A silane-modified cyanine of Formula (I) includes the valence tautomers thereof: wherein R1 is a linear, saturated or unsaturated alkyl chain, having 1 to 30 carbon atoms, wherein one or more carbon atoms are optionally substituted by a 4-, 5- or 6-membered aromatic or non aromatic cyclic grouping of carbon atoms; R8 and R9 are independently selected from the group consisting of —OCH3, —OCH2CH3, —OCH2CH2CH3, —OCH(CH3)2, —OCH2CH2OCH3, —Cl, —Br, —I, Formula (II), Formula (III), —N(CH3)2, Formula (IV), Formula (V), methyl, ethyl, propyl, isopropyl. The synthesis method and the use as a fluorescent marker are for inorganic solid supports, for example silica nanoparticles, and/or for biomolecules such as peptides, antibodies, DNA, RNA, etc.