A new electrochemical sensor based on copper nanoparticles (Cu NPs) and multi-walled carbon nanotubes (MWCNTs) was fabricated for the determination of hydroquinone (HQ). A type of spotty-like Cu NP located on MWCNT (Cu–MWCNT) nanocomposites was synthesized with a microwave-assisted method. The morphology and phase of Cu–MWCNTs nanocomposite were characterized using scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed to characterize the electrochemical performance and surface characteristics of the as-prepared sensor. The composite electrode exhibited excellent activity with increased electrochemical signals towards the redox of HQ, owing to the synergistic effect of Cu NPs and MWCNTs. Under the optimized conditions, the linear response range was from 0.10 to 100 μM for HQ. The detection limit for HQ was as low as 0.04 μM. Moreover, the modified electrode presented a good reproducibility and excellent anti-interference performance. The performance of the developed sensor for the detection of HQ was evaluated in practical samples with satisfying results.

ZnO crystals were synthesized by a hydrothermal decomposition process in the presence of poly(vinylpyrrolidone) as the surfactant, then characterized by scanning electron microscopy and X-ray diffraction. The composites of flowerlike ZnO combined with poly(p-aminobenzene sulfonic acid) (p-ABSA) were immobilized on a glassy carbon electrode for constructing a sensitive electrochemical sensor. The electrocatalytic response to PHZ on the prepared sensor was measured using cyclic voltammetry and differential pulse voltammetry (DPV) in PBS buffer (pH 8.0). The fabricated sensor was successfully used for the detection of promethazine hydrochloride (PHZ) in a 0.10 M phosphate buffer solution (PBS) at pH 8.0. Under optimal conditions, the linear concentration range of PHZ obtained at p-ABSA/ZnO composite film using DPV technique was 0.01 μM to 59.84 μM (R = 0.997) and the detection limit was 0.004 μM at S/N = 3. Furthermore, the prepared sensor displayed voltammetric responses with excellent reproducibility, high sensitivity and stability for PHZ. Therefore, the p-ABSA/ZnO composite film has become a promising application for quantitative determination of PHZ.

The magnetic γ-Fe2O3 material was prepared in a new way and characterized by transmission electron microscopy and X-ray diffraction. It was modified on a glass carbon electrode (GCE) coated with gold film to form nano γ-Fe2O3/Au/GCE. The electrooxidation of hydrazine has been deeply explored with the resulting electrode in 0.1 M phosphate-buffered saline (pH 7.0). The affecting factors containing pH of supporting electrolyte, scan rate, deposition time, amount of γ-Fe2O3, and possible interferences were investigated, and the oxidation mechanisms of hydrazine on the γ-Fe2O3/Au/GCE were also explored. The amperometric response to hydrazine is linear in the range of 0.02 to 11 μM, and the detection limit is 6 nM at a SNR of 3. The prepared sensor exhibited good sensitivity, stability, and lower detection limit for the determination of hydrazine injection.

This work described a novel sensor for detection of l-tryptophan (Trp) by electrodeposition of gold nanoparticles (AuNPs) onto the poly(alizarin red S) film pre-cast on a glassy carbon electrode (GCE). Alizarin red S (ARS) was deposited on the surface of the GCE by electropolymerization, and gold nanoparticles (AuNPs) were attached onto the poly(ARS) film by electrodeposition, forming an AuNPs–PARS nanocomposite film-modified GCE (AuNPs–PARS/GCE). Then electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were used to characterize modified electrodes. The Nyquist diagrams of EIS indicated that the PARS film and AuNPs were successfully immobilized on the surface of GCE, and the electron transfer resistance value of electrode changed efficiently. The SEM image showed that the immobilized AuNPs were spherical in shape. The AuNPs–PARS/GEC displayed excellent amperometric response for Trp. The amperometric responses have two linear ranges from 0.02 to 0.5 μM and 0.5 to 20.0 μM, with sensitivities of 1.63(±0.08) and 0.21(±0.01) μAμM−1, respectively. Its detection limit was 6.7 nM at a signal-to-noise ratio of 3. The proposed method was applied to determine Trp.

We have developed a highly sensitive and selective sensor for lead(II) ions. A glassy carbon electrode was modified with Fe3O4 nanospheres and multi-walled carbon nanotubes, and this material was characterized by scanning electron microscopy and X-ray diffraction. The electrode displays good electrochemical activity toward Pb(II) and gives anodic and cathodic peaks with potentials at −496 mV and −638 mV (vs. Ag/AgCl) in pH 6.0 solution. The sensor exhibits a sensitive and fairly selective response to Pb(II) ion, with a linear range between 20 pM and 1.6 nM, and a detection limit as low as 6.0 pM (at a signal-to noise ratio of 3). The sensor was successfully applied to monitor Pb(II) in spiked water samples.

Shuttle-like Fe2O3 nanoparticles (NPs) were prepared by microwave-assisted synthesis and characterized by scanning electron microscopy and X-ray diffraction. The NPs were immobilized on a glassy carbon electrode and then covered with dsDNA. The resulting electrode gives a pair of well-defined redox peaks for Pb(II) at pH 6.0, with anodic and cathodic peak potentials occurring at −0.50 V and −0.75 V (vs. Ag/AgCl), respectively. The amperometric response to Pb(II) is linear in the range from 0.12 to 40 nM, and the detection limit is 0.1 nM at a signal-to-noise ratio of 3. The sensor exhibits high selectivity and reproducibility.

Hollow CuO/Fe2O3 hybrid microspheres with small uniform holes were synthesized using a convenient hydrothermal method and were applied to fabricated an amperometric sensor for kojic acid. The resulting materials were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) and then were immobilized into the chitosan (Chi) matrix onto a glassy carbon electrode to obtain CuO/Fe2O3–Chi/GCE. The potential utility of the constructed electrodes were demonstrated by applying them to the analytical determination of kojic acid concentration. The electrochemical behavior of kojic acid on CuO/Fe2O3–Chi/GCE was explored. The modified electrode displayed excellent amperometric response for kojic acid with a linear range from 0.2 μM to 674 μM with a detection limit of 0.08 μM at a signal-to-noise ratio of 3. In order to validate feasibility, the CuO/Fe2O3–Chi/GCE has been used for quantitative detecting kojic acid in real samples.

A DNA biosensor was constructed by immobilizing a 20-mer oligonucleotide probe and hybridizing it with its complementary oligomer on the surface of a glassy carbon electrode modified with gold nanoparticles. The properties of the biosensor and its capability of recognizing its complementary sequence were studied by electrochemical impedance spectroscopy. The oxidative stress caused by cadmium ions can be monitored by differential pulse voltammetry using the cobalt(III)tris(1,10-phenanthroline) complex and methylene blue as electrochemical indicators. The biosensor is capable of indicating damage caused by Cd(II) ions in pH 6.0 solution. The results showed that the biosensor can be used for rapid screening for DNA damage.

Two different hydrogen peroxide sensors were constructed with Ni/Al and Co/Al layered double hydroxides (LDHs) modified glassy carbon electrodes (GCE). Ni (Co)/Al-LDHs were synthesized by electrochemical method and were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The advantages and shortcoming of the two hydrogen peroxide sensors were described in detail. Compared to Co/Al-LDHs modified electrode, sensors fabricated by Ni/Al-LDHs showed quicker heterogeneous electron transfer rate constants (ks), lower detection and better reproducibility. But Co/Al-LDHs modified electrode held the advantages of wider linear range and higher sensitivity. Further more, the different catalytic redox mechanisms of hydrogen peroxide on the Ni/Al/GCE and Co/Al/GCE were firstly comparatively explored.

Copper (II) complex of formulation [Cu–Phen–Tyr](H2O)](ClO4) (Phen = 1,10-phenanthroline, l-Tyr = l-tyrosine), has been prepared, and their induced DNA oxidative cleavage activity studied. The complex binds to DNA by intercalation, as deduced from the absorption and fluorescence spectral data. Scatchard plots constructed from the absorption titration data gave binding constant 2.44 × 104 M−1 of base pairs. Extensive hypochromism, broadening, and red shifts in the absorption spectra were observed. Upon binding to DNA, the fluorescence from the DNA–ethidium bromide system was efficiently quenched by the copper (II) complex. Stern–Volmer quenching constant 0.61 × 103 M−1 obtained from the linear quenching plots. [Cu–Phen–Tyr] complex efficiently cleave the supercoiled DNA to its nicked circular form with gallic acid as biological reductant at appropriate complex concentration. The gallic acid as reductant could observably improve copper (II) complex to DNA damage. The pseudo-Michaelis–Menten kinetic parameters (kcat, KM) were calculated to be 1.32 h−1 and 5.46 × 10−5 M for [Cu–Phen–Tyr] complex. Mechanistic studies reveal the involvement of superoxide anions and hydroxyl radical (HO·) as the reactive species under an aerobic medium.

The oxidative DNA damage by copper (II) complexes in the presence of chlorogenic acid was explored using agarose gel electrophoresis. The extent of pBR322 DNA damage was enhanced significantly with increasing concentration of [Cu-phen-Thr] complex and incubation time. A fluorescence quenching activity of calf thymus DNA–EB was observed more remarkably with chlorogenic acid than without chlorogenic acid. The fluorescence measurements suggested that [Cu-phen-Thr] complex not only can bind to DNA by intercalation but also can damage the double strand DNA in the presence of chlorogenic acid. Further, 8-hydroxy-2′-deoxyguanosine, a biomarker of DNA oxidative damage was determined by electrochemical method. The control experiments revealed that the structure of copper (II) complexes affected capability of complex to DNA damage. The planar structure copper (II) complex showed high efficiency to DNA damage. The chlorogenic acid as biological reductant could improve copper (II) complex to DNA damage. A mechanism on [Cu-phen-Thr] complex to DNA damage in the presence of chlorogenic acid was proposed.

The interaction of taurine–salicylaldehyde Schiff base copper(II) (Cu(TSSB)22+) complex with DNA was explored by using UV–vis, fluorescence spectrophotometry, and voltammetry. In pH 7.4 Tris–HCl buffer solution, the binding constant of the Cu(TSSB)22+ complex interaction with DNA was 3.49 × 104 L mol−1. Moreover, due to the fluorescence enhancing of Cu(TSSB)22+ complex in the presence of DNA, a method for determination of DNA with Cu(TSSB)22+ complex as a fluorescence probe was developed. The fluorescence spectra indicated that the maximum excitation and emission wavelength were 389 nm and 512 nm, respectively. Under optimal conditions, the calibration graphs are linear over the range of 0.03–9.03 μg mL−1 for calf thymus DNA (CT-DNA), 0.10–36 μg mL−1 for yeast DNA and 0.01–10.01 μg mL−1 for salmon DNA (SM-DNA), respectively. The corresponding detection limits are 7 ng mL−1 for CT-DNA, 3 ng mL−1 for yeast DNA and 3 ng mL−1 for SM-DNA. Using this method, DNA in synthetic samples was determined with satisfactory results.

Shuttle-like copper oxide (CuO) was prepared by a hydrothermal decomposition process. The resulting material was characterized by scanning electron microscopy and X-ray diffraction. It was then immobilized on the surface of a glassy carbon electrode modified with a film of poly(thionine). A pair of well-defined and reversible redox peaks for Hg(II) was observed with the resulting electrode in pH 7.0 solutions. The anodic and cathodic peak potentials occurred at 0.260 V and 0.220 V (vs. Ag/AgCl), respectively. The modified electrode displayed excellent amperometric response to Hg(II), with a linear range from 40 nM to 5.0 mM and a detection limit of 8.5 nM at a signal-to-noise ratio of 3. The sensor exhibited high selectivity and reproducibility and was successfully applied to the determination of Hg(II) in water samples.

Phytic acid (PA) with its unique structure was attached to a glassy carbon electrode (GCE) to form PA/GCE modified electrode which was characterized by electrochemical impedance. The electrochemical behavior of cytochrome c (Cyt c) on the PA/GCE modified electrode was explored by cyclic voltammetry and differential pulse voltammetry. The Cyt c displayed a quasi-reversible redox process on PA modified electrode pH 7.0 phosphate buffer solution with a formal potential (E0′) of 57 mV (versus Ag/AgCl). The peak currents were linearly related to the square root of the scan rate in the range of 20–120 mV·s−1. The electron transfer rate constant was determined to be 12.5 s−1. The PA/GCE modified electrode was applied to the determination of Cyt c, in the range of 5 × 10−6 to 3 × 10−4 M, the currents increase linearly to the Cyt c concentration with a correlation coefficient 0.9981. The detection limit was 1 × 10−6 M (signal/noise = 3).

Polyacrylamide (PAM), sodium dodecyl sulfate (SDS) and cytochrome c (Cyt c) were immobilized on the surface of a glass carbon electrode (GCE), respectively, to form a Cyt c /SDS/PAM/GCE. The modified electrode was characterized with the electrochemical impedance. The direct electrochemical behaviors of Cyt c on SDS/PAM/GCE were obtained by using cyclic voltammetry. A pair of well-defined and reversible redox peaks could be observed in a 0.10 M pH 7.0 phosphate buffer solution. The anodic and cathodic peak potentials of Cyt c were at 0.051 V and − 0.003 V (vs. Ag/AgCl), respectively. The Cyt c on SDS/PAM/GCE exhibited well electrocatalytic activity to reduction of nitric oxide. The relative electrochemical parameters were obtained. The resulted electrode displayed a rapid amperometric response to the reduction of nitric oxide. The catalytic current is linear to the nitric oxide concentration in the range of 8.0 × 10− 7 M to 9.5 × 10− 5 M and the detection limit was 1.0 × 10− 7 M (Signal/Noise = 3). The proposed biosensor could be used to detect quantitatively nitric oxide.

Electrochemical behavior of gallic acid (GA) and interaction with calf thymus DNA were explored with cyclic voltammetry and differential pulse voltammetry (DPV) in acetate buffer solution using a glassy carbon electrode (GCE) and a DNA modified GCE (DNA/GCE), respectively. A pair of redox peaks of GA appeared in the range of −0.05 ∼ +0.55 V. The anodic peak potential (Epa) was at +0.329 V and the cathodic peak potential (Epc) was at +0.211 V. The oxidation peak potential of GA was dependent on pH of solution. With adding DNA into GA solution, the peak current value of GA decreased gradually, and the peak potential shifted positively. The electrochemical parameters (diffusion coefficient D, electron transfer coefficient α, and standard rate constant ks) of free GA and binding compounds were obtained. The peak current of GA increased with the time of DNA/GCE being immersed in the GA solution. The results showed that GA could interact with DNA molecule by intercalation mode. The GA could mediate the double stranded DNA (ds-DNA) in situ damage, which was directly detected according to the anodic signal of the DNA purine bases with DPV.

Silver metal nanowires were prepared with assembling Ag ions onto DNA template and reducing metal ions by a kind of electrochemical method. Silver metal nanowires were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The diameter of the nanowires is about 50 nm and the length of the nanowires is about 6.0 μm. The affection of experimental conditions on the formation of the silver nanowires was examined.

ZnO crystals were synthesized by a hydrothermal decomposition process in the presence of poly(vinylpyrrolidone) as the surfactant, then characterized by scanning electron microscopy and X-ray diffraction. The composites of flowerlike ZnO combined with poly(p-aminobenzene sulfonic acid) (p-ABSA) were immobilized on a glassy carbon electrode for constructing a sensitive electrochemical sensor. The electrocatalytic response to PHZ on the prepared sensor was measured using cyclic voltammetry and differential pulse voltammetry (DPV) in PBS buffer (pH 8.0). The fabricated sensor was successfully used for the detection of promethazine hydrochloride (PHZ) in a 0.10 M phosphate buffer solution (PBS) at pH 8.0. Under optimal conditions, the linear concentration range of PHZ obtained at p-ABSA/ZnO composite film using DPV technique was 0.01 μM to 59.84 μM (R = 0.997) and the detection limit was 0.004 μM at S/N = 3. Furthermore, the prepared sensor displayed voltammetric responses with excellent reproducibility, high sensitivity and stability for PHZ. Therefore, the p-ABSA/ZnO composite film has become a promising application for quantitative determination of PHZ.