An impedance immunosensor for the detection of the phytohormone abscisic acid
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The phytohormone abscisic acid (ABA) is the major player in mediating the adaptation of plants to stress. Previously developed phytohormonal biosensors usually employed indirect detection of the products of conjugated oxidase reactions. A label-free electrochemical impedance immunosensor for ABA detection was developed using an anti-ABA antibody adsorbed directly on a porous nanogold film. The film was produced electrochemically on a glassy carbon electrode in 0.008 mol/L hydrogen tetrachloroaurate solution containing 0.004 mol/L lead acetate with an applied potential of −0.5 V (versus Ag/AgCl) for 50 s. The anti-ABA antibody was immobilized onto the porous nanogold through electrostatic adsorption and covalent conjugation. Electrochemical impedance spectroscopy was used to characterize the successful construction of the porous nanogold film and the stepwise modification of the glassy carbon electrode. The concentration increase of the antigen brought about a decrease of the interfacial electron transfer, which also meant an increase of the impedance signal. The experimental parameters pH, antibody incubation time, and antibody concentration were optimized. The results showed significant linearity R = 0.9942, with the content of ABA in the range 0.5–5,000 ng/mL with a detection limit at about 0.1 ng/mL.
KeywordsImpedance immunosensor Abscisic acid Immunoassay Porous nanogold
This work was supported by the National Natural Science Foundation of China (grants nos. 30670190 and 30600049), Hunan Provincial Science and Technology Key Project (grants nos. 2007FJ2003 and 2006NK1001), and the National Commonweal Research Project of China for Quality Supervision, Inspection and Quarantine (grant no. 2007GYB146).
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