SPR-MS: from identifying adsorbed molecules to image tissues

Surface plasmon resonance (SPR) sensors have become valuable analytical sensors for biomolecule detection. While SPR is heralded with high sensitivity, label-free and real-time detection, nonspecific adsorption and detection of ultralow concentrations remain issues. Nonspecific adsorption can be minimized using adequate surface chemistry. For example, we have employed peptide monolayers to reduce nonspecific adsorption of crude serum or cell lysate. It is important to uncover the nature of molecules nonspecifically adsorbing to surfaces in these biofluids, to further improve understanding of the nonspecific adsorption processes. Mass spectrometry (MS) provides a complementary tool to SPR to identify biomolecule adsorbed to surface. Trypsic digestion of the proteins adsorbed to surfaces led to identification of characteristic peptides from the proteins involved in nonspecific adsorption. Nonspecific adsorption in crude cell lysate results mainly from lipids, as confirmed with SPR and MS but proteins were observed on some surfaces. In another application of SPR and MS, imaging SPR can be used in combination to imaging MS to image tissue sections. Thin sections of mouse liver were inserted in the fluidic chamber of a SPRi instrument and proteins were transferred to the SPRi chip. The SPR chip was then imaged using MALDI imaging MS to identify the biomolecules that were transferred to the SPRi chip.