Novel multi-layered MXene as laser desorption ionization mass spectrometry matrix for rapid detection of small biomolecules

Five two-dimensional multi-layered MXenes namely MO 2 C, Ti 2 C, V 2 C, Nb 2 C and Ta 2 C were synthesized by a one-step exfoliation process and evaluated as laser desorption ionization mass spectrometry (LDI-MS) matrices for fast detection of small biomolecules for the first time. Among them, Nb 2 C exhibited the best performance due to its high carrier mobility, strong photo-induced charge transfer resonance and good UV absorption ability. A simple, universal and efficient LDI-MS platform was established for small biomolecule analysis based on the Nb 2 C matrix. Key factors that affect LDI-MS efficacy were investigated and the established method demonstrated ultraclean MS background, high sensitivity with detection limits low to fmol level and good reproducibility. The Nb 2 C-based LDI-MS platform was successfully applied in the rapid determination of 13 amino acids (AAs) in human serum and 3 AAs, as potential biomarkers, were found to be significantly down-regulated in major depressive disorder patients. This work proved the feasibility of Nb 2 C MXene as an LDI-MS matrix and provided a promising and universal platform for the rapid detection of small molecules in biomedical research.