Renewable amperometric immunosensor for complement 3 (C3) assay in human serum

A renewable electrochemical immunosensor has been developed for the determination of complement 3 (C3) in human serum. It is based on a paraffin–graphite–complement 3 antiserum biocomposite, which needs no additional curing. The analytical sample containing sought-for C3 was mixed with C3 labeled with horseradish peroxidase (HRP) to form the incubation solution. A competitive binding assay was realized by dipping the biocomposite immunosensor into the incubation mixture. After rinsing away the excess of HRP–C3, the amount of HRP fixed on the sensor surface was determined amperometrically, the current signal was inversely proportional to the amount of sought-for C3 in the incubation mixture. Assay conditions were optimized including the loading of C3 antiserum in the biocomposite, the amount of labeled C3 in incubation solution, incubation time and temperature. Using o-aminophenol (o-AP) as a substrate, amperometric detection at −150 mV (versus SCE) results in a linear range of 1.17–29.25 μg/ml. Serum samples were analyzed and the results demonstrated that the concentration in this system meets the demands of clinical analysis. The surface of the immunosensor can be regenerated by simply polishing to obtain a fresh immunocomposite ready to be used in a new competitive assay.