Defect-Engineered Graphene Nanoribbons for Enhanced DNA Sequencing: A Study of Structural Defects and Their Impact on Nucleobase Interaction and Quantum Transport.

Graphene, a low-dimensional material, has shown significant promise in bioelectronics over the past two decades. Most research in this field has focused on pristine graphene. However, experimentally fabricated two-dimensional (2D) graphene and one-dimensional (1D) graphene nanoribbons (GNRs) often contain impurities, such as Stone-Wales (sw) and divacancy (dv) defects. In this study, we conducted a comparative analysis of the adsorption behavior of DNA nucleobases-adenine (A), guanine (G), thymine (T), and cytosine (C)─on three types of graphene nanoribbon (GNR) surfaces: pristine (prGNR), divacancy-defected (dvGNR), and Stone-Wales-defected (swGNR). Using semilocal (PBE) and van der Waals-corrected density functional theory methods (vdW-DF2 and PBE-D2), we evaluated the binding energies of the nucleobases on the different GNR surfaces. Our results show that defected GNRs exhibit less negative binding energies for all nucleobases compared to prGNR when dispersion interactions are taken into account. The binding energies calculated using PBE, PBE-D2, and vdW-DF2 methods range from -0.06 to -0.10, -0.55 to -0.80 and -0.59 to -0.78 eV, respectively. The vdW-DF2 method effectively captures vdW interactions, with binding energies following the order G > A > T > C. These interactions result in weak binding between nucleobase and the π-states of the GNR surfaces, inducing a small interfacial dipole and a shift in the energy bandgap. Quantum transport analysis reveals that while pristine GNRs exhibit distinct conduction channels, defects─such as dv and sw configurations─introduce localized states that interact with delocalized ones, generating pronounced