OBJECTIVE To explore a novel pH-sensitive fluorescent probe for in vivo tumor imaging.METHODS Zn5 were obtained in 140℃ after mixed with Me OH,water,Zn(NO_3)2·6 H_2O,H4L and trimethylamine.The fluorescence spectra of Zn5 with the same concentration in different pH aqueous solutions were detected.And the stability of Zn5 was investigated by time dependent fluorescence emission spectra of Zn5 in BSA aqueous solution and 5.0% serum solution.Then,the cytotoxicity of Zn5 was detected by MTT assays.To clarify whether a similar fluorescence response occurs in biological organisms,He La cells were pretreated with probe Zn5(0.5 μmol·L~(-1)) and fluorescence imaging were collected for targeting lysosomes in living cells because of lysosomes′ acidic microenvironment.The A375 tumor-bearing mice were used to assess the imaging ability of Zn5 in vivo.Mouse tumor xenografts were established by injection of A375 cells with 2×10~6 cells per flank.Probe(1 μg·g~(-1)) was administered to mice by injection.Images were obtained using IVIS Spectrum CT Imaging System.RESULTS There is a 11-fold intensity increasing as the pH values changing from 8 to 2.The almost unchanged emission intensities suggest Zn5 is stable in both BSA and serum.Zn5 has negligible cytotoxicity for He La,293 T and CHO-K1 cells.Zn5 can selectively display lysosomes in living cells.Both the 2D and 3D images in vivo distinguish the tumor from other tissues with good fluorescence contrast.CONCLUSION The high chemical stability,emission in the Vis/NIR range,pH sensitivity,a pKa located in the tumor pH range,and low toxicity make Zn5 is suitable for application as a pH-sensitive fluorescent probe for bio-imaging. OBJECTIVE To explore a novel pH-sensitive fluorescent probe for in vivo tumor imaging. METHODS Zn5 were obtained at 140 ° C after mixed with Me OH, water, Zn (NO3) 2.6H2O, H4L and trimethylamine. The fluorescence spectra of Zn5 with the same concentration in different pH aqueous solutions were detected. And the stability of Zn5 was investigated by time-dependent fluorescence emission spectra of Zn 5 in BSA aqueous solution and 5.0% serum solution. Then, the cytotoxicity of Zn 5 was detected by MTT assays. Whether or similar fluorescence response occurred in biological organisms, He La cells were pretreated with probe Zn5 (0.5 μmol·L -1) and fluorescence imaging were collected for targeting lysosomes in living cells because of lysosomes’ acidic microenvironment. A375 tumor -bearing mice were used to assess the imaging ability of Zn5 in vivo. Mouse tumor xenografts were established by injection of A375 cells with 2 × 10 ~ 6 cells per flank. Probe (1 μg · g -1) was administered to mice by injection.Images were obtained using IVIS Spectrum CT Imaging System .RESULTS There is a 11-fold intensity increasing as the pH values ​​changing from 8 to 2. The most likely emission intensities suggest Zn5 is stable in both BSA and serum. Zn5 has negligible cytotoxicity for He La, 293 T and CHO-K1 cells. Zn5 can selectively display lysosomes in living cells. But the 2D and 3D images in vivo distinguish the tumor from other tissues with good fluorescence contrast. CONCLUSION The high chemical stability, emission in the Vis / NIR range, pH sensitivity, a pKa located in the tumor pH range, and low toxicity make Zn5 is suitable for application as a pH-sensitive fluorescent probe for bio-imaging.