Efficient FRET-based colorimetric and ratiometric fluorescent chemosensor for Al3+ in living cells

In this paper, we have developed the first example for colormetric and ratiometric fluorescent detection of Al3+ based on naphthalimide-rhodamine compound (1a). The ratiometric fluorescent signal change of the chemosensor is on the basis of FRET Off-On mechanism modulated by Al3+ induced configuration transformation of the rhodamine from a spirolactam ring to the ring-opened amide. In comparison with the fluorescent chemosensors based on single emission intensity change, ratiometric chemosensors are beneficial for increasing the dynamic response range and providing built-in correction for environmental effects. Under optimized experimental conditions, the chemosensor exhibits a stable response for Al3+ over a concentration range from 5.0 × 10−7 to 1.0 × 10−5 M, with a detection limit of 1.0 × 10−7 M. The experiment results show that the response behavior of 1a toward Al3+ is pH independent in medium condition (pH 6.0–8.0). Moreover, the fluorescence changes of the chemosensor are remarkably specific for Al3+ in the presence of other metal ions except Mn2+, which can meet the selective requirements for practical application. In addition, the chemosensor was successfully applied for ratiometric visualization of Al3+ in living cells.