Facile Synthesis of Water-Soluble Rhodamine-Based Polymeric Chemosensors Schiff Base Reaction for Fe Detection and Living Cell Imaging.

Quantitative and accurate determination of iron ions play a vital role in maintaining environment and human health, but very few polymeric chemosensors were available for the detection of Fe in aqueous solutions. Herein, a water-soluble rhodamine-poly (ethylene glycol) conjugate (DRF-PEG), as a dual responsive colorimetric and fluorescent polymeric sensor for Fe detection with high biocompatibility, was first synthesized through Schiff base reaction between rhodamine 6G hydrazide and benzaldehyde-functionalized polyethylene glycol. As expected, the introduction of PEG segment in DRF-PEG significantly improved the water solubility of rhodamine derivatives and resulted in a good biosensing performance. The detection limit of DRF-PEG for Fe in pure water is 1.00 μM as a fluorescent sensor and 3.16 μM as a colorimetric sensor at pH 6.5. The specific sensing mechanism of DRF-PEG toward Fe is proposed based on the intramolecular charge transfer (ICT) mechanism, in which the O and N atoms in rhodamine moiety, together with the benzene groups from benzaldehyde-modified PEG segment, participate in coordination with Fe. Furthermore, DRF-PEG was applied for the ratiometric imaging of Fe in HeLa cells and showed the potential for quantitative determination of Fe in fetal bovine serum samples. This work provides insights for the design of water-soluble chemosensors, which can be implemented in iron-related biological sensing and clinical diagnosis.