FRET-based rational strategy for ratiometric detection of Cu2+ and live cell imaging

We present chemosensors with coumarin as donor and rhodamine as acceptor for ratiometric fluorescent imaging of Cu2+ based on metal ion induced FRET off-on mechanism. Two chemosensors coumarin–rhodamine hydrazone (CRO) and coumarin–rhodamine thiohydrazone (CRS) ratiometrically detects Cu2+ in judiciously chosen aqueous buffer medium. Free ligands (CRO and CRS) emit green fluorescence and in presence of Cu2+ the emission colour changed to red as spirolactam ring of rhodamine opens up upon complexation with metal ion. CRO and CRS can be used for successful detection of Cu2+ in presence of other competing metal ions by employing ratiometric fluorescence property. Probes CRO and CRS undergo 1:1 stoichiometric complexation with Cu2+ with the calculated association constants (log Ka) of 8.81 and 8.75 M-1 for [CRO:Cu2+] and [CRS:Cu2+] respectively. The probes CRO and CRS were employed as ratiometric biosensor for living cell imaging of Cu2+ in HEK293T cells.