Molecular detection by liquid gated Hall effect measurements of graphene

Conventional electrical biosensing techniques include Cyclic Voltammetry (CV, amperometric) and ion-sensitive field effect transistors (ISFETs, potentiometric). However, CV is not able to detect electrochemically inactive molecules where there is no redox reaction in solution, and the resistance change in pristine ISFETs in response to low concentration solutions is not observable. Here, we show a very sensitive label-free biosensing method using Hall effect measurements on unfunctionalized graphene devices where the gate electrode is immersed in the solution containing the analyte of interest. This liquid gated Hall effect measurement (LGHM) technique is independent of redox reactions, and it enables the extraction of additional information regarding electrical properties from graphene as compared with ISFETs, which can be used to improve the sensitivity. We demonstrate that LGHM has a higher sensitivity than conventional biosensing methods for l-histidine in the pM range. The detection mechanism is proposed to be based on the interaction between the ions and graphene. The ions could induce asymmetry in electron-hole mobility and inhomogeneity in graphene, and they may also respond to the Hall effect measurement. Moreover, the calculation of capacitance values shows that the electrical double layer capacitance is dominant at relatively high gate voltages in our system, and this is useful for applications including biosensing, energy storage, and neural stimulation.