Graphene Surface Functionalization with Pyrene-, Acridine-, and Fluorenyl-Linkers for DNA Hybridization Studies Using Electrolyte-Gate Graphene Field Effect Transistors

This study investigated electrolyte-gated graphene field-effect transistors (EG-gFETs) functionalized with 1-Pyrenebutyric Acid Succinimidyl Ester (PBSE), Fluorenylmethylsuccinimidyl Carbonate (FSC), and Acridine Orange (AO) Succinimidyl Ester followed by functionalization with a 25-mer DNA single-strand sequence and hybridization biosensing experiments, following the shift in the transfer curve minimum conductance point (Δ<i>V</i>_Dirac) at every stage. Using different linker molecules, the sensor demonstrated varying sensitivities: with PBSE, it achieved 19.02 mV/dec; with FSC, 12.35 mV/dec; and with AO, a slope of 13.19 mV/dec was observed. The significantly lower sensitivity of FSC was possibly attributed to a weaker binding affinity with graphene. A Hill parameter of order 0.5 was found for both PBSE and FSC cases, attributed to the combined effects of steric and Coulombic interactions. In the case of AO, a Hill parameter of 0.37 was observed. AO is the only linker among those studied that induces negative charges into graphene upon immobilization due to its positively charged N atom in its ring structure. AO provided a saturation signal similar to PBSE, albeit with lower sensitivity but a more extensive dynamic range. We suggest that this effect is related to a nonlinear screening effect arising from its molecular structure. <i>Ab initio</i> density functional simulations (DFT) were employed to evaluate the structural and electronic properties of the linkers adsorbed on a graphene surface. The results indicate that graphene exhibits either an acceptor (for AO) or donor (for PBSE or FCS) electronic charge behavior, depending on the adsorbed molecule, as evidenced by the displacement of the Dirac cone observed in the band structures.