On the role of defects and surface chemistry for surface-assisted laser desorption ionization from silicon
On the role of defects and surface chemistry for surface-assisted laser desorption ionization from silicon
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DOI：
10.1063/1.2802304
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发表时间：
2008-01-07
影响因子：
4.4
通讯作者：
Nikiforov, S.
中科院分区：
文献类型：
--
作者：
Alimpiev, S.;Grechnikov, A.;Nikiforov, S.
本文研究了表面辅助激光解吸电离（SALDI）过程中硅衬底离子的生成，并采用多种方法制备和刻蚀硅衬底。用标准液样沉积法比较了不同底物产生肽质谱的能力。采用气相分析物沉积法研究了解吸/电离过程。对气相碱度大于850 kJ/mol，分子量达370 Da的化合物进行了质谱分析。用紫外、可见和红外激光进行解吸。电离效率被测量为激光能量和累积激光辐照剂量的函数。溶剂蒸气被添加到离子源，并显示出导致基本的激光诱导的基材表面的化学和物理变化。研究表明，高效离子生成需要衬底表面的化学性质和具有高浓度“悬空键”或深间隙态的高度无序结构的存在。特别是，非晶硅被证明是一种优秀的SALDI衬底，电离效率高达1%，而氢钝化的非晶硅是SALDI非活性的。在此基础上，提出了一种新的SALDI离子生成模型，其反应步骤如下：(1)中性分析物分子在SALDI表面的吸附，与表面的Si-OH基团形成氢键；(2)衬底的电子激发形成自由电子/空穴对（它们的松弛导致在近表面深间隙态捕获正电荷，导致Si-OH基团的酸度增加和质子向分析物分子转移）；(3)分析物离子通过“松散”过渡态与表面的热激活解离。(c) 2008年美国物理研究所。
The generation of ions from silicon substrates in surface-assisted laser desorption ionization (SALDI) has been studied using silicon substrates prepared and etched by a variety of different methods. The different substrates were compared with respect to their ability to generate peptide mass spectra using standard liquid sample deposition. The desorption/ionization processes were studied using gas-phase analyte deposition. Mass spectra were obtained from compounds with gas-phase basicities above 850 kJ/mol and with molecular weights up to 370 Da. UV, VIS, and IR lasers were used for desorption. Ionization efficiencies were measured as a function of laser fluence and accumulated laser irradiance dose. Solvent vapors were added to the ion source and shown to result in fundamental laser-induced chemical and physical changes to the substrate surfaces. It is demonstrated that both the chemical properties of the substrate surface and the presence of a highly disordered structure with a high concentration of "dangling bonds" or deep gap states are required for efficient ion generation. In particular, amorphous silicon is shown to be an excellent SALDI substrate with ionization efficiencies as high as 1%, while hydrogen-passivated amorphous silicon is SALDI inactive. Based on the results, a novel model for SALDI ion generation is proposed with the following reaction steps: (1) the adsorption of neutral analyte molecules on the SALDI surface with formation of a hydrogen bond to surface Si-OH groups, (2) the electronic excitation of the substrate to form free electron/hole pairs (their relaxation results in trapped positive charges in near-surface deep gap states, causing an increase in the acidity of the Si-OH groups and proton transfer to the analyte molecules), and (3) the thermally activated dissociation of the analyte ions from the surface via a "loose" transition state. (c) 2008 American Institute of Physics.