Electroactive Metal Complexes: Design, Immobilization And Electrochemical Sensing Applications

The accurate, rapid and low-cost determination of hydrogen peroxide, nitrite and iodate, represents an especially attractive topic that relating with food, pharmaceutical, environmental and industrial research. Comparing with traditional determination methods such as chromatography, spectrophotometry, capillary electrophoresis and chemiluminescence, the electrochemical sensor has been an extremely important determination technology of analysis field due to its cost-effectiveness, fastresponse, high sensitivity, ease of miniaturization and automation, etc. We prepared many metal-complex through constructure differently functionalized terminal group, then fixed to the surfaces of electrodes using different methods, thus fabricated a serise of new types of electrochemical sensors based on metal-complex. The structure, composition and property of the constructed electrochemical sensors based on metal-complex were investigated by various morphology and surface analysis techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), etc. The electrochemical determination performances towards hydrogen peroxide, nitrite and iodate were explored through cyclic voltammetry (CV), differential pulse voltammogram (DPV) and amperometric i-t curve (i-t), etc. The main results and conclusions are summarized as follows:1. An electroactive DTPA-FeⅢ based H2O2 electrochemical sensor based on a nonelectrocatalytic mechanism. The electroactive iron(Ⅲ) diethylenetriaminepentaacetic acid (DTPA-FeⅢ) complex is immobilized on the cysteamine (cys) modified nanoporous gold (NPG) films by covalent method. The immobilized DTPA-FeⅢ complex quickly communicates an electron with the electrode. Upon addition of hydrogen peroxide, however, hydrogen peroxide inhibits the direct electron transfer of the DTPA-FeⅢ complex due to the generation of nonelectroactive DTPA-FeⅢ-H2O2 complex. Based on quenching mechanism, the first hydrogen peroxide electrochemical sensor based on a nonelectrocatalytic mechanism is developed. The novel hydrogen peroxide electrochemical sensor has the ultralow detection limit (1.0×10-14 mol L-1) and wide linear range (1.0×10-13 to 1.0×10-8 mol L-1) with excellent reproducibility and stability.2. The coordination immobilization of Ru(Ⅲ) ions on phosphonate functionalized gold nanoparticles and its application in electrochemical sensing. The phosphonate functionalized Au-NPs (P-Au-NPs) was synthesized by using vinylphosphonic acid (VPA) as the reducing agent and stabilizing agent. The morphology, composition, and structure of P-Au-NPs were fully characterized by various spectroscopy techniques. The resultant P-Au-NPs showd a remarkable colloidal stability, which likely arises from strong electrostatic effect of negatively charged phosphonate groups and the extremely hydrophilic property of phosphonate groups. In addition, the as-prepared P-Au-NPs effectively bind RuⅢ ion via coordination interaction, which can be used to construct an iodate amperometric sensor with the fast response (<3 s), wide linear range (9.90×10-8 to 1.89×10-3 mol L-1) and low detection limit (2.98×10-8 mol L-1) under applied potential of 0.1 V.3. The coordination immobilization of Ru(Ⅲ) ions on surfaces of PAH functionalized gold nanodendrites and its application in electrochemical sensing. The three-dimensional polyallylamine (PAH) functionalized gold nanodendrites (PAH-3D-Au-NDs) were successfully synthesized via a simple one-step electrodeposition method. Scanning electron microscopy, transmission electron microscopy, energy dispersive spectrum mapping and X-ray photoelectron spectroscopy measurements were used to characterize the morphology, structure, and composition of PAH-3D-Au-NDs. The PAH-3D-Au-NDs were then used as the functional interface to effectively immobilize the RuⅢ ion via coordination interaction between RuⅢ ion and polyallylamine. The obtained RuⅢ/PAH-3D-Au-NDs/Au electrode showed excellent electrocatalytic activity towards iodate reduction. With the use of PAH-3D-Au-NDs, the proposed iodate electrochemical sensor displayed the fast response (<3 s), wide linear range (4.99×10-8～8.50×10-4 mol L-1) and low detection limit (1.66×10-8 mol L-1) under applied potential of 0.2 V.4. An electroactive EDTMP-RuⅢ on PAH functionalized carbon nanotube multilayer films:self-assembly and its application in electrochemical sensing. On the basis of the electrostatic and donor-acceptor interactions between carboxylated multiwalled carbon nanotubes (MWCNT-COOH) and polyallylamine hydrochloride (PAH), PAH functionalized MWCNT multilayer films ({PAH/MWCNT-COOH}n) were readily formed on a glassy carbon (GC) electrode surface through a layer-by-layer self-assembly method. Then, the PAH functionalized MWCNT multilayer films were used as a functional interface to effectively immobilize the ruthenium(Ⅲ) ethylenediamine-tetramethylene phosphonate (EDTMP-RuⅢ) complex through the strong electrostatic and/or hydrogen bonding interactions between -NH2 and- PO3H2 groups. The immobilized EDTMP-RuⅢ complex could directly exchange electrons with the substrate electrode and showed excellent electrocatalytic activity towards iodate reduction, which possess the fast response (<3 s), wide linear range (8×10-8 to 2.3×10-4 mol L-1) and low detection limit (3×10-8 mol L-1) under applied potential of 0.1 V.5. An electroactive CoPcF on MWCNTs:self-assembly and its application in electrochemical sensing. The soluble cobalt phthalocyanine functionalized multiwalled carbon nanotubes (MWCNTs) are synthesized by π-π stacking interaction between tetrakis (3-trifluoromethylphenoxy) phthalocyaninato cobalt(II) (CoPcF) complex and MWCNTs. The physical properties of CoPcF-MWCNTs hybrids are evaluated using spectroscopy (UV-vis, XPS, and Raman) and electron microscopy (TEM and SEM). Subsequently, an amperometric nitrite electrochemical sensor is designed by immobilizing CoPcF-MWCNTs hybrids on the glassy carbon electrode. The immobilized CoPcF complex shows the fast electron transfer rate and excellent electrocatalytic activity for the oxidation of nitrite, which possess the fast response (<3 s), wide linear range (9.6×10-8 to 3.4×10-4 mol L-1) and low detection limit (6.2×10-8 mol L-1) under applied potential of 0.8 V.