Hydrazino-carbothioamide, 1, serves as a turn-on fluorescent chemosensor to Zn2+ and the mixture shows green emission (λem 492) in presence of large number of ions with impressive limit of detection (LOD), 0.59 nM. Intense fluorescence of Zn-complex is selectively turn-off upon adding H2PO4- only to the limit of detection, 26 μM, while other anions remain silent. The sensing mechanism of 1 is established by suppressing the ESIPT of 1 and complexation with Zn2+ (CHEF) is supported by Job's plot, 1H NMR, and HR-MS data. Turn-on-off sequential detection of Zn2+ and H2PO4- also have successfully been employed for the engineering of INHIBIT molecular logic gate. The sensor is non-toxic and has been used in identifying Zn2+ in the intracellular region of African green monkey kidney cells (Vero cells).