Orientation effect induced selective chelation of Fe to a glutamic acid appended conjugated polymer for sensing and live cell imaging

Intracellular detection and imaging of labile iron( ii ) pools is very important in tracking physiological processes that demand new and rapid sensing probes. In this report, we present a water soluble polymer based probe for the fluorescence sensing and live cell imaging of labile Fe 2+ ions with high selectivity for the first time. The polymer probe was based on conjugated polyfluorene which was appended with amino acid ( l -glutamic acid). The biocompatibility of the polymer was confirmed from an MTT assay which demonstrated >90% cell viability even at 300 μg ml −1 loading of polymers. Simple glutamic acid did not show selectivity towards any of the divalent ions. However, glutamic acid appended polyfluorene exhibited selective chelation to Fe 2+ ions resulting in immediate sensing activity for Fe 2+ ions in water and living cells with fluorescence turn-off response. The limit of detection of the PF-Ph-GA polymer probe was 46 (±2) nM which indicated high sensitivity for Fe 2+ over other ions reported in the literature. The polymer also exhibited improved sensing activity in the range of intracellular pH (5-9) which is advantageous in differentiating endogenous changes. The probe was successfully applied for the fluorescence imaging of intracellular and supplemented labile iron( ii ) pools in living HeLa cells. We have demonstrated the first example of highly selective sensing and bioimaging of Fe 2+ in living HeLa cells using a biocompatible glutamic acid appended polyfluorene via selective chelation of amine and acid groups with Fe 2+ .