Lai Samuel Kin-Man, Cheng Yu-Hong, Tang Ho-Wai, Ng Kwan-Ming
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, People's Republic of China.
Phys Chem Chem Phys. 2017 Aug 9;19(31):20795-20807. doi: 10.1039/c7cp04033d.
Systematically controlling heat transfer in the surface-assisted laser desorption/ionization (SALDI) process and thus enhancing the analytical performance of SALDI-MS remains a challenging task. In the current study, by tuning the metal contents of Ag-Au alloy nanoparticle substrates (AgNPs, Ag55Au45NPs, Ag15Au85NPs and AuNPs, ∅: ∼2.0 nm), it was found that both SALDI ion-desorption efficiency and heat transfer can be controlled in a wide range of laser fluence (21.3 mJ cm to 125.9 mJ cm). It was discovered that ion detection sensitivity can be enhanced at any laser fluence by tuning up the Ag content of the alloy nanoparticle, whereas the extent of ion fragmentation can be reduced by tuning up the Au content. The enhancement effect of Ag content on ion desorption was found to be attributable to the increase in laser absorption efficiency (at 355 nm) with Ag content. Tuning the laser absorption efficiency by changing the metal composition was also effective in controlling the heat transfer from the NPs to the analytes. The laser-induced heating of Ag-rich alloy NPs could be balanced or even overridden by increasing the Au content of NPs, resulting in the reduction of the fragmentation of analytes. In the correlation of experimental measurement with molecular dynamics simulation, the effect of metal composition on the dynamics of the ion desorption process was also elucidated. Upon increasing the Ag content, it was also found that phase transition temperatures, such as melting, vaporization and phase explosion temperature, of NPs could be reduced. This further enhanced the desorption of analyte ions via phase-transition-driven desorption processes. The significant cooling effect on the analyte ions observed at high laser fluence was also determined to be originated from the phase explosion of the NPs. This study revealed that the development of alloy nanoparticles as SALDI substrates can constitute an effective means for the systematic control of ion-desorption efficiency and the extent of heat transfer, which could potentially enhance the analytical performance of SALDI-MS.
在表面辅助激光解吸/电离（SALDI）过程中系统地控制热传递，从而提高SALDI-MS的分析性能仍然是一项具有挑战性的任务。在当前的研究中，通过调整Ag-Au合金纳米颗粒基底（AgNPs、Ag55Au45NPs、Ag15Au85NPs和AuNPs，直径：约2.0 nm）的金属含量，发现在很宽的激光能量密度范围（21.3 mJ/cm²至125.9 mJ/cm²）内，SALDI离子解吸效率和热传递都可以得到控制。研究发现，通过提高合金纳米颗粒的Ag含量，在任何激光能量密度下都可以提高离子检测灵敏度，而通过提高Au含量可以减少离子碎裂程度。发现Ag含量对离子解吸的增强作用归因于随着Ag含量增加激光吸收效率（在355 nm处）的提高。通过改变金属组成来调整激光吸收效率，在控制从纳米颗粒到分析物的热传递方面也很有效。通过增加纳米颗粒的Au含量，可以平衡甚至抵消富含Ag的合金纳米颗粒的激光诱导加热，从而减少分析物的碎裂。在实验测量与分子动力学模拟的相关性研究中，还阐明了金属组成对离子解吸过程动力学的影响。随着Ag含量的增加，还发现纳米颗粒的相变温度，如熔化、汽化和相爆炸温度，可以降低。这进一步通过相变驱动的解吸过程增强了分析物离子的解吸。在高激光能量密度下观察到的对分析物离子的显著冷却效应也被确定源于纳米颗粒的相爆炸。这项研究表明，开发合金纳米颗粒作为SALDI基底可以构成一种有效手段，用于系统地控制离子解吸效率和热传递程度，这有可能提高SALDI-MS的分析性能。
