Nanostructuring surfaces in order to improve the quality of determinations, in terms of detection limit and signal-to-noise ratio, had received a great attention in the last years. At this effect, a potentiometric for the determination of lactate, based on a nanostructured (ND) Si4N3 surface, is presented here. The potentiometric sensor developed is an electrolyte¿membrane¿insulator¿semiconductor (EMIS). The surface was first modified by a polyacrylic acid (PAA) layer, deposited by plasma enhanced chemical vapor deposition (PECVD), that can covalently link to the NH2 groups of the lactate dehydrogenase. Secondly, the nanostructures were formed on the surface by colloidal lithography. The obtained nanostructured surface was characterized. The stability of the biosensor in aqueous media was investigated obtaining a sensitivity of 49.7mV per decade. The detection limit for the determination of lactate was 2×10-7 M, with a linear range up to 10-5 M. The intra- and inter-electrode standard deviation were about 2.4% and 11%, respectively. Nanostructuring leads to a signal amplification of one order of magnitude when compared to the values obtained with the same device based on flat surface. ; JRC.I.4-Nanotechnology and Molecular Imaging