Dual Electronic and Optical Monitoring of Biointerfaces by a Grating-Structured Coplanar-Gated Field-Effect Transistor

We present a novel, portable sensor platform that enables concurrent monitoring of surface mass and charge density variations at thin biointerfaces. This platform combines a coplanar-gated field-effect transistor (FET) architecture with grating-coupled surface plasmon resonance (SPR), yielding an integrated disposable sensor chip prepared by nanoimprint and maskless photolithography techniques. The sensor chip design is suitable for scalable production and relies on reduced graphene oxide (rGO), serving as the FET's semiconductor material for the electronic readout, and a metallic gate electrode surface that is corrugated with a multi-diffractive structure for optical probing with resonantly excited surface plasmons. Together with its integration in a compact instrumentation this results in a form factor optimized solution for dual-mode investigations without compromising the optical or electronic sensor performance. A poly-L-lysine (PLL) - based thin linker layer was deployed at the sensor surface to covalently attach azide-conjugated biomolecules by using incorporated "clickable"dibenzocyclooctyne (DBCO) moieties. Interestingly, the dual-mode measurements allow elucidating the role of the globular nature of the PLL chains when increasing the density of DBCO attached to their backbone, leading to PLL folding and internalization of DBCO moieties, and thus reducing the coupling yield for the used DNA oligomers. We envision that this platform can be employed to studying a range of other biointerface architectures and biomolecular interaction phenomena, which are inherently tied to mass and charge density variations.