Herein, we have reported a low cost simple aminoquinoline based pH sensor HL [HL = 2-methoxy-6-((quinolin-3-ylimino)methyl)phenol]. HL acts as a potential low pH fluorometric as well as colourimetric pH probe. In acidic media it is colourless whereas, in basic media, it is yellow in colour. HL is thoroughly characterized by different spectroscopic techniques viz. UV-visible, fluorescence, ¹H and ¹³C NMR spectroscopy along with ESI-MS and elemental analysis. We are successful in elucidating the X-ray crystal structure of HL. Theoretical calculations such as DFT and TDDFT are also performed to support our experimental findings. The ability of this biocompatible pH sensor (HL) to differentiate normal and cancer cells by alteration of pH will open new vistas for various biomedical applications.