Amine-Functionalized Graphene Quantum Dots for Fluorescence-Based Immunosensing of Ferritin

The current work demonstrates the fabrication and optimization of a fluorescence-based immunosensor for ferritin estimation wherein amine-functionalized graphene quantum dots (afGQDs) and methyl orange are used as a fluorophore–quencher couple. The synthesis of afGQDs is achieved by the hydrothermal method. The synthesized QDs were characterized using analytical techniques such as UV–vis, fluorescence, FTIR, and Raman spectroscopies, XRD diffraction studies, elemental analysis, and morphological studies through transmission electron microscopy. The QDs showed a quantum yield of 51%, which is one of the highest reported for this class of material. Exploiting the high fluorescence of this material, these afGQDs, were conjugated with antiferritin antibodies (Ab) for specific fluorescence-based immunosensing of ferritin. The conjugation was confirmed from contact angle measurements and electrophoresis, which confirmed successful bioconjugation. With methyl orange (MO) as the quencher, the Stern–Volmer plot showed a linear upward trend indicating a static quenching process. After elucidating the quenching mechanism, a nanoprobe-based fluorophore–quencher (Ab@afGQDs-MO) couple was employed for ferritin sensing. Using a dynamic linear range from 10 to 4000 ng·mL^–1 with an R² value of 0.994, a limit of detection of 0.723 ng·mL^–1 is achieved. With optimization of other input parameters, the ferritin is estimated in spiked serum samples as well.