Various sensor-based immunoassay methods have been extensively developed for the detection of interleukin-6 (IL6), but most often exhibit low detection signals and low detection sensitivity, and are unsuitable for routine use. The aim of this work is to develop a simple and sensitive conductometric immunoassay for IL6 in human serum by using an organic/inorganic hybrid membrane-functionalized interface. Initially, thionine-bound 3,4,9,10-perylenetetracarboxylic acid was doped into colloidal alumina, then nanogold particles were immobilized onto the thionine surface, and then horseradish peroxidase-labeled anti-IL6 antibodies were conjugated on the nanogold surface. The organic/inorganic hybrid membrane provides a good microenvironment for the immobilization of biomolecules, enhanced the surface coverage of protein, and improved the sensitivity of the immunosensor. The performance and factors influencing the performance of the immunosensor were evaluated. The detection is based on the change in local conductivity before and after the antigen-antibody interaction in 0.02 M phosphate buffer solution (pH 6.8) containing 50 microM H(2)O(2), 0.01 M KI and 0.15 M NaC1. Under optimal conditions, the proposed immunosensor exhibited a wide linear range from 25 to 400 pg/ml towards IL6 with a relatively low detection limit of 5 pg/ml (S/N = 3). The stability, reproducibility and precision of the immunosensor were acceptable. 37 serum specimens were assayed by the developed immunosensor and standard enzyme-linked immunosorbent assay, respectively, and the results obtained were almost consistent. More importantly, the detection methodology provides a promising approach for other proteins or biosecurity.