Using Graphene Field-Effect Transistors for Real-Time Monitoring of Dynamic Processes at Sensing Interfaces. Benchmarking Performance against Surface Plasmon Resonance

Graphene field-effect transistors (gFETs) are promising tools for the development of precise and affordable techniques for the study of molecular binding kinetics, crucial in applications such as biomolecule therapies, drug discovery, and medical diagnostics. Nevertheless, determining the reliability and modeling the gFET signal for the monitoring of molecular binding and adsorption are still needed. Here, we prove that the gFET technology allows monitoring in real time the adsorption of both positive and negative polyelectrolytes, used as model charged macromolecules, using a low-cost portable gFET setup (Zaphyrus-W10), whose graphene channel was produced by reduction of graphene oxide. The gFET response is compared and validated against the surface plasmon resonance (SPR) technique. Remarkably, the electronic response is directly correlated with the mass adsorption, and very similar kinetic profiles are obtained for both techniques. Moreover, the adsorption kinetics of a polyelectrolyte assembled in a layer-by-layer give evidence that, even at ionic strengths near to the physiological conditions, the electrostatic interactions can be sensed at large distances from the graphene surface (20-fold higher in comparison to the solution Debye length). Biasing the gFET with a Ag/AgCl coplanar gate electrode avoids capacitive current contributions from nonbinding phenomena and displays a transistor signal proportional to the adsorbed mass. Furthermore, a marked amplification of the electronic signal without alteration of the macromolecule adsorption kinetics by using a Ag/AgCl gate in comparison with a nongated device is evidenced. Thus, the suitability of the coplanar-gated gFET technology for the study of molecular binding kinetics is illustrated.