A nanoparticle comprising (i) a core comprising a first population of quantum dots (QDs) embedded in silica, (ii) a shell comprising a second population of QDs embedded in silica, (iii)at least one biomolecule selected from a peptide, a nucleic acid, a carbohydrate or a lipid which comprises a cleavage site that is susceptible of being cleaved by a hydrolytic enzyme, said biomolecule being bound to the surface of the shell through a moiety selected from the moieties of formula and, wherein Si shell is a silicium atom comprised in the shell and C biomolecule is a carbon atom comprised in the biomolecule; n is an integer comprised of from 0 to 10; FG 1 and FG 2 are each a diradical independently selected from the group consisting of the diradicals of formula,,,,, (VIII) and where X is S or O; R 1 is H or (C 1 -C 12)alkyl; L is a diradical selected from the diradicals deriving from a compound selected from (C 1 -C 12)alkane, (C 1 -C 12)alkene, (C 1 -C 12)alkyne, (C 3 -C 6)cycloalkane and benzene; and (iv)a photoluminescent label for each biomolecule, wherein the label is bound to the part of the biomolecule which detaches from the nanoparticle after cleavage of said biomolecule by a hydrolytic enzyme through a diradical of formula FG 3 which is selected from the group consisting of the diradicals of formula,,,,, (VIII) and defined above; wherein the first and second QD populations have different maximum photoluminescence emission wavelengths, and only the second QD population is susceptible of producing Förster resonance energy transfer (FRET) with the photoluminescent label. (i) a core comprising a first population of quantum dots (QDs) embedded in silica, (ii) a shell comprising a second population of QDs embedded in silica, (iii)at least one biomolecule selected from a peptide, a nucleic acid, a carbohydrate or a lipid which comprises a cleavage site that is susceptible of being cleaved by a hydrolytic enzyme, said biomolecule being bound to the surface of the shell through a moiety selected from the moieties of formula and, wherein Si shell is a silicium atom comprised in the shell and C biomolecule is a carbon atom comprised in the biomolecule; n is an integer comprised of from 0 to 10; FG 1 and FG 2 are each a diradical independently selected from the group consisting of the diradicals of formula,,,,, (VIII) and where X is S or O; R 1 is H or (C 1 -C 12)alkyl; L is a diradical selected from the diradicals deriving from a compound selected from (C 1 -C 12)alkane, (C 1 -C 12)alkene, (C 1 -C 12)alkyne, (C 3 -C 6)cycloalkane and benzene; and wherein Si shell is a silicium atom comprised in the shell and C biomolecule is a carbon atom comprised in the biomolecule; n is an integer comprised of from 0 to 10; FG 1 and FG 2 are each a diradical independently selected from the group consisting of the diradicals of formula,,,,, (VIII) and where X is S or O; R 1 is H or (C 1 -C 12)alkyl; L is a diradical selected from the diradicals deriving from a compound selected from (C 1 -C 12)alkane, (C 1 -C 12)alkene, (C 1 -C 12)alkyne, (C 3 -C 6)cycloalkane and benzene; and (iv)a photoluminescent label for each biomolecule, wherein the label is bound to the part of the biomolecule which detaches from the nanoparticle after cleavage of said biomolecule by a hydrolytic enzyme through a diradical of formula FG 3 which is selected from the group consisting of the diradicals of formula,,,,, (VIII) and defined above;