title: Digital microfluidics with in-line sample purification for proteomics analyses with MALDI-MS.
abstract: An in-line sample purification method for MALDI-MS, which relies on the electrowetting-on-dielectric (EWOD)-based technique for digital microfluidics, is reported. In this method, a droplet containing peptides and impurities is moved by EWOD and deposited onto a Teflon-AF surface. A droplet of water is subsequently moved over the spot, where it dissolves and removes the impurities. A droplet containing MALDI matrix is then moved to the spot, which is analyzed by MALDI-MS. This purification method reduces the number of salt adduct peaks caused by low concentrations of impurities (e.g., 20 mM sodium phosphate), and reduces or eliminates the catastrophic effects of high concentrations of impurities (e.g., 8 M urea). The method was used to purify spots made by depositing multiple droplets of contaminated peptides. Spectra from the purified spots showed an increase in the S/N ratio as a function of the number of droplets deposited; when not purified, the S/N ratio remained constant regardless of the number of droplets. Finally, the method was used to purify protein digests for peptide mass fragment (PMF) searches, and was shown to be more efficient than the conventional method of purification with reversed-phase-packed pipet tips. We anticipate this new, in-line sample purification technique for EWOD-MALDI-MS will enable development of integrated high-throughput proteomics analysis methodologies.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
authors.forename: Aaron R
authors.initials: AR
authors.lastname: Wheeler
authors.forename: Hyejin
authors.initials: H
authors.lastname: Moon
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Bird
authors.forename: Rachel R Ogorzalek
authors.initials: RR
authors.lastname: Loo
authors.forename: Chang-Jin C J
authors.initials: CJ
authors.lastname: Kim
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Loo
authors.forename: Robin L
authors.initials: RL
authors.lastname: Garrell
mesh_terms: D053000:Analytic Sample Preparation Methods; D000804:Angiotensin II / Q000032:analysis; D008666:Metalloendopeptidases / Q000378:metabolism; D046210:Microfluidic Analytical Techniques / Q000379:methods*; D009211:Myoglobin / Q000378:metabolism; D040901:Proteomics / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D009211:Myoglobin; D025801:Ubiquitin; D000804:Angiotensin II; D008666:Metalloendopeptidases; C039830:peptidyl-Lys metalloendopeptidase