A ferrocene-integrated fluorinated molecularly imprinted sensor for external-probe-free and portable PFOA detection

Per- and polyfluoroalkyl substances (PFAS) require sensitive, selective, and field-compatible monitoring in aquatic environments. Perfluorooctanoic acid (PFOA) remains challenging for electrochemical detection because of its intrinsic redox inactivity and amphiphilic structure. Here, an external-probe-free electrochemical sensor was developed by constructing a ferrocene-integrated fluorinated molecularly imprinted polymer on a screen-printed electrode (Fc-F-MIP/SPE). Methacrylic acid, 2,2,2-trifluoroethyl methacrylate, and ferrocenylmethyl methacrylate were rationally combined to provide polar recognition, fluorinated affinity, and built-in redox signaling, respectively. PFOA rebinding restricted the accessibility of the embedded ferrocene units, producing a concentration-dependent signal-off response. Theoretical calculations supported cooperative interactions between PFOA and the functional monomers, while response-based Langmuir-Freundlich-type fitting was consistent with heterogeneous apparent affinities within the imprinted layer. Under optimized conditions, Fc-F-MIP/SPE exhibited a wide detection range of 4.14-4.14 × 10⁸ ng L^-1 and a low detection limit of 3.11 ng L^-1. The sensor also showed good selectivity against common coexisting substances and PFAS analogues, acceptable 7-day storage stability, and satisfactory recoveries in drinking water, tap water, and river water. By integrating amphiphilic recognition with internal ferrocene-mediated signal transduction, this work provides a reagent-minimized and portable strategy for PFOA monitoring in environmental waters.