Tuning the performance of graphene as a dual-ion-mode MALDI matrix by chemical functionalization and sample incubation

Graphene-based materials have emerged as a new class of matrix for matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS), but the factors governing the performance of graphene are not fully understood. In this study, we show two independent novel approaches to tune the performance of graphene as a dual-ion-mode MALDI matrix, i.e., chemical modification of graphene (e.g., oxidation, fluorination, amination, and carboxylation) and incubation of samples with graphene. We found that both approaches could significantly affect the MS signals, enabling a deep optimization of the performance of graphene in both positive and negative ion mode MALDI-TOF MS. Results showed that the performance of graphene in MALDI was dependent on its inherent chemical properties, self-assembly behavior, and interaction with targets. The two approaches were also validated in surface-enhanced laser desorption/ionization (SELDI). Under the optimized conditions, high sensitivity and good reproducibility were obtained for targets. To our knowledge, this is also the first report that aminated and carboxylated graphene were used as MALDI matrices. This work shows novel approaches to tailor graphene for its applications, and it also helps better understand the mechanism of the LDI process.