Serum protein profiling by miniaturized solid‐phase extraction and matrix‐assisted laser desorption/ionization mass spectrometry

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Abstract
Serum profiling by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) holds promise as a clinical tool for early diagnosis of cancer and other human diseases. Sample preparation is key to achieving reproducible and well‐resolved signals in MALDI‐MS; a prerequisite for translation of MALDI‐MS based diagnostic methods to clinical applications. We have investigated a number of MALDI matrices and several miniaturized solid‐phase extraction (SPE) methods for serum protein concentration and desalting with the aim of generating reproducible, high‐quality protein profiles by MALDI‐MS. We developed a simple protocol for serum profiling that combines a matrix mixture of 2,5‐dihydroxybenzoic acid and α‐cyano‐4‐hydroxycinnamic acid with miniaturized SPE and MALDI‐MS. Functionalized membrane discs with hydrophobic, ion‐exchange or chelating properties allowed reproducible MALDI mass spectra (m/z 1000–12 000) to be obtained from serum. In a proof‐of‐principle application, SPE with chelating material and MALDI‐MS identified protein peaks in serum that had been previously reported for distinguishing a person diagnosed with breast cancer from a control. These preliminary results indicate that this simple SPE/MALDI‐MS method for serum profiling provides a versatile and scalable platform for clinical proteomics. Copyright © 2005 John Wiley & Sons, Ltd.