In this work, we report a new hydrazine-functionalized Al(III)- based metal-organic framework having MIL-53 (MIL = Material of Institute Lavoisier) framework topology for the sensitive and selective detection of formaldehyde (FA). The phase purity of the thermally activated and as-synthesized forms of the material was examined by X-ray powder diffraction experiments, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The desolvated material (1') showed great potential for the selective sensing of FA in the existence of other potentially competitive aldehydes in both aqueous and 10 mM HEPES buffer (pH = 7.4) media. The fluorescence "turn-on" behavior of the reaction-based probe can be ascribed to the inhibition of the photoinduced electron transfer process (from the hydrazine group to the phenyl ring) because of the formation of the hydrazone moiety. The detection limit of the probe toward FA in HEPES buffer is 8.37 mu M (0.25 ppm), which lies below the intracellular concentration of FA (100-400 mu M). A very short response time (1 min) has been displayed by 1' for FA sensing. Moreover, a remarkable enhancement in the emission intensity (sevenfold and fourfold in aqueous and HEPES buffer media, respectively) of 1' was observed after 1 min of FA addition. Furthermore, the ability of the probe to detect FA in the vapor phase was demonstrated. Interestingly, the material is also capable to detect endogenous FA in cancer cells. All the above discussed features clearly reveal that the present material has a huge potential for selective recognition of FA in both real water and biological samples.