Non-Functionalized Graphene Ribbons FET Biosensor Platform: SARS-CoV-2 Detection on TiO₂Gate Dielectric Windows

In this work, we report a graphene field-effect transistor (GFET) biosensor platform able to sense the SARS-CoV-2 contamination in blood plasma and saliva. The GFET was fabricated on a Si/SiO2 wafer with thin metallic films deposited by sputtering. The gate structure is formed by Ti/Au and the source/drain structure are formed by TiN layer. The dielectric gate is formed by 10 nm TiO2. The transistor channel is formed by ten parallel ribbons of monolayer graphene defined by photolithography and O2 plasma etching. The virus sensing tests were performed with contaminated and non-contaminate SARS-CoV-2 plasma and saliva as analytes on the channel region. The channel shape allows the analyte to contact the ten graphene ribbons and the TiO2 gate dielectric. The sensitivity of the GFET biosensor to SARS-CoV-2 was evidenced by drain-source current versus gate-source voltage ( <tex-math notation="LaTeX">IDS × VGS </tex-math> ) and normalized transconductance ( <tex-math notation="LaTeX">GM </tex-math> ) curves, where these measurements with the infected samples showed higher electric currents. The Kelvin probe force microscopy (KPFM) technique was used to extract the graphene ribbons and TiO2 characteristics. These analyses indicate that the TiO2 film promotes the interaction of the two hydroxyl groups at their atomic terminations with the viral proteins in contaminated solutions. Indeed, sensing occurs when the viral particles or induced molecules meet the TiO2 surface, injecting carriers into the graphene channel. Therefore, the main contribution of this work is the presentation of a GFET transistor platform for BioFET to detect the SARS-CoV-2, with no need to functionalize the graphene surface on the channel.