Selective and Fast Cortisol Sensing in Human Saliva Using Graphene‐Based On‐Chip Field‐Effect Transistors

Monitoring of biomarkers in body fluids is highly sought after for medical diagnostics and tracking health conditions. Conventional analytical methods require centralized facilities and complex protocols, limiting applicability for real‐time or point‐of‐care use. In recent years, graphene‐based transducers have shown high potential for miniaturized biosensing, however they have so far been hardly tested in real‐case scenarios. In this work, electrolyte‐gated graphene field‐effect transistors (EG‐GFETs) are developed for the detection of the primary stress hormone cortisol in human saliva. The sensor consists of chemical vapor deposition (CVD)‐grown graphene functionalized with perylene bisimide (PBI) linkers for immobilizing anticortisol (17) Fab fragments. Cortisol is detected over a dynamic range from 100 fM to 1 μM, covering physiologically relevant concentration ranges. The measurements show high correlation with enzyme‐linked immunosorbent assay (ELISA) tests performed in parallel on the same samples. The immediate, label‐free sensing of biomarkers in human saliva represents a major advance in miniaturized biosensing and can potentially be extended to further analytes and integrated portable monitoring units.