The fluorescence response of Schiff base capped ZnS NPs; in the presence of carious concentrations of (a) Fe3+, (b) Cr2+ and (c) Cd2+ ions; (d) bar diagram of the effect of Fe3+, Cr2+ and Cd2+ concentrations (10 to 100 μM) in the ZnS fluorescence intensity; (e) the relationship between relative concentrations (10 to 500 μM) of Fe3+, Cr2+ and Cd2+ with ZnS fluorescence intensity; (f) the relation between fluorescence response (F0/F) of ZnS NPs and the concentration of Fe3+, Cr2+ and Cd2+ from 10 to 100 μM.