Single-emulsion toluene oil droplets (femtoliter) containing a hydrophobic redox probe that are dispersed in water stochastically collide with an ultramicroelectrode (UME). The fast-scan cyclic voltammetry (FSCV) or Fourier-transformed sinusoidal voltammetry (FTSV) is applied: the UME was scanned with a fast, repetitive triangular, or sinusoidal potential, and its current in time/frequency domains were monitored. The electron transfer at the UME/oil interface is coupled with ion transfer at the oil/water interface. Thus, the obtained transient voltammograms of a myriad of ions were used to estimate thermodynamics of ion transfer at the toluene/water interface. Additionally, the single-droplet voltammogram combined with finite element simulations reveal the droplet’s size and shape distributions. Four collision mechanisms with new physical insights were also uncovered via comprehensive analysis of phase angle in the frequency domain, time domain FSCVs, and finite element simulations.

•An electrochemical technique to characterize mercury electroplating process and coalescence events is proposed.•Two dimension analyses are provided to investigate coalescence events associated with individual mercury droplets.•After using Hg2+ for mercury electroplating, surface oxide is visually observed by metaloscope.•The mechanism of mercury film oxidation is revealed with the assistance of fast scan voltammetry.Mercury film modified electrode based stripping voltammetry has become a rapid and low cost method in routine trace element environmental analysis. However, the understanding of the physical and chemical properties of the plated mercury film still needs to be enhanced till now. It has been recognized that the so-called mercury film actually consists of numerous micro mercury droplets, so it is of significant importance to directly investigate the properties and behaviors associated with the individual droplet. Thus, a platinum ultramicroelectrode was used as the substrate for mercury plating, and only one mercury droplet is formed under this condition. Herein, Fourier Transformed Sinusoidal Voltammetry (FTSV) was employed to investigate both the growth process of a mercury droplet and the behaviors of the droplet after plating. Meanwhile, an optical microscope was used to provide direct visual observation. Investigation suggests that: (a) Both the gradual growth process and the fast coalescence event of individual mercury droplet can be resolved with FTSV; (b) The plated mercury droplet can be partially oxidized immediately after the disconnection between the working electrode and the potentiostat in some circumstances, e.g. the presence of trace amount of chloride ion. The present study not only sheds new light on the properties of mercury film electrode but also demonstrates the feasibility of employing FTSV as a new tool for the characterization of micrometer or even nanometer sized particles.

In this contribution, we combine the advantages of both Pt nanospheres and polyfurfural film and successfully develop a novel Pt nanospheres/polyfurfural film modified glassy carbon electrode (GCE) for electrochemical sensing of a nitro group containing pentatomic cyclic compound, metronidazole. In particular, the polyfurfural film and Pt nanospheres were handily obtained by a one-step electropolymerization method and a potential step method, respectively. Benefiting from their excellent synergistic catalytical properties, the Pt nanospheres/polyfurfural film/GCE shows significantly enhanced electrocatalytic activity towards metronidazole. A series of experimental parameters including the electropolymerization cycles of furfural, the deposition time of platinum, accumulation time, accumulation potential and pH of the supporting electrolyte for metronidazole was also investigated and optimized. The proposed sensor exhibited excellent selectivity, stability and reproducibility for the determination of metronidazole, providing a wide linear detection range from 2.5 to 500 μmol dm−3 and a low detection limit of 50 nmol dm−3 (S/N = 3) under optimal experimental conditions. When the proposed sensor was applied to determine metronidazole in real human serum samples, it gave a satisfactory result.

Pyrimidine-type radicals have been demonstrated to be able to attack their 3′ or 5′ neighboring purine nucleotides forming diverse DNA intrastrand cross-links, but whether or not these radicals can attack their surrounding pyrimidine nucleotides forming pyrimidine–pyrimidine type DNA intrastrand cross-links remains unclear. To resolve this question, probable additions of the uracil-5-methyl (˙UCH2) radical to the C5C6 double bond of its 3′/5′ neighboring pyrimidine nucleotides in the four models, 5′-T(˙UCH2)-3′, 5′-C(˙UCH2)-3′, 5′-(˙UCH2)T-3′, and 5′-(˙UCH2)C-3′, are explored in the present work employing density functional theory (DFT) methods. The C6 site of its 5′ neighboring thymidine is the preferred target for ˙UCH2 radical addition, while additions of the ˙UCH2 radical to the C6 and C5 sites of its 5′ neighboring deoxycytidine are found to be competitive reactions. The ˙UCH2 radical can react with both the C6 and C5 sites of its 3′ neighboring pyrimidine nucleotides, but the efficiencies of these reactions are predicted to be much lower than those of the corresponding addition reactions to its 5′ neighboring pyrimidine nucleotides, indicating the existence of an obvious sequence effect. All the addition products could be finally transformed into closed-shell intrastrand cross-links, the molecular masses of which are found to be exactly the same as certain MS values determined in a recent study of an X-irradiated deoxygenated aqueous solution of calf thymus DNA. The present study thus not only definitely corroborates the fact that the reactive ˙UCH2 radical can attack its 3′/5′ neighboring pyrimidine nucleotides forming several pyrimidine–pyrimidine type DNA intrastrand cross-links, but also provides a plausible explanation for the identities of these structurally unknown intrastrand cross-links.

In this work, we firstly propose and confirm a novel coordination matrix/signal amplifier strategy to construct a highly sensitive lead(II) electrochemical sensor. Lead(II) ions can be efficiently accumulated and deposited on the electrode surface by strong coordination bonds between the unoccupied d-orbital of lead(II) ions and conjugated π-electron backbones of polyfurfural film (coordination matrix), and then the anodic stripping current can be significantly enhanced by multi-walled carbon nanotubes (MWCNTs, signal amplifier), finally realizing the highly sensitive determination of lead(II). The polyfurfural film/MWCNT modified glassy carbon electrode (GCE) sensor provided a wide linear detection range from 0.05 to 10 μg L−1 and a low detection limit of 0.01 μg L−1 (S/N = 3) for lead(II). Compared with a classical mercury film sensor (a classical and effective method for determining heavy metal ions), our proposed sensor was more sensitive and achieved better results. Moreover, based on the coordination matrix/signal amplifier strategy, the polyfurfural film/MWCNTs/GCE sensor was further successfully utilized for the simultaneous determination of Cd2+, Pb2+, Cu2+, and Hg2+, demonstrating a wide linear detection range for Cd2+ (0.5–15 μg L−1), Pb2+ (0.1–15 μg L−1), Cu2+ (0.1–12 μg L−1), and Hg2+ (1.5–12 μg L−1) and a low detection limit for Cd2+ (0.03 μg L−1, S/N = 3), Pb2+ (0.01 μg L−1, S/N = 3), Cu2+ (0.06 μg L−1, S/N = 3), and Hg2+ (0.1 μg L−1, S/N = 3). Finally, the proposed sensor was successfully applied to simultaneously determine Cd2+, Pb2+, Cu2+, and Hg2+ in real tap water samples. This work provides a novel and effective analytical strategy for constructing novel electrochemical sensors and shows broad application prospects in heavy metal ion determination for the future.

•A new method for HIV-p24 detection with the advantages of molecularly imprinted polymers and electrochemical sensor.•MWCNTs on the surface of electrode to improve the electrode response.•The sensor displays broader linear and lower detection limit compared with the existed methods.•The sensor shows acceptable stability, reproducibility and good accuracy in human serum.To develop a rapid, simple and sensitive method for the determination of human immunodeficiency virus p24 (HIV-p24), a novel molecularly imprinted polymers (MIPs) electrochemical sensor was constructed on the surface of a multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE) by surface polymerization using acrylamide (AAM) as functional monomer, N,N′-methylenebisacrylamide (MBA) as cross-linking agent and ammonium persulphate (APS) as initiator. Each modification step was carefully examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and scanning electron microscope (SEM). The proposed MIPs electrochemical biosensor exhibited specific recognition to HIV-p24 and displayed a broad linear detection range from 1.0×10−4 to 2 ng cm−3 with a low detection limit of 0.083 pg cm−3 (S/N=3). This performance is superior to most HIV-p24 sensors based on other methods. Meanwhile, this sensor possessed of good selectivity, repeatability, reproducibility, stability and was successfully applied for the determination of HIV-p24 in real human serum samples, giving satisfactory results. The accuracy and reliability of the sensor is further confirmed by enzyme-linked immunosorbent assay (ELISA).

The authors describe an amperometric assay for the detection of prostate specific antigen (PSA) that combines the advantages of using a molecularly imprinted polymer (MIP) and of a nanocomposite composed of  graphene nanoplatelets (graphene sheets; GS), gold nanoparticles (AuNPs) and chitosan (Chit). The GS-AuNP composite was synthesized by a single-step reduction of GS and HAuCl4 solution. The MIP was synthesized by electropolymerization of dopamine and characterized by scanning electron microscopy and differential pulse voltammetry (DPV). Sensitivity is strongly improved by the magnified current obtained by using the GS-AuNP hybrid. Chit was further employed as a film-forming material to prevent the leakage of nanomaterials. Under optimized conditions, the method displays good analytical performance for the detection of PSA by DPV and by using hexacyanoferrate as the electrochemical probe. The peak current (typically measured at 0.16 V vs. SCE) increases linearly in the 1 pg mL−1 to 100 ng mL−1 PSA concentration range, and the detection limit is 0.15 pg mL−1 at a signal to noise ratio of 3. The method was successfully applied to the determination of PSA in serum. The assay is highly selective, sensitive, reproducible and stable. In our perception, it represents an attractive alternative to the commercially available ELISA kits for PSA.

In this work, we fabricated a sensitive electrochemical sensor based on a PEDT–Au/reduced graphene oxide nanocomposites (PEDT–Au/rGO) modified glassy carbon electrode (PEDT–Au/rGO/GCE) for electrochemical determination of morin. A facile, effective and high-efficiency one-pot method was employed to synthesize the PEDT–Au/rGO nanocomposites. The morphology and structure of as-prepared PEDT–Au/rGO nanocomposites were characterized by using a scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray spectroscopy (EDS), and its electrochemical characteristics were studied by EIS, CV and SWV. The PEDT–Au/rGO nanocomposites modified electrode exhibited excellent catalytic activities for morin oxidation, which was attributed to the synergistic catalytic effect that occurred at the interface of PEDT–Au and rGO layers. The effects of square wave voltammetry (SWV) parameters, accumulation time, accumulation potential and pH of the supporting electrolyte for morin were optimized. At the optimal experimental conditions, the PEDT–Au/rGO/GCE presented a high sensitivity of 0.0083 μmol dm−3 and a wide linear range from 1 to 150 μmol dm−3 toward morin oxidation with satisfactory selectivity and stability.

Currently, all known DNA intrastrand cross-links are found to be induced by pyrimidine-type radicals; however, whether or not purine-type radicals are able to cause DNA intrastrand cross-links remains unclear. In the present study, probable additions of the highly reactive deoxyguanosine-8-yl radical to its 3′/5′ neighboring pyrimidine nucleotides in four model compounds, 5′-G˙T-3′, 5′-TG˙-3′, 5′-G˙C-3′, and 5′-CG˙-3′, were studied using density functional theory (DFT) methods. In single-stranded DNA, the deoxyguanosine-8-yl radical is preferred to efficiently attack the C5 site of its 3′ neighboring deoxythymidine or deoxycytidine, forming the G[8-5]T or G[8-5]C intrastrand cross-link rather than the C6 site forming the G[8-6]T or G[8-6]C intrastrand cross-link. The four corresponding sequence isomers, namely T[5-8]G, T[6-8]G, C[5-8]G, and C[6-8]G, formed by additions of deoxyguanosine-8-yl radical to its 5′ neighboring pyrimidine nucleotides are predicted to be formed inefficiently. In double-stranded DNA, considering the detrimental effects of stabilizing weak interactions on related structural adjustments required in each addition reaction path, relatively lower reaction yields are suggested for the G[8-5]T and G[8-5]C intrastrand cross-links, while the formation of the other six intrastrand cross-links becomes quite difficult. All calculations definitely demonstrate that, in addition to pyrimidine-type radicals, the purine-type deoxyguanosine-8-yl radical is able to attack its 3′/5′ neighboring pyrimidine nucleotides forming several DNA intrastrand cross-links.

In this paper, novel ε-MnO2 microspheres with uniform flaky texture were synthesized by a precursor conversion method. Basing on this material, a novel ε-MnO2 microspheres/chitosan/GCE (glassy carbon electrode) electrochemical sensor prepared by a simple physical deposit method was developed for the ultrasensitive determination of Ponceau 4R. The proposed electrochemical sensor exhibits remarkable electrocatalytic activity towards Ponceau 4R, suggesting a potentially detailed reaction mechanism catalyzed by ε-MnO2 and demonstrating a wide linear detection range from 0.005 to 1000 μmol dm−3 and a low detection limit of 0.1 nmol dm−3 (S/N = 3) for Ponceau 4R. The sensor also shows promising selectivity, stability and reproducibility and finally, is applied to determine Ponceau 4R in real samples, giving satisfactory results.

Detection of nanoparticle (NP) collision events at ultramicroelectrode (UME) has emerged as a new methodology for the investigation of single NP in recent years. Although the method was widely employed, some fundamental knowledge such as how the NP moves to and interacts with the UME remain less understood. It was generally recognized that the recorded rate of collision was determined by diffusion that should follow Fick’s first law. However, significant lower collision frequency compared with that of predicted by theory were frequently reported. Experiments carried out by us suggest that the collision frequency will increase dramatically if forced convection (stir or flow injection) is applied during detection. Furthermore, the collision frequency gradually increases to a maximum and then decreases, along with the increase of the convection intensity. This phenomenon is interpreted as follows: (a) there are two steps for a freely moving NP to generate a detectable collision signal. The first step is the move of NP from bulk solution to the surface of the UME which is mass transfer limited; the second step is the landing of NP on the surface of UME which is affected by many factors and is the critical step; (b) there is a barrier that must be overcame before the contact between freely moving NP and UME. Forced convection with moderate intensity can not only increase the mass transfer rate but also help to overcome this barrier and thus enhance the collision frequency; (c) the landing of NP on the surface of UME can be suppressed by stronger convections, because NP will be swept away by hydrodynamic force.

Compared to visible light, near infrared (NIR) light is attractive for the development of novel assay method because it can provide deeper imaging penetration and lower fluorescence background and scattering intensity. In this paper, near infrared (NIR) quantum dots (QDs) were synthesized under a convenient and mild condition, afterwards applied to highly sensitive detection of Cu2+ and monitoring the change of Cu2+ concentration through in vitro and in vivo fluorescent imaging. The quenching of NIR light was resulted from the aggregation of NIR QDs induced by the competitive binding between 3-mercaptopropionic acid (MPA) and the Cu2+ present in the solution. A low detection limit of 5 × 10−8 M and a broad linear detection range from 1 × 10−7 to 5 × 10−5 M could be realized in this strategy for the quantitative evaluation of Cu2+. This NIR QDs based sensor possess high selectivity, rapid response and excellent photostability. Furthermore, the great potential of this NIR nanosensor has also been fully proved by the in vitro cellular imaging and in vivo imaging.

Discrimination and quantification of electroactive species are traditionally realized by a potential difference which is mainly determined by thermodynamics. However, the resolution of this approach is limited to tens of millivolts. In this paper, we described an application of Fourier transformed sinusoidal voltammetry (FT-SV) that provides a new approach for discrimination and quantitative evaluation of electroactive species, especially thermodynamic similar ones. Numerical simulation indicates that electron transfer kinetics difference between electroactive species can be revealed by the phase angle of higher order harmonics of FT-SV, and the difference can be amplified order by order. Thus, even a very subtle kinetics difference can be amplified to be distinguishable at a certain order of harmonics. This method was verified with structurally similar ferrocene derivatives which were chosen as the model systems. Although these molecules have very close redox potential (<10 mV), discrimination and selective detection were achieved by as high as the thirteenth harmonics. The results demonstrated the feasibility and reliability of the method. It was also implied that the combination of the traditional thermodynamic method and this kinetics method can form a two-dimension resolved detection method, and it has the potential to extend the resolution of voltammetric techniques to a new level.

•The modified electrode exhibits electrocatalytic activity towards reduction of nitro.•The modified electrode is used for simultaneous determination of nitrophenol isomers.•The modified electrode shows much lower detection limits or wider linear range.•The proposed method can determine nitrophenol isomers in real water samples.A simple and highly selective electrochemical sensor based on a polyfurfural film modified glassy carbon electrode was developed for simultaneous detection of nitrophenol isomers. The modified electrode exhibited remarkable electrocatalytic activity towards the reduction of nitro. The redox peaks for each nitrophenol isomer can be well resolved and their simultaneous determination was achieved. Under optimal conditions, the proposed sensor had wider linear ranges of 5–100 μmol L−1, 0.75–100 μmol L−1 and 0.75–100 μmol L−1 with lower detection limits of 0.3, 0.05 and 0.04 μmol L−1 for o-nitrophenol, m-nitrophenol and p-nitrophenol, respectively. The modified electrode also showed promising selectivity, stability and reproducibility. Moreover, the proposed sensor can be applied to simultaneous determination of nitrophenol isomers in real water samples, giving satisfactory recoveries.

•We designed a novel sandwich-type electrochemical immunosensor for human immunodeficiency virus p24 antigen detection.•The immunosensor combined a simple immunosensor array and an effectively designed trace tag.•This proposed method shows better accuracy, stability, reproducibility, sensitivity.•The LOD for HIV-p24 was remarkably lower compared with other current techniques.•The proposed system can provide a further platform for other immunoassays.We report a new electrochemical immunosensor for enhanced sensitive detection of human immunodeficiency virus p24 (HIV-p24) based on graphene oxide (GO) as a nanocarrier and enzyme encapsulated in carbon nanotubes-silica as a matrix in a multienzyme amplification strategy. Greatly enhanced sensitivity was achieved by using the bioconjugates featuring horseradish peroxidase–HIV-p24 signal antibody (HRP–HIV-p24) linked to functionalized GO and thionine (TH) as well as efficient encapsulation of enzyme (HRP) in the silica matrix with retained bioactivity. After a sandwich immunoreactions, the HRP in carbon nanotubes-silica matrix and the HRP–HIV-p24-TH/GO captured onto the electrode surface produced an amplified electrocatalytic response by the reduction of enzymatically oxidized thionine in the presence of hydrogen peroxide. The increase of response current was proportional to the HIV-p24 concentration in the range of 0.5 pg/mL–8.5 ng/mL with the detection limit of 0.15 pg/mL, which was lower than that of the traditional sandwich electrochemical measurement for HIV-p24. The amplified immunoassay developed in this work shows acceptable stability and reproducibility, and the assay results for HIV-p24 spiked in human plasma also show good accuracy. This simple and low-cost immunosensor shows great promise for detection of other proteins and clinical applications.

•We designed a novel sandwich-type electrochemical immunosensor for Clostridium difficile toxin B antigen detection.•The immunosensor combined a simple immunosensor array and an effectively designed trace tag.•This proposed method shows better accuracy, stability, reproducibility, and sensitivity.•The LOD for Tcd B was remarkably lower compared with other current techniques.•The proposed system can provide a further platform for other immunoassays.Clostridium difficile toxin B (Tcd B), as one of the primary contributing factors to the pathogenesis of C. difficile-associated diseases, has raised serious public concerns due to its virulence, spore-forming ability and persistence with major types of infectious diarrhea diseases, and been used as a potential biomarker in clinical diagnoses. Thus, a simple method for the determination of Tcd B was developed based on a sandwich-type electrochemical immunosensor. Greatly enhanced sensitivity was achieved based on fabricating the immunosensor by layer-by-layer coating carbon nanotubes (MWCNTs), Prussian blue (PB), Chitosan (CS), Glutaraldehyde (GA) composite on the working electrode as well as using graphene oxide (GO) as a nanocarrier in a multienzyme amplification strategy. In comparison with conventional methods, the proposed immunoassay exhibited high sensitivity and selectivity for the detection of Tcd B, providing a better linear response range from 0.003 to 320 ng/mL and a lower limit of detection (LOD) of 0.7 pg/mL (S/N=3) under optimal experimental conditions. The immunosensor exhibited convenience, low cost, rapidity, good specificity, acceptable stability and reproducibility. Moreover, satisfactory results were obtained for the determination of Tcd B in real human stool samples, indicating that the developed immunoassay has the potential to find application in clinical detection of Tcd B and other tumor markers as an alternative approach.

•We designed a novel sandwich-type electrochemical immunosensor for Procalcitonin.•Combining by a simple immunosensor array and an effectively designed trace tag.•This proposed method shows better accuracy, stability, reproducibility, and sensitivity.•The LOD for PCT was remarkably lower compared with other current techniques.•The proposed system can provide a further platform for other immunoassays.Procalcitonin, as a medium of inflammation, has become a new marker of the identification of severe bacterial infections in recent years and has received high attention due to its most ideal diagnostic indicators of specificity with major types of organism systemic inflammation of bacterial infection in the early stages. Thus, a novel method for the determination of procalcitonin (PCT) was developed based on a sandwich-type electrochemical immunosensor, which combined a simple immunosensor array as well as an effectively designed trace tag. The immunosensor was fabricated by layer-by-layer coating graphene (GC), carbon nanotubes (MWCNTs), chitosan (CS), glutaraldehyde (GA) composite on the working electrode, which can increase the electronic transfer rate and improve the surface area to capture a large number of primary antibodies (Ab1). The trace tag was prepared by loading high-content signal horseradish peroxidase labeled secondary PCT antibody (HRP-Ab2) with AuNPs, which were coated with mesoporous silica nanoparticles (MCM-41) through thionine linking. In comparison with conventional methods, the proposed immunosensor for PCT provided a better linear response range from 0.01 to 350 ng/mL and a lower limit of detection (LOD) of 0.5 pg/mL under optimal experimental conditions. In addition, the immunosensor exhibited convenience, low cost, rapidity, good specificity, acceptable stability and reproducibility. Moreover, satisfactory results were obtained for the determination of PCT in real human serum samples, indicating that the developed immunoassay has the potential to find application in clinical detection of PCT and other tumor markers as an alternative approach.

Traditionally, the selectivity of voltammetric analysis depends on the difference of redox potential. Unfortunately, the limit of discrimination imposed by the voltammogram itself is dozens of millivolts. This suggests that it is impossible to achieve selective detection of one chemical under the interference of chemicals which have very close redox potential with the target chemical. Herein, we provided an attractive solution to this problem, using phase angle instead of potential as the basis of selectivity. Specifically, the electrochemical system was perturbed with a large-amplitude sinusoidal potential signal and the responsive current signal was subsequently analyzed in the frequency domain. This technique was termed as sinusoidal voltammetry (SV). The selective detection can be realized by quantifying the amplitude of a certain harmonic element at the characteristic “fingerprint” phase angle of each redox couple; and their phase angle difference can be regulated to be close to 90° to eliminate interferences and optimize the selective detection. Feasibility of the proposed approach was verified with a model system consisting of two ferrocene derivatives. The underlying theoretical basis was interpreted as that there are inherently several phase angle dramatic transition regions near the redox potential, and thus a minimum redox potential difference can generate a significant phase angle difference in those regions.

A series of bismuth oxyhalides with controllable composition and band structure have been successfully synthesized by a facile and general one-pot hydrothermal route using Bi2O3 as the starting material; their band structures and visible-light-induced photocatalytic performances are investigated.

A polyfurfural film modified glassy carbon electrode was prepared by electrochemical polymerization of furfural in acetonitrile solutions and the electrode exhibited a good electrocatalytic activity on the oxidation of polyphenols in 0.1 mol L−1 phosphate buffer solution (pH 6.0). Applications of the polyfurfural film electrode for simultaneous determination of hydroquinone (HQ), catechol (CC) and resorcinol (RS), and for simultaneous determination of resveratrol (RT) and quercetin (QC) were demonstrated. The linear relationship for HQ, CC and RS were obtained in the range of 0.5–10, 1–40 and 0.5–10 μmol L−1, respectively. The detection limits (S/N = 3) were 0.04 μmol L−1, 0.08 μmol L−1 and 0.06 μmol L−1, respectively. While for RT and QC, the oxidation peak current of RT was linear with the concentration of RT from 0.8 to 8 μmol L−1 and the detection limit (S/N = 3) was 0.4 μmol L−1. Meanwhile the oxidation peak current of QC was linear with the concentration of QC from 0.8 to 12 μmol L−1 and the detection limit (S/N = 3) was 0.3 μmol L−1. Simultaneous determination of relevant polyphenols without interference with each other was realized by the polyfurfural film modified electrode. The electrodes are expected to be used as sensors for the three dihydroxybenzene isomers. The electrode also has the potential application of rapid determination of RT and QC in wine and food.Highlights► We provided a novel polyfurfural film modified glassy carbon electrode. ► EIS characterization suggested polyfurfural film formation conditions. ► The modified electrode can be used for simultaneous determination of hydroquinone, catechol and resorcinol. ► The modified electrode can also be used simultaneous determination of resveratrol and quercetin.

The (WO3)NCs/Nafion film electrode was prepared by immobilizing the synthesized WO3 NCs on the surface of a glassy carbon electrode (GCE) with the help of Nafion. The ECL emission of the electrode in aqueous solution was affected by the buffer solution with respect to the pH and composition. And the strongest ECL was observed in an NH3–NH4Cl buffer with pH being 8.2. Only a weak ECL peak at 1.14 V which was originated from the annihilation process between oxidized and reduced species of WO3 NCs was found. By adding coreactant triproplamine (TPrA) in buffer solution, an additional ECL peak at 1.13 V which was attributed to the electron-transfer reaction between the oxidized WO3 NCs and reduced intermediate of TPrA was observed. The (WO3)NCs/Nafion film electrode exhibits excellent ECL property and good stability, which would promote the potential application of WO3 NCs as a luminescence material for solid-state ECL detection.Highlights► The preparation, characterization of WO3 nanocrystals. ► The ECL behavior of WO3 nanocrystals. ► One weak ECL peak at 1.14 V was observed in aqueous solution with the absence of the coreactant TPrA. ► Two ECL peaks at 1.13 V and 1.14 V were observed in aqueous solution with the presence of the coreactant TPrA.

Many challenges are encountered in the practical application stage of the impedimetric biosensing technique although an ever-increasing interest has been drawn to this area. Lack of a fast and simple readout method and the corresponding portable, low-cost instrument is one of the greatest obstacles. Here we described a potential attractive solution to this problem, specifically impedance spectra are measured by perturbing the system under investigation with a small-amplitude potential step followed by appropriate processing of the resulting chronoamperometric current response. This measurement strategy makes fabricating a portable impedance measurement instrument for routine analysis with low-cost possible. We constructed such a device which was credit-card sized and mainly comprise a mixed signal microcontroller and several operational amplifiers. The reliabilities of the technique/device were verified by experiments carried out with real electrochemical samples. Relevant problems and limitations of this technique are discussed as well. Obvious advantages with respect to the simplicity, rapidity and ease of miniaturization make the technique/device a competitive candidate for practical point-of-care applications.Highlights► Provided a low-cost instrumental solution for practical impedimetric biosensing. ► A simplified impedance measurement setup. ► Described an efficient noise removal strategy. ► Discussed the limitations of the technique.

A glassy carbon electrode modified with organic–inorganic pillared montmorillonite was used for voltammetric detection of mercury(II) in water. High sensitivity is obtained due to the use of the montmorillonites which displays outstanding capability in terms of adsorbing mercury ion due to its high specific surface and the presence of multiple binding sites. The experimental parameters and the effect of a chelating agent were optimized to further enhance sensitivity and selectivity. Linear calibration curves were obtained over the Hg(II) concentration range from 10 to 800 μg L−1 for 5 min accumulation, with a detection limit of 1 μg L−1. Simultaneous determination of Hg(II) and Cu(II) was also studied, and no interference was observed.

A novel kind of nanocomposite, titanate nanotubes (TNTs) decorated by electroactive Prussian blue (PB), was fabricated by a simple chemical method. The as-prepared nanocomposite was characterized by XRD, XPS, TEM, FT-IR and Cyclic voltammetry (CV). Experimental results revealed that PB was adsorbed on the surface of TNTs, and the adsorption capacity of TNTs was stronger than that of anatase-type TiO2 powder (TNP). The PB-TNTs nanocomposite was modified onto a glassy carbon electrode and the electrode showed excellent electroactivity. The modified electrode also exhibited outstanding electrocatalytic activity towards the reduction of hydrogen peroxide and can serve as an amperometric sensor for H2O2 detection. The sensor fabricated by casting Nafion (NF) above the PB-TNTs composite film (NF/PB-TNTs/GCE) showed two linear ranges of 2 × 10−5–5 × 10−4 M and 2 × 10−3–7 × 10−3 M, with a detection limit of 1 × 10−6 M. Furthermore, PB-TNTs modified electrode with Nafion (NF/PB-TNTs/GCE) showed wider linear range and better stability compared with PB-TNTs modified electrode without Nafion (PB-TNTs/GCE) and PB modified electrode with Nafion (NF/PB/GCE).

This paper describes a novel application of Fourier transformed large-amplitude square-wave voltammetry (FT-SWV) in combination with three-phase edge plane pyrolytic graphite (EPPG) electrode to investigate both the kinetics and thermodynamics of anion transfer across the liquid/liquid interface using a conventional three-electrode arrangement. The transfer of anion from aqueous phase to organic phase was electrochemically driven by reversible redox transformation of confined redox probe in the organic phase. The kinetics and thermodynamics of anion transfer were inspected by a so-called “quasi-reversible maximum” (QRM) emerged in the profile of even harmonic components of power spectrum obtained by Fourier transformation (FT) of time-domain total current response and formal potential Ef of first harmonic voltammogram obtained by application of inverse FT on the power spectrum. Besides, a systematic study of patterns of behavior of a variety of anions at the same concentration and a specific anion at different concentrations on kinetics and thermodynamics and the effect of amplitude ΔE on QRM were also conducted, aiming to optimize the measurement conditions. The investigation mentioned above testified that the ion transfer across the liquid/liquid interface controls the kinetics of overall electrochemical process, regardless of either FT-SWV or traditional SWV investigation. Moreover, either the kinetic probe fmax or the thermodynamic probe Ef can be served as a way for analytical applications. Interestingly, a linear relationship between peak currents of the first harmonic components and concentrations of perchlorate anion in the aqueous solutions can be observed, which is somewhat in accordance with a finding obtained by Fourier transformed alternating current voltammetry (FT-ACV) [Bond, A. M.; Duffy, N. W.; Elton, D. M.; Fleming, B. D. Anal. Chem. 2009, 81, 8801−8808]. This may open a new door for analytical detection of a wide spectrum of electrochemically inactive analytes of biological and environmental significance. Compared with traditional SWV, FT-SWV is much simpler and faster in ion transfer kinetics estimation and also provides a new access to thermodynamics evaluation.

A novel method of Fourier transformed square-wave voltammetry (FT-SWV) in combination with thin-film modified electrode was employed to investigate the kinetics of anion transfer across the liquid/liquid interface using a conventional three-electrode arrangement. Other than traditional SWV in which currents are sampled only at the end of each pulse, FT-SWV continuously collects the current response and then transforms it into frequency domain. Even harmonic frequencies, which are derived from the faradaic current response, will emerge in the power spectrum. The profile of the even harmonic power spectrum is parabolic and shows a maximum at a certain frequency. The maximum and the corresponding frequency are equivalent to the well-known “quasireversible maximum” and “critical frequency” (fmax) in traditional SWV, respectively. The rate constant and ion transfer coefficient α can be estimated by the obtained fmax. Compared with traditional SWV, FT-SWV is much simpler and faster in ion transfer kinetics estimation.

A new form of Fourier transformed square wave voltammetry (FT-SWV) is proposed to simplify and accelerate the electron transfer kinetics evaluation procedures for surface-confined redox systems. Even harmonic frequencies, which are derived from the nonlinear Faradaic response, will arise in the power spectrum after Fourier transformation of the current response of FT-SWV. The profile of the even harmonic power spectra is bell-shaped and shows a maximum at a certain frequency. The electrode kinetics-dependent maximum and the corresponding frequency are equivalent to the so-called “quasi-reversible maximum” and “critical frequency” (fmax) in traditional SWV, respectively. The critical frequency can be regarded as a frequency that is synchronized to the electron transfer rate constant (k0). As a result, it can serve as a probe of k0 by means of a very simple equation, k0 = kmax fmax. Compared with traditional cyclic voltammetry, square wave voltammetry, alternating current voltammetry, and several other voltammetric techniques, this method exhibits great advantages for its simplicity, rapidity, and sensitivity.

Nanoparticles of cadmium sulfide (nano-CdS) have been successfully prepared from an aqueous solution of cadmium chloride and sodium sulfide by a novel sonochemical method. Through adding polyvinylpyrrolidone K30 (PVP) as the dispersant, a yellow translucent colloidal solution of cadmium sulfide which was considerably stable within at least one month was obtained. The characterizations of nanoparticles by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM) and FT-IR spectroscopy showed good properties of small size, high surface area and crystal structure. The size of the prepared nanoparticles was about 3–5 nm according to XRD spectra and TEM images. Poly(diallyldimethylammonium chloride) (PDDA) has been employed to fabricate multilayer films on quartz wafer and indium tin oxide (ITO) electrode in a layer-by-layer manner. Atomic force microscopy (AFM) displayed the dense coverage of the substrate surface by the nanoparticles. UV–vis absorption spectroscopy confirmed the consecutive growth of PDDA/nanoparticles layer pairs. The photoelectrochemical and the electrochemical behaviors of the prepared CdS particle were examined as well.

Titanate nanotubes (TNT) were proven to be efficient support for the immobilization of methylene blue (MB). UV–vis absorption and Fourier transform infrared spectra showed that the effect of MB absorbed on TNT was better than nanocrystalline anatase TiO2 (TNP). The quantity of MB absorbed onto TNT was found to be greater than that of TNP and the electrode modified with the MB–TNT film was more stable due to the strong interaction between TNT and MB as well. The absorption of MB on TNT was impacted by the pH value of the reaction solution for the change of surface charge. Electrochemical oxidation of dopamine (DA) at different electrodes was studied. The result showed that the MB–TNT composite film exhibited excellent catalytic activities to DA compared to those of pure TNT, which is a result of the great promotion of the electron-transfer rate between DA and the electrode surface by the MB–TNT film. Furthermore, the layer-by-layer self-assembly behavior of the electrochemically functional MB–TNT nanocomposite was also discussed after obtaining the stable colloid suspension of MB–TNT. The excellent electrochemical ability and the easy fabrication of layered nanocomposite make the MB–TNT nanocomposite very promising in electrochemistry study and new nanotube-based devices.

Complex matrices and rather high acidity in environmental samples are often the impelling challenges for the used running buffers of capillary electrophoresis. Twelve binary acid–base buffers were evaluated for separation of Cr(VI)/Cr(III), Co2+ and Zn2+ in a sample containing various salts by capillary electrophoresis with contactless conductivity detector. The malic acid (MA) systems including MA–His (histidine), MA–Arg (arginine) and MA–Tris (tris(hydroxymethyl)aminomethane) were selected as the candidates with powerful separation efficiency and good response sensitivity. In the MA–Tris buffer, optimization were further carried out in terms of the pH value and the concentration of MA, and the optimal conditions were obtained as 6 mM MA–Tris and 2 mM 18-crown-6 at pH 3.5. Furthermore, a real application was demonstrated by analyzing the plating rinse water (pH 0.8), in which the Ca2+, Na+, Cr(VI)/Cr(III), Co2+ and Zn2+ were all detected by adjusting at pH 3.5 with 5% (v/v) diluent ammonia. Both the cations, e.g., K+, Ca2+, Na+, Mg2+, and the common high concentration anions in the sample, e.g., Cl−, SO42− and NO3− did not cause any disturbance to the concerned analytes.

An electrochemical sensor with high selectivity in addition to sensitivity was developed for the determination of cardiac troponin I (cTnI), based on the modification of cTnI imprinted polymer film on a glassy carbon electrode (GCE). The sensor was fabricated by layer-by-layer assembled graphene nanoplatelets (GS), multiwalled carbon nanotubes (MWCNTs), chitosan (CS), glutaraldehyde (GA) composites, which can increase the electronic transfer rate and the active surface area to capture a larger number of antigenic proteins. MWCNTs/GS based imprinted polymers (MIPs/MWCNTs/GS) were synthesized by means of methacrylic acid (MAA) as the monomer, ethylene glycol dimethacrylate (EGDMA) as the cross linker α,α′-azobisisobutyronitrile (AIBN) as the initiator and cTnI as the template. In comparison with conventional methods, the proposed electrochemical sensor is highly sensitive for cTnI, providing a better linear response range from 0.005 to 60 ng cm−3 and a lower limit of detection (LOD) of 0.0008 ng cm−3 under optimal experimental conditions. In addition, the electrochemical sensor exhibited good specificity, acceptable reproducibility and stability. Moreover, satisfactory results were obtained in real human serum samples, indicating that the developed method has the potential to find application in clinical detection of cTnI as an alternative approach.

A series of bismuth oxyhalides with controllable composition and band structure have been successfully synthesized by a facile and general one-pot hydrothermal route using Bi2O3 as the starting material; their band structures and visible-light-induced photocatalytic performances are investigated.

Currently, all known DNA intrastrand cross-links are found to be induced by pyrimidine-type radicals; however, whether or not purine-type radicals are able to cause DNA intrastrand cross-links remains unclear. In the present study, probable additions of the highly reactive deoxyguanosine-8-yl radical to its 3′/5′ neighboring pyrimidine nucleotides in four model compounds, 5′-G˙T-3′, 5′-TG˙-3′, 5′-G˙C-3′, and 5′-CG˙-3′, were studied using density functional theory (DFT) methods. In single-stranded DNA, the deoxyguanosine-8-yl radical is preferred to efficiently attack the C5 site of its 3′ neighboring deoxythymidine or deoxycytidine, forming the G[8-5]T or G[8-5]C intrastrand cross-link rather than the C6 site forming the G[8-6]T or G[8-6]C intrastrand cross-link. The four corresponding sequence isomers, namely T[5-8]G, T[6-8]G, C[5-8]G, and C[6-8]G, formed by additions of deoxyguanosine-8-yl radical to its 5′ neighboring pyrimidine nucleotides are predicted to be formed inefficiently. In double-stranded DNA, considering the detrimental effects of stabilizing weak interactions on related structural adjustments required in each addition reaction path, relatively lower reaction yields are suggested for the G[8-5]T and G[8-5]C intrastrand cross-links, while the formation of the other six intrastrand cross-links becomes quite difficult. All calculations definitely demonstrate that, in addition to pyrimidine-type radicals, the purine-type deoxyguanosine-8-yl radical is able to attack its 3′/5′ neighboring pyrimidine nucleotides forming several DNA intrastrand cross-links.