electrochemical oxidation of ADP. A well-defined irreversible oxidation peak of ADP appeared at +1.381 V with an adsorption-controlled process, which was due to the presence of high conductive IL on the electrode. The experimental conditions were optimized and the electrochemical parameters of ADP were calculated with the electron transfer coefficient (α) as 0.293, the electron transfer number (n) as 1.23, the apparent heterogeneous electron transfer rate constant (ks) as 3.325 × 10−6 s−1 and the surface coverage (ΓT) as 0.92 × 10−8 mol/cm2. Under the optimum conditions, the oxidation peak current was linear to ADP concentration in the range from 3.0 to 1000.0 μmol/L with the detection limit as 2.78 μmol/L (3σ) by differential pulse voltammetry. The CILE also eliminated the interferences of commonly coexisting substances and was successfully applied to detect the ADP artificial samples.

A nanohybrid biomaterial was fabricated by mixing Co3O4 nanorods, gold nanoparticles (Au-NPs) and myoglobin (Mb), and depositing it on the surface of a carbon paste electrode containing the ionic liquid N-hexylpyridinium hexafluorophosphate as the binder. UV–vis and FT-IR revealed the Mb in the composite film to have remained in its native structure. A pair of well-defined redox peaks appears in cyclic voltammograms and indicates direct electron transfer from the Mb to the underlying electrode. The results are attributed to the favorable orientation of Mb in the composite film, to the synergistic effects of Co3O4 nanorods and Au-NPs. The modified electrode shows excellent electrocatalytic ability towards the reduction of substrates such as trichloroacetic acid and nitrite, and displays good stability and reproducibility.

A novel and sensitive electrochemical DNA biosensor was fabricated by using the 4-aminothiophenol (4-ATP) self-assembled on electrodeposited gold nanoparticles (NG) modified electrode to anchor capture ssDNA sequences and Au nanoparticles (AuNPs) labeled with reporter ssDNA sequences, which were further coupled with electroactive indicator of hexaammineruthenium (III) ([Ru(NH3)6]3+) to amplify the electrochemical signal of hybridization reaction. Different modified electrodes were prepared and characterized by cyclic voltammetry, scanning electron microscope and electrochemical impedance spectroscopy. By using a sandwich model for the capture of target ssDNA sequences, which was based on the shorter probe ssDNA and AuNPs label reporter ssDNA hybridized with longer target ssDNA, the electrochemical behavior of [Ru(NH3)6]3+ was monitored by differential pulse voltammetry (DPV). The fabricated electrochemical DNA sensor exhibited good distinguish capacity for the complementary ssDNA sequence and two bases mismatched ssDNA. The dynamic detection range of the target ssDNA sequences was from 1.4 × 10−11 to 2.0 × 10−9 mol/L with the detection limit as 9.5 × 10−12 mol/L (3σ). So in this paper a new electrochemical DNA sensor was designed with gold nanoparticles as the immobilization platform and the signal amplifier simultaneously.

A novel biocompatible sensing strategy based on a graphene (GR), ionic liquid (IL) 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) and chitosan (CTS) composite film for the immobilization of myoglobin (Mb) was adopted in this paper. The UV–vis and FT-IR spectroscopic results demonstrate that the Mb in the composite film maintained its native structure. The direct electron transfer properties and the bioelectrocatalytic activity of the Mb in the nanocomposite film were further investigated. The cyclic voltammetric results indicate that a pair of quasi-reversible redox waves appeared, thereby signifying that the direct electrochemistry of the Mb was realized in the nanocomposite film. This result can be attributed to the specific properties of the material used, including the large surface-to-volume ratio and high conductivity of the GR, the high ionic conductivity of the IL, the interaction of the IL with the GR, and the high biocompatibility of the CTS, which enhanced the absorption of the Mb and promoted the direct electron transfer between the Mb and the substrate electrode. The CTS–Mb–GR–IL modified electrode exhibited a high electrochemical catalytic ability to reduce trichloroacetic acid, which demonstrates the material's potential application in third-generation biosensor.

A new hydroxyl functionalized ionic liquid (IL) 1-(3-chloro-2-hydroxy-propyl)-pyridinium acetate was used as the binder for the preparation of carbon ionic liquid electrode (CILE), which was further used for the voltammetric determination of adenosine-5′-monophosphate (5′-AMP). The modified electrode was characterized by different electrochemical methods including cyclic voltammetry and electrochemical impedance spectroscopy. The results indicated that the presence of IL in the carbon paste greatly improved the electrochemical performances of the modified electrode. A remarkable oxidation peak of 5′-AMP appeared on CILE with the oxidation peak potential of 1.38 V (vs. SCE) at pH 4.0 Britton-Robinson buffer. The electrochemical parameters of 5′-AMP electrooxidation were calculated with the electron transfer coefficient (α) as 0.27, the electron transfer number (n) as 1.11 and the apparent heterogeneous electron transfer rate constant (ks) as 1.03 × 10−5 s−1. Under the selected condition and by using sensitive differential pulse voltammetry the oxidation peak current was proportional to 5′-AMP concentration in the range from 3.0 to 2500.0 μmol/L with the detection limit as 0.60 μmol/L (3σ). The proposed method showed good selectivity to the 5′-AMP detection without the interference from coexisting substances and was further applied to the vidarabine monophosphate injection samples determination with satisfactory results.Graphical abstractHighlights► Hydroxyl functionalized ionic liquid (IL) was used for the modification of carbon paste electrode. ► Specific characteristics of hydroxyl functionalized IL enhanced the oxidation peak currents of 5′-AMP. ► Detection of commercial injection samples with satisfactory results.

In this paper a graphene (GR) modified carbon ionic liquid electrode that was obtained by one-step potentiostatic electroreduction of a graphene oxide solution was described. The resulting electrode displayed excellent electrochemical performance due to the formation of highly conductive GR film on the electrode surface. Electrochemistry of rutin was carefully studied with a pair of well-defined redox peaks appeared in pH 2.5 buffer solution. Rutin exhibited a diffusion-controlled two-electron and two-proton transfer reaction on the modified electrode with the electrochemical parameters calculated. The reduction peak currents are linearly related to rutin concentration in the concentration range from 0.070 to 100.0 μmol/L with a detection limit as low as 24.0 nmol/L (3σ). The modified electrode displayed excellent selectivity with good stability, and was applied to the determination of rutin content in tablet, human serum and urine samples with satisfactory results.Highlights► Electroreduced graphene modified carbon ionic liquid electrode was obtained. ► Electrochemical behaviors of rutin were investigated on the modified electrode. ► Rutin in different samples were detected by the proposed electrode.

In this paper 1-ethyl-3-methylimidazolium tetrafluoroborate based carbon ionic liquid electrode (CILE) was fabricated and further modified with chitosan (CTS) and graphene (GR) composite film. The fabricated CTS-GR/CILE was further used for the investigation on the electrochemical behavior of bisphenol A (BPA) by cyclic voltammetry and differential pulse voltammetry. A well-defined anodic peak appeared at 0.436 V in 0.1 mol/L pH 8.0 Britton–Robinson buffer solution, which was attributed to the electrooxidation of BPA on the modified electrode. The electrochemical parameters of BPA on the modified electrode were calculated with the results of the charge transfer coefficient (α) as 0.662 and the apparent heterogeneous electron transfer rate constant (ks) as 1.36 s− 1. Under the optimal conditions, a linear relationship between the oxidation peak current of BPA and its concentration can be obtained in the range from 0.1 μmol/L to 800.0 μmol/L with the limit of detection as 2.64 × 10− 8 mol/L (3σ). The CTS-GR/CILE was applied to the detection of BPA content in plastic products with satisfactory results.Highlights► A graphene modified carbon ionic liquid electrode was fabricated and characterized. ► Electrochemical behaviors of bisphenol A were investigated. ► Bisphenol A was detected by the proposed electrode.

A new carbon ionic liquid electrode was constructed by mixing graphite powder, 1-(3-chloro-2-hydroxypropyl)pyridinium tetrafluoroborate, and liquid paraffin together. The electrode showed strong electrocatalytic activity in the oxidation of guanosine-5′-triphosphate (5′-GTP). A single well-defined irreversible oxidation peak of 5′-GTP appeared in the voltammogram measured using the traditional carbon paste electrode, and the electrochemical response was greatly enhanced on the new electrode, which was due to the presence of highly conductive ionic liquid in the electrode. The electrochemical parameters of 5′-GTP on the carbon ionic liquid electrode were calculated: the electron transfer coefficient (α) was 0.29, the electron transfer number (n) was 1.91, the apparent heterogeneous electron transfer rate constant (ks) was 7.46 × 10−8 s−1, and the surface coverage (ГT) was 9.71 × 10−10 mol cm−2. Under the optimal conditions, the plot of oxidation peak current versus 5′-GTP concentration was linear over the range from 0.80 to 400.0 μM with a detection limit of 0.026 μM (3σ). The proposed method showed good selectivity in the detection of 5′-GTP without interference from coexisting substances and was further applied to the determination of artificial samples with satisfactory results.

A novel biocompatible nanocomposite prepared by Mg2Al–Cl layered double hydroxide (LDH) and ionic liquid (IL) 1-carboxyl-methyl-3-methylimidazolium tetrafluoroborate was used as the matrix for the immobilization of myoglobin (Mb). The IL-LDH-Mb composite was characterized by UV–vis adsorption spectroscopy and the results indicated that Mb retained its native structure in the IL-LDH nanocomposite. The IL-LDH-Mb bionanocomposite was modified on the surface of carbon ionic liquid electrode to get an Mb modified electrode. Electrochemical experiments showed that direct electrochemistry of Mb in the composite was realized with a pair of well-defined redox peaks appeared, which could be attributed to the specific microenvironment provided by layer structured LDH and high ionic conductive IL present for Mb molecule. The modified electrode exhibited good direct electrocatalytic ability to the reduction of trichloroacetic acid and hydrogen peroxide with good stability and reproducibility. Different kinds of real samples were detected by the modified electrode with satisfactory results. So the IL-LDH nanocomposite provided a novel and efficient platform for the immobilization of enzymes, which had potential applications in the fabrication of third-generation biosensors.

An ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) modified carbon paste electrode was fabricated and used as the substrate electrode. Then a gold nanoparticle and graphene (GR) composite film was co-electrodeposited on the carbon ionic liquid electrode (CILE) surface by immersing CILE in the graphite oxide and tetrachloroauric acid dispersion solution with cyclic voltammetric reduction. The fabricated Au–GR/CILE exhibited good electrochemical performances with higher conductivity and lower electron transfer resistance. Electrochemical behaviors of hydroquinone (HQ) were further investigated on the modified electrode by cyclic voltammetry and differential pulse voltammetry. A pair of well-defined redox peaks appeared with the peak-to-peak separation (ΔEp) as 0.077 V in 0.1 mol/L pH 2.5 PBS, indicating a fast quasi-reversible electron transfer process. The result could be attributed to the presence of high conductive Au–GR nanocomposites on the electrode surface. The electrochemical parameters of HQ on the Au–GR/CILE were calculated and the experimental conditions were optimized. Under the optimal conditions, the linear relationship between the oxidation peak current of HQ and its concentration can be obtained in the range from 0.06 μmol/L to 800.0 μmol/L with the detection limit as 0.018 μmol/L (3σ). The coexisting catechol exhibited no interference and Au–GR/CILE was applied to the detection of HQ in synthetic wastewater samples with satisfactory results.

In this paper a novel nanocomposite material prepared by Co3O4 nanorods (nano-Co3O4), graphene (GR) and chitosan (CTS) was fabricated and further modified on carbon ionic liquid electrode (CILE), which was used as the substrate electrode to construct a new electrochemical DNA biosensor. The single-stranded DNA (ssDNA) probe was immobilized on the CTS–Co3O4–GR/CILE surface by electrostatic attraction, which could hybridize with the target ssDNA sequence under the selected conditions. By using methylene blue (MB) as the electrochemical indicator, the hybridization reactions were monitored with the reduction peak current. By combining the biocompatibility of Co3O4 nanorods, excellent electron transfer ability and big surface of GR, good film-forming ability of CTS and the high conductivity of CILE, the amount of ssDNA adsorbed on the electrode surface was increased and the electrochemical response of MB was accelerated. Under the optimal conditions differential pulse voltammetric responses of MB were in linear with the specific target ssDNA sequence in the concentration range from 1.0 × 10− 12 to 1.0 × 10− 6 M with the detection limit as 4.3 × 10− 13 M (3σ). Good discrimination ability to the one-base and three-base mismatched ssDNA sequences could be achieved and the polymerase chain reaction (PCR) amplification products of Staphylococcus aureus nuc gene sequence were detected with satisfactory results.Highlights► A novel Co3O4 nanorod, graphene and chitosan nanocomposite material was fabricated. ► Nanocomposite modified CILE was used for the construction of DNA biosensor. ► Polymerase chain reaction product of Staphylococcus aureus nuc gene was detected.

An electrochemical DNA biosensor was fabricated by self-assembling probe single-stranded DNA (ssDNA) with a nanogold decorated on ionic liquid modified carbon paste electrode (IL-CPE). IL-CPE was fabricated using 1-butylpyridinium hexafluorophosphate as the binder and the gold nanoparticles were electrodeposited on the surface of IL-CPE (Au/IL-CPE). Then mercaptoacetic acid was self-assembled on the Au/IL-CPE to obtain a layer of modified film, and the ssDNA probe was further covalently-linked with mercaptoacetic acid by the formation of carboxylate ester with the help of N-(3-dimethylamino-propyl)-N′-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. The hybridization reaction with the target ssDNA was monitored with methylene blue (MB) as the electrochemical indicator. Under the optimal conditions, differential pulse voltammetric responses of MB was proportional to the specific ssDNA arachis sequences in the concentration range from 1.0 × 10−11 to 1.0 × 10−6 mol L−1 with the detection limit as 1.5 × 10−12 mol L−1 (3σ). This electrochemical DNA sensor exhibited good stability and selectivity with the discrimination ability of the one-base and three-base mismatched ssDNA sequences. The polymerase chain reaction product of arachis Arabinose operon D gene was successfully detected by the proposed method, which indicated that the electrochemical DNA sensor designed in this paper could be further used for the detection of specific ssDNA sequence.Graphical abstract.Highlights► Nanogold decorated on ionic liquid modified carbon paste electrode was fabricated by electrodeposition to get a new substrate electrode. ► The ssDNA probe was further covalently-linked with self-assembled mercaptoacetic acid film on the electrode surface to prepare the electrochemical DNA biosensor. ► The polymerase chain reaction product of arachis Arabinose operon D gene was successfully detected by the proposed method.

An ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) based carbon ionogel electrode (CIE) was fabricated for the sensitive voltammetric sensing of hydroquinone (HQ) in this paper. Due to the specific characteristics of the prepared working electrode, HQ exhibited an enhanced electrochemical response on CIE with a pair of well-defined redox peaks appeared in pH 2.5 phosphate buffer solution. The electrochemical behaviors of HQ on CIE were investigated by different electrochemical methods such as cyclic voltammetry and differential pulse voltammetry with the electrochemical parameters calculated. Under the optimal conditions the oxidation peak currents exhibited good linear relationship with the HQ concentration in the range from 0.13 to 100.0 μmol L−1 with the detection limit of 0.07 μmol L−1 (3σ). The CIE showed separated electrochemical response to HQ and catechol in the mixture solution. The proposed method was successfully applied to HQ detection in artificial wastewater with the recovery in the range from 98.9% to 102.0%.

In this paper an ionic liquid (IL) 1-butylpyridinium hexafluorophosphate (BPPF6) modified carbon paste electrode was constructed and further used to establish a sensitive method for the detection of 5-fluoro-1H-pyrimidine-2 (5-FU). Compared with the carbon paste electrode (CPE), a single well-defined irreversible oxidation peak of 5-FU appeared on the IL-CPE with a great improvement of the electrochemical response, which was due to the presence of a high ionic conductive ionic liquid in the electrode that exhibited accumulation and electrocatalytic ability. The electrochemical parameters of 5-FU on the IL-CPE were calculated with the electron transfer coefficient (α) as 0.62 and the diffusional coefficient (D) as 7.02 × 10−5 cm2 s−1. Under the optimal conditions, the oxidation peak current was linear to 5-FU concentration in the range from 5.0 × 10−7 to 8.0 × 10−4 mol L−1 with a detection limit of 1.3 × 10−8 mol L−1 (3σ). Good selectivity to 5-FU detection was observed without the interference of coexisting substances and the method was further applied to determination in injection samples with satisfactory results.

A novel kind of carbon paste electrode (CPE) was prepared by mixing graphite powder, liquid paraffin and the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate. The resulting electrode was used for the simultaneous determination of guanosine and adenosine by differential pulse voltammetry. Compared to a conventional CPE, the oxidation peak currents are largely increased, and the oxidation peak potentials are negatively shifted. The electrochemical responses to guanosine and adenosine were investigated. Under optimized conditions, the calibration curves are linear in the concentration range from 1.0 × 10-6 mol L-1 to 1.6 × 10-4 mol L-1 for guanosine, and from 1.0 × 10-6 mol L-1 to 2.7 × 10-4 mol L-1 for adenosine at pH 3.5. Substances potentially interfering in the biological matrix do no interfere. The method was successfully applied to detect adenosine and guanosine in human urine without sample treatments.

In this paper a Fe3O4 microsphere, graphene (GR) and chitosan (CTS) nanocomposite material modified carbon ionic liquid electrode (CILE) was used as the platform for the construction of a new electrochemical DNA biosensor. The single-stranded DNA (ssDNA) probe was immobilized directly on the surface of the CTS/Fe3O4–GR/CILE, which could hybridize with the target ssDNA sequence at the selected conditions. By using methylene blue (MB) as the electrochemical indicator the hybridization reaction was investigated with the reduction peak current measured. By combining the specific properties such as the biocompatibility and big surface area of Fe3O4 microspheres, the excellent electron transfer ability of GR, the good film-forming ability of CTS and the high conductivity of CILE, the synergistic effects of nanocomposite increased the amounts of ssDNA adsorbed on the electrode surface and then resulted in the greatly increase of the electrochemical responses. Under the optimal conditions differential pulse voltammetric responses of MB were proportional to the specific ssDNA sequences concentration in the range from 1.0 × 10−12 to 1.0 × 10−6 mol/L with the detection limit as 3.59 × 10−13 mol/L (3σ). This DNA biosensor showed good stability and discrimination ability to one-base and three-base mismatched ssDNA sequences. The polymerase chain reaction (PCR) product of soybean Lectin gene sequence was detected by the proposed method with satisfactory result, suggesting that the CTS/Fe3O4–GR/CILE was a suitable sensing platform for the sensitive detection of specific gene sequence.Highlights► A Fe3O4 microsphere, graphene and chitosan nanocomposite material modified carbon ionic liquid electrode was fabricated. ► DNA was immobilized on the modified electrode surface to get an electrochemical DNA biosensor. ► The specific ssDNA sequence can be detected in the range from 1.0 × 10−12 to 1.0 × 10−6 mol/L with the detection limit as 3.59 × 10−13 mol/L.

In this paper an urchinlike MnO2 nanoparticle was synthesized by hydrothermal method and applied to the protein electrochemistry for the first time. By using a carbon ionic liquid electrode (CILE) as the basal electrode, hemoglobin (Hb) was immobilized on the surface of CILE with chitosan (CTS) and MnO2 nanoparticle composite materials. Spectroscopic results indicated that Hb molecules retained its native structure in the composite film. A pair of well-defined redox peaks appeared on the cyclic voltammogram with the formal peak potential as −0.180 V (vs. SCE), which indicated that direct electron transfer of Hb was realized on the modified electrode. The result can be attributed to the specific characteristic of MnO2 nanoparticle and the advantages of CILE, which facilitated the electron transfer rate. The fabricated CTS–MnO2–Hb/CILE showed good electrocatalytic ability to the reduction of trichloroacetic acid (TCA). Under the optimal conditions the catalytic current was in linear to TCA concentration in the range from 0.5 to 16.0 mmol L−1 with the detection limit calculated as 0.167 mmol L−1 (3σ). The result indicated that urchinlike MnO2 nanoparticle had the potential application in the third generation electrochemical biosensors.

A composite bionanomaterial was prepared by combining Nafion, flowerlike cobalt oxide (CoO) nanoparticles, hemoglobin (Hb), and ionic liquid (IL) 1-ethyl-3-methylimidazolium tetrafluoroborate. Then it was further applied on the surface of a carbon ionic liquid working electrode fabricated with 1-ethyl-3-methylimidazolium ethylsulfate as the modifier. 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–1 pH 4.0 phosphate buffer solution, indicating that the direct electron transfer of Hb with the underlying electrode was realized. The results could be attributed to the synergistic effect of CoO nanoflower and IL in the composite film, which provided a specific microenvironment to keep the native structure of Hb and promoted the electron transfer rate of Hb. The electrochemical parameters of Hb on the modified electrode were carefully calculated. The composite material modified electrode showed excellent electrocatalytic ability toward the reduction of different substrates such as trichloroacetic acid and H2O2, which exhibited advantages such as high sensitivity, good stability, and wide dynamic range. Therefore, it has potential application in third-generation electrochemical biosensors.

An electrochemical biosensor was constructed based on the immobilization of myoglobin (Mb) in a composite film of Nafion and hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) for a modified carbon paste electrode (CPE). Direct electrochemistry of Mb in the Nafion–BMIMPF6/CPE was achieved, confirmed by the appearance of a pair of well-defined redox peaks. The results indicate that Nafion–BMIMPF6 composite film provided a suitable microenvironment to realize direct electron transfer between Mb and the electrode. The cathodic and anodic peak potentials were located at −0.351 V and −0.263 V (vs. SCE), with the apparent formal potential (Ep) of −0.307 V, which was characteristic of Mb Fe(III)/Fe(II) redox couples. The electrochemical behavior of Mb in the composite film was a surface-controlled quasi-reversible electrode process with one electron transfer and one proton transportation when the scan rate was smaller than 200 mV/s. Mb-modified electrode showed excellent electrocatalytic activity towards the reduction of trichloroacetic acid (TCA) in a linear concentration range from 2.0 × 10−4 mol/L to 1.1 × 10−2 mol/L and with a detection limit of 1.6 × 10−5 mol/L (3σ). The proposed method would be valuable for the construction of a third-generation biosensor with cheap reagents and a simple procedure.

A new electrochemical method was proposed for the determination of thymine, which relied on the oxidation of thymine at a carbon ionic liquid electrode (CILE) in a pH 5.0 Britton–Robinson buffer solution. CILE was fabricated by using ionic liquid 1-(3-chloro-2-hydroxy-propyl)-3-methylimidazole acetate as the binder, which showed strong electrocatalytic ability to promote the oxidation of thymine. A single well-defined irreversible oxidation peak appeared with adsorption-controlled process and enhanced electrochemical response on the CILE, which was due to the presence of high conductive ionic liquid on the electrode. The reaction parameters of thymine were calculated with the electron transfer coefficient (α) as 0.27, the electron transfer number (n) as 1.23, the apparent heterogeneous electron transfer rate constant (ks) as 6.87 × 10−6 s−1 and the surface coverage (ГT) as 5.71 × 10−8 mol cm−2. Under the selected conditions the oxidation peak current was proportional to thymine concentration in the range from 3.0 to 3000.0 μM with the detection limit as 0.54 μM (3σ) by differential pulse voltammetry. The proposed method showed good selectivity to the thymine detection without the interferences of coexisting substances.

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 NaNO2 with good stability and reproducibility.

An ionic liquid (IL) and double-stranded DNA (dsDNA) composite material was used to investigate the direct electron transfer of myglobin (Mb) on carbon ionic liquid electrode (CILE). The presence of the IL–dsDNA biocomposite film on the electrode surface provided great improvement to the direct electron transfer rate of Mb with the CILE, which was due to the synergistic contributions of specific characteristics of dsDNA, IL and their interaction. The electrochemical parameters of Mb in the IL–dsDNA composite film modified electrode were carefully investigated with the charge transfer coefficient (α) and the electron transfer rate constant (ks) calculated as 0.42 and 0.84 s−1, respectively. The fabricated Mb modified electrode exhibited good electrocatalytic ability to the reduction of trichloroacetic acid and H2O2, which showed the potential applications in the third-generation electrochemical biosensor.

A new electrochemical DNA biosensor was fabricated by using a V2O5 nanobelts (nano-V2O5), multi-walled carbon nanotubes (MWCNTs) and chitosan (CTS) nanocomposite materials modified carbon ionic liquid electrode (CILE) as the working electrode. The CILE was prepared by using N-hexylpyridinium hexafluorophosphate (HPPF6) as the binder with the graphite powder. The CTS–V2O5–MWCNTs/CILE was used as the basal electrode for the immobilization of the single-stranded DNA (ssDNA) probe. After the hybridization with the target ssDNA sequence, the electrochemical indicator of methylene blue (MB) was used to monitor the hybridization reaction. Experimental data indicated that the synergistic effect of nano-V2O5 and MWCNTs increased the amounts of ssDNA adsorbed on the electrode surface and resulted in the corresponding increase of the electrochemical responses. This DNA biosensor combined the advantages such as the biocompatibility of V2O5 nanobelt, the excellent electron transfer ability of MWCNTs, the good film-forming ability of CTS and the high conductivity of CILE. Under the optimal conditions differential pulse voltammetry (DPV) was used to record the electrochemical response of MB and the specific ssDNA sequence could be detected in the concentration range from 1.0 × 10−11 to 1.0 × 10−6 mol L−1 with the detection limit as 1.76 × 10−12 mol L−1 (3σ). The DNA biosensor showed good stability and discrimination ability to the one-base and three-base mismatched ssDNA sequence. The loop-mediated isothermal amplification (LAMP) product of Yersinia enterocolitica gene sequence in pork meat was detected by the proposed method with satisfactory result, suggesting that the CTS–V2O5–MWCNTs/CILE had the potential for the sensitive detection of specific gene sequence.

An ionic liquid (IL) modified carbon ceramic electrode (CCE) was designed and further used for the voltammetric detection of rutin in this paper. IL-CCE was prepared by mixing graphite powder with 1-butyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) doped silicate sol–gel matrix together and further characterized by different methods. Then electrochemical behaviors of rutin on the IL-CCE were investigated by different electrochemical methods such as cyclic voltammetry and differential pulse voltammetry (DPV). Due to the presence of IL in the CCE, an enhanced electrochemical response of rutin appeared with a pair of well-defined redox peaks in pH 2.5 phosphate buffer solution (PBS). The electrochemical behaviors of rutin on the IL-CCE were carefully investigated. Under the selected conditions the oxidation peak currents exhibited good linear relationship with the rutin concentration in the range from 0.3 to 100.0 μmol/L with the detection limit as 0.09 μmol/L (3σ). The proposed method was further applied to the rutin tablets sample detection with satisfactory results.

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.

In this paper a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM]EtOSO3) 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 (E0′) 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.

The single-walled carbon nanotubes (SWCNTs) modified carbon ionic liquid electrode (CILE) was designed and further used for the voltammetric detection of rutin in this paper. CILE was prepared by mixing graphite powder with ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate and liquid paraffin together. Based on the interaction of SWCNTs with IL present on the electrode surface, a stable SWCNTs film was formed on the CILE to get a modified electrode denoted as SWCNTs/CILE. The characteristics of SWCNTs/CILE were recorded by different methods including cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The electrochemical behaviors of rutin on the SWCNTs/CILE were investigated by cyclic voltammetry and differential pulse voltammetry. Due to the specific interface provided by the SWCNTs-IL film, the electrochemical response of rutin was greatly enhanced with a pair of well-defined redox peaks appeared in pH 2.5 phosphate buffer solution. The oxidation peak currents showed good linear relationship with the rutin concentration in the range from 1.0 × 10− 7 to 8.0 × 10− 4 mol/L with the detection limit as 7.0 × 10− 8 mol/L (3σ). The SWCNTs/CILE showed the advantages such as excellent selectivity, improved performance, good stability and it was further applied to the rutin tablets sample detection with satisfactory results.

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]EtOSO3) 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 (3σ).

In this paper a Ni/Al layered double hydroxide (LDH) was first synthesized and further immobilized on a carbon ionic liquid electrode (CILE), which was prepared by using 1-(3-chlorine-2-hydroxypropyl)-3-methylimidazolium acetate as the modifier. The characteristics of LDH/CILE were investigated by scanning electron microscopy (SEM) and cyclic voltammetry. Under the selected conditions the LDH/CILE showed better electrochemical response towards the detection of dopamine (DA) than the CILE. The parameters of DA electro-oxidation on the LDH/CILE were calculated with the values of the electron transfer coefficient (α), the number of electrons transferred (n), the apparent heterogeneous electron transfer rate constant (ks) and the diffusion coefficient (D) as 0.426, 2.25, 1.66 s−1 and 7.06 × 10−5 cm2/s, respectively. This modified electrode can be further used to detect DA content in the real drug samples.

The electrochemical behaviors of the interaction of chromotrope 2R (CH2R) with human serum albumin (HSA) are investigated on the hanging mercury drop electrode with linear sweep voltammetry. In the acidic buffer solution (pH 2.5) CH2R has a well-defined voltammetric reductive wave at −0.34 V (SCE). On the addition of HSA into the CH2R solution, the reductive peak current of CH2R decreases with little movement of the peak potential. The voltammetric study shows that the electrochemical parameters of interaction solution do not change and a new electrochemically non-active complex is formed via interaction of CH2R with HSA, which cannot be reduced on the Hg electrode and results in the decrease of the free concentration of CH2R. The decrease of reductive peak current is proportional to HSA concentration and further used for protein detection. The binding ratio and the binding constant are further calculated with the experimental voltammetric data.

A multi-walled carbon nanotubes (MWCNTs) modified carbon ionic liquid electrode (CILE) was fabricated and used to investigate the electrochemical behavior of guanosine. CILE was prepared by mixing hydrophilic ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4), graphite powder and liquid paraffin together. The fabricated MWCNTs/CILE showed great electrocatalytic ability to the oxidation of guanosine and an irreversible oxidation peak appeared at 1.067 V (vs. SCE) with improved peak current. The electrochemical behavior of guanosine on the MWCNTs/CILE was carefully studied by cyclic voltammetry and the electrochemical parameters such as the charge transfer coefficient (α) and the electrode reaction standard rate constant (ks) were calculated with the result as 0.66 and 2.94 × 10−4 s−1, respectively. By using differential pulse voltammetry (DPV) as the detection method, a linear relationship was obtained between the oxidation peak current and the guanosine concentration in the range from 1.0 × 10−7 to 4.0 × 10−5 mol/L with the detection limit as 7.8 × 10−8 mol/L (3σ). The common coexisting substances showed no interferences to the guanosine detection and the modified electrode showed good ability to distinguish the electrochemical response of guanosine and adenosine.

The direct electrochemistry of hemoglobin (Hb) on multi-walled carbon nanotubes (MWCNTs) modified carbon ionic liquid electrode (CILE) was achieved in this paper. By using a hydrophilic ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) as the modifier, a new CILE was fabricated and further modified with MWCNTs to get the MWCNTs/CILE. Hb molecules were immobilized on the surface of MWCNTs/CILE with polyvinyl alcohol (PVA) film by a step-by-step method and the modified electrode was denoted as PVA/Hb/MWCNTs/CILE. UV–vis and FT-IR spectra indicated that Hb remained its native structure in the composite film. Cyclic voltammogram of PVA/Hb/MWCNTs/CILE showed a pair of well-defined and quasi-reversible redox peaks with the formal potential (E0′) of −0.370 V (vs. SCE) in 0.1 mol/L pH 7.0 phosphate buffer solution (PBS), which was the characteristic of the Hb heme FeIII/FeII redox couples. The redox peak currents increased linearly with the scan rate, indicating the direct electron transfer was a surface-controlled process. The electrochemical parameters of Hb in the film were calculated with the results of the electron transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (ks) as 0.49 and 1.054 s−1, respectively. The immobilized Hb in the PVA/MWCNTs composite film modified CILE showed excellent electrocatalytic activity to the reduction of trichloroacetic acid (TCA) and hydrogen peroxide. So the proposed electrode showed the potential application in the third generation reagentless biosensor.

An electrochemical DNA detection method for the phosphinothricin acetyltransferase (PAT) gene sequence from the transgenetic plants was established by using a microplate hybridization assay with cadmium sulfide (CdS) nanoparticles as oligonucleotides label. The experiment included the following procedures. Firstly target PAT ssDNA sequences were immobilized on the polystyrene microplate by physical adsorption. Then CdS nanoparticle labeled oligonucleotide probes were added into the microplate and the hybridization reaction with target ssDNA sequences took place in the microplate. After washing the microplate for three times, certain amounts of HNO3 were added into the microplate to dissolve the CdS nanoparticles anchored on the hybrids and a solution containing Cd2+ ion was obtained. At last differential pulse anodic stripping voltammetry (DPASV) was used for the sensitive detection of released Cd2+ ion. Based on this principle a sensitive electrochemical method for the PAT gene sequences detection was established. The voltammetric currents of Cd2+ were in linear range with the target ssDNA concentration from 5.0 × 10− 13 to 1.0 × 10− 10 mol/L and the detection limit was estimated to be 8.9 × 10− 14 mol/L (3σ). The proposed method showed a good promise for the sensitive detection of specific gene sequences with good selectivity for the discrimination of the mismatched sequences.

An electrochemical method for the determination of lysozyme (LYS) based on its interaction with alizarin red S (ARS) was established by linear sweep voltammetry in this paper. The electrochemical behaviour of ARS with LYS was investigated on a dropping mercury working electrode in 0·2 mol/L pH 4·8 Britton-Robinson (B-R) buffer solution. ARS showed a sensitive second order derivative linear sweep voltammetric reductive peak at −0·42 V (vs SCE). After the addition of LYS, the reductive peak current of ARS decreased without the shift of the reductive peak potential and no new waves appeared, which was due to the formation of a supramolecular complex of ARS with LYS in the solution. The stoichiometry of the ARS-LYS complex was further calculated by the electrochemical data with the results of the binding ratio as 3: 1 and the binding constant as 2·82 × 1014. Under the selected conditions, the decrease of the second order derivative linear sweep voltammetric reductive peak current of ARS was in proportion to the LYS concentration in the range from 0·8 to 35·0 mg/L and the detection limit of LYS was calculated as 0·52 mg/L (3σ). Different kinds of LYS samples were detected satisfactorily with this method.

The direct electrochemistry of herring sperm double-stranded DNA (dsDNA) on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode was investigated. The cyclic voltammogram showed two irreversible oxidation peaks at 0.868 V and 1.188 V (vs. SCE), which corresponded to the oxidation of guanine and adenine residues, respectively. Compared to the common carbon paste electrode the electrochemical response was greatly improved. The electrochemical behavior of dsDNA on the modified electrode was carefully investigated with the electrochemical parameters were calculated. Under optimal conditions the dsDNA can be directly determined in the concentration range from 50 to 600 μg mL−1 with a detection limit of 17 μg mL−1 (3σ).

The electrochemical behaviors of metol on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode (IL-CPE) were studied in this paper. The results indicated that a pair of well-defined quasi-reversible redox peaks of metol appeared with the decrease of overpotential and the increase of redox peak current, which was the characteristics of electrocatalytic oxidation. The electrocatalytic mechanism was discussed and the electrochemical parameters were calculated with results of the charge-transfer coefficient (α) as 0.45, the electrode reaction rate constant (ks) as 4.02 × 10−3 s−1, and the diffusion coefficient (D) as 6.35 × 10−5 cm2/s. Under the optimal conditions, the anodic peak current was linear with the metol concentration in the range of 5.0 × 10−6 ∼ 1.0 × 10−3 mol/L (n = 11, γ = 0.994) and the detection limit was estimated as 2.33 × 10−6 mol/L (3σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions.

The electrochemical deposition of Co nanoparticles on carbon ionic liquid electrode (CILE) was described and further used as the platform to construct a myoglobin (Mb) electrochemical biosensor. CILE was prepared by mixing a certain ratio of carbon powder, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4), and liquid paraffin together. The presence of ionic liquid on the electrode surface facilitated the formation of Co nanoparticles, and a layer of Co nanoparticles was deposited on the surface of CILE with the average diameter of 300 nm after the cyclic voltammetic scan in the CoCl2 solution. The formed Co/CILE was used as a new basal electrode for the investigation on the direct electrochemistry of protein. Mb molecules were further cast on the surface of Co/CILE and immobilized with Nafion film. The fabricated Nafion/Mb/Co/CILE showed good electrochemical behaviors with a pair of well-defined quasi-reversible redox peaks of Mb obtained, which was attributed to the electrochemical reaction of heme Fe(III)/Fe(II) redox couples. The results indicated that the presence of Co nanoparticles exhibited great promotion to the direct electron transfer of Mb. The Mb electrochemical biosensor showed good electrocatalytic activity to the reduction of hydrogen peroxide and trichloroacetic acid (TCA). The modified electrodes showed good stability and reproducibility, which had potential application in third generation biosensor.

In this paper, a cationic dye of phenosafranine (PSF) was selected as a bioprobe to determine hyaluronic acid (HA) by linear sweep voltammetry on the dropping mercury working electrode (DME). In pH 4.5 Britton-Robinson (B-R) buffer solution, PSF has a well-defined second order derivative linear sweep voltammetric reductive peak at −0.42 V (vs. SCE). After the addition of HA into the PSF solution, the reductive peak current decreased apparently without the movement of reductive peak potential. Based on the decrease of the reductive peak current, a new voltammetric method for HA determination was established. The conditions for the interaction and the electrochemical detection were optimized and the interference substances for the detection were investigated. Under the optimal experimental conditions the difference of peak current was directly proportional to the concentration of HA in the range from 0.8 to 50.0 mg/l with the linear regression equation as Δip″ (nA) = 93.85 + 22.92c (mg/l) (n = 14, γ = 0.995) and the detection limit was calculated as 0.901 mg/l (3). This new method was further applied to determine the HA content in the synthetic samples with satisfactory results and good recovery. The stoichiometry of PSF-HA complexes was calculated and the binding mechanism was also discussed.

In this paper a hydrophilic ionic liquid of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) was used as modifier to make a new kind of ionic liquid-modified carbon paste electrode (IL-CPE), which was further characterized by different methods including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and scanning electron microscope (SEM). The fabricated IL-CPE showed good electrocatalytic behaviors towards the oxidation of metol with the enhancement of the redox peak current and the decrease of the peak-to-peak separation. The electrochemical behaviors of metol on the IL-CPE were carefully studied and the electrochemical parameters were calculated. Based on the electrocatalytic reaction, a new electrochemical method for the metol determination was established in the concentration range from 4.0 × 10−6 to 5.0 × 10−3 mol L−1 by cyclic voltammetry with the detection limit estimated to be 2.0 × 10−6 mol L−1 (3σ). The established method was successfully applied to the synthetic samples and photographic solutions detection with good recovery.

In this paper the direct electron transfer of hemoglobin (Hb) was carefully investigated by using a room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) modified carbon paste electrode (CILE) as the basal working electrode. Hb was immobilized on the surface of CILE with the nanocomposite film composed of Nafion and CdS nanorods by a step-by-step method. UV–vis and FT-IR spectra showed that Hb in the composite film remained its native structure. The direct electrochemical behaviors of Hb in the composite film were further studied in a pH 7.0 phosphate buffer solution (PBS). A pair of well-defined and quasi-reversible cyclic voltammetric peaks of Hb was obtained with the formal potential (E0′) at −0.295 V (vs. SCE), which was the characteristic of heme Fe(III)/Fe(II) redox couples. The direct electrochemistry of Hb was achieved on the modified electrode and the apparent heterogeneous electron transfer rate constant (ks) was calculated to be 0.291 s−1. The formal potentials of Hb Fe(III)/Fe(II) couple shifted negatively with the increase of buffer pH and a slope value of −45.1 mV/pH was got, which indicated that one electron transfer accompanied with one proton transportation. The fabricated Hb sensor showed good electrocatalytic manner to the reduction of trichloroacetic acid (TCA).

Lead sulfide (PbS) nanoparticles were synthesized in aqueous solution and used as oligonucleotide labels for electrochemical detection of the 35 S promoter from cauliflower mosaic virus (CaMV) sequence. The PbS nanoparticles were modified with mercaptoacetic acid and could easily be linked with CaMV 35 S oligonucleotide probe. Target DNA sequences were covalently linked on a mercaptoacetic acid self-assembled gold electrode, and DNA hybridization of target DNA with probe DNA was completed on the electrode surface. PbS nanoparticles anchored on the hybrids were dissolved in the solution by oxidation of HNO3 and detected using a sensitive differential pulse anodic stripping voltammetric method. The detection results can be used to monitor the hybridization reaction. The CaMV 35 S target sequence was satisfactorily detected with the detection limit as 4.38 × 10−12 mol/L (3σ). The established method extends nanoparticle-labeled electrochemical DNA analysis to specific sequences from genetically modified organisms with higher sensitivity and selectivity.

A new linear-sweep voltammetric assay of nucleic acids (NAs) based on their interaction with crystal violet (CV) is proposed. In a pH 3.5 Britton—Robinson (B-R) buffer solution, CV had an irreversible voltammetric reductive peak at −0.77 V and the peak current greatly decreased by the addition of NAs. Under the experimental conditions, the decrease in the peak current was used for the NAs assay 0.5–18.0 μg/mL of fish sperm DNA, 0.6–15.0 μg/mL of calf thymus DNA, and 0.8–12.0 μg/mL of yeast RNA. The detection limits (3σ) were 0.32, 0.47, and 0.61 μg/mL for fsDNA, ctDNA, and yRNA, respectively. The binding reaction can be completed after mixing DNA with CV within 10 min and the electrochemical response is stable for 2 h. There are seldom interferences in this method and three synthetic samples were analyzed with satisfactory results. The stoichiometry of the supramolecular complex with the binding number 3 and the binding constant 2.78 × 1014 is calculated using electrochemical data.

In this paper, a diazo dye of arsenazo III (AAIII) was selected as a new electrochemical probe for the determination of proteins. In Britton-Robinson (B-R) buffer solution of pH 2.4, AAIII had a sensitive second order derivative linear sweep voltammetric reductive peak at −0.39 V (vs. SCE). After the addition of human serum albumin (HSA) into AAIII solution, an interaction was taken place in the mixed solution and a biosupramolecular complex was formed, which resulted in the decreased reductive peak currents of AAIII. Based on the observed decrease in peak current, a sensitive electrochemical method was proposed for the determination of different proteins such as HSA, bovine serum albumin (BSA) and bovine hemoglobin (BHb). The optimal conditions for the interaction and the interfering effects of coexisting substances on the detection were investigated. The proposed method was successfully applied to the determination of HSA in synthetic samples with the recoveries in the range of 99.13–100.50%. The stoichiometry of HSA-AAIII biocomplex was calculated by voltammetric data with a binding number of 2 and a binding constant of 7.53 × 109.

A novel biocompatible composite film containing sodium alginate (SA), room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6), SiO2 nanoparticle, and hemoglobin (Hb) was fabricated and covered on the surface of a traditional carbon paste elecrode (CPE). The immobilized Hb on the electrode surface showed good direct electrochemical behaviors, and a pair of quasi-reversible redox peaks of Hb was obtained, which indicated that the direct electron transfer of Hb with the electrode surface had been achieved. The SA/nano-SiO2/BMIMPF6/Hb/CPE showed dramatically electrocatalytic activity to the reduction of trichloroacetic acid, hydrogen peroxide (H2O2), and oxygen (O2). The kinetic parameters for the electrocatalytic reactions were evaluated. The composite film showed the potential to the biosensor and biocatalysis.

A carbon ionic liquid electrode (CILE) was constructed using graphite powder mixed with N-butylpyridinium hexafluorophosphate (BPPF6) in place of paraffin as the binder, which showed strong electrocatalytic activity to the direct oxidation of catechol. In pH 3.0 phosphate buffer solution (PBS) a pair of redox peaks appeared on the CILE with the anodic and the cathodic peak potential located at 387 and 330 mV (vs. SCE), respectively. The electrochemical behaviors of catechol on the CILE were carefully investigated, and the electrochemical parameters were calculated with the results of the electrode reaction standard rate constant ks as 1.27 s−1, the charge-transfer coefficient α as 0.58 and the electron transferred number n as 2. Under the selected conditions, the anodic peak current increased linearly with the catechol concentration over the range from 1.0 × 10−6 to 8.0 × 10−4 mol L−1 by cyclic voltammetry at the scan rate of 100 mV s−1. The detection limit was calculated as 6.0 × 10−7 mol L−1 (3σ). The CILE showed good ability to separate the electrochemical responses of catechol and ascorbic acid (AA) with the anodic peak potential separation as 252 mV (vs. SCE). The proposed method was further applied to the synthetic samples determination with satisfactory results.

A mercaptoacetic acid (MAA)-modified cadmium sulfide (CdS) nanoparticle was synthesized in aqueous solution and used as an oligonucleotide label for the electrochemical detection of nopaline synthase (NOS) terminator gene sequence. The carboxyl groups on the surface of the CdS nanoparticle can be easily covalently linked with NH2-modified NOS oligonucleotide probe sequences. The target ssDNA sequence was fixed onto the electrode surface by covalently linking to a mercaptoethanol self-assembled gold electrode, and the DNA hybridization of target ssDNA with probe ssDNA was accomplished on the electrode surface. The CdS nanoparticles anchored on the hybrids were dissolved in the solution by the oxidation with HNO3 and further detected by a sensitive differential pulse anodic stripping voltammetric method. The detection results can be used for monitoring the hybridization, and the NOS target sequence was satisfactorily detected in the approximate range from 8.0 × 10−12 to 4.0 × 10−9 mol L−1 with a detection limit of 2.75 × 10−12 mol L−1 (3σ). The established method extended the nanoparticle-labeled electrochemical DNA analysis to genetically modified organisms (GMOs) specific sequence samples with higher sensitivity and selectivity.