Synergistic enhancement of the Ag/ZIF-67 cage@MXene 3D heterogeneous structure for ultrahigh SERS sensitivity and stability

Abstract

There is an urgent need in the in situ field for rapid extraction and analysis of target molecules from irregular surfaces. The application of SERS technology is often limited by low adhesion between precious metal nanoparticles and the substrate and complex fabrication processes. In order to solve this problem, a carbon fiber cloth (CFC) loaded Ag/ZIF-67 cage@MXene 3D detection platform (AZMC) was constructed in this study. The platform takes advantage of the large surface area and defects of MXene flakes to host noble metals, the high carrier transport efficiency between flakes, and van der Waals forces to build highly sensitive and stable composite SERS substrates. The hydrophilicity and subsurface oxidation behavior of MXene make its optoelectronic performance unstable. In this study, the ZIF-67 cage was chemically bonded to MXene through the Co–O–Ti bond, and the ZIF 67@MXene heterojunction was successfully constructed to maintain the optimal photoelectric stability and excellence of MXene. The high performance of the substrate stems from the synergistic effects of charge transfer (CT) and surface plasmon resonance (SPR) of AgNPs and MXene flakes, while the 3D nanocage structure provides additional hotspot regions. Substrate sensitivity was analyzed using rhodamine 6G (R6G) as a probe molecule (detection limit as low as 10⁻¹¹ M). Notably, the AZMC substrate is highly stable (SERS performance remains essentially unchanged after 45 days of exposure to air). Using this substrate, we also successfully analyzed methylene blue (MB) molecules and Sudan I molecules on apple epidermis, which were successfully detected at concentrations of 0.5 mg L⁻¹ and 1 mg L⁻¹, respectively.