Polyethyleneimine-derived fluorescent conjugate for trace-level detection of multiple ions via signal amplification

Abstract

Fluorescent conjugates, based on polyethyleneimine were prepared by incorporating salicylaldehyde and 2-hydroxynaphthaldehdye respectively in the aqueous medium. The polymer derived from salicylaldehyde showed a dual-mode response with Cu2+ and Zn2+ ions. The addition of Zn2+ could change the cyan fluorescence into a blue-colored one, while the Cu2+ ion could result in a turn-off response. On the contrary, the polymer functionalized with 2-hydroxynaphthaldehdye showed fluorescence response only with Cu2+ ions. The fluorescent polymers prepared at different polyethyleneimine and salicylaldehyde ratios not only showed the formation of nanoparticles of different sizes but also, interacted with Cu2+ ions to different extents. The mechanistic investigation suggested that the enhanced sensitivity of such fluorescent nanoparticles was due to the signal amplification attributed to the polymeric backbone. Further, the in-situ synthesized Cu and Zn complex of polymers showed interaction with pyrophosphate in the aqueous medium. However, the mode of interaction as well as fluorescence response depended on the nature of the metal ions involved.