A photochemical process for decorating hydrophobic surfaces with nanoparticles includes the steps of providing a metal precursor having hydrophobic parts adapted to interact with assistance of a photosensitizer; and forming a reactive adduct photosensitizer/precursor-metal/surface, preparing the surface to grow metal nanoparticles in situ having sizes and shapes governed by the morphology of the surface. The formed nanoparticles are sufficiently isolated, not aggregated and not interconnected, and do not create a film but maintain the chemical properties of substrate and metal. Surfaces so selectively decorated have hydrophobic properties even with hydrophilic substrates. Substrates with multiple chemical functionalities are thereby obtained, which can selectively bind different molecules or biomolecules onto the substrate and the surface of the metal nanoparticles surface. A process according to the invention also allows decorating surfaces with two or more metallic species. Decorated substrates obtained with a process according to the invention are also disclosed.