Nanoparticle comprising or consisting of a complex of a nucleic acid, which is a DNA or RNA, and a polymeric carrier molecule according to generic formula: L-P 1 -S-[S-P 2 -S] n -S-P 3 -L (formula I) wherein, P 1 and P 3 are different or identical to each other and represent a linear or branched hydrophilic polymer chain, each P 1 and P 3 exhibiting at least one -SH-moiety, capable to form a disulfide linkage upon condensation with component P 2, the linear or branched hydrophilic polymer chain selected independent from each other from polyethylene glycol, poly- N -(2-hydroxypropyl)methacrylamide, poly-2-(methacryloyloxy)ethyl phosphorylcholines, poly(hydroxyalkyl L-asparagine), poly(2-(methacryloyloxy)ethyl phosphorylcholine), hydroxyethylstarch or poly(hydroxyalkyl L-glutamine), wherein the hydrophilic polymer chain exhibits a molecular weight of 1 kDa to 100 kDa, P 2 is a cationic or polycationic peptide or protein, having a length of 3 to 100 amino acids, or is a cationic or polycationic polymer, having a molecular weight of 0.5 kDa to 30 kDa, each P 2 exhibiting at least two -SH-moieties, capable to form a disulfide linkage upon condensation with further components P 2 or component(s) P 1 and/or P 3; -S-S- is a (reversible) disulfide bond; L is an optional ligand, which may be present or not, and may be selected independent from the other from RGD, Transferrin, Folate, a signal peptide or signal sequence, a localization signal or sequence, a nuclear localization signal or sequence, an antibody, a cell penetrating peptide, TAT, a ligand of a receptor, cytokines, hormones, growth factors, small molecules, carbohydrates, mannose, galactose, synthetic ligands, small molecule agonists, inhibitors or antagonists of receptors, or RGD peptidomimetic analogues; and n is an integer, selected from a range of 1 to 50, preferably in a range of 1, 2, 3, 4, or 5 to 10, more preferably in a range of 1, 2, 3, or 4 to 9, wherein the nanoparticle is coated with a biodegradable polymer and wherein the biodegradable polymer is a PLGA polymer. P 1 and P 3 are different or identical to each other and represent a linear or branched hydrophilic polymer chain, each P 1 and P 3 exhibiting at least one -SH-moiety, capable to form a disulfide linkage upon condensation with component P 2, the linear or branched hydrophilic polymer chain selected independent from each other from polyethylene glycol, poly- N -(2-hydroxypropyl)methacrylamide, poly-2-(methacryloyloxy)ethyl phosphorylcholines, poly(hydroxyalkyl L-asparagine), poly(2-(methacryloyloxy)ethyl phosphorylcholine), hydroxyethylstarch or poly(hydroxyalkyl L-glutamine), wherein the hydrophilic polymer chain exhibits a molecular weight of 1 kDa to 100 kDa, P 2 is a cationic or polycationic peptide or protein, having a length of 3 to 100 amino acids, or is a cationic or polycationic polymer, having a molecular weight of 0.5 kDa to 30 kDa, each P 2 exhibiting at least two -SH-moieties, capable to form a disulfide linkage upon condensation with further components P 2 or component(s) P 1 and/or P 3; -S-S- is a (reversible) disulfide bond; L is an optional ligand, which may be present or not, and may be selected independent from the other from RGD, Transferrin, Folate, a signal peptide or signal sequence, a localization signal or sequence, a nuclear localization signal or sequence, an antibody, a cell penetrating peptide, TAT, a ligand of a receptor, cytokines, hormones, growth factors, small molecules, carbohydrates, mannose, galactose, synthetic ligands, small molecule agonists, inhibitors or antagonists of receptors, or RGD peptidomimetic analogues; and n is an integer, selected from a range of 1 to 50, preferably in a range of 1, 2, 3, 4, or 5 to 10, more preferably in a range of 1, 2, 3, or 4 to 9,