Silina Yuliya E, Koch Marcus, Volmer Dietrich A
Institute of Bioanalytical Chemistry, Department of Chemistry, Saarland University, Saarbrücken, Germany.
J Mass Spectrom. 2014 Jun;49(6):468-80. doi: 10.1002/jms.3362.
Fundamental parameters influencing the ion-producing efficiency of palladium nanostructures (nanoparticles [Pd-NP], nanoflowers, nanofilms) during laser irradiation were studied in this paper. The nanostructures were immobilized on the surface of different solid inorganic carrier materials (porous and mono-crystalline silicon, anodic porous aluminum oxide, glass and polished steel) by using classical galvanic deposition, electroless local deposition and sputtering. It was the goal of this study to investigate the influence of both the nanoparticular layer as well as the carrier material on ion production for selected analyte molecules. Our experiments demonstrated that the dimensions of the synthesized nanostructures, the thickness of the active layers, surface disorders, thermal conductivity and physically or chemically adsorbed water influenced signal intensities of analyte ions during surface-assisted laser desorption/ionization (SALDI) while no effects such as plasmon resonance, photoelectric effect or catalytic activity were expected to occur. Excellent LDI abilities were seen for Pd-NPs immobilized on steel, while Pd nanoflowers on porous silicon exhibited several disadvantages; viz, strong memory effects, dependency of the analytical signal on amount of physically and chemically adsorbed water inside porous carrier, reduced SALDI activity from unstable connections between Pd and semiconductor material, decrease of the melting point of pure silicon after Pd immobilization and resulting strong laser ablation of metal/semiconductor complex, as well as significantly changed surface morphology after laser irradiation. The analytical performance of Pd-NP/steel was further improved by applying a hydrophobic coating to the steel surface before galvanic deposition. This procedure increased the distance between Pd-NPs, thus reducing thermal stress upon LDI; it simultaneously decreased spot sizes of deposited sample solutions.
本文研究了激光辐照过程中影响钯纳米结构（纳米颗粒[Pd-NP]、纳米花、纳米薄膜）离子产生效率的基本参数。通过经典的电沉积、化学局部沉积和溅射，将纳米结构固定在不同的固体无机载体材料（多孔和单晶硅、阳极多孔氧化铝、玻璃和抛光钢）表面。本研究的目的是研究纳米颗粒层以及载体材料对选定分析物分子离子产生的影响。我们的实验表明，合成纳米结构的尺寸、活性层的厚度、表面无序度、热导率以及物理或化学吸附的水会影响表面辅助激光解吸/电离（SALDI）过程中分析物离子的信号强度，而预计不会发生诸如等离子体共振、光电效应或催化活性等效应。固定在钢上的Pd-NP具有出色的激光解吸/电离（LDI）能力，而多孔硅上的钯纳米花则存在几个缺点；即，强烈的记忆效应、分析信号对多孔载体内物理和化学吸附水量的依赖性、由于钯与半导体材料之间不稳定连接导致的SALDI活性降低、钯固定后纯硅熔点降低以及由此导致的金属/半导体复合物强烈激光烧蚀，以及激光辐照后表面形态显著变化。通过在电沉积前对钢表面施加疏水涂层，进一步提高了Pd-NP/钢的分析性能。该过程增加了Pd-NP之间的距离，从而降低了LDI时的热应力；同时减小了沉积样品溶液的斑点尺寸。
