A new Zn2+ fluorescent sensor NIDPA (1) which takes 1,8-naphthalimide as a reporting group and di-2-picolylamine (DPA) as a recognizing group has been synthesized via simple steps. Based on photo-induced electron transfer (PET) mechanism, NIDPA has a nearly 5-fold fluorescent enhancement under simulated physiological conditions corresponding to the binding of Zn2+. Apparent dissociation constant for Zn2+ (K-d) is in the sub-nM range, and Ca2+, Mg2+, Fe3+, Ni2+, and Cr3+ have little influence on fluorescence enhancement.