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A sensitive blue fluorescent probe based on carbon dots has been synthesized by a one-pot hydrothermal method for the rapid detection of FA. [Display omitted] • A facile one-step hydrothermal synthesis of N-doped carbon dots (N-CDs) for FA detection using salicylic acid as a precursor was proposed. • N-CDs was used for selective and sensitive detection of FA with excellent detection limits (28 nM). • The fluorescence quenching of N-CDs caused by FA could be attributed to the synergy of static quenching mechanism and internal filtering effect (IFE). • N-CDs possessed good biocompatibility and had been successfully applied to cell imaging. The folic acid (FA) level in human body can be used as an indicator for body's normal physiological activities and offer insight into the growth and reproduction of the body's cells. But the abnormal level of FA can cause some diseases. Herein, we designed a simple and convenient approach to prepare fluorescent N-doped carbon dots (N-CDs) for the FA detection. These N-CDs have excellent hydrophilicity, high photostability, and outstanding biocompatibility, as well as excitation-independent emission behavior with typical excitation/emission peaks at 295 nm/412 nm. Upon the existence of FA, the fluorescence emission spectrum of N-CDs was significantly quenched through the synergy of static quenching mechanism and internal filtering effect (IFE). Under optimal conditions, the limit of detection was 28.0 nM (S/N = 3) within the FA concentration range of 0–200.0 μM. In addition, N-CDs were successfully employed to detect FA in real samples such as urine and fetal bovine serum (FBS), with a recovery rate of 99.6%-100.7% for quantitative addition. Furthermore, cell experiments confirmed the low toxicity and the cell imaging performance of these N-CDs, indicating that the obtained N-CDs could be served as a credible quantitative probe for FA analysis in the field of biosensing. [ABSTRACT FROM AUTHOR]