Smart block copolymers as fluorescence chemosensors of copper ions with high detection limit

Abstract

Stimuli-responsive block copolymers were synthesized to detect copper ions with high limit based on a fluorescence quenching mechanism. For this purpose, poly(7-acryloyloxy 4-methylcoumarin-r-methyl methacrylate)-b-poly(dimethylaminoethyl methacrylate) in three different block ratios was synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization. Successful synthesis of the block copolymers was confirmed by Fourier-transformed infrared and proton nuclear magnetic resonance spectroscopies. Self-assembly of the copolymers in aqueous media resulted in formation of micellar structures, as confirmed by transmission electron microscopy images and also estimated form the hydrophilic fraction of the block copolymers. Micellar size and dispersity were studied by dynamic light scattering in different conditions. In addition, dimerization kinetics of the coumarin molecules in the micellar assemblies were studied by ultraviolet–visible spectroscopy. The sample with higher molar ratio of CMA in the hydrophobic block and shorter length of PDMAEMA in the hydrophilic block showed faster dimerization reaction. The micellar assemblies formed from all the copolymers were used to sense potassium, calcium, and copper cations. All the self-assembled structures showed high sensitivity to detect copper cation, by quenching their fluorescence intensity. The copolymer sample with the highest ratio of PDMAEMA/CMA in the chain structure has the highest detection limit of 0.002 ppm for copper ion.