Defect-Engineered MXene/Polypyrrole-TiN Hybrid Enables Ultrasensitive Molecularly Imprinted Electrochemical Sensor for Highly Selective Detection of PFOS

Drinking water safety represents a critical global environmental challenge. Perfluorooctanesulfonate (PFOS), a persistent organic pollutant widely distributed worldwide, poses severe threats to human health due to its bioaccumulative potential and inherent toxicity. In this study, we developed a molecularly imprinted electrochemical sensor based on an MXene/polypyrrole (PPy) hybrid for the highly sensitive quantification of PFOS in aqueous environments. Through controlled pyrolysis-induced carbon confinement on MXene surfaces, defect-engineered structures were constructed. This strategy simultaneously expanded MXene interlayer spacing while mitigating oxidation-induced structural degradation and layer stacking, thereby enhancing electrical conductivity and interfacial electron transfer kinetics. The resulting signal amplification significantly increased the detection sensitivity. Furthermore, the titanium nitride (TiN) formed during high-temperature pyrolysis enhanced sensor stability and mitigated performance deterioration during electrochemical detection cycles. Under optimized conditions, the molecularly imprinted sensor exhibited a linear response to PFOS across a concentration range from 0.02 nM to 1000 nM, with an ultralow detection limit of 0.5 pM (5 × 10^-13 M). The fabricated sensor also displayed excellent anti-interference capability, reproducibility (RSD < 5.2%), and stability. It was successfully applied to the analysis of tap water, river water, and simulated wastewater, with satisfactory recoveries ranging from 90.3% to 113.3%. This work provides an efficient and cost-effective strategy for monitoring PFOS in water samples.