Desorption Electrospray Ionization: Proteomics Studies by a Method That Bridges ESI and MALDI.

INTRODUCTIONDesorption electrospray ionization (DESI) is a desorption ionization (DI) method by nature, and, like matrix-assisted laser desorption/ionization (MALDI), it is used for the analysis of material present on a surface. DESI includes features reminiscent of electrospray ionization (ESI) in respect to both its instrumental and mechanistic aspects. However, the analyte in the DESI experiment is not in solution as in ESI. Instead, a microelectrospray ion source is used to produce charged droplets, ionic clusters, and/or gas-phase ions (depending on chosen experimental conditions), and these are directed at the sample surface. The sample is present in the ambient environment. An electrical potential of several kilovolts (kV) is applied to the spray solution, and pneumatic nebulization is used to assist in desolvation. Ionization of molecules present on the sample surface occurs upon the impact of the ESI-originated, charged particles with the surface. Surfaces include deposited samples on sample holder targets as well as surfaces of natural objects such as biological tissues or minerals.