Direct MS/MS analysis in mammalian tissue sections using MALDI‐QIT‐TOFMS and chemical inkjet technology

Mass spectrometry on 2D samples is known as imaging mass spectrometry , which enables us to visualize molecular distribution on a tissue surface. This technology has been developed using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometers (MALDI‐TOFMS). However, it is difficult to determine constituents of interested regions on the tissue sections. We developed the methodology to overcome this problem. We designated it on‐tissue digestion. It is performed with the chemical inkjet technology to apply enzymes and the matrix‐assisted laser desorption/ionization‐quadrupole ion trap‐time‐of‐flight tandem mass spectrometer (MALDI‐QIT‐TOFMS) to identify molecules directly on the tissue surface. This technique provided us with a tool for an in‐depth understanding of composites of biostructures, especially proteins.