A modified nanoparticle for use in a therapeutic method, wherein the therapeutic method comprises the administration of the modified nanoparticle to an organism, the targeting of the modified nanoparticles to a specific site in the organism followed by an uptake of the modified nanoparticle into a cell, and wherein the modified nanoparticle is obtainable by a process comprising the steps of i) providing a nanoparticle and ii) contacting the nanoparticle with one or more antibodies as targeting moieties at a pH value of less than 7.0 so as to non-covalently bind the one or more antibodies via its/their Fc region onto the surface of the nanoparticle, wherein the nanoparticle provided in step i) is made of a material having at least one protonable or deprotonable group on the surface thereof and/or the one or more targeting moieties contacted with the nanoparticle in step ii) has at least one protonable or deprotonable group, and wherein a) the nanoparticle provided in step i) has at least one deprotonable group on the surface thereof, wherein the deprotonable group is selected from the group consisting of carboxy groups, hydroxyl groups, thiol groups, sulfenic acid groups, sulfinic acid groups, sulfonic acid groups, thiocarboxylic groups, peroxy carboxylic groups, oxime groups and arbitrary combinations of two or more of the aforementioned groups, wherein the nanoparticle provided in step i) is made of a material being selected from the group consisting of polystyrene, polyacrylate, polymethacrylate, poly-L-lactic acid, poly-L-lactic acid-co-glycolic acid, polyamino acid and hydroxyethyl starch, and wherein preferably the nanoparticle is either contacted with the one or more antibodies in step ii) at a pH value of 1.0 to 4.2 or is contacted with the one or more antibodies in step ii) at a pH value of 5.0 to 6.5, or b) the nanoparticle provided in step i) has at least one protonable group on the surface thereof, wherein the protonable group is selected from the group consisting of amino groups, hydrazine groups, hydrazide groups, carboxy hydrazide groups, sulfonic acid amide groups, amide groups and arbitrary combinations of two or more of the aforementioned groups, wherein the nanoparticle provided in step i) is made of polystyrene and/or polyamino acid, and wherein preferably the nanoparticle is contacted with the one or more antibodies in step ii) at a pH value of 1.0 to 4.2, or c) the nanoparticle provided in step i) is made of a material selected from the group consisting of crosslinked proteins, dextran, waxes, silicas, iron oxides and polymethylmethacrylates, wherein preferably the nanoparticle, when made from a crosslinked protein or a wax, is contacted with the one or more antibodies in step ii) at a pH value of 1 to 5, or the nanoparticle, when made from a dextran, a silica, a polymethylmethacrylate or an iron oxide, is contacted with the one or more antibodies in step ii) at a pH value of 4 to 7. a) the nanoparticle provided in step i) has at least one deprotonable group on the surface thereof, wherein the deprotonable group is selected from the group consisting of carboxy groups, hydroxyl groups, thiol groups, sulfenic acid groups, sulfinic acid groups, sulfonic acid groups, thiocarboxylic groups, peroxy carboxylic groups, oxime groups and arbitrary combinations of two or more of the aforementioned groups, wherein the nanoparticle provided in step i) is made of a material being selected from the group consisting of polystyrene, polyacrylate, polymethacrylate, poly-L-lactic acid, poly-L-lactic acid-co-glycolic acid, polyamino acid and hydroxyethyl starch, and wherein preferably the nanoparticle is either contacted with the one or more antibodies in step ii) at a pH value of 1.0 to 4.2 or is contacted with the one or more antibodies in step ii) at a pH value of 5.0 to 6.5, or b) the nanoparticle provided in step i) has at least one protonable group on the surface thereof, wherein the protonable group is selected from the group consisting of amino groups, hydrazine groups, hydrazide groups, carboxy hydrazide groups, sulfonic acid amide groups, amide groups and arbitrary combinations of two or more of the aforementioned groups, wherein the nanoparticle provided in step i) is made of polystyrene and/or polyamino acid, and wherein preferably the nanoparticle is contacted with the one or more antibodies in step ii) at a pH value of 1.0 to 4.2, or c) the nanoparticle provided in step i) is made of a material selected from the group consisting of crosslinked proteins, dextran, waxes, silicas, iron oxides and polymethylmethacrylates, wherein preferably the nanoparticle, when made from a crosslinked protein or a wax, is contacted with the one or more antibodies in step ii) at a pH value of 1 to 5, or the nanoparticle, when made from a dextran, a silica, a polymethylmethacrylate or an iron oxide, is contacted with the one or more antibodies in step ii) at a pH value of 4 to 7.