Intermolecular p-orbital overlaps in unsaturated π-conjugated systems, such as graphene and fluorescent molecules with aromatic structure, serve as the electron-exchanged path. Using Raman-mapping measurements, we observe that the fluorescence intensity of fluorescein isothiocyanate (FITC) is quenched by graphene, whereas it persists in graphene-absent substrates (SiO2). After identifying a mechanism related to photon-induced electron transfer (PET) that contributes to this fluorescence quenching phenomenon, we validate this mechanism by conducting analyses on Dirac point shifts of FITC-coated graphene. From these shifts, Fermi level elevation and the electron-concentration surge in graphene upon visible-light impingements are acquired. Finally, according to this mechanism, graphene-based biosensors are fabricated to show the sensing capability of measuring fluorescently labeled-biomolecule concentrations.
Keywords: Dirac-point shift; Graphene; Raman mapping; electrons transfer; fluorescence quenching; π−π stacking.