A ruthenium complex, pentaamine ruthenium [3-(2-phenanthren-9-yl-vinyl)-pyridine] (which we refer to as RuL in the text) generated in situ has been used as a sensitive and selective electrochemical indicator in DNA sensing. The complex incorporates dual functionalities with the Ru center providing a redox probe and the ligand (L) providing a fluorescent tag. The presence of the aromatic groups in the ligand endows the complex with an intercalative character and makes it capable of binding to double-stranded DNA (dsDNA) more efficiently than to single-stranded DNA (ssDNA). Combining spectroscopic and electrochemical techniques, we have elucidated the nature of the interactions. From these data we conclude that the binding mode is fundamentally intercalative. The ligand-based fluorescence allows characterization of the complex formation as well as for melting experiments to be carried out. The metal-based redox center is employed as an electrochemical indicator to detect the hybridization event in a DNA biosensor. The biosensor has been developed by immobilization of a thiolated capture probe sequence from Helicobacter pylori onto gold electrodes. With the use of this approach, complementary target sequences of Helicobacter can be quantified over the range of 106 to 708 pmol with a detection limit of 92+/-0.4 pmol and a linear correlation coefficient of 0.995. In addition, this approach allows the detection, without the need for a hybridization suppressor in solution, such as formamide, of not only a single mismatch but also its position in a specific sequence of H. pylori, due to the selective interaction of this bifunctional ruthenium complex with dsDNA.

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22Insulin sensors based on glassy carbon electrodes modified with nafion-multiwalled carbon 23 nanotubes decorated with nickel hydroxide nanoparticles (Ni(OH) 2 NPs/Nafion-24 MWCNTs/GC), were prepared by electrochemical deposition of Ni(OH) 2 NPs from a 25 dinuclear paddle-wheel Ni monothiocarboxylate complex on the MWCNTs/GC surface. 26The size and distribution of the Ni(OH) 2 NPs/Nafion-MWCNTs were characterized by 27 transmission electron microscopy (TEM). The results show that Ni(OH) 2 nanoparticles 28 were electrodeposited on the surface of carbon nanotubes. Moreover, the electrochemical 29 behavior of the modified electrodes in aqueous alkaline solutions of insulin was studied by 30 cyclic voltammetry and chronoamperometry. It was found that the as-prepared 31 nanoparticles have excellent electrocatalytic activity towards insulin oxidation due to their 32 special properties, reducing the overpotential and improving the electrochemical behavior, 33 compared to the bare GC electrode. Amperometry was used to evaluate the analytical 34 performance of modified electrode in the determination of insulin. Excellent analytical 35 features, including high sensitivity (5.0 A mol cm -2 μM -1 ), low detection limit (85 nM) and 36 wide dynamic range (up to 10.00 µM), were achieved under optimum conditions. 37 Moreover, these insulin sensors show good repeatability and a high stability after 38 successive potential cycling. Common substances such as ascorbic acid, uric acid and 39 acetaminophen do not interfere. Finally, the developed sensors have been applied to the 40 determination of insulin in pharmaceuticals and in human plasma. Efficient recoveries for 41 pharmaceuticals and human plasma demonstrate that the proposed methodology can be 42 satisfactorily applied to these types of samples.43 Page 3 of 37 A c c e p t e d M a n u s c r i p t 3 44 Keywords 45 Dinickel complexes, paddle-wheel complexes, nickel hydroxide nanoparticles, insulin 46 electrocatalysis.