Flow-injection immuno-bioassay for interleukin-6 in humans based on gold nanoparticles modified screen-printed graphite electrodes.

A flow-injection electrochemical immunoassay system based on a disposable immunosensor for the determination of interleukin-6 (IL-6) was proposed. The immunosensor was prepared by entrapping horseradish peroxidase (HRP)-labeled IL-6 antibody into gold nanoparticles-modified composite membrane at a screen-printed graphite electrode. With a non-competitive immunoassay format, the immunosensor was inserted in the flow system with an injection of sample, and the injected sample containing IL-6 antigen was produced transparent immunoaffinity reaction with the immobilized HRP-labeled IL-6 antibody. The formed antigen-antibody complex inhibited partly the active center of HRP, and decreased the immobilized HRP to H2O2 reduction. The performance and factors influencing the performance of the immunosensor were investigated. Under optimal conditions, the current change obtained from the labeled HRP relative to thionine-H2O2 system was proportional to the IL-6 concentration in the range of 5-100 ng L(-1) with a detection limit of 1.0 ng L(-1) (at 3delta). The flow-injection immunoassay system could automatically control the incubation, washing and measurement steps with acceptable reproducibility and good stability. Moreover, the proposed immunosensors were used to analyze IL-6 in human serum specimens. Analytical results of clinical samples show the developed immunoassay has a promising alternative approach for detecting IL-6 in the clinical diagnosis.