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This paper reports a simple and sensitive approach for the determination of troxerutin using a zirconia oxide/graphene doped carbon paste electrode (ZrO2/Gr-CPE). Highly uniform and stable ZrO2 nanoparticles were deposited on Gr sheet via a rapid route. By introducing this nanocomposite into carbon paste electrode, the obtained electrochemical sensor showed sensitive response for troxerutin. Based on this sensor, an accurate sensitive analytical method for troxerutin was established with a linear range from 2 × 10−9 to 3 × 10−7 mol L−1 and a detection limit 6 × 10−10 mol L−1. Meanwhile, the electrochemical properties of troxerutin were investigated in detail. Finally, the proposed method was applied to the analysis of real-life samples with satisfactory results. [ABSTRACT FROM AUTHOR]

A novel, economic, and highly sensitive electrochemical sensor for the determination of trans-resveratrol (RES) was fabricated by electropolymerization of poly(L-lysine) films onto glassy carbon electrode (GCE) surface. The electrochemical behavior of RES in Britton–Robinson buffer solution (pH 2.0) on the poly(L-lysine)/GCE was investigated by cyclic voltammetry and linear sweep voltammetry for the first time. Results showed that the detection range of the proposed sensor to RES was from 0.20 to 12.0 μM with the minimum detectable concentration of 0.06 μM. The reported electrochemical sensor also exhibited high selectivity, good reproducibility, and long-term stability for RES detection. In addition, the proposed method can be employed for the determination of RES in red wines with satisfactory results. The proposed electrochemical strategy presents valuable information related to evaluation of RES levels in real samples. [ABSTRACT FROM AUTHOR]

A simple, highly sensitive voltammetric method for the determination of urapidil at poly(sodium4-styrenesulfonate) functionalized graphene-modified electrode (PSS-Gr/GCE) was described. Based on the PSS-Gr composites-modified glassy carbon electrode as a simple voltammetric sensor, it exhibited good conductivity and high sensitivity to urapidil. Under the optimize condition, a good linear relationship was obtained between peak currents and urapidil concentrations in the wider range of 2.0 × 10−9–8.0 × 10−8 mol L−1 and 2.0 × 10−7–2.0 × 10−5 mol L−1 with detection limit of 8 × 10−10 mol L−1 (S/N = 3). Based on the high sensitivity and good selectivity of the proposed electrode, the proposed method could apply to the detect of urapidil in urapidil sustained release tablets with satisfactory results. [ABSTRACT FROM AUTHOR]

trans-Resveratrol is often considered as one of the quality standards of red wine, and the development of a sensitive and reliable method for monitoring the trans-resveratrol levels in red wine is an urgent requirement for the quality control. Here, a novel voltammetric approach was described for probing trans-resveratrol using a graphene-modified glassy carbon (GC) electrode. The proposed electrode was prepared by one-step electrodeposition of reduced graphene oxide (ERGO) at a GC electrode. Compared with the bare GC electrode, the introduced graphene film on the electrode surface dramatically improved the sensitivity of the sensor response due to the π-π interaction between the graphene and trans-resveratrol. The developed sensor exhibited low detection limit of 0.2 μM with wide linear range of 0.8–32 μM and high stability. For the analysis of trans-resveratrol in red wine, the high anti-interference ability and the good recoveries indicated the great potential for practical applications. [ABSTRACT FROM AUTHOR]

A new and sensitive voltammetric sensor for palmatine, based on an electrochemically reduced l-methionine functionalized graphene oxide modified glassy carbon electrode (l-Met-ERGO/GCE), is reported. The electrochemical characteristics of palmatine at the proposed sensor were studied systematically and some dynamic parameters were calculated for the first time. A reasonable reaction mechanism for palmatine on the l-Met-ERGO/GCE electrode was proposed and discussed, and this could be a reference for the pharmacological action of palmatine in clinical study. Under optimized conditions, the peak current had a linear relationship with palmatine concentration in the range of 1 × 10−7 to 5 × 10−5 mol L−1 with a detection limit of 6 × 10−8 mol L−1. Additionally, the proposed method was also used to detect palmatine in human urine samples, medicinal tablets and the Chinese herb Fibraurea recisa Pierre with satisfactory results. [ABSTRACT FROM AUTHOR]

A simple and sensitive voltammetric sensor for esculetin, based on electrochemically reduced graphene oxide film modified glassy carbon electrode, was reported for the quantitative determination of esculetin in the Chinese traditional herbal drug Viola yedoensis Makino. Electrochemical impedance spectroscopy and scanning electron microscopy were employed to study the characteristic of the graphene oxide film. The electrochemical behavior of esculetin on this sensor was investigated in pH 3.0 phosphate buffer solution by cyclic voltammetry. Significant advantages were achieved by the excellent conductivity and the high surface-to-volume ratio of electrochemically reduced graphene oxide. A calibration plot of oxidation peak currents versus esculetin concentrations was linear in the range of 4.0 ξ 10-8 mol L-1 to 5.0 ξ 10-6 mol L-1 with a detection limit of 2.0 ξ 10-8 mol L-1. The practical application of the present sensor was demonstrated by determining the concentration of esculetin in real sample with no interference. [ABSTRACT FROM AUTHOR]

A new voltammetric sensor, based on multi-walled carbon nanotubes (MWCNTs) composite poly(aspartic acid) film modified glassy carbon electrode, was fabricated and used for determination of pesticide imidacloprid. The synergistic effect of MWCNTs and the polymer resulted in a significantly improved electrochemical response (in terms of sensitivity, accuracy and analytical range) towards imidacloprid. Under selective conditions, the determination linear range was from 1.53 × 10−5 g L−1up to 1.53 × 10−2 g L−1with a detection limit of 1.15 × 10−5 g L−1(S/N = 3). The sensor also had an easily renewable surface, good fabrication reproducibility, and inherent stability. Moreover, satisfactory results were obtained with complex samples and demonstrate the reliability of the proposed method. [ABSTRACT FROM PUBLISHER]

A composite LangmuirBlodgett film prepared from DNA and polyaniline was deposited on the surface of a glassy carbon electrode (GCE) to give a new voltammetric sensor for the β2-agonist salbutamol (SAL). Cyclic voltammetry and electrochemical impedance spectroscopy were employed to study the characteristic of the modified electrode. The electrochemistry of SAL at the modified electrode was investigated at pH 6.8 by cyclic voltammetry and differential pulse anodic voltammetry. The oxidation of SAL at this electrode is an adsorption-controlled irreversible process. A sensitive electroanalytical method for determination of SAL was worked out that displays high precision and good reproducibility. The method was applied to quantify SAL in tablets with satisfactory results. [ABSTRACT FROM AUTHOR]

A novel voltammetric sensor using multi-wall carbon nanotubes (MWNTs) coupled with Nafion modified glassy carbon electrode (GCE) was developed for the detection of methylparaben (MP). The sensor exhibited good electrocatalytic activity toward the oxidation of MP in the phosphate buffer solution (PBS, pH 6.5). It displayed good sensitivity, repeatability, reproducibility, and long-term stability. Under the optimized conditions, the anodic peak current was linear with the concentration of MP in the range of 3 × 10−6 mol L−1 to 1 × 10−4 mol L−1. The detection limit was 1 × 10−6 mol L−1. The proposed method was successfully applied to determine MP in cosmetics with satisfactory results. [ABSTRACT FROM AUTHOR]

We report on the voltammetric determination of the flavonoid Baicalein by using a carbon paste electrode that was doped with multi-walled carbon nanotubes. The resulting sensor exhibits excellent redox activity towards Baicalein due to the large surface area and good conductivity of the electrode. Cyclic voltammetry at various scan rates was used to investigate the redox properties of Baicalein. At the optimum conditions, the sensor displays a linear current response to Baicalein in the 0.02-10 μM concentration range, with a limit of detection of 4.2 n M. The method was successfully applied to the determination of Baicalein in spiked human blood serum samples and in a Chinese oral liquid. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A double-stranded (ds) DNA-octadecylamine Langmuir-Blodgett film was attached to the surface of glassy carbon electrode (GCE) to create a novel voltammetric sensor (DNA-LB/GCE) for epinephrine (EP). Atomic force microscopy and electrochemical impedance spectroscopy were employed to study the characteristic of the DNA-LB film. The electrochemical behavior of EP at the modified electrode was investigated in pH 6.0 phosphate buffer solutions by cyclic voltammetry and amperometric methods. Compared with bare GCE, the DNA-LB/GCE sensor demonstrated an electrocatalytic effect on the oxidation of EP. In addition, the sensor shows excellent selectivity for EP detection, being free of interference from excess ascorbic acid and uric acid, and the method was also applied successfully to detect EP in the human urine samples. [ABSTRACT FROM AUTHOR]

A novel voltammetric sensor, based on single-walled carbon nanotubes (SWNT) dispersed in Nafion and modified glassy carbon electrode (GCE), was fabricated and used to determine the trace amounts of dihydromyricetin (DMY). The electrochemical behavior of DMY at this sensor was investigated in 0.1 mol L sulfuric acid solutions + 0.1 mol L NaCl by cyclic voltammetry and squarewave voltammetry. Compared with bare GCE, the electrode presented an excellent response of DMY through an adsorption-controlled quasi-reversible process. Under the optimum conditions, the response peak currents were linear relationship with the DMY concentrations in the range of 1.0 × 10-1.0 × 10 mol L with a detection limit of 9 × 10 mol L. Based on this voltammetric sensor, a simple and sensitive electroanalytical method for DMY was proposed and applied to quantitative determination of DMY in Ampelopsis grossedentata samples. In addition, the oxidation mechanism was proposed and discussed, which could be a reference for the pharmacological action of DMY in clinical study. [ABSTRACT FROM AUTHOR]

We report on a voltammetric sensor for caffeine that is based on a glassy carbon electrode modified with Nafion and graphene oxide (GO). It exhibits a good affinity for caffeine (resulting from the presence of Nafion), and excellent electrochemical response (resulting from the pressence of GO) for the oxidation of caffeine. The electrode enables the determination of caffeine in the range from 4.0 × 10 to 8.0 × 10 mol L, with a detection limit of 2.0 × 10 mol L. The sensor displays good stability, reproducibility, and high sensitivity. It was successfully applied to the quantitative determination of caffeine in beverages. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We have prepared a new voltammetric sensor for guanine and adenine. It is based on a glassy carbon electrode modified with a Langmuir-Blodgett film made from tetraoxocalix[2]arene[2]triazine. The direct electro-oxidation of adenine and guanine was investigated and the results indicat that in contrast to a bare glassy carbon electrode both guanine and adenine cause an increase in the oxidation peak currents along with a negative shift of the oxidation potentials. The electrode enables the simultaneous determination of guanine and adenine using square wave voltammetry. Analysis of acid denatured calf thymus DNA was carried out and the value of (G + C)/(A + T) was correctly found to be 0.75. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Gold nanoparticles (GNPs) were allowed to self-assemble onto a glassy carbon electrode (GCE) that was prior modified by l-cysteine. The modified electrode was then used as a voltammetric sensor in detecting the neurotransmitter serotonin. The electrode exhibited a linear voltammetric response for serotonin within a concentration range of 6.0 × 10−8M to 6 × 10−6M, with a detection limit of 2 × 10−8M. The detection of serotonin was found to be unaffected by the presence of epinephrine, dopamine, ascorbic acid and folic acid. The electrode was applied to detect serotonin added to human blood serum, with an average recovery value of 104.67%. [ABSTRACT FROM AUTHOR]

A new p-tetra-butyl calix [6] arene-L-Histidine chemically modified glassy carbon electrode (BCH/GCE) has been proposed for simultaneous investigation and determination of epinephrine (Ep) and serotonin (5-HT) by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). In potassium dihydrogen phosphate-borax (PDPB) buffer solution (pH 5.8), the anodic peaks of Ep and 5-HT were observed at 0.27 and 0.45 V, respectively, with E up to 180 mV. The peak currents on the DP voltammogram are in a linear relationship with the concentrations of Ep in the range of 1.0 × 10−6−1.30 × 10−4 M in the presence of 1.0 × 10−4 M 5-HT. A linear relationship was similarly found for 5-HT in the range 1.0 × 10−6− 1.40 × 10−4 M in the presence of 1.0 × 10−4 M Ep. It is found that Ep and 5-HT could be simultaneously determined with good sensitivity in the presence of 1.0 × 10−3 M ascorbic acid (AA). The developed method has been applied to the determination of Ep and 5-HT in synthetic samples with satisfactory results. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel electrochemical sensor (Ag-Gly-Gr/GCE) for the determination of bergenin was proposed. • The fabrication process of electrochemical sensor is simple and environmentally friendly. • The electrochemical behavior of bergenin was investigated, which is significant for the research of pharmacological properties. Herein, an efficient method for in-situ assembly of silver (Ag) nanoparticles on glycine functionalized graphene (Gly-Gr) has been proposed, which only requires a simple one-step hydrothermal reaction. The microstructure of the material (Ag-Gly-Gr) was characterized by a series of methods, such as FT-IR, XRD, and TEM. For comparison, glycine functionalized graphene (Gly-Gr) was prepared by the same way without adding silver nitrate. The electrochemical sensor (Ag-Gly-Gr/GCE or Gly-Gr/GCE) was prepared by coating the glassy carbon electrode (GCE) surface with dispersive droplets of the related material. The outcomes of the electrochemical impedance test showed that the charge transfer resistance of Ag-Gly-Gr/GCE was less than that of Gly-Gr/GCE and GCE. Compared with the other two sensors, Ag-Gly-Gr/GCE showed a more sensitive response for bergenin. By studying the influence of the pH and sweep rate on the peak potential, the dynamics parameters were discussed to understand the electrochemical reaction mechanism of bergenin. The strategy for quantitative analysis of bergenin was further established at the working potential of 0.8 V (vs SCE). The peak current of bergenin displayed a linear dependence for concentration in 0.01–1 μM with a detection limit of 3.0 nM. Additionally, the analytical availability of Ag-Gly-Gr/GCE was demonstrated by determining bergenin in real-life samples. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical behaviour of the anticancer herbal drug emodin was investigated by cyclic voltammetry (CV) at glassy carbon electrode. In 0.05M NH3-NH4Cl (50% ethanol, pH 7.2) buffer solution, a pair of quasi-reversible redox peaks at potentials of =−0.688V and =−0.628V and one irreversible anodic peak, which was a typical anodic peak of emodin, at =−0.235V appeared at a scan rate of 100mV/s. The irreversible anodic peak currents are linearly related to the emodin concentrations in a range from 8.9×10−8 M to 7.8×10−6 M with a pre-concentration time of 80s under −0.620V. Using the established method without pretreatment and pre-separation, emodin in herbal drug was determined with satisfactory results. Moreover, the electrode process dynamics parameters were also investigated by electrochemical techniques. [Copyright &y& Elsevier]

A label-free electrochemical aptasensor was developed for the sensitive detection of interferon-gamma (IFN-γ). To do this, a diblock dual-aptamer allosteric hairpin (DDAH) was designed, followed by conjugation with gold nanoparticles (DDAH&AuNP). The presence of target destroyed the stable hairpin structure, and then the catalytic cleavage of DNAzymes removed the IFN-γ-binding molecules, triggering the allosteric switching from inactive hairpin to active streptavidin aptamer (A-DDAH&AuNP) in homogeneous system. Moreover, streptavidin-inorganic hybrid nanoflowers decorated with graphene composites (SFG) were synthesized and used as substrates to modify glassy carbon electrodes (SFG/GCE). SFG specifically bind to the A-DDAH&AuNP to realize high-efficient readout of signals. Under the optimal conditions and by using differential pulse stripping voltammetry (DPSV), the response peak currents increases linearly with the logarithm of the IFN-γ concentration in the range between 0.1 pg mL−1 and 500 ng/mL. The detection limit is as low as 19 fg mL−1. The aptasensor also has excellent electrochemical performances, which exhibits broad application prospects in biometric analysis. Image 1 • A new diblock dual-aptamer allosteric hairpin switch is designed and used to improve the sensitivity and selectivity of aptasensor. • SFG was used as substrate material to amplify the signal of sensor. • The electrochemical aptasensor showed a low detection limit of 19 fg mL−1 for IFN-γ. [ABSTRACT FROM AUTHOR]

The nanocomposite of ruthenium oxide (RuO 2 ) loaded on Poly-(dimethyldiallylammonium chloride) (PDDA) functionalized reduced graphene oxide (RuO 2 -PDDA-rGO) was synthesized based on a one-step method. Based on the RuO 2 -PDDA-rGO modified glassy carbon electrode (GCE), a new electrochemical sensor (RuO 2 -PDDA-rGO/GCE) was fabricated and used in detection of baicalein for the first time. Compared with other reported electrochemical sensors for the detection of baicalein, the prepared RuO 2 -PDDA-rGO/GCE had a wider linear range (2–400 nM) and lower detection limit (0.6 nM, S/N = 3). The other advantages were the excellent repeatability of proposed method and good stability of prepared sensor. [ABSTRACT FROM AUTHOR]

Chrysin and baicalein are the major flavonoids found in oroxylum indicum, an essential herb in traditional Chinese medicine (TCM). Owing to their similar characteristics and physiochemical property, it is a great challenge to detect both of them simultaneously. In this work, tantalum oxide (Ta 2 O 5 ) particles and chitosan modified carbon paste electrode (Ta 2 O 5 -CTS-CPE) was prepared and characterized by scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectrum(EIS). Under the optimum conditions, the prepared Ta 2 O 5 -CTS-CPE exhibited excellent electrocatalytic activity toward the oxidation of chrysin and baicalein, and it could serve as the sensor for highly sensitive and simultaneous determination both of them. The linear range is 0.08–4.0 μM for both of them, and the detection limits were determined to be 0.03 and 0.05 μM (S/N=3) for chrysin and baicalein, respectively. Furthermore, the proposed electrochemical sensor displayed high sensitivity, excellent stability and got satisfactory results in oroxylum indicum samples analysis. [ABSTRACT FROM AUTHOR]

In this paper, a simple, low cost, highly sensitive voltammetric method for determination of tetrahydropalmatine was described, which was based on a new electrochemical sensor, poly (L-glutamic acid) functionalized electrochemical reduction graphene oxide modified glassy carbon electrode. The electrochemical behavior of tetrahydropalmatine was investigated in detail and some dynamic parameters of electrode process were calculated for the first time. Due to large surface area and good conductivity of proposed sensor, a wider linear range (3.0×10 −7 –2.0×10 −5 mol L −1 ) and lower detection limit (1.0×10 −7 mol L −1 ) were achieved for determination of tetrahydropalmatine. Meanwhile, the proposed method was used in determination of tetrahydropalmatine in Rhizoma Corydalis with well results. [ABSTRACT FROM AUTHOR]

Arctigenin was determinated by an electrochemical method for the first time based on a novel voltammetric sensor, which was prepared by simple dipping-drying of SWCNTs on glassy carbon electrode (GCE) initially and then electrochemical deposition of Iodide. The resulting Iodide/SWCNTs/GCE displayed a significant voltammetric response to arctigenin due to the electrocatalytic ability of Iodide for arctigenin and a large specific surface area, excellent electric conductivity of SWCNTs. Meanwhile, the redox mechanism of arctigenin on Iodide/SWCNTs/GCE was also studied. The wide linear range of 3 × 10 − 8 mol L − 1 to 5 × 10 − 6 mol L − 1 and low detection limit of 1 × 10 − 8 mol L − 1 for the determination of arctigenin were achieved together with high sensitivity, selectivity, good stability. To examine the practical analytical utility of the proposed electrode, the real sample Fructus Arctii was examined and the result was found satisfactory. [ABSTRACT FROM AUTHOR]

With the aid of polyaniline (PANI), multi-wall carbon nanotubes (MWCNTs) were vertically arrayed on electrode surface by Langmuir–Blodgett technology, which was a novel preparation strategy of vertically aligned MWCNTs modified electrode. The proposed method was applied to design a sensitive voltammetric sensor for the determination of daidzein. Compared to the randomly dispersed MWCNTs modified electrode, a lower detection limit (8 × 10 −8 mol L −1 ) and wider linear range (1.0 × 10 −7 –9.0 × 10 −6 mol L −1 ) were achieved by the proposed sensor. The results indicated that the aligned morphology of MWCNTs could effectively facilitate the transportation of electrons and electrolyte ions. [ABSTRACT FROM AUTHOR]

A highly sensitive voltammetric sensor, based on reduced graphene oxide on SWCNTs modified glassy carbon electrode (GCE), was constructed and used for sensitive detection of hesperetin. The electrochemical behavior of hesperetin at this sensor was investigated systematically and a novel voltammetric method for determination of hesperetin was proposed. The redox characters of hesperetin was discussed in detail and a reasonable reaction mechanism was proposed also. As the analytical method, the response currents were linear relationship with the hesperetin concentrations in the range of 5.0×10 −8 to 3.0×10 −6 mol L− 1 , with a detection limit of 2.0×10 −8 mol L −1 ( S / N =3). The method was also applied successfully to detect hesperetin in biological samples and Chinese herbal medicine Flos buddlejae with satisfactory results. [ABSTRACT FROM AUTHOR]

A novel voltammetric sensor was constructed by simple dripping single-walled carbon nanotubes (SWCNTs) on to the glass carbon electrode (GCE) firstly and electro-polymerizing l -Citrulline film subsequently. The resulting poly( l -Citrulline)/SWCNTs/GCE showed a significant voltammetric response to picroside II due to the synergistic effect of SWCNTs and poly( l -Citrulline) film. The first electroanalytical method of picroside II was proposed with detection linear range from 8.0×10 −8 to 5.0×10 −6 mol L −1 and a detection limit of 3×10 −8 mol L −1 .The high sensitivity, selectivity and long-term stability made the sensor suitable for the determination of picroside II. Moreover, based on the systematically investigation and some kinetics parameters calculated in the experimentation, the reaction mechanism of picroside II at the poly( l -Citrulline)/SWCNTs modified GCE was obtained reliably. Lastly, the proposed sensor was used for the determination of picroside II in real sample with satisfactory results. This work promoted the potential applications of amino acid materials and SWCNTs in electro-chemical sensors. [ABSTRACT FROM AUTHOR]

The electro-polymerization of l -Norvaline was investigated for the first time on glassy carbon electrode. The polymeric conditions and mechanism were discussed in detail. The electrochemical behaviors of metribuzin were studied systematically at this sensor and the dynamic parameters of electrode process were calculated. This electrochemical sensor, fabricated simply and very easy surface update, showed good response for metribuzin with a wide linear range from 6.43 × 10 − 3 to 1.07 μg/mL and a low detection limit of 2.14 × 10 − 3 μg/mL (S/N = 3). The proposed method was successfully applied to determine metribuzin in soil sample with satisfactory results. This work promoted the potential applications of amino acid materials in electrochemical sensors. [ABSTRACT FROM AUTHOR]

This work establishes a highly sensitive and simple stripping voltammetric method for the direct determination of trace iodide. In the presence of abounding bromide and appropriate amount of cetylpyridine bromide (CPB), the iodine was accumulated on the glassy carbon electrode surface as ion association complex (CPBI 2 Br). After accumulation for a period of time, a linear sweep potential with negative scanning was applied and the I 2 in CPBI 2 Br was reduced again into the solution. Under the optimization conditions, the stripping signals (peak current) were linear relationship with iodide concentration in range of 3.81×10 −3 µg/mL to 0.114 μg/mL and 0.127 μg/mL to 2.54 μg/mL, with a detection limit of 1.02 ng/mL ( S / N =3) for a accumulation time of 180 s. Determination of trace iodine in pharmaceutical sample, kelp and table salt were performed with high accuracy and satisfactory recovery results. [ABSTRACT FROM AUTHOR]

Langmuir–Blodgett (LB) film of C-Undecylcalix[4]resorcinarene (CUCR) as molecular receptor and pretreated glassy carbon electrode (GCE) as enhancer of electron transfer are integrated in the electrochemical sensor system. The new electrochemical sensor possesses the properties of calixarene (high supramolecular recognition and enrichment capability) and pretreated GCE (large surface area and high active sites). At the resulting electrode, the peak current of dopamine (DA) and uric acid (UA) increased dramatically compared with that on the bare GCE and pretreated GCE which due to the synergetic effects of LB film of CUCR and pretreated GCE. Using differential pulse voltammetry, the resulting electrode was applied to develop a high sensitive electrochemical sensor for the simultaneous determination of DA and UA in the presence of ascorbic acid (AA) for the first time. Under the selected conditions, the linear response ranges for DA and UA are 8.0 × 10 −8 to 6.0 × 10 −6 mol L −1 and 4.0 × 10 −7 to 4.0 × 10 −5 mol L −1 , with the detection limits of 2.0 × 10 −8 mol L −1 and 8.0 × 10 −8 mol L −1 , respectively. Besides, the resulting electrode also showed an excellent selectivity, stability and reproducibility. [ABSTRACT FROM AUTHOR]

A sensitive electrochemical method for determination of daphnetin at reduced graphene oxide (RGO) modified glassy carbon electrode (GCE) was developed. The graphene nanosheets were simply directly deposited onto a GCE surface through cyclic voltammetric reduction of graphene oxide colloidal solution. The redox character of daphnetin at ERGO/GCE was studied systematically and some dynamic parameters were calculated for the first time. The electroanalytical method for determination of daphnetin was established by differential pulse voltammograms (DPV). Under optimum conditions, the response peak currents were linear related with daphnetin concentrations in the range of 5.0 × 10 −8 to 2.0 × 10 −6 mol L −1 with a detection limit of 3.0 × 10 −8 mol L −1 . Therefore, the high sensitivity for daphnetin sensing at the proposed electrode was achieved, which was attributed to the introduced graphene films modified on GCE. Additionally, the proposed method could also be used to detect daphnetin in the medicinal capsules and Chinese medicinal herb Zushima with satisfactory results. [ABSTRACT FROM AUTHOR]

A new type of voltammetric sensor, Langmuir-Blodgett (LB) film of multi-walled carbon nanotubes (MWCNTs) perpendicularly modified glassy carbon electrode (GCE), was prepared and applied in determination of methylparaben. Based on the excellent electrochemical property of vertical MWCNTs on the GCE (MWCNTs-LB/GCE), a sensitive voltammetric method for determination of methylparaben was erected with liner range from 1 × 10 −6 mol L −1 to 8 × 10 −5 mol L −1 and detection limit of 4 × 10 −7 mol L −1 . The electrochemical characters of MWCNTs-LB/GCE were investigated in detail and the reaction mechanism of methylparaben was discussed. Meanwhile, cosmetic samples were analyzed using proposed method and the results obtained were well satisfactory. [ABSTRACT FROM AUTHOR]

The electrodeposition of reduced graphene oxide (ERGO) film with preferred vertical orientation was fabricated on a glassy carbon electrode by using pulse potential method in a graphene oxide colloidal solution. Using square wave adsorptive stripping voltammetry (SWASV), the ERGO film was applied for the first time, in developing a high-sensitive electrochemical sensor for detection of taxifolin. Compared with bare glassy carbon electrode (GCE), the resulting electrodes (ERGO/GCE) exhibited excellent response toward the redox of taxifolin by significantly enhancing the redox peak currents and decreasing the peak-to-peak separation. Under the selected conditions, the peak currents were linear relationship with taxifolin concentration in the range of 1.0 × 10 −8 –1.0 × 10 −6 mol L −1 , with detection limit of 2.0 × 10 −9 mol L −1 . Besides, the ERGO/GCE also exhibited an excellent selectivity, stability, reproducibility and repeatability. [ABSTRACT FROM AUTHOR]

A simple, rapid and green method was described for sensitive voltammetric detection of sophoridine based on graphene nanosheets directly deposited onto a glassy carbon electrode (GCE) by pulsed potentiostatic reduction of a graphene oxide (GO) colloidal solution. The resulting electrodes (PP-ERGO/GCE) were characterized by electrochemical methods and scanning electron microscopy. Moreover, the electrochemical behaviors of sophoridine at the modified electrode were investigated in detail by cyclic voltammetry (CV), chronoamperometry (CA) and chronocoulometry (CC). Compared with the bare GCE and the preparation of reduced graphene oxide (RGO) films by potentiostatic method (PM) modified GCE, PP-ERGO/GCE could intensively enhance the oxidation peak currents and decrease the overpotential of sophoridine. Under the selected conditions, the modified electrode showed a linear voltammetric response to sophoridine within the concentration range of 8.0 × 10 −7 ∼ 1.0 × 10 −4 mol L −1 1 , with the detection limit of 2.0 × 10 −7 mol L −1 . And, the method was also applied to detect sophoridine in spiked human urine with wonderful satisfactory. [ABSTRACT FROM AUTHOR]

A simple, inexpensive and highly sensitive electrochemical method for the determination of jatrorrhizine was developed using an electrochemically pretreated glassy carbon electrode (EPGCE). The electrochemical behavior of jatrorrhizine was systematically investigated in detail and some kinetic parameters were calculated for the first time. A reasonable reaction mechanism of jatrorrhizine on the EPGCE was also discussed and proposed, which could be a reference for the pharmacological action of jatrorrhizine in clinical study. And the first electroanalytical method of jatrorrhizine was established with a wide linear range from 7.0×10−8 to 2.0×10−5 molL−1 and a low detection limit of 5.0×10−8 molL−1. The proposed method was successfully applied in determination of jatrorrhizine in pharmaceutical sample, Tinospora capillipes Gagnep (a traditional Chinese medicine), with satisfactory results. [ABSTRACT FROM AUTHOR]

A facile and highly sensitive electrochemical sensor for kaempferol was fabricated by doping polyvinyl pyrrolidone cladding quantum dots to the carbon paste electrode. The quantum dots were characterized with transmission electron microscopy, ultraviolet spectrum and infrared spectrum. The electrochemical behaviors and kinetic parameters of kaempferol were investigated on the sensor by cyclic voltammetry and chronocoulometry in NaAc–HAc (pH 4.4). The proposed sensor accelerated the redox processes of kaempferol obviously, and the oxidation currents were linearly relationship with kaempferol in two concentration intervals: one was 6.0×10−8–2×10−6 mol/L and the other was 5.0×10−6–2.5×10−5 mol/L. The quantification limit obtained by square wave voltammetry was 6.0×10−8 mol/L. Merits such as extreme simplicity, low cost, good sensitivity, high sensitivity, good stability and reproducibility made it an excellent electrochemical sensor for kaempferol. A new electroanalytical method for kaempferol was proposed and used for determination of kaempferol in tablets with satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, electrochemical method was used to investigate the interactions between DNA and amphiphilic ferrocenylimine. The method was developed using the system of electrode modified with the amphiphilic ferrocenylimine LB films. Electrochemical results obtained from amphiphilic ferrocenylimine LB films modified electrode suggested that the forrocenium derivative could interact strongly with dsDNA. It was observed that the binding of amphiphilic ferrocenylimine to DNA led to a significant peak current decrease of amphiphilic ferrocenylimine LB films modified electrode. The interactions between amphiphilic ferrocenylimine and four basic groups were also investigated, the results revealed that the basic groups cytosine, thymine and adenine could interact with forrocenium complex, but guanine showed no interaction with forrocenium complex. The order of interaction intensity for four basic groups with forrocenium complex (from strong to feeble) is cytosine>thymine>adenine>guanine. Therefore, the amphiphilic ferrocenylimine interacted with DNA through the basic groups cytosine, thymine and adenine. [Copyright &y& Elsevier]

Abstract: Gold nanoparticles/polyaniline nanocomposite thin film was deposited onto the surface of glassy carbon electrode(GCE) by Langmuir–Blodgett(LB) technology to fabricate a new voltammetric sensor (GNPs/PAn-LB GCE) for epinephrine(EP) and uric acid(UA) detection. Cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy were employed to study the characteristic of the GNPs/PAn-LB film. Electrochemical behaviors of EP and UA at the modified electrode were investigated in pH 6.6 phosphate buffer solutions. A sensitive electroanalytical method for simultaneous determination of EP and UA was proposed with high precision and good reproducibility. [Copyright &y& Elsevier]

Abstract: A simple but highly sensitive and selective electrochemical sensor for the determination of serotonin (5-HT) was presented. Pretreated glassy carbon electrode (GCE) as enhancer of electron transfer and C-undecylcalix[4]resorcinarene film as molecular receptor are integrated in the electrochemical sensor system. The electrochemical behavior of 5-HT at the modified electrode had been investigated in pH 7.0 phosphate buffers solutions by cyclic voltammetry, square wave voltammetry and chronocoulometry. Compared with bare GCE, the proposed integrated sensor showed improved analytical performance characteristics in catalytic oxidation of 5-HT. Under the selective conditions, the modified electrode showed a linear voltammetric response for the 5-HT within a concentration range of 1.0×10−7 to 1.0×10−5 molL−1, and a value of 3.0×10−8 molL−1 was calculated for the detection limit. Besides, due to the difference of potentials, the modified electrode exhibited an excellent immunity from dopamine, epinephrine, ascorbic acid and folic acid interference. [Copyright &y& Elsevier]

Abstract: A highly sensitive electrochemical biosensor for the detection of trace amounts of methotrexate had been designed. Gold nanoparticles were allowed to self-assemble onto a glassy carbon electrode that was prior modified by l-cysteine. The anodic voltammetric behaviors of methotrexate at the electrode were then explored by cyclic voltammetry (CV) and square wave voltammetry (SWV). Compared with bare GCE, the electrode can greatly improve the measuring sensitivity of methotrexate. More, the dependences of the current on pH, nature of buffer, instrumental parameters, accumulation time and potential were investigated to optimize the experimental conditions for the determination of methotrexate. Under the selected conditions, the modified electrode in pH=2.0 Britton–Robinson (B–R) buffer solutions showed a linear voltammetric response to methotrexate within the concentration range of 4.0×10−8–2.0×10−6 molL−1, with the detection limit of 1.0×10−8 molL−1. The method was applied to detect methotrexate in medicinal tablets and spiked human blood serum samples. [Copyright &y& Elsevier]

Abstract: Safranine T was electropolymerised on a glassy carbon electrode and then characterised by scanning electron microscope (SEM), X-ray diffraction (XRD) and electrochemical impedance spectroscopy (EIS). This uniform electropolymerised film was crystallisable and showed a high electrocatalytic ability towards the oxidation of caffeine. To avoid the interferences of the anions, Nafion was covered on the surface of poly(safranine T) film modified glassy carbon electrode. As a new voltammetric sensor, this modified electrode is sensitive, selective and stable to determine caffeine content in tea. The peak current increased linearly with the concentration of caffeine in the range of 3×10−7–1×10−4 M, with a detection limit of 1×10−7 M. All of these make it a useful tool for determining caffeine content in tea. What’s more, it produces much less organic waste compared with other analytical techniques. [Copyright &y& Elsevier]

Abstract: In this paper, a multiwall carbon nanotube/Nafion composite modified glassy carbon electrode (MWNT/Nafion/GCE) was used as a voltammetric sensor to determine 8-hydroxyquinoline (8-HQ) in cosmetic. This voltammetric sensor exhibited strong catalytic effect toward the oxidation of 8-HQ and caused an anodic peak at 0.97V in HAc-NaAc buffer solution (0.2M, pH 3.6). Under the optimized condition, the anodic peak current was linear with the concentration of 8-HQ in the range of 2×10−8 M–1.0×10−5 M. The detection limit was 9×10−9 M. The practical application of MWNT/Nafion/GCE was carried out for determining 8-HQ in cosmetic sample with satisfactory results. The electrode reaction mechanism was studied by cyclic voltammetry and UV–vis spectra. [Copyright &y& Elsevier]

Abstract: The present paper describes to modify a double stranded DNA–octadecylamine (ODA) Langmuir–Blodgett film on a glassy carbon electrode (GCE) surface to develop a voltammetric sensor for the detection of trace amounts of baicalein. The electrode was characterized by atomic force microscopy (AFM) and cyclic voltammetry (CV). Electrochemical behaviour of baicalein at the modified electrode had been investigated in pH 2.87 Britton–Robinson buffer solutions by CV and square wave voltammetry (SWV). Compared with bare GCE, the electrode presented an electrocatalytic redox for baicalein. Under the optimum conditions, the modified electrode showed a linear voltammetric response for the baicalein within a concentration range of 1.0×10−8–2.0×10−6 molL−1, and a value of 6.0×10−9 molL−1 was calculated for the detection limit. And the modified electrode exhibited an excellent immunity from epinephrine, dopamine, glucose and ascorbic acid interference. The method was also applied successfully to detect baicalein in the medicinal tablets and spiked human blood serum samples with satisfactory results. [Copyright &y& Elsevier]

Abstract: A highly sensitive electrochemical sensor made of a glassy carbon electrode (GCE) coated with a Langmuir–Blodgett film (LB) containing polyaniline (PAn) doped with p-toluenesulfonic acid (PTSA) (LB/PAn-PTSA/GCE) has been used for the detection of trace concentrations of Ag+. UV–vis absorption spectra indicated that the PAn was doped by PTSA. The surface morphology of the PAn LB film was characterized by atomic force microscopy (AFM). The electrochemical properties of this LB/PAn-PTSA/GCE were studied using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The LB/PAn-PTSA/GCE was used as a voltammetric sensor for determination of trace Ag+ at pH 5.0 using linear scanning stripping voltammetry. Under the optimal experimental conditions, the stripping current was proportional to the Ag+ concentration over the range from 6.0×10−10 molL−1 to 1.0×10−6 molL−1, with a detection limit of 4.0×10−10 molL−1. The high sensitivity, selectivity, and stability of this LB/PAn-PTSA/GCE also demonstrated its practical utility for simple, rapid and economical determination of Ag+ in water samples. [Copyright &y& Elsevier]

Abstract: The π–A isotherms and UV–vis spectra of the transferred films suggested that the monolayer of p-tert-butylthiacalix[4]arene can coordinate with Hg2+ at the air–water surface. From these observations, a glassy carbon electrode coated with Langmuir–Blodgett film of p-tert-butylthiacalix[4] arene as a new voltammetric sensor is designed for the determination of trace amounts of Hg2+. Compared with bare glassy carbon electrode and modified glassy carbon electrode using direct coating method, the Langmuir–Blodgett film-modified electrode can greatly improve the measuring sensitivity of Hg2+. Under the selected conditions, the Langmuir–Blodgett film-modified electrode in 0.1molL−1 H2SO4 +0.01molL−1 KCl solution shows a linear voltammetric response for Hg2+ in the range of 5.0×10−10 to 1.5×10−7 molL−1, with a detection limit of 2.0×10−10 molL−1. The proposed method was also applied to determine Hg2+ in water samples (tap, lake and river water). In addition, the fabricated electrode exhibited a distinct advantage of simple preparation, non-toxicity, good reproducibility and good stability. [Copyright &y& Elsevier]

Abstract: The π–A isotherms and UV–vis spectra of the transferred films suggested that the monolayer of p-tert-butylthiacalix[4]arene can coordinate with Ag+ at the air–water surface. From these observations, a glassy carbon electrode coated with Langmuir–Blodgett film of p-tert-butylthiacalix[4]arene is designed for the determination of trace amounts of Ag+. Compared with bare glassy carbon electrode and modified glassy carbon electrode using direct coating method, the Langmuir–Blodgett film modified electrode can greatly improve the measuring sensitivity of Ag+. Under the optimum experimental conditions, the Langmuir–Blodgett film modified electrode in 0.1molL−1 HNO3 shows a linear voltammetric response in the range of 5.0×10−9–2.0×10−6 molL−1 with detection limit 3.0×10−9 molL−1 for Ag+. The high sensitivity, selectivity, and stability of this Langmuir–Blodgett film modified electrode also demonstrate its practical application for a simple, rapid and economical determination of Ag+ in water sample. [Copyright &y& Elsevier]

Abstract: A highly sensitive electrochemical biosensor for the detection of trace amounts of methotrexate has been designed. Double stranded (ds)DNA molecules are immobilized onto a pretreated glassy carbon electrode (GCE(ox)) surface with Langmuir–Blodgett (LB) technique. The adsorptive voltammetric behaviors of methotrexate on DNA-modified electrode were explored by means of cyclic voltammetry (CV) and square wave voltammetry (SWV). The oxidation mechanism was proposed and discussed in this work. In addition, the optimum experimental conditions for the detection of methotrexate were explored, and the currents measured by SWV presented a good linear property as a function of the concentrations of methotrexate in the range of 2.0×10−8 to 4.0×10−6 molL−1, with an LOD of 5.0×10−9 molL−1. The method proposed was applied for the determination of methotrexate in pharmaceutical dosage and diluted human urine with wonderful satisfactory successfully. [Copyright &y& Elsevier]

Abstract: The interaction of anticancer herbal drug berberine with double-strand DNA (dsDNA) and single-strand DNA (ssDNA) in solution, dsDNA immobilized on the glassy carbon electrode prepared by Langmuir–Blodgett technique, were investigated by electrochemical techniques (cyclic voltammetry, differential pulse voltammetry) and UV spectroscopy. The presence of DNA results in a decrease of the currents and a negative shift of the electrode potentials from the DPV curves of berberine, indicating the dominance of electrostatic interactions. The spectroscopy data confirmed that the predominant interaction between berberine and DNA is electrostatic. The binding of berberine with DNA, when analyzed in terms of the cooperative Hill model, yields the binding constant K a =2.2(±0.2)×104 M−1, corresponding to the dissociation equilibrium constant K d =4.6(±0.3)×10−5 M, which in the range of the applied concentrations of DNA (bp) and berberine, and a Hill coefficient m =1.82(±0.08) in Britton–Robinson buffer solution (0.05 M, pH 5.72) at T =298 K (25 °C). Apparently, at least two molecules of berberine have to bind as a couple to cause, e.g., the “elementary event” of current change. The results are suggestive for further fruitful applications of this anticancer herbal drug and DNA-modified electrodes. [Copyright &y& Elsevier]

Abstract: A glassy carbon electrode (GCE) modified with a Langmuir–Blodgett (LB) film of p-tert-butylthiacalix[4]arene (TCA) has been investigated as a disposable sensor for measuring the trace levels of lead and cadmium. The possibility of determining lead and cadmium at trace levels was examined with differential pulse stripping voltammetry in the measurement step. The electrochemical response was characterized with respect to supporting electrolyte, pH of solution, accumulation time, accumulation potential, layers of the LB films, and possible interferences. Calibration plots were found to be linear in the range 2×10−7 to 5×10−5 moll−1 (Cd2+) and 1×10−7 to 2.5×10−5 moll−1 (Pb2+); the detection limits were 2×10−8 moll−1 (Cd2+) and 8×10−9 moll−1 (Pb2+). Possible recognition mechanism was also discussed. From the analysis of real samples (river, lake and tap water) it can be concluded that the method is sensitive and reproducible in determining of these elements and can be used in the analysis of natural water samples. [Copyright &y& Elsevier]

Abstract: A glassy carbon electrode (GCE) coated with Langmuir–Blodgett (LB) film of p-allylcalix[4]arene is described for simultaneous determination of traces of thallium and cadmium in environmental water. The LB film electrode in a 0.1M KH2PO4 solution shows a linear voltammetric response in the range of 5–250μgl−1 for thallium and 10–300μgl−1 for cadmium. The detection limits of thallium(I) and cadmium(II) are estimated to be 1.0μgl−1 (ca. 5.0×10−9 M) and 2.2μgl−1 (ca. 2.0×10−8 M), respectively. Above all, the indium does not respond to this LB film electrode. [Copyright &y& Elsevier]

A new voltammetric sensor for simultaneous detection of bisphenol A and bisphenol S with high sensitivity has been constructed based on a three-component composite modified glassy carbon electrode. The three-component composite used herein is composed of AuAgPt ternary alloy nanocrystals (AuAgPt), porous β-cyclodextrin polymer (PCD) and oxide graphene (GO), abbreviated as AuAgPt-PCD-GO. The obtained composites were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM). The proposed modified electrode showed excellent electrochemical response to bisphenol A and bisphenol S simultaneously. Under optimal experiment conditions, the response linear ranges for bisphenol A and bisphenol S are from 6 nM to 4000 nM and 8 nM–8000 nM with detection limits of 2 nM and 2.67 nM (S/N = 3), respectively. Furthermore, this electroanalytical sensor could also be successfully applied to real sample analysis with satisfactory results. Image 1 • The three-component composite material AuAgPt-PCD-GO was designed to construct a novel electrochemical sensor for simultaneous BPA and BPS assay. • The possible electrochemical oxidation mechanism of BPA and BPS on the modified electrode was deduced. • The proposed sensor can be used for real sample assay with satisfactory results. [ABSTRACT FROM AUTHOR]