Development of a novel ultrasensitive and stable potentiometric immunosensor A stable potentiometric immunosensor for the detection of various analytes of interest from complex real world samples such as blood, serum and milk has been described [48] . The biosensor detects enzyme labelled immunocomplexes formed at the surface of polypyrrole coated, screen-printed gold or silver electrodes. Detection is through a secondary reaction that produces charged products with a shift in potential, being measured by local changes in redox state, pH and/or ionic strength. The magnitude of the change in potential is directly related to the level of target in the matrix such that the assays are quantitative and the numerical output is rapidly transmissible. The bioassays produce very rapid results (5-15 minutes), are highly reproducible (%CV,5%) and are ultra-sensitive (,50 fM). Thus this sort of biosensor offers the rapidity of production of signal of a lateral flow device with the sensitivity of third generation ELISAs. Immunoassays can be developed in a sandwich or competitive format for small (e.g. Digoxin; MW 780 Da) or large (e.g. hepatitis B surface antigen; .300 kDa) molecules [49] . In addition to immunoassays, it is also possible to detect specific nucleic acids and whole cells using the technology. Due to the method of production of the electrode strips, the base assays are inexpensive (,US$1 per strip) as is the detection hardware (US$2,000). In addition, most immunoassays can be readily adapted to this format with minimal additional optimisation. Potentiometric immunosensors for detecting the rabies virus nucleoprotein are in progress and offer the ability to rapidly screen complex non-clarified matrices, possibly at pen-side, in a cost-effective manner.