Interlayer-confined redox in Ti₃C₂Tₓ-MXene laminates: a reagent-free screen-printed platform for the detection of...

Electrochemical MXene sensors are attractive for point-of-care analysis but are often limited by MXene oxidation, reliance on soluble mediators, and multi-step surface chemistries that complicate their use in complex samples. Herein, an interlayer-confined redox (ICR) strategy is implemented based on Ti₃C₂T_x-MXene laminates, where Ti₃C₂T_x is co-filtered with methylene blue (MB) to trap a redox mediator network within its galleries. These free-standing laminates are readily cut and transferred to commercial screen-printed electrodes (SPEs) featuring carbon working and counter electrodes with an integrated Ag pseudo-reference, yielding a sharp, intrinsic voltammetric MB signal at - 0.25 V vs. on-chip Ag without the need for external reagents. Structural and spectroscopic analyses confirm gallery expansion, intact in-plane crystallinity, absence of crystalline TiO₂, minimal mediator leaching, and robust stability through repeated cycling and storage. Optimized differential pulse voltammetry (DPV) with the ICR-MB-MX-11 laminate (optimized from ICR-MB-MX-x variants, x = 4, 7, 11, 14, based on filtrate MB concentration) enables reagent-free detection of the fibroblast growth factor receptor (FGFR) inhibitor erdafitinib (ERD) across 0.05-10.5 µM, achieving a 0.01 µM limit of detection (LOD), ≤ 0.8% intra-/inter-electrode relative standard deviation (RSD; n = 3), and 98 - 102% recoveries in spiked, PBS-diluted human urine. Density‑functional calculations indicate that ERD adsorption perturbs the MB‑induced electronic arrangement at the Fermi level, consistent with a mediator‑gated inhibition mechanism. More broadly, the reagent-free MXene/SPE configuration may also support field-deployable analysis of complex aqueous matrices relevant to environmental and resource-processing applications.