In this work we have explored the use of a Surface Plasmon resonance (SPR) phenomenon for the detection of interleukin-6 (IL-6), a pro-inflammatory cytokine. It plays an important role in the muscle tissues, having direct relation with muscle contraction and, thus, it is considered a biomarker for some types of muscular dystrophies. Here we show that SPR can be used as a real-time monitoring of the shift of the reflectance dip of a gold diffraction grating in front to the antibody adhesion to gold.