A rhodamine-quinoline based chemodosimeter (RHQ) has been designed, synthesized and characterized in this paper. The structure of the sensor is confirmed through single crystal X-ray study. It detects hypochlorite (OCl -) selectively among other analytes studied. It showed colorimetric and orange-red fluorescence "turn-on" upon addition of OCl -. The OCl--promoted ring opening of the rhodamine spirolactam ring in RHQ evokes a large absorbance as well as fluorescence enhancement in water-acetonitrile (1/1, v/v) medium with no significant response to other competitive analytes. Furthermore, we demonstrate here that RHQ can endogenously detect OCl- in human blood cells (peripheral blood mononuclear cells). It also exhibits excellent performance in the "dip stick" method. The optimized structure of the probe is calculated by density functional theory calculations. Moreover, the limit of detection of the probe is in the 10-8 M range. © 2014 the Partner Organisations.