The work consisted in functionalizing gold nanoparticles to analytically detect heavy metals in contaminated water; in Tayacaja-Huancavelica-Peru, using physical method of laser ablation. The 450 mJ/p Nd:YAG was used as a pulsed laser generator for the production of colloids from AuNPs by the top-down approach; the target was a 1 cm x 1.5 cm high purity gold metallic plate with a thickness of 1 mm, inside a 20 ml cuvette of deionized water, containing 5 ml of L-Cysteine ≥ 75% purity. Nanoparticle colloids were characterized by UV-Vis spectroscopy from 200 to 1160 nm range. Using a convex lens, the gold metal plate was ablated by the laser equipment, located 10 cm from the focus; with λ = 1064 nm and λ = 532 nm with energy equivalent to 60.28 mJ/p and 32.99 mJ/p respectively, with a ratio of 2 Hz, for 30 and 60 min. All the samples produced were subjected to the dispersion process by sonication at 40 KHz for one hour. The functionalized nanoparticles presented a resonance displacement of the maximum wavelength peak with respect to the reference at approximately 22.51 nm; consequently, the increase in diameter occurred at 52.10 nm. The sensitive capacity of the functionalized nanoparticles was verified for different concentrations of analytes in water, made up of divalent heavy metal ions Cd2+, Pb2+, and trivalent nonmetal As3+. At a concentration greater than 500 uM, the color of the functionalized nanoparticles turned bluish, due to the presence of positive ions. Therefore, it was stated that the functionalized nanoparticles enable the detection of heavy metals in water by color variation.