Homogeneous chitosan films of various thicknesses (10–65 nm) were deposited on thin gold films through spin coating. The resulting interfaces were characterized using surface plasmon resonance (SPR), AFM, profilometry and cyclic voltammetry. The strong chelating properties of chitosan films to Fe3+ were investigated using cyclic voltammetry. Through SPR measurements, an affinity constant between chitosan and Fe3+ of 9.49 × 105 M−1 was determined with a detection limit as low as 250 ppb.