Tissue Validation by DESI-MSI
A commercial DESI system (Prosolia, Indianapolis, U.S) was employed for tissue imaging. N, N-dimethyl formamide-acetonitrile (1:1, v/v) was used as the spray solvent with a flow rate at 1.0 μL/min and nebulizer gas pressure at 1.6 MPa. The impact angle between sprayer and section mounting stage was 56°. High voltage of +4.0 kV was provided by the mass spectrometer and applied onto the sprayer to generate the electrospray for desorbing and ionizing the components across the tumor cryosection (12 μm). Target ion image reconstruction was achieved using Massimager (Chemmind Technologies Co., Ltd, China).