A FRET-based colorimetric and ratiometric fluorescent probe for the detection of Cu2+ with a new trimethylindolin fluorophore

Abstract

In this study, a novel rhodamine-based probe for the detection of Cu²⁺ which is conjugated with a 2-(1,3,3-trimethylindolin-2-ylidene) acetaldehyde moiety has been designed and synthesized. The detection is based on the fluorescence resonance energy transfer (FRET) mechanism. The probe exhibits colorimetric and ratiometric responses to Cu²⁺ with a large Stokes shift (237 nm) and is not disturbed by other coexisting metal ions. The probe can achieve the nanomolar detection of Cu²⁺ with a detection limit of 1.168 × 10⁻⁸ mol L⁻¹. The 1 : 1 stoichiometry of the RhF–Cu²⁺ complex is supported by the Job's plot, ESI-MS analysis, IR spectral data and density functional theoretical (DFT) studies. More importantly, potential applications of the probe can also be achieved by using test paper strips. Furthermore, the probe can be used for the detection of Cu²⁺ in actual water samples.