Figure 4:

The principle of MALDI-MSI in the context of spatial resolution, analyte delocalization, and dimensions of cells, matrix crystals, and laser beam focus.

(A) In this case, matrix crystal size and laser diameter are both bigger than the average cell size and therefore prevent MSI at cellular resolution. (B) Here, the matrix crystal size is the limiting factor. (C) Here, the laser diameter is bigger than the matrix crystal size and the cell size, hence defining the resolution limit. (D) In this case, matrix and laser allow for resolving single cells. A third limiting factor is diffusion of molecules, which can happen during sample preparation, causing delocalization.