Novel application of 4-nitro-7-(1-piperazinyl)-2,1,3-benzoxadiazole to visualize lysosomes in live cells.

4-Nitro-7-(1-piperazinyl)-2,1,3-benzoxadiazole (NBD-PZ) reacts with carboxylic acids in the presence of condensing agents and is utilized for the fluorescence detection of the generated derivatives in high performance liquid chromatography or capillary electro-phoresis. Although the fluorescence intensity of derivatives of NBD-PZ-CH2CH2NH2 with carboxylic acids is elevated at low pH, the pH-dependent fluorescence of NBD-PZ itself has not yet been investigated. In this study, we determined the fluorescence spectra of NBD-PZ at various pH and found that the fluorescence intensity of NBD-PZ was elevated dramatically at pH <or=7.0. When NBD-PZ was applied to live HGC-27 cells, CW-2 cells, IEC-18 cells, and RAW264.7 cells, we observed that NBD-PZ clearly visualized lysosomes under fluorescence microscopy within 3 min. These findings indicate a novel application of NBD-PZ to visualize lysosomes in live cells, a strategy that offers substantial cost savings over commercially available lysosomal probes.