Organic Molecular Detection without Debye-Length Limitation by Desorption of Receptor from the Surface of a Graphene Field-Effect Transistor

Charge-based detection of low concentrations of organic molecules using field-effect transistors (FETs) cannot distinguish between functional groups or detect charges beyond the Debye length. This study uses the desorption of modified molecules on the graphene surface, obtained by changing their solubility in water, to detect the target molecules on the graphene FETs. The thiol–ene reaction, which binds maleimide groups to thiol groups, is used to vary the solubility of the modified molecules in water. N-(1-Pyrenyl) maleimide (PMI) was modified on graphene to immobilize the maleimide groups on graphene in a π-stack. The modification changed the potential of graphene and shifted the transfer characteristics in the positive direction. Next, a glutathione (GSH) solution rich in hydrophilic groups was introduced under UV irradiation. The reaction of PMI with GSH increased the water solubility of the former, and a relatively weak π-stack was released, causing PMI to be desorbed from graphene. Consequently, the potential of graphene changed, and the transfer characteristics shifted in the negative direction. From this shift, the graphene FET detected the desorption of PMI from graphene. The FET detected at least 0.1 nM (3.8 pg) of GSH. This method detects the desorption of the modified molecules instead of the adsorption of target molecule having charge. The proposed method can detect low concentrations of target molecules in a solution while circumventing the electric double-layer effect that prevents the detection of charges outside the Debye length. The method can be applied to detect a variety of targets for higly sensitive sensors.