title: Patterned monolayer/polymer films for analysis of dilute or salt-contaminated protein samples by MALDI-MS.
abstract: This paper describes a surface science/mass spectrometry effort to develop and characterize a patterned gold surface that serves as a MALDI sample platform capable of concentrating and purifying proteins. Using microcontact printing, small (200-microm diameter) hydrophilic spots of bare gold or chemically anchored poly(acrylic acid) (PAA) are patterned at 5-mm intervals in a hydrophobic field consisting of a self-assembled monolayer of hexadecanethiol. Building on recent innovations by others, the small hydrophilic spots concentrate the sample to achieve good reproducibility and high sensitivity in the MALDI signal. One of the key features in this work is the combination of the high density of carboxylate groups in PAA with a small spot size to afford both concentration and purification of proteins via ionic interactions. This translates into detection limits for salt-contaminated proteins that are 20-100 times lower (low femtomole) than those reported for previous polymer- or monolayer-modified MALDI probes (using proteins in the 3-15-kDa range). Reflectance FT-IR spectroscopy and ellipsometry were used to determine the amount of protein adsorbed to a PAA-modified sample plate as a function of pH and salt concentration. Amide absorbances in IR spectra correlate well with MALDI-MS signals measured after addition of 2,5-dihydroxybenzoic acid as a matrix.
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Yingda
authors.initials: Y
authors.lastname: Xu
authors.forename: J Throck
authors.initials: JT
authors.lastname: Watson
authors.forename: Merlin L
authors.initials: ML
authors.lastname: Bruening
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000327:Adsorption; D006046:Gold / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D011506:Proteins / Q000032:analysis / Q000302:isolation & purification*; D012492:Salts; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods* / Q000592:standards; D013499:Surface Properties
chemical_list: D000180:Acrylic Resins; D011506:Proteins; D012492:Salts; C006903:carbopol 940; D006046:Gold