LAUSR

Surface of MALDI-MS (matrix assisted laser desorption/ionization mass spectrometry) target is modified for improved signal strength and detection of analytes. Developed method includes on-target enrichment and detection of phosphopeptides / phospholipids using graphene oxide - lanthanide metal oxides (samarium, gadolinium, dysprosium, and erbium) nanocomposites. Enriched phosphopeptides are detected using material enhanced laser desorption/ionization mass spectrometry (MELDI-MS) and phospholipids by LDI-MS. Nanocomposites are prepared using graphene oxide with respective metal salts at high pH. They are characterized for nano-morphology, chemistry, porosity, composition, crystallinity, and thermal stability. Phosphopeptides enrichment protocol is developed and optimized for tryptic β-casein digest and that of phospholipids by phosphatidylcholine standard. Statistical analyses of phosphopeptides and phospholipids from milk show overlapping results for gadolinium, dysprosium and erbium oxide nanocomposites. GO-Gd2 O3 has better enrichment efficiency and application as LDI material. Selectivity for GO-Dy2 O3 is 1:2500, for GO-Sm2 O3 is 1:3500 and 1:4000 for GO-Gd2 O3 . GO-Er2 O3 has sensitivity of 25 fmol whereas the highest sensitivity is down to 0.5 fmol for GO-Gd2 O3 . On-target enrichment is batch to batch reproducible with standard deviation of <1, reduced time of enrichment to 10 min and ease of operation compared to solid phase batch extraction. Developed method enriches serum phosphopeptides characteristic of cancer related phosphoproteins. This article is protected by copyright. All rights reserved.