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Abstract
Graphene-based vertical electrodes may have applications in biomolecular recognition for producing low-cost biodevices with high electronic conductivity. However, they are unsuitable for measuring small interfacial capacitance variations because graphene is mostly composed of basal sp2 carbon surface, which limits its sensitivity as an electrochemical biosensor. Herein, we introduce an unconventional device alternative based on a three-component vertically designed (TCVD) surface comprising ferrocene/graphene/gold deposited on SiO2/Si wafers. Ferrocene is the top layer that promotes reversible redox communication with the electrolyte, while graphene–gold is the strategically projected layer underneath. Bader charge analysis indicated that graphene donates electronic density to the gold surface, thereby significantly increases the charge transfer exchange rate with ferrocene. The TCVD surface is much more reactive and sensitive to charge variations compared with pristine graphene, and it maintains excellent conductive properties. The TCVD device was used to detect DNA hybridization in solutions, since this is well-known to be a challenging process on a pristine graphene vertical device. A TCVD device can detect small interfacial charge perturbations from DNA hybridization. Based on quantum mechanics calculations combined with spectromicroscopy data, it was realized that the unique synergic interaction between gold and graphene amplified biomolecular recognition, whereby DNA in nanomolar range concentration correlated to 0.8 ± 0.1 µF cm-2, which was effortlessly detected. This result is promising since 3.0 µF cm-2 is the limit of quantum capacitance for bare graphene. Notably, these results open a new possibility for next-generation TCVD bioelectronics based on van der Waals surfaces, while further innovation and material scrutiny may lead to the achievement of TCVD devices with robust biomolecular recognition abilities.
