CuO–Cu2O heterojunction was synthesized via a one-step flame spray pyrolysis (FSP) process and employed as photoactive material in construction of a photoelectrochemical (PEC) sensing device. The surface analysis showed that CuO–Cu2O nanocomposites in the size less than 10 nm were formed and uniformly distributed on the electrode surface. Under visible light irradiation, the CuO–Cu2O-coated electrode exhibited admirable cathodic photocurrent response, owing to the favorable property of the CuO–Cu2O heterojunction such as strong absorption in the visible region and effective separation of photogenerated electron–hole pairs. On the basis of the interaction of l-cysteine (l-Cys) with Cu-containing compounds via the formation of Cu–S bond, the CuO–Cu2O was proposed as a PEC sensor for l-Cys detection. A declined photocurrent response of CuO–Cu2O to addition of l-Cys was observed. Influence factors including CuO–Cu2O concentration, coating amount of CuO–Cu2O, and applied bias potential on the PEC response toward l-Cys were optimized. Under optimum conditions, the photocurrent of the proposed sensor was linearly declined with increasing the concentration of l-Cys from 0.2 to 10 μM, with a detection limit (3S/N) of 0.05 μM. Moreover, this PEC sensor displayed high selectivity, reproducibility, and stability. The potential applicability of the proposed PEC sensor was assessed in human urine samples.Keywords: cathodic photocurrent; CuO−Cu2O heterojunction; flame spray pyrolysis; l-cysteine; photoelectrochemical sensor;

•Ni(OH)2/TiO2 photoanode is prepared for developing non-enzymatic glucose sensors.•Photoelectrochemical sensing of glucose is realized on Ni(OH)2/TiO2 at low voltage.•A glucose-air photofuel cell is constructed for self-powered glucose sensing.•Ni(OH)2/TiO2 is effective for glucose oxidation driven by visible light.A Ni(OH)2/TiO2 photoanode possessing high photoelectrocatalytic activity toward glucose oxidation driven by visible light was fabricated. The results indicated that deposition of Ni(OH)2 on TiO2 film electrode could remarkably promote the catalytic oxidation of glucose under visible light illumination. By applying a low voltage, the Ni(OH)2/TiO2 electrode showed a linear photoelectrochemical response to glucose in the concentration range from 0.5 μM to 20 μM. Furthermore, the high photoelectrocatalytic activity of Ni(OH)2/TiO2 electrode toward glucose oxidation was utilized to construct a glucose-air photofuel cell, which generated electrical signal responding to glucose concentration from 5 μM to 100 μM, without using external electrical power supply. Thus, dual non-enzymatic glucose sensors based on photocatalytic oxidation of glucose on the Ni(OH)2/TiO2 electrode under visible light illumination were demonstrated.Download high-res image (239KB)Download full-size image

In this work, Mo-doped BiVO4 (Mo-BiVO4) and graphene nanocomposites were prepared and explored as photoactive material to construct a visible light-driven photoelectrochemical biosensor. The photoelectrochemical measurements indicated that suitable amount of graphene incorporated into Mo-BiVO4 greatly promoted the photocurrent response, owing to improved charge transfer rate and enhanced absorption of visible light. Moreover, graphene in the nanocomposites played a crucial role in immobilization of streptomycin aptamer through π-π stacking interaction. In the absence of streptomycin, photoelectrochemical aptasensor exhibited a weak photoresponse due to steric hindrance from the aptamer. After specific interaction between streptomycin and the aptamer, the sensor exhibited an enhanced photocurrent response to streptomycin, attributed to the oxidation of streptomycin molecules by photogenerated holes. Under optimal conditions, the designed photoelectrochemical sensor exhibited a linear photocurrent response to streptomycin in the concentration range of 0.1–100 nM, with a detection limit (3S/N) of 0.0481 nM. The applicability of the PEC aptasensor was successfully assessed by measuring streptomycin in commercial veterinary drugs.Download high-res image (75KB)Download full-size image

•Visible light-driven photoelectrocatalysis is coupled with electroenzymatic process.•The coupling system consists of CdS/WO3/FTO photoanode and hemin-graphene cathode.•The coupling system is applied to effective degradation of chloramphenicol.•A degradation pathway for chloramphenicol in the developed system is proposed.Photoelectrocatalysis (PEC) and electroenzymatic (EEC) process are two important techniques for degradation of refractory organic compounds. In this work, we coupled PEC and EEC (PEC-EEC) to develop a novel system for efficient removal of chloramphenicol (CAP) driven by visible light. This coupling system was constructed by a CdS/WO3/FTO photoanode and a hemin-graphene immobilized cathode. The photoanode was fabricated by layer-by-layer assembly of CdS quantum dots on WO3/FTO to provide high visible light activity. In order to achieve the EEC process, graphite cathode was modified with hemin-graphene composite, in which hemin served as the mimic enzyme. When CdS/WO3/FTO anode was irradiated under visible light, photogenerated holes participated in the formation of hydroxyl radicals while photogenerated electrons were driven by bias potential to the cathode for the reduction of oxygen into hydrogen peroxide. Thus, organic pollutant could be degraded by the oxidation reactions either with the hydroxyl radicals or the hydrogen peroxide under the catalysis of hemin. The visible light-driven PEC-EEC system was applied to the removal of CAP. The intermediates formed during the degradation process were separated by high-performance liquid chromatography and identified by liquid chromatography-mass spectrometry, and a degradation pathway for CAP in such a PEC-EEC system was proposed.

Graphitic carbon nitride (g-C3N4) is a new type of metal-free semiconducting material with promising applications in photocatalytic and photoelectrochemical (PEC) devices. In the present work, g-C3N4 coupled with CdS quantum dots (QDs) was synthesized and served as highly efficient photoactive species in a PEC sensor. The surface morphological analysis showed that CdS QDs with a size of ca. 4 nm were grafted on the surface of g-C3N4 with closely contacted interfaces. The UV–visible diffuse reflection spectra (DRS) indicated that the absorption of g-C3N4 in the visible region was enhanced by CdS QDs. As a result, g-C3N4–CdS nanocomposites demonstrated higher PEC activity as compared with either pristine g-C3N4 or CdS QDs. When g-C3N4–CdS nanocomposites were utilized as transducer and tetracycline (TET)-binding aptamer was immobilized as biorecognition element, a visible light-driven PEC aptasensing platform for TET determination was readily fabricated. The sensor showed a linear PEC response to TET in the concentration range from 10 to 250 nM with a detection limit (3S/N) of 5.3 nM. Thus, g-C3N4 sensitized with CdS QDs was successfully demonstrated as useful photoactive nanomaterials for developing a highly sensitive and selective PEC aptasensor.Keywords: aptamer; CdS quantum dots; graphitic carbon nitride; photoelectrochemical aptasensor; tetracycline

A self-powered sensing system possesses the capacity of harvesting energy from the environment and has no requirement for external electrical power supply during the chemical sensing of analytes. Herein, we design an enzyme-free self-powered sensing platform based on a photofuel cell (PFC) driven by visible-light, using glucose as a model analyte. The fabricated PFC consists of a Ni(OH)2/CdS/TiO2 photoanode and a hemin-graphene (HG) nanocomposite coated cathode in separated chambers. Under visible-light irradiation, glucose in the anodic chamber is facilely oxidized on Ni(OH)2/CdS/TiO2 while H2O2 in the cathodic chamber is catalytically reduced by HG, which generates a certain cell output sensitive to the variation of glucose concentration. Thus, a PFC based self-powered sensor is realized for glucose detection. Compared to the existing enzymatic self-powered glucose sensors, our proposed PFC based strategy exhibits much lower detection concentration. Moreover, it avoids the limitation of conventional enzyme immobilized electrodes and has the potential to develop high-performance self-powered sensors with broader analyte species.

Molecularly imprinted polymer (MIP) of 4-chlorophenol (4-CP) was synthesized and combined with poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene (PDDA-G) to develop an electrochemical sensor for selective determination of 4-CP. The chemical structures of the imprinted films were analyzed using Fourier transform infrared (FTIR) spectroscopy. The morphology and interfacial behavior of MIP and PDDA-G modified glassy carbon electrodes (GCEs) were investigated by scanning electron microscopic (SEM) and electrochemical impedance spectroscopic (EIS) techniques, respectively. The obtained MIP/PDDA-G/GCE showed high sensing performance towards 4-CP. Under optimized conditions, the sensor showed a linear response to the concentration of 4-CP in a wide range from 0.8 to 100 μmol L−1 with a detection limit (3S/N) of 0.3 μmol L−1. Moreover, the imprinted sensor exhibited excellent specific recognition ability to 4-CP which could avoid the interference of other structurally similar phenolic compounds. The developed sensor was successfully applied to the detection of 4-CP in real-life water samples.

•Graphene-doped Bi2S3 nanorods are prepared and used to construct PEC aptasensor.•The photocurrent response of Bi2S3 nanorods is promoted by graphene doping.•A highly sensitive and selective PEC aptasensor for SDM is developed.•SDM in veterinary drug formulation is successfully determined using the proposed sensor.Bismuth sulphide (Bi2S3) nanorods doped with graphene (G) were synthesized and explored as photoactive materials for constructing a photoelectrochemical (PEC) aptasensor for sulfadimethoxine (SDM) detection. The formation of Bi2S3 nanorods and G nanosheets was observed by scanning electron microscopy (SEM) and further characterized by X-ray diffraction (XRD) spectroscopy. The PEC measurements indicated that the photocurrent response of Bi2S3 was obviously improved by doping suitable amount of G. The G-Bi2S3 composite coated electrode was utilized for fabricating a PEC aptasensor by covalently immobilizing a 5′-amino-terminated SDM aptamer on the electrode surface. Based on the specific interaction between SDM and the aptamer, a PEC sensor responsive to SDM was obtained. Under optimal conditions, the proposed sensor showed a linear photocurrent response to SDM in the concentration range of 1.0–100 nM, with a low detection limit (3S/N) of 0.55 nM. Moreover, the sensor showed high sensitivity, stability and reproducibility. The potential applicability of the PEC aptasensor was confirmed by detecting SDM in veterinary drug formulation and milk.

In this work, CdS quantum dots (QDs) were proposed as electrochemical sensing materials for ciprofloxacin (CIP) determination for the first time. The CdS QDs-modified glassy carbon electrode (GCE) exhibited a well-defined anodic stripping response in acidic solution, attributed to the release of Cd(II) ions from CdS QDs. The influences of supporting electrolyte and CdS QDs concentration on the response of CdS QDs-modified electrode were investigated and optimized. When CIP was added into the solution, the anodic stripping current of Cd(II) on CdS QDs/GCE decreased due to the complexation of CIP with in situ generated Cd(II) ions from CdS QDs. A linear relationship existed between the anodic stripping voltammetric response of CdS QDs/GCE and CIP concentration in the range from 1.0 × 10−7 to 1.0 × 10−5 mol L−1. The detection limit (3S/N) was 2.2 × 10−8 mol L−1. The applicability of the CdS QDs-modified electrode for CIP determination was demonstrated in biological fluids.

A novel cathodic “signal-off” strategy was proposed for photoelectrochemical (PEC) aptasensing of oxytetracycline (OTC). The PEC sensor was constructed by employing a p-type semiconductor BiOI doped with graphene (G) as photoactive species and OTC-binding aptamer as a recognition element. The morphological structure and crystalline phases of obtained BiOI-G nanocomposites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The UV–visible absorption spectroscopic analysis indicated that doping of BiOI with graphene improved the absorption of materials in the visible light region. Moreover, graphene could facilitate the electron transfer of BiOI modified electrode. As a result, the cathodic photocurrent response of BiOI under visible light irradiation was significantly promoted when a suitable amount of graphene was doped. When amine-functionalized OTC-binding aptamer was immobilized on the BiOI-G modified electrode, a cathodic PEC aptasensor was fabricated, which exhibited a declined photocurrent response to OTC. Under the optimized conditions, the photocurrent response of aptamer/BiOI-G/FTO was linearly proportional to the concentration of OTC ranging from 4.0 to 150 nM, with a detection limit (3S/N) of 0.9 nM. This novel PEC sensing strategy demonstrated an ultrasensitive method for OTC detection with high selectivity and good stability.

•Photovoltammetric behavior of PPD on CdS–GS hybrid film was studied.•GS doped in CdS greatly improved the photoelectrochemical response of PPD.•CV of PPD on CdS–GS film became a sigmoidal shape under photoirradiation.•Novel photoelectrochemical strategy for PPD determination was developed.A photoelectroactive film composed of CdS quantum dots and graphene sheets (GS) was coated on F-doped SnO2 (FTO) conducting glass for studying the electrochemical response of p-phenylenediamine (PPD) under photoirradiation. The result indicated that the cyclic voltammogram of PPD on CdS–GS hybrid film became sigmoidal in shape after exposed under visible light, due to the photoelectrocatalytic reaction. Such a photovoltammetric response was used to rapidly optimize the photoelectrocatalytic activity of hybrid films composed of different ratios of CdS to GS toward PPD. The influences of scan rate and pH on the photovoltammetric behavior of PPD on CdS–GS film revealed that although the controlled step for electrochemical process was not changed under photoirradiation, more electrons than protons might participate the photoelectrocatalytic process. Furthermore, the photoelectroactive CdS–GS hybrid film was explored for PPD determination based on the photocurrent response of film toward PPD. Under optimal conditions, the photocurrent signal on CdS–GS film was linearly proportional to the concentration of PPD ranging from 1.0 × 10−7 to 3.0 × 10−6 mol L−1, with a detection limit (3S/N) of 4.3 × 10−8 mol L−1. Our work based on CdS–GS hybrid film not only demonstrated a new facile photovoltammetric way to study the photoinduced electron transfer process of PPD, but also developed a sensitive photoelectrochemical strategy for PPD determination.

•An electroanalytical method for CIP is developed based on CIP interacting with Cd2+.•Anodic stripping voltammetry of Cd2+ provides sensitive indicating signal for CIP.•Anodic stripping signal of Cd2+ at −0.72 V endows the method with good selectivity.•The method is applied to CIP determination in pharmaceutical tablet and human urine.An indirect electrochemical determination method for ciprofloxacin (CIP) was developed based on the complexation of CIP with Cd2+. On graphene-modified electrode, Cd2+ showed a strong anodic stripping peak current response, which was efficiently prohibited in the presence of CIP. Thus, the anodic stripping peak current of Cd2+ was employed as the indicating signal for CIP determination, which was more sensitive than the direct electrochemical oxidation response of CIP. Some influence factors such as the modified volume of graphene, solution pH, accumulation time, complexation reaction time were systematically investigated. Under optimum conditions, the anodic stripping response of Cd2+ on the graphene-modified electrode was inversely proportional to CIP in the concentration range from 1.0 × 10−7 to 1.0 × 10−5 mol L−1 with a detection limit (3S/N) of 5.9 × 10−8 mol L−1. The method showed high selectivity, good reproducibility and was successfully applied to the determination of CIP in pharmaceutical formulation and human urine.

An indirect electrochemical sensing strategy for the determination of ofloxacin (OFL) was developed using cupric ion (Cu2+) as an electrochemical probe. The method was based on the complexation of OFL with Cu2+, which was investigated by UV-visible spectrophotometry and differential pulse voltammetry (DPV). When OFL was added into the electrolyte solution containing Cu2+, the electro-reduction peak current of Cu2+ on glassy carbon electrode (GCE) was decreased. Some influencing factors in terms of pH, quiet time, and reaction time were systematically studied. Under optimal conditions, the Cu2+ reduction peak current difference (ΔIp) before and after adding OFL was found to be linear to the concentration of OFL in the range from 1.0 × 10−7 to 1.0 × 10−4 M. The detection limit (3S/N) was 8.2 × 10−8 M. Moreover, the proposed sensor displayed high selectivity and good reproducibility, which was successfully applied to the detection of OFL in pharmaceutical tablet and chicken fodder.

Photoactive material and recognition element are two crucial factors which determine the sensitivity and selectivity of the photoelectrochemical (PEC) sensor. Herein we developed a novel PEC aptamer sensor for the specific detection of kanamycin using water-dispersible graphite-like carbon nitride (w-g-C3N4) as visible light-active material and aptamer as the biorecognition element. While a suitable amount of graphene oxide (GO) was doped in w-g-C3N4, the visible light photocurrent response was enhanced, which was beneficial to the construction of PEC sensor. On the other hand, the large specific surface area and π-conjugated structure of GO/w-g-C3N4 provided an excellent platform for immobilizing the kanamycin-binding DNA aptamer on the surface of the sensor via π–π stacking interaction. On such a sensor, the capture of kanamycin molecules by aptamer resulted in increased photocurrent. The PEC response of the sensor was found to be linearly proportional to the concentration of kanamycin in the range from 1 nM to 230 nM with a detection limit (3S/N) of 0.2 nM. Moreover, the proposed sensor displayed high selectivity, good reproducibility, and high stability, demonstrating the successful combination of GO/w-g-C3N4 with aptamer in fabricating high performance PEC sensors.

•Liquid phase deposition is developed for preparing WO3/TiO2 heterojunction films.•TiO2 film provides an excellent platform for WO3 deposition.•WO3 expands the absorption band edge of TiO2 film to visible light region.•WO3/TiO2 heterojunction film shows high photoelectrocatalytic activity.The heterojunction films of WO3/TiO2 were prepared by liquid phase deposition (LPD) method via two-step processes. The scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopic analysis indicated that flower-like WO3 film was successfully deposited on TiO2 film with the LPD processes. The TiO2 film provided an excellent platform for WO3 deposition while WO3 obviously expanded the absorption of TiO2 film to visible light. As the result, the heterojunction film of WO3/TiO2 exhibited higher photocurrent response to visible light illumination than pure TiO2 or WO3 film. The photoelectrocatalytic (PEC) activity of WO3/TiO2 film was evaluated by degrading Rhodamin B (RhB) and 4-chlorophenol (4-CP) under visible light irradiation. The results showed that the LPD WO3/TiO2 film possessed high PEC activity for efficient removal of various refractory organic pollutants.

A facile method for preparation of Cr-doped TiO2 nanotubes (Cr–TiO2 NTs) modified with polyaniline (PANI) was developed. The obtained materials were analyzed with scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy. The photoelectrochemical property of PANI/Cr–TiO2 nanotubes was studied by voltammetry, photocurrent and electrochemical impedance spectroscopy (EIS). Using PANI/Cr–TiO2 NTs as photoanode, the removal of p-nitrophenol (PNP) by photoelectrocatalytic oxidation technique was investigated. Compared with Cr–TiO2 NTs, PANI/Cr–TiO2 NTs showed an increased efficiency in the photoelectrocatalytic degradation of PNP. Moreover, photoelectrocatalysis was more efficient for PNP degradation than electrochemical oxidation, direct photolysis, and photocatalysis. The influences of applied bias potential, initial concentration of PNP and solution pH on the photoelectrocatalytic degradation of PNP were investigated. Under optimized conditions, almost all PNP could be degraded on PANI/Cr–TiO2 NTs after 2-h photoelectrocatalytic treatment.

Liquid phase deposition (LPD) technique was developed to prepare zinc oxide (ZnO) thin film with high photoelectrochemical activity. The field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) characterization showed that the deposited film was composed of many stick microcrystalline structured ZnO. The photoelectrochemical property of LPD film was analyzed by chronoamperometry and electrochemical impedance spectroscopy (EIS) under UV-light excitation. Using the LPD ZnO film as photoanode, the removal of p-nitrophenol (PNP) was studied by photoelectrocatalytic (PEC) oxidation technique. The influencing factors such as initial concentration of PNP, pH and bias potential were systematically investigated. Under optimized conditions, PNP was effectively degraded by photoelectrocatalysis on the LPD ZnO film.

Ofloxacin has been widely used as a form of quinolone antibiotics. However, it has the potential to exert biological effects on aquatic organisms and cause surface water pollution. It is necessary to find an efficient way to remove ofloxacin. This study reports on the degradation of ofloxacin in solution using TiO2 nanotubes (TiO2 NTs) as photocatalyst. The TiO2 NTs were synthesized through anodization. The morphology, elemental composition and state, crystalline phase, and photocatalytic activity of this photocatalyst were characterized by a variety of surface analysis techniques. The obtained TiO2 NTs were applied to ofloxacin degradation by photoelectrocatalysis. The degradation efficiency was assessed by in situ monitoring the UV-vis absorbance spectrum of ofloxacin solution during the degradation process. The effects of initial pH, bias potential, and initial concentration of ofloxacin were investigated systematically. Moreover, the toxicity of ofloxacin during the photoelectrocatalytic degradation process was evaluated using the growth inhibition test with Microcystis aeruginosa. The TiO2 NT-based photoelectrocatalytic method provided a high degradation rate for ofloxacin removal.

•Nitrogen doped graphene decorated with gold nanoparticles were synthesized.•Au nanoparticles improved the surface area and electron transfer properties of N-G.•Au/N-G composite markedly enhanced the voltammetric response of chloramphenicol.•CAP in real sample was successfully determined on Au/N-G modified electrode.Nitrogen-doped graphene nanosheets decorated with gold nanoparticles (Au/N-G) were synthesized by the reduction of HAuCl4 on the surface of N-G using ethylene glycol as the reducing agent. The surface characterization with various techniques such as scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy showed that many gold nanoparticles were effectively loaded on the surface of N-G via the proposed synthesis process. The impedance analysis indicated that Au/N-G was an excellent electrode material possessing outstanding electrochemical features for electron transfer. Using Au/N-G modified electrode, the electrochemical response of chloramphenicol (CAP) was significantly increased due to the synergetic effect of two nanomaterials. Thus, a high-performance electrochemical sensor for CAP based on Au/N-G was developed.

•Photocatalysis, SERS activity and recyclability of Au NPs-TiO2 NTs are characterized.•In situ monitored the photodegradation of methylene blue (MB) by applying SERS.•Analysis of time course SERS spectra interpreted the MB degradation pathway.•The kinetics of photodegradation of MB on the substrate/air interface are analyzed.•Mapping of temporal distribution of methylene blue on substrate are achieved.An in situ method that is able to quickly and accurately detect not only the photocatalytic degradation process but also the molecular structure information of intermediates is critical to analyzing the degradation mechanism of organic contaminants. This work successfully applied Raman microspectroscopy to in situ detect and monitor the photocatalytic degradation process of methylene blue (MB) on a recyclable substrate (gold nanoparticles dispersed TiO2 nanotube arrays, noted as Au NPs-TiO2 NTs) that exhibits multifunctionalities including photocatalysis activity and surface-enhanced Raman scattering (SERS) effect. In addition, by analyzing time course SERS spectra during the photocatalytic degradation process, the intermediates produced in the proposed photocatalytic degradation pathway were identified and the kinetics of photocatalytic degradation of MB on the Au NPs-TiO2 NTs/air interface were interpreted. This work demonstrated the potential of using these recyclable, highly photocatalytical and SERS active nanostructures as a platform to analyze the photocatalytic degradation mechanism and kinetics of other environmental pollutants.

Highly ordered Cr-doped TiO2 nanotube arrays (Cr-TiO2NTs) were prepared by the electrochemical oxidation of Ti substrate in glycerol/fluoride electrolyte solution containing potassium dichromate. The Cr-TiO2NTs were characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicated that Cr3+ was successfully introduced into TiO2 nanotubes and Cr doping inhibited the crystal phase change of TiO2 from anatase to rutile under high annealing temperature. Compared with pure TiO2NTs, the Cr-doped TiO2NTs exhibited higher photocurrent response, which was influenced by the concentration of Cr(VI) dopant and annealing temperature. The efficient removal of methyl orange (MO) indicated the high photoelectrocatalytic (PEC) activity of Cr-TiO2NTs.Highlights► Cr-TiO2NTs were prepared via an electrochemical oxidation method. ► Potassium dichromate was used as the source of Cr dopant. ► Cr-TiO2NTs showed high photoelectrocatalytic activity to remove organic pollutant.

The electrochemical behavior of ketoconazole (KC) on a multi-walled carbon nanotubes (MWCNTs)-modified glassy carbon (GC) electrode was investigated in this work. The result indicated that MWCNTs remarkably promoted the electrochemical response of KC on the GC electrode. To achieve a sensitive voltammetric determination of KC, experimental conditions such as solution pH, amount of MWCNTs, accumulation time as well as scan rate were systematically studied and optimized. Under optimized conditions, the differential pulse voltammetric (DPV) response on the MWCNTs-modified electrode was proportional to the KC concentration in the range of 1.0 × 10−6–3.0 × 10−5 mol L−1 with a detection limit of 4.4 × 10−7 mol L−1. Based on this MWCNTs-modified electrode, KC in a pharmaceutical drug (Ketoconazole®) was successfully determined without requirement of complicated sample pretreatment.

We have investigated the interaction between diclofenac and deoxyribonucleic acid (DNA) by the electrochemical method. On glassy carbon electrode, the voltammetric curve of diclofenac showed an oxidation peak, which was obviously influenced by the addition of DNA. Accordingly, a series of electrochemical experiments were carried out to elucidate the interaction between diclofenac and DNA. Based on the diclofenac–DNA interaction, a biosensor for diclofenac was developed. When a film of DNA was immobilized on the electrode surface, DNA showed an oxidation signal promoted by graphene oxide. Due to the diclofenac–DNA interaction, the peak current of DNA decreased and the peak potential shifted positively with increasing the concentration of diclofenac. The response of the biosensor was linear to the concentration of diclofenac in the range of 1 to 130 μM. Using such a biosensor, the photodegradation of diclofenac was successfully monitored.

This work demonstrates that liquid phase deposition (LPD) technique provides a novel approach to the immobilization of hemoglobin (Hb) in TiO2 film for studying the direct electron transfer of Hb. Using the LPD process, a hybrid film composed of Hb, TiO2 and sodium dodecylsulfonate (SDS) is successfully prepared on the electrode surface. The surface morphology of as-deposited Hb/SDS/TiO2 film shows a flower-like structure. The cyclic voltammetric measurement indicates that the LPD hybrid film facilitates the electron transfer of Hb, which yields a pair of redox peaks prior to the characteristic voltammetric peaks of TiO2. Due to the electrocatalytic activity of Hb towards H2O2, the Hb/SDS/TiO2 hybrid LPD film can be utilized as an H2O2 sensor, showing a sensitive response linearly proportional to the concentration of H2O2 in the range of 5.0 × 10− 7–4.0 × 10− 5 mol/L. At the same time, the Hb/SDS/TiO2 hybrid film preserves the photoelectrochemical activity of TiO2. The photovoltaic effect on the electrochemical behavior of Hb/SDS/TiO2 film is observed after long-time UV irradiation on the film, which could improve the calibration sensitivity for H2O2.Research highlights► Hb/SDS/TiO2 hybrid film is prepared on electrode surface by LPD technique. ► Electron transfer between Hb and electrode is facilitated in the hybrid LPD film. ► The LPD Hb/SDS/TiO2 film preserves the photoelectrochemical activity of TiO2. ► The sensitivity for H2O2 is improved based on the photovoltaic effect of TiO2.

A photoelectroactive TiO2/DNA hybrid film was synthesized via the liquid phase deposition (LPD) process. Scanning electron microscopic (SEM) characterization showed that the compact TiO2 film was changed to a mesoporous structure when DNA was present in the deposition solution, which might be the result of TiO2 particles growing along the backbones of the double-helical structure of DNA molecules. Although UV absorption spectra and cyclic voltammograms indicated that the deposited TiO2 on the substrate surface was decreased in the presence of DNA, an enhanced photocurrent response was observed. The electrochemical impedance and cyclic voltammetric measurements using K3[Fe(CN)6] as a redox probe suggested that the mesoporous film provided a relatively more efficient electron transfer interface, which could improve the photoelectron transfer rate from the semiconducting film to the electrode and reduce the recombination of photoelectrons and holes. This results in an enhanced photocurrent. Even after long-term and continuous UV irradiation, the mesoporous film exhibited a promoted photoelectrochemical response. The promoted photoelectrocatalytic degradation of methylene blue was obtained on the TiO2/DNA composite film, which is consistent with the enhanced photocurrent, and this demonstrates that DNA behaved as a useful biomaterial for the synthesis of a photoelectroactive hybrid film with improved performance.

This work investigated the electrocatalytic oxidation of oxalic acid on multiwall carbon nanotubes (MWNTs) modified glassy carbon (GC) electrode. The result indicated that the oxidation of oxalic acid was greatly improved at the MWNTs-modified GC (MWNTs/GC) electrode as compared with the bare GC electrode. The effects of the MWNTs suspension amount, pH and scan rate on the electrooxidation response of oxalic acid were studied by voltammetry. The surface concentration and diffusion coefficient (DR) of oxalic acid at the MWNTs/GC electrode were determined by chronocoulometry. This MWNTs/GC electrode presented a wide linear response ranging from 5.0 × 10−5 to 1.5 × 10−2 M for oxalic acid. The detection limit (S/N = 3) was estimated to be 1.20 × 10−5 M. Based on this MWNTs/GC electrode, the content of oxalic acid in spinach was successfully determined.

Electroactive TiO2 films were prepared by liquid-phase deposition (LPD) in the presence of sodium dodecylsulfonate. The doping of dodecylsulfonate (DS) converted the TiO2 film from a structure of globular nanoparticles to a structure of nano-flakes, which directly influenced the electrochemical behavior of the film. The DS-doped TiO2 film yields an enhanced reduction peak in the cyclic voltammograms, being attributed to the reduction of hydroxylated titanium(IV) species. The varied surface structure of the DS-doped TiO2 film provided a biocompatible platform for immobilizing hemoglobin (Hb), and the Hb-immobilized film electrode exhibited good electrocatalytic activity to the reduction of H2O2. As a sensor for the determination of H2O2, the Hb-immobilized film electrode yielded an excellently linear range from 0.003 to 1.5 mM H2O2 in the correlation between reduction peak current and H2O2 concentration, with a low detection limit of 1.0 μM.

A DNA biosensor was constructed by immobilizing DNA on a glassy carbon (GC) electrode modified with multiwall carbon nanotubes (MWNTs) dispersed in Nafion (DNA/MWNTs/GCE). The DNA-modified electrode exhibited two well-defined oxidation peaks corresponding to the guanine and adenine residues of DNA, respectively. The effects of the adsorption potential, DNA concentration and quantity of MWNTs used for DNA immobilization were investigated, as were the effects of buffer, pH and scan rate on the voltammetric behavior of DNA. Phenol, m-cresol and catechol showed noticeable inhibition towards the response of the electrode due to their interactions with DNA. These findings were used to design biosensors with linear response to these phenolic pollutants.

Titanium dioxide (TiO2) films on glassy carbon (GC) electrode surface were prepared by the liquid phase deposition (LPD) process for different deposition times. The morphological structure, interfacial property and electrocatalytic activity of as-prepared LPD TiO2 films on GC surface were studied by field-emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The FE-SEM observation showed that the deposition time controlled the morphology of film on GC surface. With increasing deposition time, TiO2 formed nanoparticles at the initial 5-h stage and compact thick films after 20 h. Due to the semiconducting properties of TiO2, the LPD films inhibited the electron transfer process of [Fe(CN)6]3−/[Fe(CN)6]4− on GC by increasing the redox reaction peak potential separation of CV curve and electron transfer resistance of EIS. The inhibition was increased with TiO2 film thickness. Nevertheless, the onset reduction potential of maleic acid decreased with increasing LPD TiO2 film thickness while the cathodic and anodic currents increased, demonstrating the useful electrocatalytic activity of LPD TiO2 films.

3-Mercaptopropionic acid (MPA) was assembled on gold nanoparticle arrays to form three-dimensional monolayer. The electrochemical behavior of small biomolecules such as NADH, ascorbic acid (AA), uric acid (UA) and dopamine (DA) on the as-prepared three-dimensional monolayer was studied. The cyclic voltammetric results indicated that three-dimensional MPA monolayer promoted the electron transfer between NADH and electrode, which was similar to two-dimensional MPA monolayer assembled on planar gold electrode. However, to the electrooxidation of AA, although two-dimensional MPA monolayer exhibited a blocking effect, three-dimensional MPA monolayer showed an obvious promotion. The catalytic activity of three-dimensional MPA monolayer towards UA and DA was also observed, which was attributed to its three-dimensional structure that might effectively prevent the poison of the electrode surface by the oxidation products.

•Pd and reduced graphene oxide are deposited on foam-Ni via electrodeposition.•Pd particles supported on RGO possess large active surface area.•Pd/RGO/foam-Ni shows high electrocatalytic activity for dechlorination of 4-CP.•100% 4-CP can be removed on Pd/RGO/foam-Ni under optimum ECH conditions.A high-performance palladium (Pd) and reduced graphene oxide (RGO) composite electrode was prepared on foam-nickel (foam-Ni) via two-step electrodeposition processes. The scanning electron microscopic (SEM) observation showed that the obtained Pd/RGO/foam-Ni composite electrode displayed a uniform and compact morphology. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopic (XPS) analysis confirmed the successful deposition of Pd and RGO on nickel substrate. The cyclic voltammetric (CV) measurements indicated that the presence of RGO greatly enhanced the active surface area of Pd particles deposited on foam-Ni. The as-deposited Pd/RGO/foam-Ni electrode was applied to electrocatalytic hydrodechlorination (ECH) of 4-chlorophenol (4-CP). Various factors influencing the dechlorination of 4-CP such as dechlorination current, initial concentration of 4-CP, Na2SO4 concentration and initial pH were systematically investigated. The thermodynamic analysis showed that the dechlorination reaction of 4-CP at different temperatures followed the first-order kinetics and the activation energy for 4-CP dechlorination on Pd/RGO/foam-Ni electrode was calculated to be 51.96 kJ mol−1. Under the optimum conditions, the dechlorination efficiency of 4-CP could reach 100% after 60-min ECH treatment. Moreover, the prepared Pd/RGO/foam-Ni composite electrode showed good stability for recycling utilization in ECH of 4-CP.

The electrochemical behavior of ketoconazole (KC) on a multi-walled carbon nanotubes (MWCNTs)-modified glassy carbon (GC) electrode was investigated in this work. The result indicated that MWCNTs remarkably promoted the electrochemical response of KC on the GC electrode. To achieve a sensitive voltammetric determination of KC, experimental conditions such as solution pH, amount of MWCNTs, accumulation time as well as scan rate were systematically studied and optimized. Under optimized conditions, the differential pulse voltammetric (DPV) response on the MWCNTs-modified electrode was proportional to the KC concentration in the range of 1.0 × 10−6–3.0 × 10−5 mol L−1 with a detection limit of 4.4 × 10−7 mol L−1. Based on this MWCNTs-modified electrode, KC in a pharmaceutical drug (Ketoconazole®) was successfully determined without requirement of complicated sample pretreatment.