Direct writing of flexible two-dimensional MXene arrays for SERS sensing

Two-dimensional (2D) MXene materials have emerged as promising candidates for surface-enhanced Raman scattering (SERS) to replace conventional noble metal substrates. In this work, we develop a novel method to directly write flexible MXene substrates for the first time. Handwritten high-performance MXene SERS substrates, such as Ti2C, V2C, Mo2C, and Nb2C, are demonstrated, among which the Ti2C MXene shows the highest Raman enhancement factor of up to 4.7 x 105. The underlying SERS mechanisms of the handwritten Ti2C MXene substrates are primarily attributed to the efficient charge transfer at Ti2C/molecule interfaces, which is activated by the vibronic coupling of charge transfer resonance and molecular resonance. Furthermore, the handwritten MXene substrates realize sensitive detection of the prohibited fish drugs and selective detection of the target molecule in a multicomponent environment, suggesting the great potential of MXene substrates in practical applications. This work not only provides a simple method to prepare high-performance SERS substrates, but also opens up a new horizon for the applications of MXenes in SERS sensing. A simple direct writing method to on-demand design flexible 2D M2C (M = Ti, V, Mo, Nb) MXene SERS substrates is developed.