A new NBD-based probe for specific colorimetric and turn-on fluorescence sensing of Cu2+ and bio-imaging applications

Herein we present a new colorimetric and fluorescent probe , AH, derived from the Schiff base condensation between 4-(2-aminophenylimino)-7-nitrobenzofurazan and 2-hydroxy-1-naphthaldehyde for optical sensing of Cu 2+ ions. In aqueous CH 3 CN solution (CH 3 CN/H 2 O, 1:1, v/v , pH7.4), AH effectively complexed with Cu 2+ at a stoichiometric ratio of 1:1, producing nearly 25-fold fluorescence enhancement at 540 nm along with a significant color change from orange to grey blue. The sensing system exhibits high specificity for the detection of Cu 2+ . The detection limit is as low as 42.2 nM. The observed switching on fluorescence emission can be attributed to the suppression of photo-induced electron transfer (PET) as well as chelation enhanced fluorescence (CHEF) effect after coordination of AH with Cu 2+ ion via the unshared electron pair on the phenyl amine. A test strip with AH has been fabricated for identifying Cu 2+ . Fluorescence imaging study reveals that probe AH is capable to sense Cu 2+ in living HeLa cells, Malpighian tubules of locust and zebrafish.