An amperometric immunosensor with a thiolated Protein G scaffold

The orientation of the analyte-specific capture antibody on the surface of electrochemical immunosensors plays an important role on their overall performance. We have employed a self-assembled layer of Protein G that was thiolated with succinimidyl-6-[3′-(2-pyridyldithio)-propionamido] hexanoate for the orientation-controlled immobilisation of a capture antibody in a flow-type amperometric immunosensor based on a two-site sandwich immunoassay. After establishing the formation of the thiolated Protein G layer on 1-mm screen printed electrodes, amperometric immunosensors for the detection of the hormone, human chorionic gonadotrophin (hCG), were successfully constructed upon this scaffold. These sensors were characterised by a limit of detection (based on three times the standard deviation of the blank signal) of 175 IU l−1 and a linear response up to approximately 5000 IU l−1 of hCG.