Ionization Mechanism in Surface Plasmon Enhanced Laser Desorption/Ionization

Abstract

We researched contribution of a charge transfer (CT) effect to desorption/ionization mechanism in our ultra-high sensitive laser desorption/ionization mass spectrometry based on surface plasmon (SP) excitation (SPLDI-MS). A quantity of CT electrons between a metal surface and sample molecules estimated from Raman measurement is correlated to a mass signal intensity of sample molecule in our SPLDI-MS method. A sample system with a larger quantity of CT electrons gave a higher mass signal intensity. Efficient use of the CT effect would lead to development of a higher sensitive SPLDI-MS and this development would contribute to advancement of various fields.

Synergistic Effect of the Heterostructure of Au Nanoislands on TiO2 Nanowires for Efficient Ionization in Laser Desorption/Ionization Mass Spectrometry

“…26,27 Additionally, the ionization and desorption of analytes were also reported to occur through nonthermal processes by surface plasmon excitation to generate large density of charges as well as by the laser ablation to generate laser-induced plasma. 28,29 Among the various nanomaterials, TiO 2 -based nanostructures of nanoparticles, nanowires, and nanofilms have been used as solid matrices for LDI MS. This is because TiO 2 is an n-type semiconductor with a photocatalytic activity under UV light and can efficiently generate electron−hole pairs for ionization of analytes.…”

“…After the UV laser irradiation, reductive electrons at conduction bands and holes at valence bands are produced, and analytes are ionized through reduction with exited electrons and oxidation with remaining holes . (3) In the case of noble metal nanomaterials, free electrons absorb UV laser energy and ionize the analytes through thermal energy transfer. , Additionally, the ionization and desorption of analytes were also reported to occur through nonthermal processes by surface plasmon excitation to generate large density of charges as well as by the laser ablation to generate laser-induced plasma. , …”

Mechanisms of Nanophase-Induced Desorption in LDI-MS. A Short Review

“…Besides the importance of NP size [ 59 , 72 ] and composition [ 60 ], discussed in the previous section, other factors have been reported to influence the LDI process. Since the early appearance of nanostructures for MS applications, it was shown that surface plasmon (SP) excitation could enhance both the electromagnetic field and the charge transfer between the NP and the adsorbate molecules [ 73 ], thus affecting both desorption and ionization phenomena [ 59 , 74 , 75 ]. Such correlation was deeply studied for gold nanostructures, demonstrating that a visible laser at 532 nm, which can be resonantly absorbed by AuNPs (SP band falling in the 500 nm–600 nm range), positively affects analyte detection [ 74 , 75 , 76 , 77 ], provided that no aggregation phenomena occur.…”