Multifunctional rhodamine B appended ROMP derived fluorescent probe detects Al³⁺ and selectively labels lysosomes in live cells

There a few reports of rhodamine-based fluorescent sensors for selective detection of only Al³⁺, due to the challenge of identifying a suitable ligand for binding Al³⁺ ion. The use of fluorophore moieties appended to a polymer backbone for sensing applications is far from mature. Here, we report a new fluorescent probe/monomer 4 and its ROMP derived polymer P for specific detection of Al³⁺ ions. Both monomer 4 and its polymer P exhibit high selectivity toward only Al³⁺ with no interference from other metal ions, having a limit detection of 0.5 and 2.1 µM, respectively. The reversible recognition of monomer 4 and P for Al³⁺ was also proved in presence of Na₂EDTA by both UV–Vis and fluorometric titration. The experimental data indicates the behavior of 4 and P toward Al³⁺ is pH independent in medium conditions. In addition, the switch-on luminescence response of 4 at acidic pH (0 < 5.0), allowed us to specifically stain lysosomes (pH ~ 4.5–5.0) in live cells.