Tissue imaging with in situ solid-phase extraction micro-funnel based spray ionization mass spectrometry.

Current imaging mass spectrometry techniques are faced with a major challenge related to ion suppression effect. Data regarding low-abundance components or low-polarity compounds cannot be normally obtained presumably because of the discrimination effect of easily ionized chemical components on desorption/ionization process. In this study, a new method was proposed to obtain images of chemical components in biological tissues or sections through in situ solid-phase extraction in sorbent mounted micro-funnel based spray ionization mass spectrometry. An imprint of a strawberry section was formed by gently pressing against a 2D array of micro-funnels. The sorbent mounted micro-funnels were then subjected to in situ single-pixel solid-phase extraction to alleviate the matrix-related ion suppression effect. The achievable spatial resolution is approximately 250 µm. The imaging of the spatial distribution of low-abundance or low-polarity chemicals in the strawberry imprint could be obtained by using a gradient elution strategy. Results demonstrated that the "not observed" remark does not necessarily indicate that a specific compound is non-existent when traditional imaging mass spectrometry techniques are used. The proposed method can be applied to conduct low-abundance chemical imaging through in situ single-pixel sample pretreatment.