Sensitive and selective fluorescent on/off switch for detection of Fe (III) ion in human urine using luminol-functionalized graphene quantum dots

A fluorescent switch based on graphene quantum dots (GQDs) has been synthesized and modified using luminol to detect Fe (III) in human urine selectively. The pyrolysis of anhydrous citric acids produced GQDs abundant in amino groups. The luminol modification shows distinct optical characteristics, improving the fluorescence intensity by approximately 6.41 times compared to GQD alone. The probe employs static quenching to initiate the fluorescence response by utilizing the interaction between Fe (III) and luminol-GQDs, resulting in the suppression of fluorescence. The probe is capable of detecting Fe (III) in both a pure aqueous solution and synthetic urine. Furthermore, it is also able to detect Fe (III) in human urine. The concentration of Fe (III) required to quench the fluorescence intensity of luminol-GQDs exhibits a strong linear relationship. A good linear relationship was obtained for Fe (III) concentrations ranging from 50 to 400 μM. Notably, this sensitivity surpasses that of earlier studies. The detection limit of Fe (III) using luminol-GQDs is approximately 1.5 μM. The real sample detection was conducted using a human urine sample, and satisfactory recoveries of approximately 94.57% were achieved.