Since the engineering control of the deposition of nanometric gold plates on substrates the Surface Plasmon Resonance (SPR) based sensor has become one of the most successful label-free and commercially developed optical sensor, with applications to biology (Hoaa et al., 2007; Kolomenskii et al., 1997; Kretschman & Raether, 1968; Lecaruyer et al., 2006). This technique is currently employed in biomolecular engineering, drug design, monoclonal antibody characterization, virus-protein interaction, environmental pollutants detection, among other interesting problems. The basic principle of such transducer is the measurement of the sudden absorbtion of light by the thin metallic layer, under particular illumination conditions (p-polarization) and a specific angle of incidence of the illumination (Barchiesi, Kremer, Mai & Grosges, 2008; Barchiesi, Macias, Belmar-Letellier, Van Labeke, Lamy de la Chapelle, Toury, Kremer, Moreau & Grosges, 2008; Kretschman & Raether, 1968), leading to a highly sensitive device (Kolomenskii et al., 1997; Lecaruyer et al., 2006). The conditions of such absorption are linked to the plasmon resonance in metallic structure, and therefore a tiny change of the optical properties of medium above the gold plate, produces an angular shift of this absorption, due to the detuning of the resonance. The sensing principle relies therefore on the shift of the plasmonic resonance caused by the surrounding dielectric environmental change in a binding event. The Plasmonic biosensors use the property of resonance between an illumination and the metallic part of the sensor. This resonance is used to increase the sensitivity of the biosensor and the threshold of detection. Actually, a given set of parameters of the biosensor can lead to a maximum of the absorption of the incoming light. A slight change of its immediate environment (presence/Absence of biomoecules to be detected) produces a strong change of the detected light due to the detuning of the resonance. This property is also used in cancer therapy or imaging, throughmetallic nanoparticles or nanoshells (Grosges, Barchiesi, Toury& Grehan, 2008). The design of specific shapes for nanoparticles can help to tune the resonance for specific applications (Billot et al., 2006). In the case of planar SPR (Surface Plasmon Resonance) biosensors, the reflected intensity vanishes for a specific angle of incidence. The illumination is almost totally coupled in the metal layer. A tiny change of the optical index of the upper medium, due to the presence of biomolecules, produces a measurable shift of this minimum. Therefore, to improve the efficiency of the sensor, the material and geometrical characteristics of the materials involved in the biosensor must be adjusted correctly. Surprisingly, the optimization of such structures has rarely been addressed (Ekgasit et al., 2005; Kolomenskii et al., 1997; Lecaruyer et al., 5