The probe comprises: a) an oligonucleotide or oligodeoxyribonucleotide part constituted by a DNA or RNA nucleic acid sequence S, depending on the type of molecule to be detected, and b) a non-nucleotide part possessing chemical properties enabling direct or indirect atttachment of one or more detection units or marking elements M detectable non-isotopically by production of colour or light. The probe is characterized by the fact that part b) is constituted by a chain of phosphate units interspersed with alkyl groups, viz.: b1) certain alkyl groups uniting the different phosphate groups and presenting no special functionality b2) alkyl groups presenting primary amine groups which allow splicing with varied reagents to carry out direct or indirect detection, the b2) groups being bonded to part a) or sequence S by way of groups b1). Sequence S is bonded at its 5' and/or 3' extremity to one or more marking elements M. The probes of this type are used to detect and diagnose hereditary genetic diseases, oncogenes, viral, bacterial or parasitic diseases.