Rhodamine B conjugate for rapid colorimetric and fluorimetric detection of aluminium and tin ions and its application in aqueous media

A new fluorescent chemosensor (MEK) was synthesized from conjugation of rhodamine B hydrazide and methyl ethyl ketone. It exhibited features that would facilitate the 'naked-eye' detection, including excellent selectivity and high sensitivity towards Al3+ and Sn2+ ions. Stronger binding strength was recorded in the formation of sensor-Al3+ complex, where the binding constant (K-a) was 3.58 x 10(10) M-1. Detection limits of MEK for Sn2+ and Al3+ was 5.10 mu M and 8.96 mu M respectively. Moreover, a 1:2 and 1:1 binding stoichiometry between this sensor with Al3+ and Sn2+ was verified via Job's plot and ESI-MS. Reversibility of the sensor as metal ions detector was evaluated with the introduction of the common quencher EDTA and it showed that MEK can be used repeatedly up to 6 times. Differences in the fluorescence profiles of sensor and the sensor-metal complexes (Al3+ and Sn2+) suggested the possible applications of MEK as detection kit for these metal ions. Interestingly, the on-site assay study shown obvious colour changes and fluorescence, thereby reflecting a potentially useful way in differentiating Al3+ and Sn2+. The combination of significant fluorescence response along with tunable selectivity is therefore notably practical for the application of this sensor.