Selective and sensitive turn-on chemosensor for Al(iii) ions applicable in living organisms: nanomolar detection in aqueous medium

Abstract

A highly sensitive and selective fluorescent reporter L for Al(III) ions was synthesized and characterized by physicochemical and spectroscopic tools along with single crystal X-ray crystallographic study. This is so far the first report of a crystallographically established fluorescence probe having two rhodamine units which make this probe highly sensitive towards Al(III) ions. L, with a high binding affinity towards Al(III) ions of 3.33 × 10⁸ M⁻², selectively detects Al(III) ions with almost no interference among various competitive, biologically relevant ions by a strong fluorescence (250 times) as well as colour change in HEPES buffer (1 mM, pH 7.4; acetonitrile/water: 1/3, v/v). The quantum yields (Ф) and molar extinction coefficient (ε) of [Al₂(L)₂(CH₃CN)(H₂O)(NO₃)₄](NO₃)₂ (complex-1) were significantly greater than the sensor L, meaning this probe (L) can detect Al(III) ions at concentrations as low as 3.26 nM, which is comparable with the lowest LOD available in the literature. This non-cytotoxic probe (L) is also an efficient candidate to detect the intercellular distribution of aluminium ions in human lung cancer cells (A549) and Al(III) ions in matured tea leaves.