As one of the most important post-translational modifications, protein phosphorylation regulates various biological functions and involves in several diseases including cancer.^[1] While phosphoproteomics attracts increasing interest, the detection of phosphorylated proteins/peptides by mass spectrometry (MS) is still challenging due to their low abundance, high dynamic range and poor ionization efficiency. Currently metal oxide affinity chromatography (MOAC) is considered more applicable^[2] compared to other pre-treatment strategies. Various metal oxides have been proposed as affinity probes (APs), and among them SnO₂ is considered as a selective and effective material^[2].

Recently we applied porous SnO₂ spheres with large surface area and high activity on phosphopeptide enrichment, and compared their performance with non-porous SnO₂ and commercial TiO₂. In a typical enrichment process the protein digests were incubated with the MOAC materials in a batch mode, and then the eluted peptides were analyzed by MALDI-TOF MS (matrix-assisted laser desorption/ionization-time of flight mass spectrometry). The mass spectra showed that better results could be obtained using porous SnO₂ in both sensitivity and real sample analysis. For tryptic digests of β-casein, when the concentration was as low as 4×10^-10 M, three phosphopeptides can still be detected after enrichment by porous SnO₂.

References
[1] Stern, D. F. Phosphoproteomics. Experimental and Molecular Pathology, 2001, 70 (3), 327-331.
[2] Leitner, A. Phosphopeptide enrichment using metal oxide affinity chromatography. Trac-Trends in Analytical Chemistry, 2010, 29 (2), 177-185.