Colorimetric and ratiometric fluorescent probes for sensitive visualization of hydrazine in water and in living cells

Taking account of the strong nucleophilicity of hydrazine, two fluorescent probes, DEA-A and Jul-B, were designed and synthesized. These probes employed 2,3,5,6-1<i>H</i>,4<i>H</i>-tetrahydroquinolo[9,9a,1-gh]coumarin (Jul-B) or <i>N</i>,<i>N</i>-diethyl-7-aminocoumarin (DEA-A) as the fluorophore, and 2-benzothiazole acetonitrile as the recognition moiety for N₂H₄. The formation of hydrazones weakened the intramolecular charge transfer (ICT) process in the probes, leading to blue-shifts of more than 100 nm in both absorption and emission. DEA-A and Jul-B demonstrated notable colorimetric and ratiometric fluorescence responses to N₂H₄, which enabled us to realize the identification of hydrazine using the "naked-eye". In the case of DEA-A, the <i>I</i>₅₁₃/<i>I</i>₆₁₆ ratio exhibits a linear relationship with N₂H₄ concentration in the range of 1.0-150 μM, and the detection limit for N₂H₄ was determined to be 0.10 μM. With the assistance of smartphones, N₂H₄ concentrations in realistic samples were visualized <i>via</i> RGB image analysis. In addition, both probes were applied in ratiometric fluorescence imaging of N₂H₄ in the living L929 cell line.