Electrochemical immunosensor based on graphene–polyaniline composites and carboxylated graphene oxide for estradiol detection

A novel estradiol immunosensor based on graphene–polyaniline (GR–PANI) composites and carboxylated graphene oxide (GO) was developed. GR–PANI composites were used to enhance the electroactivity and stability of the electrode. The current response of the immunosensor was remarkably improved due to the synergistic effects of GR and PANI. Horseradish peroxidase–graphene oxide–antibody (HRP–GO–Ab) conjugates which were constructed by using the carboxylated GO as the carrier of the antibody and horseradish peroxidase as the label improved the catalytic activity for hydrogen reduction of the electrode. A competitive immunoassay was facilitated between 17β-estradiol and the HRP–GO–Ab conjugates. Based on this competitive immunoassay, the immunosensor showed a wide linear response to estradiol in the range 0.04–7.00 ng/mL and a limit of detection of 0.02 ng/mL (S/N = 3). The developed immunosensor was successfully applied to the detection of estradiol in real samples.