We describe the fabrication and characterization of components of a biosensor system that can be used for simultaneous screening of multiple pathogens in a sample. The two sub-systems are: (1) a mixed antibody immunosensor based on molecular biowires and (2) a multi-channel potentiostat for measuring conductance across the immunosensor. The immunosensor operates by converting binding events between antigen and antibody into a measurable electrical signal using polyaniline nanowires as labels and transducers. By mixing and patterning antibodies on a substrate, the response of the biosensor can detect the presence of either one of several pathogens present in the analyte through an equivalent change in conductance. The paper also presents a 42-channel potentiostat array which can be used for measuring the conductance change across the immunosensor. Each channel of the array uses a novel semi-synchronous ΣΔ modulator which enables detection down to femtoampere current ranges.