Here, gold/Ni(OH)2 nanocomposites supported on reduced graphene oxide (Au/Ni(OH)2/rGO) were synthesized by a one-step wet-chemical method, which were characterized by TEM, IR, SEM, XPS and XRD techniques. The experiments demonstrated that the as-prepared nanocomposites showed a collection of unique characteristics, for example, high loading and homogeneous distribution. The nanocomposite modified electrode was prepared based on a glassy carbon substrate, which possessed excellent electrocatalytic activity to the redox reaction of catechol (CC). Under optimal conditions, the concentration of CC showed a linear relationship with its response current from 0.4 μM to 33.8 μM with a detection limit (S/N = 3) of 0.13 μM. The proposed sensor was successfully applied to detect CC in water with satisfactory results, which exhibited excellent selectivity and sensitivity, with potential applications.

Carbon nanoparticles (CNs) were successfully synthesized at room temperature, which were used to construct a novel electrochemical sensor combined with multi-walled carbon nanotubes and chitosan. The proposed CN-based sensor showed excellent electrocatalytic performance for the oxidation of nitrite and the redox of hydrogen peroxide. Based on this, new methods for the determination of nitrite and hydrogen peroxide were established. Compared with other reports, the methods were sensitive, accurate and rapid with good reproducibility, stability and certain anti-interference ability, which can be used for the measurement of nitrite and hydrogen peroxide.

•Multiwalled carbon nanotubes/polydopamine/gold nanoparticles composite (MWCNTs/PDA/AuNPs) was synthetized successfully.•A novel electrochemical sensor for simultaneous determination of hydroquinone and catechol based on MWCNTs/PDA/AuNPs and chitosan was developed.•The peak potential of the oxidation peaks of HQ and CC were at 192 mV and 297 mV, respectively, indicating an anodic ΔEp of 105 mV, which is wide enough to separate the two components.•The sensor showed wide linear responses for HQ and CC with detection limits of 35 nM and 47 nM, respectively.In this work, a highly sensitive and selective electrochemical sensor based on multiwalled carbon nanotubes/polydopamine/gold nanoparticles composites (MWCNTs/PDA/AuNPs) and chitosan (CS) was developed, which was used for simultaneous determination of hydroquinone (HQ) and catechol (CC) derived from a large specific area of MWCNTs and superexcellent electroconductibility of AuNPs. It was found that HQ and CC could be completely separated on the electrode using cyclic voltammetry and differential pulse voltammetry technique under optimal conditions. The proposed sensor based on MWCNTs/PDA/AuNPs exhibited linear responses for HQ and CC from 0.1 to 10 μmol L−1 with detection limits (S/N = 3) of 0.035 μmol L−1 and 0.047 μmol L−1, respectively. In addition, the modified electrode was successfully implemented in the simultaneous determination of CC and HQ in tap and lake water samples. And compared with other methods, this sensor exhibited good sensitivity, stability and reproducibility.

In this work, water-soluble ZnS:Ni/ZnS quantum dots (QDs) with core/shell structure were obtained successfully using mercaptoacetic acid as dressing agent, which were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy and transmission electron microscopy. A highly sensitive and stable electrochemical sensor was developed by immobilizing L-cysteine and ZnS:Ni/ZnS QDs on the surface of glassy carbon electrode. The sensor showed excellent catalytic activity to catechol (CC). Experimental results showed that the oxidation peak current of CC was linear over the range from 0.5 to 100 μM, and the detection limit (S/N = 3) for CC was 32 nM. The developed sensor was successfully used for determination of CC in lake water samples with satisfactory recoveries.

•ZnS:Ni/ZnS QDs were synthesized easily with nontoxic.•It shows fluorescent characteristic with good water-solubility and stability.•ZnS:Ni/ZnS QDs was firstly used as fluorescent probe to detect CPZ–SBT.•This novel method is sensitive with good selectivity and a low detection limit.ZnS:Ni quantum dots (QDs) have been synthesized via a water-soluble route, which were coated by ZnS shell through surface modification to give ZnS:Ni/ZnS QDs. The QDs were characterized by atomic force microscope, X-ray diffraction, infrared spectrometry and fluorescent spectrometry. Then, a novel method for the determination of cefoperazone–sulbactam (CPZ–SBT) in aqueous solutions has been developed based on the enhancement of fluorescence of ZnS:Ni/ZnS QDs in the presence of CPZ–SBT. Under the optimal conditions, the enhanced fluorescence intensity (ΔF) was proportional to CPZ–SBT concentration in the range of 8.0 × 10−6–1.0 × 10−4 g/L with a detection limit of 1.0 × 10−7 g/L. The method was employed for the determination of CPZ–SBT in sample to give satisfactory result. Compared with others, this method was more sensitive, fast and simple with low limit detection.Graphical abstract