The biosensors based on DNA aptamers immobilized by electrostatic adsorption onto electropolymerized Methylene Green (MG)) imprinted with DNA have been developed and examined for thrombin detection in the range from 1 nM to 1 mM using electrochemical impedance spectroscopy (EIS) and potentiometry. The participation of DNA in MG electropolymerization and imprints formation was proved by measurements of EIS and redox signals of neutral and charged indicators. Changes in the morphology of the layers were examined using atomic force microscopy (AFM). The addition of DNA at the electropolymerization stage followed by acidic treatment of the coating significantly improved the efficiency of electrostatic adsorption of the DNA aptamer and provided sensitive detection of thrombin with limit of detection 0.5 nM.

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We report the development of a novel quartz crystal microbalance immunosensor with the simultaneous measurement of resonance frequency and motional resistance for the detection of antibodies to double-stranded DNA (dsDNA). The immobilization of poly(L-lysine) and subsequent complexation with DNA resulted in formation of a sensitive dsDNA-containing nanofilm on the surface of a gold electrode. Atomic force microscopy has been applied for the characterization of a poly(L-lysine)-DNA film. After the blocking with bovine serum albumin, the immunosensor in flow-injection mode was used to detect the antibodies to dsDNA in purified protein solutions of antibodies to dsDNA and to single-stranded DNA, monoclonal human immunoglobulin G, DNase I and in blood serum of patients with bronchial asthma and systemic lupus erythematosus. Experimental results indicate high sensitivity and selectivity of the immunosensor.

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