The research outlined a novel approach for creating a sensitive and efficient ratio fluorescent probe for ciprofloxacin (CIP) detection. The method used the biomass materials passionfruit shell and diethylenetriamine as carbon and nitrogen sources, respectively, to prepare blue fluorescent carbon quantum dots (b-CQDs) with an average size of 3.29 nm and a quantum yield of 19.6% by a hydrothermal method. The newly designed b-CQDs/riboflavin ratio fluorescent probe demonstrates a distinct advantage for CIP monitoring, exhibiting a marked increase in fluorescence intensity at 445 nm upon interaction with CIP, while maintaining a stable intensity at 510 nm. In the water system, the I 445 nm /I 510 nm ratio of the fluorescent probe showed a significant linear relationship with CIP at the concentrations of 0-250 μmol·L -1 , and the probe boasts a low detection limit of 0.86 μmol·L -1 . The outstanding selectivity, broad detection range, low detection limits, and high quantum yield of the b-CQDs highlight their significant potential in the development of advanced sensing probes for efficient detection of ciprofloxacin, offering promising insights for future sensor technology advancements.