Engineering a Gd₂(WO₄)₃-P@rGO heterostructure for enhanced electrochemical sensing and therapeutic drug monitoring of erdafitinib.

Erdafitinib (ERDF), a pan-FGFR tyrosine kinase inhibitor used in metastatic urothelial carcinoma, demands precise quantification due to its narrow therapeutic index and potential for severe side effects. We report for the first time the fabrication of a Gd₂(WO₄)₃-P@rGO heterostructure as a hybrid electrochemical sensing interface for ERDF detection. The material was synthesized via a facile hydrothermal-ultrasonic approach, producing a structurally integrated composite that leverages the redox activity of Gd₂(WO₄)₃ and the conductivity and defect-rich nature of P-doped rGO. Comprehensive characterization by SEM, TEM, FTIR, XRD, and XPS confirmed the successful formation of a well-dispersed nanocomposite with a crumpled-sheet morphology, uniform Gd₂(WO₄)₃ anchoring, and strong interfacial bonding. The composite electrode demonstrated enhanced electron-transfer kinetics and a significantly amplified ERDF oxidation signal, with a detection limit of 0.0024 nM, high sensitivity (16.670 µA nM⁻¹ cm⁻²), and a wide linear range (0.01-800 nM, R² = 0.9980). Recovery studies in spiked human serum and urine samples yielded excellent results (95.7-104.8% recovery, RSD ≤ 3.65%), validating the sensor's real-world applicability. Importantly, the sensor offers scalable fabrication, requires no toxic reducing agents, and exhibits strong selectivity and long-term stability, making it a novel and sustainable platform for therapeutic drug monitoring, pharmacokinetics, and point-of-care diagnostics.