Fluorinated Covalent Organic Framework Films Modified Graphene Field-Effect Transistor Biosensors with Size-Dependent Sieving and Antibiofouling Effect

Graphene field-effect transistors (GFETs) promise label-free biosensing but suffer from nonspecific protein adsorption and poor selectivity in complex biofluids. Herein, we proposed a surface-engineering strategy to endow GFET arrays with antifouling robustness and molecular-sieving selectivity. Two fluorine-rich covalent organic framework (F-COF) films synthesized at the liquid–liquid interface were transferred onto GFET channels through a gentle, solvent-free lamination protocol, creating F-COF/GFET sensors with high transconductance and typical bipolar characteristics of graphene. F-COF films in the modified GFET sensors functioned as size-selective gates for smaller metal ions (e.g., divalent cations like Zn²⁺), but excluded anionic methyl orange and larger cationic Rhodamine B. The F-COF/GFET sensors reduced the nonspecific protein adsorption and allowed the detection of Ca²⁺ at low concentrations (10^–6 M) when exposed to a simulated physiological milieu containing 10^–4 M bovine serum albumin. Decoupling antifouling from recognition at the monomer level provides a generalizable strategy for selective, real-time GFET biosensors in biofluids.