SURFACE-PLASMON RESONANCE-LASER DESORPTION IONIZATION-TIME-OF-FLIGHT MASS-SPECTROMETRY/

The laser desorption/ionization (LDI) process is investigated under su rface plasmon resonance (SPR) conditions using time-of-flight mass spe ctrometry (TOFMS). We demonstrate that LDI-TOFMS at the SPR angle requ ires a lower minimum laser fluence for the production of silver monome r and cluster cations from ablation of a thin silver film substrate. I n the LDI of gramicidin S deposited on a thin silver film substrate, t he largest intensity for the molecular cation peak occurs when the las er light is incident on the substrate at a specific SPR angle. These r esults fully confirm SPR enhancement of the LDI process. The capabilit y to perform SPR-LDI on a larger molecular weight analyte (1141 amu fo r gramicidin S) represents a new milestone beyond the previous achieve ment with rhodamine B (479 amu). A better understanding of the SPR mec hanism is gained with respect to the substrate metals (silver vs alumi num), desorption (microscopic vs mesoscopic), and ionization (chemical vs multiphoton). These findings may be useful in the future design of SPR-LDI techniques for better TOFMS analysis of higher mass biomolecu les.