Nanoscience and nanotechnology are emerging fields where some phenomena were recently discovered, allowing the design of some new devices. One of these phenomena is extraordinary optical transmission - EOT -, which was discovered in 1998 by Ebbesen. He reported that light can be amplified in certain conditions, due to a resonant behaviour, using metallic arrays. Even more, he associated this behaviour to surface plasmon polaritons and suggested that devices, as optical sensors, can be designed based on this phenomenon. To understand the surface plasmon polaritons theory, classical theories will be studied and compared with it. Also, the composite diffracted evanescent waves - CDEW -, model, which is not the most accurate model in comparison with the surface plasmon polaritons, will be presented, in order to cover an important topic on the theoretical foundations. After it, the application of nanoantennas as a sensor is going to be analysed. Finally, stationary simulations for a 16-slit gold array were performed using COMSOL Multiphysics and they are going to be presented in order to observe the occurrence of EOT.