We propose a novel ethylenediamine plasma-polymerized film matrix that is deposited on gold surfaces for use in surface plasmon resonance immunosensing. The films formed on the gold surfaces are extremely thin (∼100 nm), are homogeneous, demonstrate good adhesion, have a flat profile, and incorporate amino groups to introduce a chemical functionality. A sensor chip made with the film has many advantages when compared with conventionally used designs such as carboxylated dextran hydrogels. For example, a sensor chip made with the film shows a better sensor response than a conventional design partly because antibodies are densely and two-dimensionally immobilized onto the surface of the plasma-polymerized film.