Ion-Desorption Efficiency and Internal-Energy Transfer in Surface- Assisted Laser Desorption/Ionization: More Implication(s) for the Thermal-Driven and Phase-Transition-Driven Desorption Process
KM Ng and SL Chau and HW Tang and XG Wei and KC Lau and F Ye and AMC Ng, JOURNAL OF PHYSICAL CHEMISTRY C, 119, 23708-23720 (2015).
Fundamental factors governing the ion-desorption efficiency and extent of internal-energy transfer to a chemical thermometer, benzylpyridinium ion (BP(+)), generated in the surface-assisted laser desorption/ionization (SALDI) process, were systematically investigated using noble metal nanopartides (NPs), including AuNPs, AgNPs, PdNPs, and PtNPs, as substrates, with an average particle size of 1.7-3.1 nm in diameter. In the correlation of ion-desorption efficiency and internal- energy transfer with physicochemical properties of the NPs, laser- induced heating of the NPs, which are dependent on their photoabsorption efficiencies, was found to be a key factor in governing the ion- desorption efficiency and the extent of internal-energy transfer. This suggested that the thermal-driven desorption played a significant role in the ion-desorption process. In addition, a stronger binding affinity of BP(+) to the surface of the NPs could hinder its desorption from the NPs, and this could be another factor in determining the ion- desorption efficiency. Moreover, metal NPs with lower melting points could also facilitate the ion-desorption process via the phase- transition process, which could lower the activation barrier (Delta G(#)) of the ion-desorption process by increasing the entropic change (Delta S-#). The study reveals that high photoabsorption efficiency, weak binding interaction with analyte molecule, and low melting point could be critical for the design of SALDI substrates with efficient ion desorption.
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