The preparation of an FITC-carbon dot nanocomposite and using a C-18 reverse phase column to improve the Hg2+ ion sensitivity of the FITC-carbon dot ratiometric fluorescent sensor

In our study, we tested the parameters that affect the labeling of fluorescein-5-isothiocyanate (FITC) on carbon dots (CDs). The results suggested that the labeling efficiency of FITC on CDs is sensitive to the amount of -NH2 functional groups and the storage environment of the CDs. The labeling experiment and liquid chromatography revealed that some of the dialyzed CDs lack -NH2 functional groups, and therefore cannot be labeled by FITC. Moreover, we further demonstrated that we can significantly improve the Hg2+ ion sensitivity of the FITC-CD nanocomposites by removing these unlabeled CDs using a C-18 reverse phase column. The results suggested that the structural heterogeneity of the CDs could significantly affect the sensitivity of the CD-based sensor and it is important to properly purify the CDs before further use.