Abstract: A fluorescent water-soluble polycationic chitosan polymer having a general formula (I) and salts thereof: wherein a is an integer between 220 and 11,200; R1 and R2 are independently selected from the group consisting of CH3CO and H, provided that at least 25% of the O-positions of the chitosan polymer structure is substituted with CH3CO; R7 is selected from the group consisting of CH3CO, H and Dye, provided that (i) at least one Dye residue is present in the chitosan polymer structure, (ii) and at least 15% of the N-positions of the chitosan polymer structure is substituted with CH3CO; Dye is a polymethine dye, having a general formula (II): wherein W represents 4-8 carbon atoms forming a benzo-condensed or a naphto-condensed ring; R3 and R4 are independently selected from the group consisting of CH2CH3, (CH2)3SO3?, (CH2)3N+(CH3)3; R5 and R6 are independently selected from the group consisting of H, SO3?; Q is selected from the group consisting of wherein D is selected from the group