In this study, a novel mercapto-terminated trinuclear Ni(II) complex (Ni3) was synthesized and used as an electrocatalyst for the detection of hydrazine hydrate in real water samples. The as-prepared Ni3 molecule possesses six thiomethyl groups at its periphery and these SCH3 groups can react with Au electrodes to immobilize the Ni3 molecules on their surface through the formation of a self-assembled monolayer. The Ni3-modified Au electrode (Ni3/Au) demonstrates excellent electrocatalytic activity for the oxidation of hydrazine hydrate through a significant decrease in overpotential. The chronoamperometry study shows a diffusion coefficient (D) of 5.82 × 10−5 cm2 s−1 and a catalytic rate constant of 8.57 × 103 M−1 s−1. Using the square wave voltammetry (SWV) technique, this Ni3/Au electrode based hydrazine hydrate sensor exhibits a high sensitivity in quantitative analysis, and its detection limit could be as low as ∼0.07 μM with linearity ranging from 0.2 to 50 μM. In addition, due its good reproducibility, anti-interference performance, and long-term stability, the proposed sensor is capable of detecting trace levels of hydrazine hydrate in real water samples.

•A mercapto-terminated hexanuclear Fe(III) complex based novel sensor was prepared.•The sensor was applied to detect DA in the presence of UA.•Quantification in drug samples is accomplished using this novel sensor.In this study, a novel mercapto-terminated hexanuclear iron(III) cluster [Fe6O2(OH)2(O2CC6H4SCH3)10(hep)2]·CH3CN·CH2Cl2 [hep=2-(2-hydroxyethyl) pyridine] (Fe6) modified Au electrode was fabricated, having highly sensitive dopamine (DA) detection capabilities. In such Fe6 molecules, 10 thiomethyl groups are located at the periphery of the cluster, which enable the Fe6 molecules to self-assemble onto the surface of Au electrodes through the formation of Au–S bonds. The as-prepared Fe6-modified Au electrode (Au/Fe6) exhibits excellent electrocatalytic activity for the oxidation of dopamine (DA) in PBS with a diffusion coefficient of 3.12×10−5 cm2/s. Using the square wave voltammetry (SWV) technique, the calibration curve for DA determination was obtained in the range of 0.2 to 30 μM, and the detection limit for DA was ~0.07 μM. Furthermore, the modified electrode can accurately separate the DA signal from the interfering effect of uric acid (UA), thus providing simultaneous detection of DA and UA in their binary mixtures. This electrode can be reliably used to assay DA in its real drug composition.

A shape-controllable, highly ordered, two-dimensional gold cavity array (GCA) electrode was prepared by electrodeposition using a closely packed monolayer of 1.2 μm-diameter polystyrene spheres as a template and was characterized by FESEM and XRD. A significant enhancement for the electrooxidation of dopamine at this nanostructured electrode was found due to the increased amount of the active surface area. By electropolymerizing a poly(metanilic acid) thin film on its surface, the enhanced electrochemical properties of the GCA electrode were maintained, and the antifouling property was improved. The SWV technique was used for the trace determination of DA, and the dependence of current vs. concentration was linear from 0.2 to 100 μM with a regression coefficient of 0.9988, and the detection limit of DA was ∼0.08 μM. Furthermore, the signals of DA and UA can be well distinguished at this poly(metanilic acid) modified GCA electrode. The proposed method was applied to the selective and precise analysis of DA in commercial injections.

A simple and sensitive method, based on surface-enhanced Raman scattering (SERS), for immunoassay and label-free protein detection is reported. A series of bowl-shaped silver cavity arrays were fabricated by electrodeposition using a self-assembled polystyrene spheres template. The reflection spectra of these cavity arrays were recorded as a function of film thickness, and then correlated with SERS enhancement using sodium thiophenolate as the probe molecule. The results reveal that SERS enhancement can be maximized when the frequency of both the incident laser and the Raman scattering approach the frequency of the localized surface plasmon resonance. The optimized array was then used as the bottom layer of a silver nanoparticle–protein–bowl-shaped silver cavity array sandwich. The second layer of silver was introduced by the interactions between the proteins in the middle layer of the sandwich architecture and silver nanoparticles. Human IgG bound to the surface of this microcavity array can retain its recognition function. With the Raman reporter molecules labeled on the antibody, a detection limit down to 0.1 ng mL−1 for human IgG is easily achieved. Furthermore, the SERS spectra of label-free proteins (catalase, cytochrome C, avidin and lysozyme) from the assembled sandwich have excellent reproducibility and high quality. The results reveal that the proposed approach has potential for use in qualitative and quantitative detection of biomolecules.