Selective Formation of Analyte-Matrix Cocrystals on the Surface of Carbon Nanomaterials for MALDI Mass Spectrometry of Neuropeptides

Abstract

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a powerful tool for analyzing peptides and proteins due to its sensitivity, accuracy, and high salt tolerance. However, biological samples are often limited in quantity, being as low as femtomole to attomole levels. Therefore, preconcentration of analytes is required to obtain sufficient mass intensity. Herein, we demonstrate a novel approach for preconcentration by selectively forming matrix-analyte cocrystals on the surface of carbon nanomaterials (graphene or carbon nanotubes). A CHCA (α-cyano-4-hydroxycinnamic acid) matrix solution containing analytes forms cocrystals uniformly and selectively on the surface of carbon nanomaterials. Unlike the random crystal formation observed on bare silicon or glass substrates, patterning with carbon nanomaterials enables precise and reproducible crystallization at targeted locations. This is evidenced by fluorescence microscope images, which reveal uniform and controlled cocrystal formation specifically in the carbon nanomaterial regions. This targeted enrichment is validated by the significantly enhanced MALDI-MS signals from these areas, demonstrating the effectiveness of our approach in concentrating analytes for MALDI-MS analysis. Such precision makes our method particularly advantageous for the analysis of cell-to-cell signaling molecules such as neuropeptides released from single cells.