Abstract: Chemical compounds consisting of an alpha or beta oligo-4'-thioribonucleotide or oligo-4'-thio-2'-deoxyribonucleotide characterized in that they comprise a concatenation of 4'-thioribonucleotides or 4'-thio-2'deoxyribonucleotides, respectively. The concatenation is optionally linked to an effector, in particular a radical corresponding to an intercalating agent or a photoactivatable or chemical radical, e.g. a radical carrying a function which reacts directly or indirectly with the nucleotide chains, or a radical whose presence enables easy and sensitive detection. Methods for preparing said compounds, and their uses in therapeutics, diagnostics and as laboratory reagents, are also described.