A novel polyethylenimine (PEI)-salicylaldehyde (SA) fluorescence probe, simply prepared by stirring procedure, can sensitively detect Zn2+ (25 nM) and Cd2+ (10 nM) in aqueous solution. Formation of metal-toligand complexes (Zn2+@ PEI-SA and Cd2+@ PEI-SA) between ions and Schiff base generate a new emission at 454 nm, which increase with the concentration of the ions (turn-on). Furthermore, after adding S-2 into the complexes, we can distinguish them due to the fluorescence quenching for Cd2+@ PEI-SA (turn-off). Both response times for turning on and off the fluorescence are less than 1 min. (C) 2016 Elsevier B. V. All rights reserved.