Two sensors for the detection of the metal ion Cu(II), based on the same sensing layer, are compared. They rely on different transduction methods, i.e., electrochemistry and surface plasmon resonance (SPR). D,L-penicillamine was used as the specific receptor since it is a strong ligand for copper(II). Moreover it is easily immobilized on a gold layer by a self assembling procedure by contacting the gold layer overnight with water/EtOH (80/20) containing D,L-penicillamine, taking advantage of the spontaneous interaction of thiols with gold surfaces. Both the electrochemical and SPR platforms were derivatized in the same way. In the first case a gold disc was used as working electrode, and in the second one a thin gold layer (60 nm thick) was deposited by sputtering over the exposed core of a plastic optical fiber (POF), after removing the cladding along half circumference.