Exploration and application of a highly sensitive bis(salamo)-based fluorescent sensor for B₄O₇^2- in water-containing systems and living cells

A highly selective fluorescent sensor H₄L based on a bis(salamo)-type compound with two N₂O₂ chelating moieties as ionophore was successfully developed. Sensor H₄L was found to have excellent selectivity for B₄O₇^2- over many other anions (Br^-, CI^-, CN^-, CO₃^2-, HCO₃^-, H₂PO₄^-, HSO₄^-, NO₃^-, OAc^-, S₂O₃^-, SCN^-, SO₄^2-, Hcy (homocysteine) and H₂O₂), and it exhibited an approximately 150-fold enhancement of the fluorescence response to B₄O₇^2- in Tris-HCl buffer (DMF/H₂O = 9:1, v/v, pH = 7) solutions. Significantly, its fluorescence intensity was enhanced in a linear fashion with increasing concentrations of B₄O₇^2-. The detection limit of sensor H₄L towards B₄O₇^2- was 8.61 × 10^-7 M. The test strips could conveniently, efficiently and simply detect B₄O₇^2- ions in Tris-HCl buffer (DMF/H₂O = 9:1, v/v, pH = 7) solutions. Furthermore, sensor H₄L showed excellent membrane permeability in living cells, and it was successfully used to monitor intracellular B₄O₇^2- by confocal luminescence imaging.