A method for modifying a textile yarn or textile fabric by immobilising on said yarn or fabric a cyclodextrin derivative comprising a group reactive towards organophosphorus agents, said cyclodextrin derivative having the following formula: in which: - n is 1, 2 or 3; - Y is a linker selected from the following groups: • -O-(CH 2) m -, m being 1, 2, or 3, preferably 1 or 3; • -NH-C(=O)-(CH 2) p -, p being 0, 1, or 2, preferably 0 or 2; • -CONH-(CH 2) q -, q being 1, 2, or 3, preferably 1 or 3; • -C(=O)O-(CH 2) r -, r being 1, 2, or 3, preferably 1 or 3; • -OC(=O)-(CH 2) s -, s being 0, 1, or 2, preferably 0 or 2; • -O-CH 2 -C≡C-(CH 2) t -, t being 1, 2, or 3, preferably 1 or 3; - Nu has the following formula: in which: • either R is COOH and X is C-I=O, • or R is CH=N-OH and X is N or N + -(C 1 -C 6)alkyl, • or R is CO-NH-OH and X is N, said method comprising a step (a) of contacting said textile yarn or fabric with the cyclodextrin derivative of formula and with a bridging agent selected from the group consisting of 1,2,3,4-butanetetracarboxylic acid, succinic acid, citric acid, oxalic acid and mixtures thereof, optionally in the presence of a catalyst or coupling agent selected from the group consisting of cyanamide, N, N, N', N' -tetramethyl- O -( N -succinimidyl)uronium tetrafluoroborate, O - [N -succinimidyl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TSTU), O -(5-norbornene-2,3-dicarboximido)- N,N,N',N'- tetramethyluroniumtetrafluoroborate (TNTU) and 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride, to obtain a textile yarn or fabric on which the cyclodextrin derivative of formula is immobilised. - n is 1, 2 or 3; - Y is a linker selected from the following groups: • -O-(CH 2) m -, m being 1, 2, or 3, preferably 1 or 3; • -NH-C(=O)-(CH 2) p -, p being 0, 1, or 2, preferably 0 or 2; • -CONH-(CH 2) q -, q being 1, 2, or 3, preferably 1 or 3; • -C(=O)O-(CH 2) r -, r being 1, 2, or 3, preferably 1 or 3; • -OC(=O)-(CH 2) s -, s being 0, 1, or 2, preferably 0 or 2; • -O-CH 2 -C≡C-(CH 2) t -, t being 1, 2, or 3, preferably 1 or 3; • -O-(CH 2) m -, m being 1, 2, or 3, preferably 1 or 3; • -NH-C(=O)-(CH 2) p -, p being 0, 1, or 2, preferably 0 or 2; • -CONH-(CH 2) q -, q being 1, 2, or 3, preferably 1 or 3; • -C(=O)O-(CH 2) r -, r being 1, 2, or 3, preferably 1 or 3; • -OC(=O)-(CH 2) s -, s being 0, 1, or 2, preferably 0 or 2; • -O-CH 2 -C≡C-(CH 2) t -, t being 1, 2, or 3, preferably 1 or 3; - Nu has the following formula: in which: • either R is COOH and X is C-I=O, • or R is CH=N-OH and X is N or N + -(C 1 -C 6)alkyl, • or R is CO-NH-OH and X is N, • either R is COOH and X is C-I=O, • or R is CH=N-OH and X is N or N + -(C 1 -C 6)alkyl, • or R is CO-NH-OH and X is N, said method comprising a step (a) of contacting said textile yarn or fabric with the cyclodextrin derivative of formula and with a bridging agent selected from the group consisting of 1,2,3,4-butanetetracarboxylic acid, succinic acid, citric acid, oxalic acid and mixtures thereof, optionally in the presence of a catalyst or coupling agent selected from the group consisting of cyanamide, N, N, N', N' -tetramethyl- O -( N -succinimidyl)uronium tetrafluoroborate, O - [N -succinimidyl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TSTU), O -(5-norbornene-2,3-dicarboximido)- N,N,N',N'- tetramethyluroniumtetrafluoroborate (TNTU) and 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride, to obtain a textile yarn or fabric on which the cyclodextrin derivative of formula is immobilised.