Simple and Environmentally Friendly Fabrication of Superhydrophobic Alkyl Ketene Dimer Coated MALDI Concentration Plates

An antibody-free sample pretreatment method for osteopontin combined with MALDI-TOF MS/MS analysis

Osteopontin is an osteoblast-secreted protein with an aspartic acid-rich, highly phosphorylated, and glycosylated structure. Osteopontin can easily bind to integrins, tumor cells, extracellular matrix and calcium, and is related to bone diseases, various cancers, inflammation etc. Here, DEAE-Cibacron blue 3GA was used to extract recombinant osteopontin from human plasma, and to deplete abundant plasma proteins with an antibody-free method. Using selected buffer systems, osteopontin and human serum albumin could be bound to DEAE-Cibacron blue 3GA, while immunoglobulin G was excluded. The bound osteopontin could then be separated from albumin by using different sequential elution buffers. By this method, 1 μg/mL recombinant osteopontin could be separated from the major part of the most abundant proteins in human plasma. After trypsin digestion, the extracted osteopontin could be successfully detected and identified by MALDI-TOF MS/MS using the m/z 1854.898 peptide and its fragments.

Superhydrophobic candle soot/PDMS substrate for one-step enrichment and desalting of peptides in MALDI MS analysis

Superhydrophobic substrate is applied in matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) detection due to its confinement effect. The weak interaction of superhydrophobic surface with water/salts makes it potential in one-step enrichment and desalting of peptide in MALDI MS analysis. We fabricate a superhydrophobic substrate by spin-coating poly(dimethyl siloxane) (PDMS) on a candle soot layer. On this substrate, the peptide analytes can be confined and enriched in a small area due to the confinement effect and its strong hydrophobic interactions with PDMS. Meanwhile, the desalting can be easily realized by removing the residual solution after the absorption of analyst molecules due to the weak interaction between water/salt contaminants and the superhydrophobic surface. Using this substrate, angiotensin III (Ang III) in the presence of salt with high concentration (2 M or saturated) can be analyzed, and the peptide sequence coverage of 10 μg/mL myoglobin (MYO) and bovine serum albumin (BSA) digests is enhanced to 51% and 26%, which is 37% and 21% analyzed with the commercial ZipTipC₁₈ pipette tips. The LOD of bacitracin A (Bac A) in milk with this substrate is 100 pM and nearly 360 times lower than the LOD of standard testing method. This substrate has potential practical applications in proteomics research and actual sample analysis.