Ultrasensitive biomolecular detection using charge transfer and fluorescence quenching in monolayer Graphene-CdSe quantum dots

We present our experimental and computational investigation of charge transfer interactions between monolayer graphene and CdSe quantum dots (QDs) using a graphene field effect transistor (gFET) and ab-initio calculations. The system comprises multichannel gFETs, based on chemical vapor deposition-grown monolayer graphene, where the Dirac points and Fermi levels are monitored through liquid gating in response to biotin-streptavidin and IgG-anti-IgG interactions. When CdSe QDs conjugated with antibodies (Ab) are deposited onto the graphene monolayer, we detect charge transfer using gFET measurements. This charge transfer leads to substantial fluorescence quenching, even in the presence of only a single graphene layer. By combining optical and electrical detection methods, we demonstrate that the presence of an analyte alters the charge transfer between QD-Abs and graphene, disrupting the quenching effect and restoring QD fluorescence. Additionally, we will present both experimental results and density functional theory calculations on graphene-CdSe gFET sensors, which can detect IgG concentrations as low as 0.5 fM.