The present invention concerns a method for functionalising at least one ribonucleic acid (RNA) molecule, contained in a liquid sample, which comprises the following steps: a) providing at least: - one binding molecule constituted by an azaisatoic anhydride or one of the derivatives of same, - a moiety of interest, and - a binding arm connecting the binding molecule with the moiety of interest, b) causing the anhydride function of the binding molecule to react with at least one hydroxyl moiety carried: - in position 2' of the ribose of one of the RNA nucleotides, and/or - in position(s) 2' and/or 3' of the ribose of the nucleotide at terminal end 3' of the RNA, and c) obtaining an aza-anthranylate that binds the RNA to the moiety of interest via the binding arm.