MOF-Assisted Nanocellulose Paper-Based Platform for Multiple Surface-Enhanced Raman Scattering Detection

Metal organic frameworks (MOFs), crystalline solids consisting of organic ligands and metal ions, have attracted increasing interest in various areas, including catalysis and biology. Functionalizable pore interiors and ultrahigh surface-to-volume ratios of MOFs make them excellent materials, especially for surface-enhanced Raman scattering (SERS) by the photoinduced charge transfer (PICT) between the MOFs and adsorbed molecules for SERS signal amplification. In our previous work, we demonstrated a p-n junction-assisted MOF substrate for enhancing the SERS signal through additional charge transfer, while the notable structural characteristics of MOFs benefit the SERS selectivity. However, due to this characteristic, a single MOF can only detect analytes at specific energy levels, thereby reducing the efficiency and limiting the detection range of SERS. To address this challenge, in this article, we attempted to synthesize multiple MOFs on the same substrate to achieve SERS with multiple detection functionality. In this study, we demonstrated a ZIF-8/Zn(OH)₂ n-n junction SERS substrate, which can achieve a 4.44 nM limit of detection using methyl orange (MO) as a model analyte, by trapping the additional electrons from Zn(OH)₂ to ZIF-8 to provide stronger electromagnetic enhancement. Then, we developed a multiple MOFs-based SERS analytical platform, incorporating both in situ ZIF-8 and ZIF-67, and utilized them together as SERS substrates. These two systems operated independently under different incident light wavelengths and successfully detected MO and Rhodamine 6G, respectively. Furthermore, this approach broadens the detection range of analytes while maintaining the tailorability and selectivity of MOF substrates simultaneously. This work offers a cutting-edge method for creating high-performance SERS substrates by demonstrating the ability to manipulate hot electrons for remarkable Raman amplification.