Herein, a convenient on-off fluorescent probe was developed to detect iron ion (Fe³⁺) with sensitivity and selectivity by using highly luminescent ionic liquid-functionalized carbon quantum dots (CQDs) which was prepared by one-step hydrothermal treatment using citric acid and 1-Aminopropyl-3-methylimidazolium. The sensitivity of CQDs for Fe³⁺ was examined by measuring the fluorescence (FL) intensity of various concentrations of Fe³⁺ in CQDs solution and the selectivity of CQDs for Fe³⁺ was examined by adding different metal ions (Na⁺, Mg²⁺, Al³⁺, K⁺, Ca²⁺, Mn²⁺, Zn²⁺, Ag⁺, Cd²⁺, Pb²⁺ and Ba²⁺) into CQDs solution, respectively. The results indicated that the FL intensity of CQDs showed a good linear response to the concentrations of Fe³⁺ in the range of 0-300 μmol L^-1 (R-2 = 0.99) with a detection limit of 13.68 μmol L^-1. Furthermore, based on the redox mechanism, after the fluorescent of CQDs was quenched by Fe³⁺, different neurotransmitters and amino acids were added and the FL test show that only ascorbic acid (AA) can recover the intensity of the CQDs/Fe³⁺, indicating that CQDs/Fe³⁺ can be further used as a on-off fluorescent probe for the detection of AA. It is expected that our strategy may offer a new approach for developing rapid, low cost and sensitive CQDs-based sensors for environmetal and biological sensing applications.