Oxide-on-graphene field effect bio-ready sensors

Electrical detection schemes using nanoscale devices offer fast and label-free alternatives to biosensing techniques based on chemical and optical interactions. Here we report on the design, fabrication, and operation of oxide-on-graphene ion-sensitive field effect sensor arrays using large-area graphene sheets synthesized by chemical vapor deposition. In this scheme, HfO₂ and SiO₂ thin films are deposited atop the graphene sheet and play the dual role of the sensing interface, as well as the passivation layer protecting the channel and electrodes underneath from direct contact with the electrolyte. We further demonstrate the functionalization of the SiO₂ surface with 3-aminopropyltrimethoxysilane (APTMS). The oxide-on-graphene sensors operate in solution with high stability and a high average mobility of 5, 000 cm²/(V·s). As a proof of principle, we demonstrate pH sensing using the bare or the APTMS-functionalized SiO₂ as the sensing surface. The measured sensitivities, 46 mV/pH and 43 mV/pH, respectively, agree well with existing studies. We further show that by applying the solution gate voltage in pulse, the hysteresis in the transfer curve of the graphene transducer can be eliminated, greatly improving the ionic potential resolution of the sensor. These experiments demonstrate the potential of oxide-on-graphene ion-sensitive field effect sensors in on-chip, label-free and real-time biosensing applications.