Plasmon-induced charge transfer desorption/ionization for mass spectrometric analysis of small biomolecules

Abstract

Laser desorption/ionization (LDI) has been an essential ionization means for biological mass spectrometry (MS). It relies on an energy transfer medium to adsorb the light energy and convert it into other forms of energy to desorb and ionize analyte molecules. Noble metal nanomaterials, which are well-known as plasmonic nanomaterials and exhibit unique plasmonic effects, have been increasingly used in LDI. Various mechanisms were proposed; however, the mechanisms remain to be elucidated and verified, especially for biomolecules. Herein, we proposed a plasmon-induced charge transfer desorption/ionization (PICTDI) mechanism. Upon being shined with a laser beam, plasmonic nanoparticles, such as gold nanoparticles (AuNPs), silver nanoparticles (AgNPs) or their mixture, transfer charges (electrons, protons or other cations) from the nanoparticles to surrounding analytes through surface plasmon, leading to analyte desorption and ionization. Hybrid plasmon-excited LDI surpassed single plasmon-excited mode, which can be proved in both positive and negative ion mode and confirmed by a variety of biomolecules, from nucleosides to saccharides to short peptides. This mechanism provides a sound understanding and a useful guideline for rational design of new plasmonic charge transfer nanomedia.