The present invention relates to a modified surface capable of having bacteriostatic and bactericidal activity when it is light irradiated, thus converting the surface of the substrate into a bacteriostatic and a bactericidal surface as many times as it is desired, and for a long time. According to the invention, the modified surface upon light irradiation avoids the attachment of a microorganism to this surface, inhibits the formation of a biofilm on this surface and destroys an already formed biofilm on this surface. These effects can be achieved as many times as it is desired, and for indefinite time.