The object of the invention is a process for the production of a molecule vector that can be used in water treatment, able to trap heavy ions, characterized in that it comprises the following stages: Diluting ornithine, NH.sub.2--(CH.sub.2).sub.3--CH(NH.sub.2)--COOH, in water, Adjusting the pH to a value of between 6.5 and 7.5, Adding glutaraldehyde, OHC--(CH.sub.2).sub.3--COH, and Awaiting the polycondensation reaction and the formation of imines, and Recovering the poly(ornithine-G) that is obtained. The invention also covers the vector that is obtained and the use as heavy-ion sensors.