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a b s t r a c tTiO 2 -graphene nanocomposite was prepared by hydrolysis of titanium isopropoxide in colloidal suspension of graphene oxide and in situ hydrothermal treatment. It provides an efficient and facile approach to yield nanocomposite with TiO 2 nanoparticles uniformly embedded on graphene substrate. The electrochemical behavior of adenine and guanine at the TiO 2 -graphene nanocomposite modified glassy carbon electrode was investigated. The results show that the incorporation of TiO 2 nanoparticles with graphene significantly improved the electrocatalytic activity and voltammetric response towards these species comparing with that at the graphene film. The TiO 2 -graphene based electrochemical sensor exhibits wide linear range of 0.5-200 M with detection limit of 0.10 and 0.15 M for adenine and guanine detection, respectively. The excellent performance of this electrochemical sensor can be attributed to the high adsorptivity and conductivity of TiO 2 -graphene nanocomposite, which provides an efficient microenvironment for electrochemical reaction of these purine bases.

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A novel experimental methodology based on a Prussian blue (PB) and gold nanoparticles (AuNPs) modified carbon ionic liquid electrode (CILE) was developed for use in a label-free amperometric immunosensor for the sensitive detection of human immunoglobulin G (HIgG) as a model protein. The CILE was fabricated by using the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate as binder. Controllable electrodeposition of PB on the surface of the CILE and coating with 3-aminopropyl triethylene silane (APS) formed a film with high electronic catalytic activity and large surface area for the assembly of AuNPs and further immobilization of HIgG antibody. The electrochemistry of the formed nanocomposite biofilm was investigated by electrochemical techniques including cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. The HIgG concentration was measured through the decrease of amperometric responses in the corresponding specific binding of antigen and antibody. The decreased differential pulse voltammetric values were proportional to the HIgG concentration in two ranges, 0.05-1.25 ng mL(-1) and 1.25-40 ng mL(-1), with a detection limit of 0.001 ng mL(-1) (S/N = 3). This electrochemical immunoassay combined the specificity of the immunological reaction with the sensitivity of the AuNPs, ionic liquid, and PB amplified electrochemical detection and would therefore be valuable for clinical immunoassays.

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