Characterizing the Interactions of DNA Oligomers with Graphene Field-Effect Transistors

Abstract

Introduction: Graphene field-effect transistors (G-FETs) constitute an emerging platform for biosensing applications. Indeed, graphene is an ideal material for the detection of biomolecules: every atom of its monolayer structure is in contact with its environment, resulting in an electrical conductivity that is highly responsive to local electrostatic fluctuations from adjacent molecules. For genomic applications, most detection methods use DNA probe sequences bound to the graphene surface, in order to capture a specific target DNA sequence and detect the corresponding change in the electrical response of the sensor1 - 2. However, the effect of interactions between DNA and graphene on the electrical conductance is still not fully understood. Here, we investigate specifically the adsorption of short DNA oligomers on graphene field-effect transistors, in order to model and control the effect of such interactions in biosensing applications with G-FETs. Methods and Results: First, we fabricated G-FET sensors as follow3: Using photolithography techniques, an array of source and drain electrodes were patterned in gold on a Si wafer with a SiO2 insulator layer, as well as a common on-chip gate electrode in platinum. High-quality monolayer CVD-grown graphene was transferred onto the substrate and then etched to create 6 x 4 µm ribbons between each source-drain pair. Transfer curves (Isd vs. Vg) performed in saline buffer solution revealed a conductance minimum at the charge neutrality point of the graphene. Devices were then exposed to solutions of DNA, consisting in 22-single-stranded nucleotides (ssDNA) or double-stranded nucleotides (dsDNA) DNA oligomers diluted in 0,01X PBS buffer. Selected G-FET devices were exposed to different ssDNA concentrations during 15 min, followed by washing steps with 0,01X PBS. Electrical curves were recorded before, during and after each DNA exposure. In this presentation, we will present results showing that ssDNA exposure causes a left-shift of the charge neutrality point above a concentration threshold, and that this shift is proportional to ssDNA concentration. In addition, non-covalent adsorption of ssDNA on graphene appears to be reversible upon washing. Finally, we will discuss differences between the adsorption of dsDNA and ssDNA. Conclusion and Relevance: Our results suggest that unspecific DNA adsorption on graphene can lead to a G-FET response, which needs to be modeled, compensated and /or passivated in biosensing experiments, especially in order to achieve low detection limits for target sequences in complex biological media.