We have explored for the first time PVDF Immobilon-P membranes, attached to interdigitated capacitor microelectrodes, as 3-D matrixes for the immobilization of antibodies in an interdigitated capacitive immunosensor format. The thick membranes allow distribution of antibodies across the entire region probed by the measuring electric field applied to the microelectrodes. This new approach is an alternative to the use of nanometer electrodes necessary to detect smaller layers of antibodies. As a proof-of-concept, a horseradish peroxidase (HRP) antibody/antigen affinity pair allowed for specific detection of the antigen in blocked membranes containing the antibody. Immobilization of antibody and penetration of antigen inside the PVDF membrane was assessed by fluorescence measurements and by an HRP enzymatic assay, respectively. The new interdigitated capacitive immunosensor was able to discriminate between buffer alone and HRP antigen in buffer, as proven by capacitance measurements.