Not only are sensors a revolution in analysis; they themselves are also experiencing a revolution brought about by parallel developments in sensor fabrication techniques and materials, polymer electrochemistry, signal processing methodologies, the increased use of biomolecular processes as a means of analyte detection, and the coupling of sensors to other techniques such as flow injection drug delivery system and patch-clamp technique. Many of these developments have been incorporated into the present study which we are undertaking in the development of our immunosensor technology onto hormone and neuropeptide detection. Incorporated into our ultra-micro carbon fiber sensor is the electroactive polymer, polypyrrole, which brings about meditorless redox coupling between the electrode and biomolecular component attached to the polymer surface. This system utilizes non-labelled monoclonal antibodies as the biomolecular recognition component for monitoring the real-time antibody-antigen interaction using electrochemical methods and in vivo detection of insulin release from rat pancreatic islet. The detection limitation of the immunosensors is lower to 10 amol/1 and the sensors exhibited a high temporal and spatial resolution as carbon fiber electrode. The dynamic properties of release of insulin was similar as that of dopamine loaded into rat islet, which indicated a quantal release of insulin.