BODIPY-derived multi-channel polymeric chemosensor with pH-tunable sensitivity: selective colorimetric and fluorimetric detection of Hg2+ and HSO4− in aqueous media

Abstract

The development of water-soluble polymeric probes capable of recognizing more than one analyte is quite challenging and has attracted significant attention. A water-soluble random copolymer (P1) consisting of hydrophilic N,N′-dimethyl acrylamide (DMA) and aldehyde-terminated difluoroboron dipyrromethene (BODIPY) methacrylate segment was synthesized via the reversible addition–fragmentation chain transfer (RAFT) polymerization for the detection of Hg²⁺ and HSO₄⁻ ions, respectively. The aldehyde terminal end of P1 was post-functionalized with 4-amino phenol through a Schiff-base condensation reaction, leading to a final polymeric probe (P2). P2 exhibited both colorimetric and fluorimetric responses according to the pH of the aqueous solution or bubbling the solution with CO₂, manifesting itself as a pH indicator and CO₂ sensor. Upon the addition of Hg²⁺ ions, P2 showed apparent color changes from pink to light yellow under ambient light and colorless to bright green emission under 365 nm UV light with a very low limit of detection (LOD = 1.10 μM). At low pH, no change in the fluorescence enhancement was observed upon exposure to Hg²⁺ ions, whereas the fluorescence intensity of P2 increased remarkably at high pH. Similar sensing behavior was observed for HSO₄⁻ ions with a LOD of 1.12 μM. P2 was quite selective toward Hg²⁺ and HSO₄⁻ over the other metal cations and anions tested, respectively. The detection of both Hg²⁺ and HSO₄⁻ ions originated from the direct hydrolysis of imine bonds of P2.