Efficient multiplexed label-free detection by flexible MXene/graphene oxide fibers with enhanced charge transfer and hot spots effect

Sensors integrated with sampling and analysis processes are the key in analytical chemistry, environmental protection and national security. However, achieving reliable and sensitive large-scale rapid screening of target analytes is still challenging. Herein, we demonstrate a robust surface-enhanced Raman scattering (SERS) sensor by constructing dense and uniform plasmonic hotspots on the flexible Ti₃C₂Tx MXene/graphene oxide (MG) fibers through a self-assemble strategy at the oil-water interface. The produced SERS substrates exhibited an ultralow limit of detection (LOD, 1 ×10⁻¹⁵ M for R6G), outstanding sensitivity (EF = 1.53 ×10¹²) and high stability for R6G molecules (RSD = 9.47%, over 60 days storage). SERS experiments and theoretical simulations suggested that acidified Ti₃C₂Tx MXene further excited charge-transfer (CT) resonance of the system, while the assembled Ag nanostructures produced a large electromagnetic (EM) field enhancement. Thus, the fiber sensor not only realizes the multiplexed and powerful detection of pesticide residues (LOD of 10⁻¹¹ M) with an error < 7.3% via an established concentration-dependent standard color barcodes, but also allows the recognization of target molecules in a wide range of fields, such as methylene blue, crystal violet and nikethamide. This work provides new insights in the development of versatile label-free sensors for the rapid multiplexed analysis of target molecules in real samples.