A fluorometric/colorimetric dual-channel Hg2+ sensor derived from a 4-amino-7-nitro-benzoxadiazole (ANBD) fluorophore

Abstract

A new visible light excitable Hg²⁺ sensor, NBD-TAEE, was prepared by bridging a 4-amino-7-nitro-benzoxadiazole (ANBD) fluorophore with thiaazacrown ethervia an ethylene spacer. Besides the specific Hg²⁺-induced absorption shift from 466 to 513 nm, this sensor exhibits the specific Hg²⁺-induced emission enhancement (∼29-fold) and fluorescent pH-independence from pH 6 to 13. Hg²⁺ addition even leads to the emission red shift from 532 to 570 nm, although NBD-TAEE is not a ratiometric fluorescent sensor due to its emission band being overlaid by the Hg²⁺-induced band. The instant and reversible “turn-on” Hg²⁺ response, fine cell permeability and cell imaging ability display its potential application in both environmental and Hg²⁺-polluted biological samples. Its analogue without the ethylene spacer, NBD-TAE, possesses the higher quantum yield and very poor Hg²⁺ binding ability. Their different emission behavior and sensing ability suggest that the spacer is quite essential for sensor construction.