AgNPs were prepared by reducing of silver nitrate with sodium with borohydride sodium. The average size of particles was 3.48 nm±0.13 and the spherical shape was confirmed by TEM. In addition, the AgNPs were conjugated to L-cysteine by adsorption of the thiol, amino and carboxyl on its surface. We studied the dependence of parameters such as L-Cys molar ratio, pH and time of process on the functionalization. The results were verified by Surface-Enhanced Raman Spectroscopy (SERS).