title: CHCA-modified Au nanoparticles for laser desorption ionization mass spectrometric analysis of peptides.
abstract: Gold nanoparticles (AuNPs) have been studied as a potential solid-state matrix for laser desorption/ionization mass spectrometry (LDI-MS) but the efficiency in ionization remains low. In this report, AuNPs are capped by a self-assembled monolayer of cysteamine and modified with alpha-cyano-4-hydroxycinnamic acid (CHCA) for effective MALDI measurements. CHCA-terminated AuNPs offer marked improvement on peptide ionization compared with citrate-capped or cysteamine-capped AuNPs. The coating also effectively suppresses formation of Au cluster ions and analyte fragment ions, leading to cleaner mass spectra. Addition of glycerol and citric acid to the peptide/AuNPs sample further improves the performance of these AuNPs for LDI-MS analysis. Glycerol appears to enhance the dispersion of AuNPs in sample spots, increasing the sample ionization and shot-to-shot reproducibility, while citric acid serves as an external proton donor, providing high production of protonated analyte ions and reducing fragmentation of peptides on the nanoparticle-based surface. Optimal ratios of citric acid, glycerol, and AuNPs in sample solution have been systematically studied. A more than 10-fold increase for desorption ionization of peptides can be achieved by combining 5% glycerol and 20 mM citric acid with the CHCA-terminated AuNPs. The applicability of the CHCA-AuNPs for LDI-MS analysis of protein digests has also been demonstrated. This work shows the potential of AuNPs for SALDI-MS analysis, and the improvement with chemical functionalization, controlled dispersion, and use of an effective proton donor.
authors.affiliation: Department of Chemistry, University of California-Riverside, Riverside, California 92521, USA.
authors.forename: Jicheng
authors.initials: J
authors.lastname: Duan
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Linman
authors.forename: Chih-Yuan
authors.initials: CY
authors.lastname: Chen
authors.forename: Quan J
authors.initials: QJ
authors.lastname: Cheng
mesh_terms: D003373:Coumaric Acids / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D010449:Peptide Mapping / Q000379:methods*; D010455:Peptides / Q000032:analysis* / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D003373:Coumaric Acids; D010455:Peptides; C007175:alpha-cyano-4-hydroxycinnamate; D006046:Gold