•A new graphene nanocomposite (CeO2-PDDA-GR) was prepared by an easy method.•CeO2-PDDA-GR was used to build a sensitive sensor for determination of eriocitrin.A new graphene nanocomposite, CeO2-poly(diallyldimethylammonium chloride)-graphene (CeO2-PDDA-GR), was prepared by an easy and low-cost hydrothermal method. The images of transmission electron microscopy (TEM) showed that well-shaped CeO2 nanoparticles distributed more uniformly on the GR sheets. Based on the CeO2-PDDA-GR composites modified glassy carbon electrode, the electrochemical properties of eriocitrin were investigated in detail and a sensitive determination method was established synchronously. Differential pulse voltammetry (DPV) measurement revealed that the oxidation peak current increased linearly with eriocitrin concentrations in range of 1.0 × 10− 8 mol L− 1–1.0 × 10− 6 mol L− 1 with detection limit of 7.0 × 10− 10 mol L− 1 (S/N = 3). Moreover, the proposed method was used in determination of eriocitrin in lemon sample with accurate results.

•Facile and fast synthesis of SnO2-PDDA-GR composite.•SnO2-PDDA-GR has high sensitivity for the determination of daidzein.•This method can be used in real samples analysis with satisfactory results.A one-step and facile method using SnCl2·H2O as reducing agent to reduce graphene oxide (GO) was performed in the aid of poly(diallyldimethylammonium chloride) solution (PDDA). SnCl2·H2O is not only a reducing agent for graphene oxide (GO), but also a precursor of SnO2. SnO2-PDDA-GR composite was characterized by various surface, structural and electrochemical analysis techniques, such as transmission electron microscopy (TEM), UV spectrum (UV–vis), Infrared Spectrum (IR), X-ray diffraction (XRD), Cyclic voltammograms (CV) and electrochemical impedance (EIS). The SnO2-PDDA-GR composite was used to constructed electrochemical sensor (SnO2-PDDA-GR/GCE) for the determination of daidzein. Under the optimized experimental condition, it was found that the response of peak current is linear to the concentration of daidzein in the ranges of 2.0×10−8 −1.0×10−6 mol L−1, and the detection limit was estimated to be 6.7×10−9 mol L−1 (S/N=3). Furthermore, this sensor was successfully applied for the determination of daidzein in traditional Chinese medicine (pueraria lobata) and Daidzein tablets.Download high-res image (246KB)Download full-size image

•PSS-GR-Pd nanocomposite has been fabricated by a simple strategy.•A new voltammetric sensor was fabricated by PSS-GR-Pd composite.•The electrochemical sensor had a wider linear range and a well sensitivity.In this work, poly(sodium p-styrenesulfonate) (PSS)-functionalized graphene supported palladium nanoparticles (Pd) composites were fabricated with simple ultrasonic bath method. The morphology and structure of PSS-GR-Pd composites were characterized using UV–vis absorption spectra, X-ray diffraction and Transmission Electron Microscopy. By combining the merits of the PSS-GR and Pd NPs, a new electrochemical sensor was erected to detect amaranth based on the PSS-GR-Pd nanocomposites. The electrochemical behavior of amaranth was investigated systematically in 0.1 mol L−1 phosphate buffer solution (PBS 2.0). At the optimum parameter, Ipa was found to be linearly dependent on the concentrations of amaranth (1×10−7–9×10−6 mol L−1). The detection limit was 7 nM (S/N=3) and sensitivity was 5.85 μA μM−1. Finally, this system was utilized for determining amaranth in soft drink using the standard addition method.Download high-res image (218KB)Download full-size image

•Simultaneous determination of baicalein and baicalin by Ta2O5-Nb2O5@CTS-CPE.•The linear response range of 0.08–8.0 μM for both of them.•The limit of detections are 0.05 and 0.03 μM (S/N=3), respectively.•The content of analytes in herb Huang-Qin was detected with satisfactory results.•The electrode was applied to investigate the hydrolysis process of baicalin in vivo.Baicalein and baicalin are the major flavonoids found in Scutellariae Radix, an essential herb which has had a presence in traditional Chinese medicine (TCMs) for more than two thousands of years. Owing to their similar characteristics and physiochemical properties, sensitive, it is a great challenge to detect both of them simultaneously. In this work, a novel, facile and sensitive electrochemical method was proposed based on tantalum oxide (Ta2O5), niobium oxide (Nb2O5) particles and antiseptic chitosan modified carbon paste electrode (Ta2O5-Nb2O5@CTS-CPE). Scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS) were used to characterize the properties and investigate the electrochemical response of the sensor. The electrochemical behaviors and redox mechanisms of two analytes were investigated at the target electrode. Under the optimum conditions, the highly sensitive and simultaneous determination of baicalein and baicalin was successfully achieved with a linear response range of 0.08–8.0 μM for both of them. The obtained detection limits for baicalein and baicalin were of 0.05 and 0.03 μM (S/N=3), respectively. Furthermore, the proposed sensor displayed high sensitivity, excellent stability and satisfactory results in Scutellariae Radix samples analysis and hydrolysis process analysis of baicalin in vivo.Download high-res image (304KB)Download full-size image

•Hemin/G4-peptide with enhanced DNAzyme activity was synthesized for the first time.•The DNAzyme served as electrocatalyst for developing electrochemical aptasensor.•PtNTs@rGO as nanocarrier for high loading of hemin/G4-peptide amplified signal.•Modification of hemin/G4 with peptide greatly promoted the detection sensitivity.In this work, we first conjugated a short peptide to thrombin binding aptamer (TBA) and bond hemin to the hybrid, effectively rendering hemin/G4-peptide more active over the original hemin/G4, so that a highly sensitive electrochemical thrombin (TB) aptasensor was developed based on it and PtNTs@rGO nanocomposite. It was the first report on the application of hemin/G4-peptide in electrochemical aptasensor. PtNTs@rGO with large surface area served as excellent nanocarrier for high loading of hemin/G4-peptide hybrids, resulting in the formation of hemin/G4-peptide–PtNTs@rGO bioconjugate as the secondary aptamer and further signal enhancement. The specific affinity of aptamer for target TB made the secondary aptamer go into the sensing interface, and then a noticeable current signal was obtained from hemin without additional redox mediators. Due to the collaborative electrocatalysis of hemin/G4-peptide and PtNTs toward H2O2, which was formed in situ during the process of hemin/G4-peptide-catalyzed oxidation of NADH with dissolved O2, the current intensity increased dramatically. Such an electrochemical aptasensing system could be used to detect TB with a linear range of 0.05 pM–60 nM and very lower detection limit of 15 fM. Notably, this method exhibited a higher sensitivity than that of many hemin/G4-based electrochemical strategies for TB detection due to the improvement of the catalytic activity of hemin/G4-peptide. The present works opened a new way for expanding the application of hemin/G4 in biological detection. With the mediator-free, proteinous enzyme-free yet high-sensitivity advantages, this electrochemical aptasensor held great promise for other biomarker detections in clinical diagnostics.

In this work, we propose a strategy for the fluorescence assay of histidine (His) and cysteine (Cys) by using lanthanide coordination polymer nanoparticles (Ln-CPN) as a fluorescent probe. The Ln-CPN were prepared by self-assembly of adenosine monophosphate (AMP) with Tb3+, i.e. AMP-Tb. The nonluminescent AMP-Tb could be efficiently sensitized by 5-sulfosalicylic acid (SSA). The fluorescence of AMP-Tb-SSA can be remarkably quenched by Cu2+, and that of the resulting Cu/SSA/AMP-Tb can be significantly enhanced by His and Cys. Thus, a specific fluorescence “turn-on” assay for His and Cys was developed by using Cu/SSA/AMP-Tb as a sensing platform. The enhanced fluorescence intensity was proportional to the His and Cys concentration in the range from 0.2 to 150 μM and 0.5 to 200 μM, respectively, with the detection limits of 70 nM and 100 nM. Additionally, taking advantage of a masking agent for His, the differentiation of His from Cys was achieved in our system. Furthermore, the protocol can also work well for analyzing His and Cys in practical plasma samples with recovery in the range of 100.3–104.1%.

•A novel and environmental friendly voltammetric sensor was fabricated.•Sensitive, simultaneous determination of chrysin and baicalein by Ta2O5-CTS-CPE.•The limit of detections are 0.03 and 0.05 μM (S/N=3), respectively.•The content of analytes in herb Mu Hu-die was detected with satisfactory results.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 (Ta2O5) particles and chitosan modified carbon paste electrode (Ta2O5-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 Ta2O5-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.

•Co-amino-Gr nanocomposites were synthesized for the first time by a simple and green one-pot hydrothermal method.•Glycine was employed as an environmentally benign reducing agent.•The proposed sensor exhibited high specific voltammetric response to baicalin.•A lower detection limit of 5 nM was achieved.The present paper reported an one-pot synthesis of Co nanoparticles doped amino-graphene nanocomposites (Co-amino-Gr), involving in situ generation of Co nanoparticles (NPs). The simultaneous reduction of graphene oxide (GO) and Co2+ to produce Co-amino-Gr had been achieved under mild reaction conditions using an environmentally benign reducing agent, glycine. By combining the merits of amino-Gr and the Co NPs, a highly sensitive electrochemical sensor was erected to detect baicalin based on the Co-amino-Gr nanocomposites. Under optimum conditions, the response peak currents were linear related with baicalin concentrations in the range of 1.0×10−8–8.0×10−7 mol L−1 with a lower detection limit of 5.0×10−9 mol L−1 (S/N=3). Additionally, the proposed method was used to detect baicalin in the medicinal capsules with satisfactory results.

•The nanocomposite PDDA-Gr-Pd was synthesized by a facile and cost-effective chemical method.•The electrochemical sensor had a wider linear range and a lower detection limit towards taxifolin.•This sensor also expressed high reproducibility (RSD of 2.1% from ten parallel modified electrodes) and excellent accuracy (RSD of 1.7% for ten parallel detections) for taxifolin assay.Palladium nanoparticles with diameter of around 5–10 nm supported on poly (diallyldimethylammonium chloride) (PDDA)-functionalized graphene composites were prepared by a simple chemical method. As-prepared nanocomposites were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), ultraviolet-visible spectrophotometry (UV–vis) and electrochemical techniques, which were clearly demonstrated that palladium nanoparticles were uniformly dispersed on the graphene sheets. Based on the PDDA-Gr-Pd nanocomposites, a new voltammetric sensor was established and exhibited excellent electrocatalytic activity and fast electron transfer rate toward taxifolin. Under the optimal conditions, a lower detection limit of 1×10−9 mol L−1 (S/N=3) and a wide linear detection range from 4×10−8 to 1×10−6 mol L−1 were achieved by square wave voltammetry (SWV). The proposed method was successfully applied for determination of taxifolin in fructus polygoni orientalis with well results.Cyclic voltammograms of taxifolin (3.0×10−6 mol L−1) at bare GCE (a), PDDA-Gr/GCE (b), Gr-Pd/GCE (c) and PDDA-Gr-Pd/GCE (d).

•A highly loaded HRP sphere was synthesized for the first time and was used as bifunctional label.•Pd@HRP served as signal indicator and electrocatalyst for the fabrication of biosensor.•DNAzyme-aided target recycling amplification and rolling circle amplification further amplify the signal.•The biosensor displayed an improved sensitivity for microRNA detection.In this work, an ultrasensitive electrochemical microRNA detection strategy was developed based on porous palladium-modified horseradish peroxidase sphere (Pd@HRP) and target-induced assembly of DNAzyme. A highly loaded HRP sphere was prepared by covalent layer-by-layer assembly with CaCO3 as sacrificial template for the first time, and was further modified with porous Pd. Notably, Pd@HRP composite showed a good redox activity of HRP and electrocatalytic activity toward H2O2. The utilization of Pd@HRP as electrochemical signal indicator and enhancer to fabricate biosensor could avoid the need for additional redox mediator and amplify the detection sensitivity. Moreover, target recycling amplification was achieved by Pb2+-induced cleavage of ternary “Y” structure, circumventing the use of labile nuclease. Subsequent DNA concatamer synthesized through rolling circle amplification (RCA) reaction with cleaved hairpin probe as primer, hybridized with plentiful Pd@HRP-DNA probes, which led to the increased loading of redox-active and electrocatalytic Pd@HRP for sensitivity improvement. So the proposed electrochemical biosensor detected miRNA-24 down to 0.2 fM (S/N = 3) with a wide linear range from 3 fM to 1 nM. With bifunctional Pd@HRP tag, DNAzyme-aided target recycle and programmable junction probe, this strategy possessed the advantages of high efficiency, high sensitivity, low cost and versatility, and thus held great promise for other low-abundance nucleic acids determination.

•The first report for the electrochemical determination of arctigenin.•The Iodide/SWCNTs/GCE was prepared for the first time.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.

•Determination of metribuzin was established with low detection limit.•The proposed method was also available to detect metribuzin in soil.•The reaction mechanism of metribuzin is for first time discussed in detail.•The electro-polymerization of L-Norvaline was investigated for the first time.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.Cyclic voltammograms of (a) GCE in supporting electrolyte: 0.1 mol L− 1 B–R (pH 1.82)-blank voltammogram; scan rate: 100 mV s− 1; (b) GCE in metribuzin (10.71 μg/mL) solution; and (c) poly(l-Norvaline)/GCE in metribuzin (10.71 μg/mL) solution.

A voltammetric sensor for polydatin sensing was simply fabricated by in-situ electrochemically reducing graphene oxide at a glassy carbon electrode. The redox behavior of polydatin was investigated systematically. For the first time, the kinetics parameters of electrode reaction of polydatin were calculated using various electrochemical techniques. Significant electrochemical signal increases were achieved by the excellent conductivity and large surface area of reduced graphene oxide. Thereafter, a highly-sensitive electroanalytical method for polydatin was established with a good linear relationship from 4.0 × 10− 8 mol L− 1 to 3.5 × 10− 6 mol L− 1 and a detection limit of 4.0 × 10− 8 mol L− 1. In addition, the practical application of present method was demonstrated by determining the concentration of polydatin in real sample with satisfactory result.

•Facile preparation of PDDA-Gr composite•PDDA-Gr was used to build a supersensitive sensor for determination of hyperin.•The electrochemical reaction mechanism of hyperin was discussed in detail.A simple electrochemical method for the highly sensitive determination of hyperin was established based on poly(diallyldimethylammonium chloride)-functionalized graphene modified electrode (PDDA-Gr/GCE). The nanocomposite was characterized by X-ray diffraction (XRD), ultraviolet/visible spectra (UV–vis), Fourier Transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The electrochemical characteristics of hyperin were studied in detail via cyclic voltammetry (CV), chronocoulometry (CC). Dynamics parameters of electrode process were also calculated to discuss the reaction mechanism. Under the optimized conditions, a lower detection limit of 5 × 10− 9 mol L− 1 (S/N = 3) and a wide linear detection range from 7 × 10− 9 to 7 × 10− 7 mol L− 1 were achieved by the differential pulse voltammetry (DPV). Additionally, this simple, sensitive sensor was proved to be suitable for the determination of hyperin in Chinese herb Hypericum Perforatum with satisfactory results.

A novel sensor for ligustrazine was fabricated by directly incorporating ZrOCl2 and β-cyclodextrin into graphite powder followed with an electrochemical treatment process. Scanning electron microscopy and cyclic voltammetry were employed to investigate the properties of the electrode. This sensor exhibited remarkable enhancement response towards ligustrazine compared with other related electrodes, which is due to the synergy between ZrO2 and β-cyclodextrin. Under the optimized conditions, the linear range of determination for ligustrazine was 2 × 10−7 to 1 × 10−5 mol L−1. As a practical application, the proposed sensor was applied to quantitatively determine ligustrazine in Chuanxiong rhizome and urine samples with satisfactory results.

In this study, the electrochemical properties of astilbin were investigated for the first time and an electroanalytical method was established synchronously, which was based on a β-cyclodextrin–graphene nanocomposite modified electrode (β-CD–GNs/GCE). The electrode process of astilbin was investigated in detail, and some dynamic parameters were calculated. The detecting sensitivity of astilbin was greatly enhanced at this voltammetric sensor. Under optimum conditions, a lower detection limit (1 × 10−8 mol L−1) and wider linear range (3.0 × 10−8 mol L−1 to 2.0 × 10−6 mol L−1) were achieved by the proposed sensor. Finally, the proposed method was applied to the analysis of a real sample, and the results showed that the method was applicable and reliable.

•A sensitive and simple electrochemical method to detect trace iodide was stablished.•The effect of different surfactants in the preconcentration process was investigated.•The formation of ion-associating compound remarkably increased the signal of iodide.•This method is suitable to determine trace iodine in real samples.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 (CPBI2Br). After accumulation for a period of time, a linear sweep potential with negative scanning was applied and the I2 in CPBI2Br 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.

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.

•Facile preparation of PLga-EPGO/GCE.•The electrochemical reaction mechanism of tetrahydropalmatine was discussed in detail.•The electrochemical sensor had a wider linear range and a lower detection limit towards tetrahydropalmatine.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.Cyclic voltammograms of THP (3.0×10−6 mol L−1) at different electrodes. (a): bare GCE, (b): EPGO/GCE, (c): PLga/GCE, (d): PLga-EPGO/GCE. Supporting electrolyte: 0.1 mol L−1 H2SO4 (pH 1.65).

•This is the first report about the electrochemical properties and electroanalytical method for picroside II.•The L-Citrulline was used as the modified materials of electrode for the first time.•The resulting sensor showed a significant voltammetric response to picroside II and used in real sample with satisfactory results.•This work promoted the potential applications of amino acid materials and SWCNTs in electro-chemical sensors.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.A novel sensor for high-sensitive determination of picroside II was constructed by simple dripping single-walled carbon nanotubes (SWCNTs) onto the glass carbon electrode (GCE) firstly and electro-polymerizing L-Citrulline film subsequently. Compared with bare GCE, SWCNTs/GCE and poly(L-Citrulline)/GCE, there were dramatic increase of the peak currents. Then the electrochemical behavior of picroside II was carefully and systematically investigated and some kinetics parameters were calculated. The reaction mechanism of picroside II at poly(L-Citrulline)/SWCNTs/GCE was also discussed. A simple and high-sensitive electroanalytical method for picroside II was established using LSV and applied in the drug sample analysis.

•A novel voltammetric method for determination of hesperetin was proposed.•The resulting sensor showed a significant voltammetric response to hesperetin.•Some dynamic parameters were calculated and a reasonable reaction mechanism of hesperetin at this sensor was proposed.•This work may be a reference for the pharmacological action of hesperetin in clinical study.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.Figure: A highly sensitive voltammetric sensor, based on reduced graphene oxide on SWCNTs modified glassy carbon electrode (ERGO/SWCNTs/GCE), was constructed and used for sensitive detection of hesperetin. Compared with bare GCE, there is a dramatic increase of the redox peak currents. Then the electrochemical behavior of hesperetin was carefully and systematically investigated and some kinetics parameters were calculated for the first time. The novel electroanalytical method of hesperetin was also established and applied in biological and Chinese herbal medicine samples analysis with satisfactory results.

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.

•Electrochemical properties of daphnetin were investigated for the first time.•The resulting sensor showed a significant voltammetric response to daphnetin.•Some dynamic parameters were calculated for the first time.•A feasible mechanism of daphnetin at modified electrode was proposed.•The proposed method detect daphnetin in nature samples with satisfactory results.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.

In this paper, a modern popular simple voltammetric sensor, graphene modified electrode (GR/GCE), was employed for studying the electrochemical characters of hymecromone. The electrode reaction of hymecromone was investigated systematically for the first time and some kinetic parameters were calculated. The reaction mechanism of hymecromone at the GR/GCE was also discussed. Based on the enhancement sensing of the GR/GCE for hymecromone, a sensitive electroanalytical method was developed with a detection linear range of 8 × 10−8 to 6 × 10−6 mol L−1 and a detection limit of 4 × 10−8 mol L−1, which were obtained under accumulation for only 180 s. For proving the practical applicability of the proposed method, the determination of hymecromone in real samples was carried out with satisfactory results.

A novel voltammetric sensor, based on a single-walled carbon nanotube (SWNT) composite poly(L-serine) film modified electrode, was fabricated by simple dipping–drying and electrodeposition methods and used for highly sensitive determination of natamycin. At this sensor, the electrochemical response of natamycin was improved greatly due to the synergistic effect of SWNTs and poly(L-serine). A new voltammetric method for the determination of natamycin was proposed with a detection linear range of 6 × 10−8 mol L−1 to 6 × 10−6 mol L−1 and a detection limit of 4 × 10−8 mol L−1. Furthermore, the electrode reaction of natamycin was investigated in detail and some dynamic parameters were calculated for the first time. Using the present method, the residual quantity of natamycin in available claret and beverage samples was evaluated with good satisfactory recovery.

A simple and sensitive electrochemical method for the determination of the insecticide pymetrozine was proposed using a simple electrochemically pretreated glassy carbon electrode (EPGCE). Compared with the bare GCE, the electrochemical response signal of pymetrozine at the EPGCE showed a significant increase. The electrochemical behavior of pymetrozine was investigated systematically and some dynamics were investigated in detail for the first time. The results indicate that the reaction of pymetrozine on the EPGCE is a two electron and two proton process, which is controlled by both diffusion and adsorption. Under optimum conditions, a good linear relationship was obtained between peak currents and pymetrozine concentrations in the range of 1 × 10−7 to 5 × 10−6 mol L−1 with a detection limit of 8 × 10−8 mol L−1 (S/N = 3). The proposed method was applied to the determination of pymetrozine in real samples with satisfactory recovery results. Finally, the degradation of pymetrozine was also studied in natural soil.

A stable voltammetric sensor (SWCNTs/GCE), single-walled carbon nanotubes (SWCNTs) cast on a glassy carbon electrode (GCE), was employed in the initial electrochemical determination of naringenin. The complex electrochemical behavior of naringenin on this sensor was investigated in detail, and the dynamic and thermodynamic parameters were calculated. The new electroanalytical method for naringenin was proposed with a low detection limit of 2.0 × 10−8 mol L−1 (S/N = 3) and wide linear ranges from 8 × 10−8 to 5 × 10−6 mol L−1 and 5 × 10−6 to 1.2 × 10−5 mol L−1, respectively. More importantly, this sensor exhibited good reproducibility and long-term stability. Then this sensor was successfully applied for the determination of naringenin in Fructus Aurantii Immaturus with satisfactory results.

•A simple, rapid and green method to build sensitive voltammetric sensor was presented.•The proposed sensor has a high electrochemical sensitivity for determination of sophoridine.•The proposed sensor exhibited an excellent selectivity.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−11, 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.A simple, rapid and green method, based on graphene nanosheets directly deposited onto a glassy carbon electrode by pulsed potentiostatic reduction of a graphene oxide colloidal solution, to build sensitive voltammetric sensor for the determination of sophoridine was presented.

A sensitive voltammetric sensor, a graphene-modified glassy carbon electrode (GR/GCE), for the detection of trace amounts of curcumin is proposed. The GR/GCE was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of curcumin at the GR/GCE was investigated by CV and liner sweep voltammetry (LSV). The reaction mechanisms of curcumin on the GR/GCE were also investigated and discussed systematically. In addition, the currents measured by LSV presented a good linear relationship with curcumin concentrations in the range of 5.0 × 10−8 to 3.0 × 10−6 mol L−1, with a low detection limit of 3.0 × 10−8 mol L−1. The method was also applied successfully to detect curcumin in a Curcuma longa L. sample with high selectivity and accuracy, as well as good recovery.

A new voltammetric sensor, based on single-walled carbon nanotubes (SWNTs) modified glassy carbon electrode, was established and used for the determination of neohesperidin dihydrochalcone (NHDC). The electrochemical characterization of NHDC on this sensor was studied systematically by cyclic voltammetry, and the kinetics parameters were calculated for the first time. Compared with a bare GCE, the proposed sensor exhibited excellent redox activity towards NHDC, and a new voltammetric analytical method for NHDC was proposed with a wide linear range from 5 × 10−8 mol L−1 to 8 × 10−6 mol L−1 and a low detection limit of 2 × 10−8 mol L−1. In addition, a reasonable mechanism was also proposed and discussed. Finally, the developed method was successfully applied for the quantitative determination of NHDC in beverages with high accuracy and satisfactory recovery results.

A very simple and sensitive voltammetric method for the determination of urapidil was proposed by electrochemical pretreatment using a glassy carbon electrode as the voltammetric sensor (EPGCE). The EPGCE was obtained by cycling the electrode between a potential of −1.5 and 2.5 V, for five cycles in 0.1 M pH 7.0 PBS. Compared with the bare GCE, the EPGCE had an excellent response towards the oxidation of urapidil. Under the optimal conditions, the selective detection of urapidil in a linear concentration range of 2.0 × 10−8 to 5.0 × 10−6 mol L−1 was obtained with a determination limit of 2.0 × 10−8 mol L−1. At the same time, the EPGCE was also applied to the detection of urapidil content in urapidil sustained-release tablets and urine samples with satisfactory results.

A novel voltammetric sensor for salbutamol is fabricated via self-assembly of gold nanoparticles on multi-walled carbon nanotubes and Nafion modified electrode. This sensor could improve the oxidation of salbutamol intensively. The oxidation process of salbutamol is studied and some dynamic parameters are calculated using various electrochemical techniques. Under the optimum conditions, the response peak currents have a linear relationship with the salbutamol concentrations in the range of 9.0 × 10−8 to 7.0 × 10−6 mol L−1 with a detectable limit of 5.0 × 10−8 mol L−1. The proposed method is successfully applied to the determination of salbutamol in commercial pharmaceuticals and human serum samples with good accuracy and satisfactory recovery.

•DNA/PAn film was modified on the GCE using Langmuir–Blodgett technique.•The sensor was applied to voltammetric detection of xanthine.•Electrochemical properties of xanthine at the sensor were investigated.•The sensor has good sensitivity and selectivity towards xanthine.•The sensor can determine xanthine in human serum samples.DNA–polyaniline (PAn) complex Langmuir–Blodgett film modified glassy carbon electrode (GCE) was used as a new voltammetric sensor (DNA/PAn-LB/GCE) for xanthine (XA) detection. The characteristic of DNA/PAn-LB film was studied by electrochemical impedance spectroscopy and scanning electron microscope. Electrochemical behaviors of XA at the sensor were studied in pH 7.0 phosphate buffer solutions by cyclic voltammetry and differential pulse anodic voltammetry. The results showed that this new modified electrode exhibited an excellent immunity from uric acid and hypoxanthine interference and a new sensitive and selective electroanalytical method for XA was proposed with wider linear range. Under the optimum conditions, the calibration curve for XA was obtained over the range of 7.0×10−8–1.0×10−5 mol L−1, with the detection limit of 3.0×10−8 mol L−1. The practicability of this method was demonstrated by determining the concentration of XA in human serum samples.A new voltammetric sensor DNA/PAn-LB/GCE was designed and successfully used in the determination of xanthine (XA) being free of interference from excess uric acid (UA) and hypoxanthine (HXA).

•Electrochemical properties of jatrorrhizine were investigated for the first time.•The resulting sensor showed a significant voltammetric response to jatrorrhizine.•This electroanalytical method is used in clinical study and in the fields of pharmaceutical analysis.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 mol L−1 and a low detection limit of 5.0×10−8 mol L−1. The proposed method was successfully applied in determination of jatrorrhizine in pharmaceutical sample, Tinospora capillipes Gagnep (a traditional Chinese medicine), with satisfactory results.A simple sensor for high-sensitive determination of jatrorrhizine based on electrochemical pretreatment glassy carbon electrode, which was prepared by cyclic voltammetry (EPGCE). Compared with bare GCE, there is a dramatic increase of the oxidation peak currents. Then the electrochemical behavior of jatrorrhizine was carefully and systematically investigated and some kinetic parameters were calculated for the first time. The first electroanalytical method of jatrorrhizine was also established and applied in pharmaceutical sample analysis.

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 mol L−1, and a value of 3.0 × 10−8 mol L−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.Graphical abstractHighlights► A calixarene-based voltammetric sensor for 5-HT was presented. ► Host–guest interaction and an electron enhancer are integrated in this sensor. ► The proposed sensor has a high electrochemical sensitivity for determination of 5-HT. ► The proposed sensor exhibited an excellent selectivity. ► This sensor can used for the determination of 5-HT in human blood serum.

The electro-polymerization of l-Theanine was investigated for the first time on glassy carbon electrode and the polymeric conditions and mechanism were discussed in detail. Hereafter, a simple and sensitive electrochemical sensor based on the poly(l-Theanine) film was established for sophoridine sensing. The electrode process of sophoridine was then studied by cyclic voltammetry and its determination was achieved by amperometry. The results revealed that the poly(l-Theanine) membrane effectively decreased the oxidation potential of sophoridine and greatly increased its response current. And this sensor, fabricated easily and simply as well as very easy surface update, showed good response for sophoridine with a wide linear range from 1.0 × 10−6 to 1.4 × 10−4 mol L−1 and a low detection limit of 5 × 10−7 mol L−1. The application of proposed method in analysis of real sample was also evaluated with good performance. This work promoted the potential applications of amino acid materials in electrochemical sensors.

A carbon paste electrode doped with multiwall carbon nanotubes was constructed for the determination of colchicine. Cyclic voltammetry, differential pulse voltammetry and chronocoulometry have been used to investigate the electrochemical response characteristics and the kinetics parameters of colchicine on the proposed voltammetric sensor. Results show that the doped multiwall carbon nanotubes can greatly promote the electrochemical response of colchicine. Under optimum conditions, the oxidation current of colchicine was proportional to the concentration of colchicine in a wide linear range from 1.0 × 10−8 mol L−1 to 2.5 × 10−5 mol L−1 with a low detection limit of 8.0 × 10−9 mol L−1 in 0.15 mol L−1 H2SO4 (pH 0.8). The newly recommended sensor shows several merits including extreme simplicity, wide linear range, low detection limit, good stability and excellent reproducibility. Furthermore, it was successfully employed for the determination of colchicine in pharmaceutical formulations with satisfactory results.

A simple and reliable electrochemical sensor based on poly(DL-aspartic acid)-modified glassy carbon electrode was proposed for direct determination of brucine. The electrochemical character of brucine on this sensor was carefully and systematically studied by cyclic voltammetry. Some kinetic parameters were calculated and a reasonable reaction mechanism for brucine at the poly(DL-aspartic acid)/GCE was also proposed. Meanwhile, a new electroanalytical method for determination of brucine was proposed with a highly sensitive detection limit of 3 × 10−8 mol L−1 (S/N = 3) and a wide linear range of 5.0 × 10−8 to 9.0 × 10−5 mol L−1. More importantly, this sensor exhibited good stability and excellent reproducibility in the response for brucine.

A sensitive and novel electrochemical sensor for detection of bergenin by linear sweep voltammetry (LSV) is presented. This sensor was fabricated by dripping well-dispersed graphene onto glassy carbon electrode (GCE) surface firstly, and then poly(L-lysine) films were subsequently electropolymerized on it to prepare poly(L-lysine)/graphene/GCE. The dynamic detection range of this sensor to bergenin was 4.0 × 10−8 to 5.0 × 10−6 mol L−1 and 6.0 × 10−6 to 1.7 × 10−5 mol L−1, with the detection limit of 1.0 × 10−8 mol L−1. A new voltammetric method for determination of bergenin was erected and shows high sensitivity and selectivity, wider linear relationship, very easy surface update and good stability. The proposed sensors were tested for bergenin detection in pharmaceutical tablets with high accuracy and satisfactory recovery results was obtained. In addition, the oxidation mechanism is proposed and discussed, which could be a reference for the pharmacological action of bergenin in clinical studies.

A voltammetric sensor for Sunset Yellow was fabricated by polymerizing L-cysteine on the surface of a glassy carbon electrode. The modified electrode was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical behavior and kinetic parameters of Sunset Yellow in phosphate buffer solution (pH 6.6) were investigated by cyclic voltammetry and chronocoulometry using the proposed sensor, and results showed that the electrochemical response of Sunset Yellow was significantly improved. The peak current (differential pulse voltammetry) of Sunset Yellow linearly increased with the concentrations in the range of 8.0 × 10−9–7.0 × 10−7 mol L−1, and the minimum detectable concentration of Sunset Yellow was estimated to be 4.0 × 10−9 mol L−1. Moreover, the linear relationship between the peak current and the concentration of Sunset Yellow in the presence of Lemon Yellow was 1.0 × 10−8–5.0 × 10−7 mol L−1, with a minimum detectable concentration of 6.0 × 10−9 mol L−1. The reported electrochemical sensor was excellent for the determination of Sunset Yellow because of merits such as extreme simplicity, low cost, high sensitivity, good stability and reproducibility.

A sensitive, fast and cheap sensor, based on a glassy carbon electrode (GCE) modified with a multiwalled carbon nanotubes (MWCNTs)/Nafion film, is reported for the quantitative determination of synephrine in the Chinese traditional herbal drug Pericarpium citri reticulatae using . The electrochemical behavior of synephrine at this sensor was explored in Britton–Robinson buffer solution using cyclic voltammetry. An oxidation peak at 1027 mV was observed for synephrine when a bare GCE was used, whereas an oxidation peak at 998 mV with greatly enhanced peak current was obtained at the MWCNTs/Nafion/GCE, showing the electrocatalytic nature of the modified electrode. Moreover, cyclic voltammetric studies indicated that the oxidation of synephrine at the modified electrode was irreversible, adsorption controlled and involved two electrons. A calibration plot of oxidation peak current versus synephrine concentration was linear in the range of 1 × 10−8 to 1 × 10−5 mol L−1. The detection limit of synephrine was found to be 8 × 10−9 mol L−1 by linear sweep voltammetry . The effect of pH and scan rate of synephrine were studied. This is currently the first report on the determination of trace synephrine by a purely electroanalytical method. The analytical performance of this sensor was also evaluated for the detection of synephrine in real samples.

•GNPs/PAn-LB GCE was constructed as voltammetric sensor for the first time.•GNPs would maintain its original state and thereby full play its electric activity.•Electrochemical behavior of EP and UA at this sensor was investigated.•Simultaneous determination of EP and UA in the sensor has better sensitivity comparing with other voltammetric sensors.•Detection of EP and UA using this sensor in human blood serum has satisfactory results.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.

A new electrochemical sensor for codeine was fabricated based on composite graphene and Nafion film modified glassy carbon electrode. It was found that the electrochemical response of this sensor was greatly improved and displayed excellent analytical performance for codeine detection, which could be attributed to the high codeine loading capacity on the electrode surface and the outstanding electric conductivity of graphene. Under the optimized conditions at pH 4.0, the peak currents were linear relationship with codeine concentrations in the range of 5 × 10−8 to 9 × 10−6 mol L−1 and 9 × 10−6 to 3 × 10−5 mol L−1, using square wave voltammetry with a detection limit of 1.5 × 10−8 mol L−1. The proposed method was successfully applied to the determination of codeine in both urine samples and cough syrup.

A novel voltammetric sensor, based on DNA immobilized on the surface of an ethylenediamine/polyglutamic (En/PGA) modified glassy carbon electrode (GCE), was constructed and used for determination of dihydromyricetin (DMY). The electrochemical behaviour of DMY at this sensor was investigated in pH 3.6 NaAc-HAc buffer solutions by cyclic voltammetry (CV) and differential pulse anodic voltammetry (DPV). The oxidation of DMY is an adsorption-controlled irreversible process. The oxidation mechanism was proposed and discussed. It was found that the modified electrode exhibited a linear voltammetric response for DMY in the range of 4.0 × 10−8 mol L−1 to 2 × 10−6 mol L−1, with a detection limit of 2 × 10−8 mol L−1. The method was also applied successfully to detect DMY in an ampelopsis sample with satisfactory results.

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 mol L−1, with the detection limit of 1.0 × 10−8 mol L−1. The method was applied to detect methotrexate in medicinal tablets and spiked human blood serum samples.Highlights► A sensitive methotrexate sensor based on GNPs modified GCE is developed. ► Electrochemical properties of methotrexate were investigated. ► The voltammetric sensor significantly improves the oxidation signal of methotrexate. ► Moreover, the proposed sensor has a long-term stability.

A novel voltammetric sensor based on graphene–Nafion and poly(L-arginine) was constructed by electrodeposited and simple dipping–drying methods and used for high-sensitive determination of Terbutaline sulfate (TBS). The resulting poly(L-arginine)/graphene–Nafion modified electrode showed a significant voltammetric response to TBS due to the synergistic effect of poly(L-arginine) and graphene–Nafion, in which poly(L-arginine) had electrocatalytic ability for TBS and graphene provided a large specific surface area, excellent electric conductivity and electrocatalytic activity. The sensor gave a good linear range over 4.0 × 10−8–5.0 × 10−6 mol L−1 with a detection limit of 1.2 × 10−8 mol L−1 towards the determination of TBS. The high sensitivity and selectivity together with the good linear relationship, very easy surface regeneration and good stability at such a modified electrode led us to construct a practical TBS biosensor successfully. This work promoted the potential applications of graphene-based materials in electrochemical sensors.Graphical abstractA novel voltammetric sensor, based on graphene–Nafion and poly(L-arginine), was constructed by electrodeposited and simple dipping–drying methods for Terbutaline sulfate (TBS).Highlights► A novel sensor based on graphene–Nafion and poly(L-arginine) was constructed. ► Electrochemical properties of Terbutaline sulfate were investigated. ► The sensor showed a significant voltammetric response to Terbutaline sulfate. ► This work promoted the applications of graphene in electrochemical sensors.

A novel self-assembly modified carbon paste electrode based on ethylenediamine and graphene oxide was proposed as a highly sensitive electrochemical sensor for detection of malachite green. The manufacturing operation of the recommended sensor was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical response of malachite green at this sensor was investigated in detail and a new electroanalytical method was erected with high sensitivity and selectivity. The proposed method exhibited good linearity for malachite green over the range from 8.0 × 10−9 mol L−1 to 8.0 × 10−7 mol L−1 with the detection limit of 5 × 10−9 mol L−1 (S/N = 3) by differential pulse voltammetry under optimum conditions. Finally, the practical application was proven by spiking malachite green standards in lake water with recoveries ranging from 98.80% to 101.10%, showing a satisfactory result.

A new voltammetric sensor for the detection of maltol was developed, based on the carbon paste electrode (CPE) which allows for lower background current and more reproducible responses. The resulting sensor exhibits excellent redox activity towards maltol. For contrast, the electrochemical properties of maltol were compared on three paste electrodes, based on graphite powder (GP), carbon nanotubes (CNT) and graphene (Gr). The best response of maltol was obtained at the CPE. Further experiments demonstrated that the oxidative peaks increased linearly with maltol concentration in the range of 1.0 × 10−7 to 4.0 × 10−5 mol L−1 with a detection limit of 4.0 × 10−8 mol L−1. The method was successfully applied to detect maltol in beers with satisfactory results. Furthermore, the dynamic parameters and mechanism of electrode reaction were investigated using various electrochemical techniques.

A new voltammetric sensor was designed by covering a layer of gold nanoparticles (AuNPs) on a carbon paste electrode that was pre-mixed in some multi-walled carbon nanotubes (MWCNT). This sensor exhibited super sensitive detection of the electroactive flavonoid rutin due to the large surface area and good conductivity of MWCNT and AuNPs. Cyclic voltammetry curves at various scan rates and pH were recorded to investigate the redox properties of rutin. Further experiments demonstrated that the oxidative peaks increased linearly with rutin concentrations in the ranges of 4.0 × 10−10 to 1.0 × 10−8 mol L−1 and 2.0 × 10−8 to 1.0 × 10−6 mol L−1 with a limit of detection of 4.0 × 10−11 mol L−1. The method was successfully applied to detect rutin in medicine tablets with satisfactory results.

In the present work, a new voltammetric sensor, Langmuir–Blodgett (LB) film of tetraoxocalix[2]arene[2]triazine (TOCT) modified glassy carbon electrode (LBTOCT-GCE), for trace analysis of copper ion in water samples, was prepared. The morphology of LBTOCT-GCE was characterized by cyclic voltammetric method, electrochemical impedance spectroscopy, and atomic force microscope. The recognizing mechanism of LBTOCT-GCE for copper ion in aqueous solution was discussed. Under the optimum experimental conditions, using square wave stripping voltammetry and accumulation time of 300 s, the peak currents were linear relationship with Cu2+ concentrations in the range of 2 × 10−9 to 1 × 10−6 mol L−1, with detection limit of 1 × 10−10 mol L−1. By this method, real samples (lake water, drinking water, and city wastewater) were analyzed with satisfactory results. In addition, the fabricated electrode exhibited a distinct advantage of simple preparation, non-toxicity, good reproducibility, and stability.

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−1 sulfuric acid solutions + 0.1 mol L−1 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 × 10−7–1.0 × 10−5 mol L−1 with a detection limit of 9 × 10−8 mol L−1. 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.

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.

An electrochemical sensor, based on a graphene oxide (GO)-Nafion composite film modified glassy carbon electrode (GCE), was developed and used for detection of trace amounts of colchicine. Owing to the large surface area, good conductivity of GO and good affinity of Nafion, the sensor exhibited excellent electrocatalytic activity for the oxidation of colchicine, displaying a wide linear response from 5.0 × 10−8 to 2.0 × 10−5 mol L−1 and a low detection limit of 1.5 × 10−8 mol L−1 in 0.1 mol L−1H2SO4 solution. And this modified electrode exhibited a superior immunity from epinephrine, dopamine and ascorbic acid interference. The method was also applied successfully to detect colchicine in medicinal tablets.

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.Highlights► PST/Nafion/GCE showed promising electrocatalysis toward the oxidation of caffeine. ► This method has wide linear range, low detection limit and high selectivity. ► This method is environment-friendly and low-cost. ► It was the first report about the electroanalytical application of PST.

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 0.97 V in HAc-NaAc buffer solution (0.2 M, 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.Research highlights► MWNT/Nafion/GCE showed promising electrocatalysis toward the oxidation of 8-HQ. ► This method has wide wide linear rage, high sensitivity and selectivity. ► This method is environment-friendly and low-cost. ► It was the first report about determining 8-HQ in cosmetic by electroanalysis.

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.

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 mol L−1, and a value of 6.0 × 10−9 mol L−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.

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 mol L−1 to 1.0 × 10−6 mol L−1, with a detection limit of 4.0 × 10−10 mol L−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.

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 × 10−8 M to 6 × 10−6 M, with a detection limit of 2 × 10−8 M. 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%.

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 0.1 mol L−1 H2SO4 + 0.01 mol L−1 KCl solution shows a linear voltammetric response for Hg2+ in the range of 5.0 × 10−10 to 1.5 × 10−7 mol L−1, with a detection limit of 2.0 × 10−10 mol L−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.

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 mol L−1, with an LOD of 5.0 × 10−9 mol L−1. The method proposed was applied for the determination of methotrexate in pharmaceutical dosage and diluted human urine with wonderful satisfactory successfully.

In this paper, the electrochemical behavior of rutin and its interaction with DNA were investigated using voltammetry and spectroscopy. In 0.05 mol L−1 B–R buffer solution (50% ethanol, pH 5.02), rutin exhibited excellent electrochemical activity. In the presence of DNA, the peak current of rutin decreased in a quantitative fashion and the peak potential shifted to a more positive potential value in both cases of DNA in solution and modified on electrode surface by Langmuir–Blodgett technique, indicating the dominance of intercalative interaction. The binding of rutin with DNA, analyzed in terms of the cooperative Hill model, yields the association constant Ka = 1.58 × 105 and a Hill coefficient m = 2.09. The results serve as a reference for the study of rutin with DNA base pairs in the natural environment of living cells.

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 Ka = 2.2(± 0.2) × 104 M− 1, corresponding to the dissociation equilibrium constant Kd = 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.

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 0.1 M KH2PO4 solution shows a linear voltammetric response in the range of 5–250 μg l−1 for thallium and 10–300 μg l−1 for cadmium. The detection limits of thallium(I) and cadmium(II) are estimated to be 1.0 μg l−1 (ca. 5.0 × 10−9 M) and 2.2 μg l−1 (ca. 2.0 × 10−8 M), respectively. Above all, the indium does not respond to this LB film electrode.

A very simple and sensitive voltammetric method for the determination of urapidil was proposed by electrochemical pretreatment using a glassy carbon electrode as the voltammetric sensor (EPGCE). The EPGCE was obtained by cycling the electrode between a potential of −1.5 and 2.5 V, for five cycles in 0.1 M pH 7.0 PBS. Compared with the bare GCE, the EPGCE had an excellent response towards the oxidation of urapidil. Under the optimal conditions, the selective detection of urapidil in a linear concentration range of 2.0 × 10−8 to 5.0 × 10−6 mol L−1 was obtained with a determination limit of 2.0 × 10−8 mol L−1. At the same time, the EPGCE was also applied to the detection of urapidil content in urapidil sustained-release tablets and urine samples with satisfactory results.

A novel self-assembly modified carbon paste electrode based on ethylenediamine and graphene oxide was proposed as a highly sensitive electrochemical sensor for detection of malachite green. The manufacturing operation of the recommended sensor was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical response of malachite green at this sensor was investigated in detail and a new electroanalytical method was erected with high sensitivity and selectivity. The proposed method exhibited good linearity for malachite green over the range from 8.0 × 10−9 mol L−1 to 8.0 × 10−7 mol L−1 with the detection limit of 5 × 10−9 mol L−1 (S/N = 3) by differential pulse voltammetry under optimum conditions. Finally, the practical application was proven by spiking malachite green standards in lake water with recoveries ranging from 98.80% to 101.10%, showing a satisfactory result.

A sensitive, fast and cheap sensor, based on a glassy carbon electrode (GCE) modified with a multiwalled carbon nanotubes (MWCNTs)/Nafion film, is reported for the quantitative determination of synephrine in the Chinese traditional herbal drug Pericarpium citri reticulatae using . The electrochemical behavior of synephrine at this sensor was explored in Britton–Robinson buffer solution using cyclic voltammetry. An oxidation peak at 1027 mV was observed for synephrine when a bare GCE was used, whereas an oxidation peak at 998 mV with greatly enhanced peak current was obtained at the MWCNTs/Nafion/GCE, showing the electrocatalytic nature of the modified electrode. Moreover, cyclic voltammetric studies indicated that the oxidation of synephrine at the modified electrode was irreversible, adsorption controlled and involved two electrons. A calibration plot of oxidation peak current versus synephrine concentration was linear in the range of 1 × 10−8 to 1 × 10−5 mol L−1. The detection limit of synephrine was found to be 8 × 10−9 mol L−1 by linear sweep voltammetry . The effect of pH and scan rate of synephrine were studied. This is currently the first report on the determination of trace synephrine by a purely electroanalytical method. The analytical performance of this sensor was also evaluated for the detection of synephrine in real samples.

A stable voltammetric sensor (SWCNTs/GCE), single-walled carbon nanotubes (SWCNTs) cast on a glassy carbon electrode (GCE), was employed in the initial electrochemical determination of naringenin. The complex electrochemical behavior of naringenin on this sensor was investigated in detail, and the dynamic and thermodynamic parameters were calculated. The new electroanalytical method for naringenin was proposed with a low detection limit of 2.0 × 10−8 mol L−1 (S/N = 3) and wide linear ranges from 8 × 10−8 to 5 × 10−6 mol L−1 and 5 × 10−6 to 1.2 × 10−5 mol L−1, respectively. More importantly, this sensor exhibited good reproducibility and long-term stability. Then this sensor was successfully applied for the determination of naringenin in Fructus Aurantii Immaturus with satisfactory results.

A carbon paste electrode doped with multiwall carbon nanotubes was constructed for the determination of colchicine. Cyclic voltammetry, differential pulse voltammetry and chronocoulometry have been used to investigate the electrochemical response characteristics and the kinetics parameters of colchicine on the proposed voltammetric sensor. Results show that the doped multiwall carbon nanotubes can greatly promote the electrochemical response of colchicine. Under optimum conditions, the oxidation current of colchicine was proportional to the concentration of colchicine in a wide linear range from 1.0 × 10−8 mol L−1 to 2.5 × 10−5 mol L−1 with a low detection limit of 8.0 × 10−9 mol L−1 in 0.15 mol L−1 H2SO4 (pH 0.8). The newly recommended sensor shows several merits including extreme simplicity, wide linear range, low detection limit, good stability and excellent reproducibility. Furthermore, it was successfully employed for the determination of colchicine in pharmaceutical formulations with satisfactory results.

A sensitive voltammetric sensor, a graphene-modified glassy carbon electrode (GR/GCE), for the detection of trace amounts of curcumin is proposed. The GR/GCE was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of curcumin at the GR/GCE was investigated by CV and liner sweep voltammetry (LSV). The reaction mechanisms of curcumin on the GR/GCE were also investigated and discussed systematically. In addition, the currents measured by LSV presented a good linear relationship with curcumin concentrations in the range of 5.0 × 10−8 to 3.0 × 10−6 mol L−1, with a low detection limit of 3.0 × 10−8 mol L−1. The method was also applied successfully to detect curcumin in a Curcuma longa L. sample with high selectivity and accuracy, as well as good recovery.

A simple and sensitive electrochemical method for the determination of the insecticide pymetrozine was proposed using a simple electrochemically pretreated glassy carbon electrode (EPGCE). Compared with the bare GCE, the electrochemical response signal of pymetrozine at the EPGCE showed a significant increase. The electrochemical behavior of pymetrozine was investigated systematically and some dynamics were investigated in detail for the first time. The results indicate that the reaction of pymetrozine on the EPGCE is a two electron and two proton process, which is controlled by both diffusion and adsorption. Under optimum conditions, a good linear relationship was obtained between peak currents and pymetrozine concentrations in the range of 1 × 10−7 to 5 × 10−6 mol L−1 with a detection limit of 8 × 10−8 mol L−1 (S/N = 3). The proposed method was applied to the determination of pymetrozine in real samples with satisfactory recovery results. Finally, the degradation of pymetrozine was also studied in natural soil.

A new voltammetric sensor, based on single-walled carbon nanotubes (SWNTs) modified glassy carbon electrode, was established and used for the determination of neohesperidin dihydrochalcone (NHDC). The electrochemical characterization of NHDC on this sensor was studied systematically by cyclic voltammetry, and the kinetics parameters were calculated for the first time. Compared with a bare GCE, the proposed sensor exhibited excellent redox activity towards NHDC, and a new voltammetric analytical method for NHDC was proposed with a wide linear range from 5 × 10−8 mol L−1 to 8 × 10−6 mol L−1 and a low detection limit of 2 × 10−8 mol L−1. In addition, a reasonable mechanism was also proposed and discussed. Finally, the developed method was successfully applied for the quantitative determination of NHDC in beverages with high accuracy and satisfactory recovery results.

A sensitive and novel electrochemical sensor for detection of bergenin by linear sweep voltammetry (LSV) is presented. This sensor was fabricated by dripping well-dispersed graphene onto glassy carbon electrode (GCE) surface firstly, and then poly(L-lysine) films were subsequently electropolymerized on it to prepare poly(L-lysine)/graphene/GCE. The dynamic detection range of this sensor to bergenin was 4.0 × 10−8 to 5.0 × 10−6 mol L−1 and 6.0 × 10−6 to 1.7 × 10−5 mol L−1, with the detection limit of 1.0 × 10−8 mol L−1. A new voltammetric method for determination of bergenin was erected and shows high sensitivity and selectivity, wider linear relationship, very easy surface update and good stability. The proposed sensors were tested for bergenin detection in pharmaceutical tablets with high accuracy and satisfactory recovery results was obtained. In addition, the oxidation mechanism is proposed and discussed, which could be a reference for the pharmacological action of bergenin in clinical studies.

A novel voltammetric sensor for salbutamol is fabricated via self-assembly of gold nanoparticles on multi-walled carbon nanotubes and Nafion modified electrode. This sensor could improve the oxidation of salbutamol intensively. The oxidation process of salbutamol is studied and some dynamic parameters are calculated using various electrochemical techniques. Under the optimum conditions, the response peak currents have a linear relationship with the salbutamol concentrations in the range of 9.0 × 10−8 to 7.0 × 10−6 mol L−1 with a detectable limit of 5.0 × 10−8 mol L−1. The proposed method is successfully applied to the determination of salbutamol in commercial pharmaceuticals and human serum samples with good accuracy and satisfactory recovery.

A simple and reliable electrochemical sensor based on poly(DL-aspartic acid)-modified glassy carbon electrode was proposed for direct determination of brucine. The electrochemical character of brucine on this sensor was carefully and systematically studied by cyclic voltammetry. Some kinetic parameters were calculated and a reasonable reaction mechanism for brucine at the poly(DL-aspartic acid)/GCE was also proposed. Meanwhile, a new electroanalytical method for determination of brucine was proposed with a highly sensitive detection limit of 3 × 10−8 mol L−1 (S/N = 3) and a wide linear range of 5.0 × 10−8 to 9.0 × 10−5 mol L−1. More importantly, this sensor exhibited good stability and excellent reproducibility in the response for brucine.

A new voltammetric sensor for the detection of maltol was developed, based on the carbon paste electrode (CPE) which allows for lower background current and more reproducible responses. The resulting sensor exhibits excellent redox activity towards maltol. For contrast, the electrochemical properties of maltol were compared on three paste electrodes, based on graphite powder (GP), carbon nanotubes (CNT) and graphene (Gr). The best response of maltol was obtained at the CPE. Further experiments demonstrated that the oxidative peaks increased linearly with maltol concentration in the range of 1.0 × 10−7 to 4.0 × 10−5 mol L−1 with a detection limit of 4.0 × 10−8 mol L−1. The method was successfully applied to detect maltol in beers with satisfactory results. Furthermore, the dynamic parameters and mechanism of electrode reaction were investigated using various electrochemical techniques.

A new voltammetric sensor was designed by covering a layer of gold nanoparticles (AuNPs) on a carbon paste electrode that was pre-mixed in some multi-walled carbon nanotubes (MWCNT). This sensor exhibited super sensitive detection of the electroactive flavonoid rutin due to the large surface area and good conductivity of MWCNT and AuNPs. Cyclic voltammetry curves at various scan rates and pH were recorded to investigate the redox properties of rutin. Further experiments demonstrated that the oxidative peaks increased linearly with rutin concentrations in the ranges of 4.0 × 10−10 to 1.0 × 10−8 mol L−1 and 2.0 × 10−8 to 1.0 × 10−6 mol L−1 with a limit of detection of 4.0 × 10−11 mol L−1. The method was successfully applied to detect rutin in medicine tablets with satisfactory results.

A voltammetric sensor for Sunset Yellow was fabricated by polymerizing L-cysteine on the surface of a glassy carbon electrode. The modified electrode was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical behavior and kinetic parameters of Sunset Yellow in phosphate buffer solution (pH 6.6) were investigated by cyclic voltammetry and chronocoulometry using the proposed sensor, and results showed that the electrochemical response of Sunset Yellow was significantly improved. The peak current (differential pulse voltammetry) of Sunset Yellow linearly increased with the concentrations in the range of 8.0 × 10−9–7.0 × 10−7 mol L−1, and the minimum detectable concentration of Sunset Yellow was estimated to be 4.0 × 10−9 mol L−1. Moreover, the linear relationship between the peak current and the concentration of Sunset Yellow in the presence of Lemon Yellow was 1.0 × 10−8–5.0 × 10−7 mol L−1, with a minimum detectable concentration of 6.0 × 10−9 mol L−1. The reported electrochemical sensor was excellent for the determination of Sunset Yellow because of merits such as extreme simplicity, low cost, high sensitivity, good stability and reproducibility.