Körsgen Martin, Tyler Bonnie J, Pelster Andreas, Lipinsky Dieter, Dreisewerd Klaus, Arlinghaus Heinrich F
Physikalisches Institut, University of Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany.
Institute for Hygiene, University of Münster, Robert-Koch-Str. 41, 48149 Münster, Germany and Interdisciplinary Center for Clinical Research (IZKF), University of Münster, Domagkstr. 3, 48149 Münster, Germany.
Biointerphases. 2016 Jun 1;11(2):02A318. doi: 10.1116/1.4940911.
Time of flight secondary ion mass spectrometry (ToF-SIMS) is a powerful technique for the nanoanalysis of biological samples, but improvements in sensitivity are needed in order to detect large biomolecules, such as peptides, on the individual cell level at physiological concentrations. Two promising options to improve the sensitivity of SIMS to large peptides are the use of cluster primary ions to increase desorption of intact molecules or the use of matrix-assisted laser desorption/ionization (MALDI) matrices to increase the ionization probability. In this paper, the authors have combined these two approaches in order to improve understanding of the interaction between ionization and fragmentation processes. The peptides bradykinin and melittin were prepared as neat monolayers on silicon, in a Dextran-40 matrix and in two common MALDI matrices, 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxy cinnamic acid (HCCA). ToF-SIMS spectra of these samples were collected using a range of small Bi cluster primary ions and large Ar cluster primary ions. The trends observed in the molecular ion yield and the M+H/C4H8N(+) ratio with primary ion cluster size were sample system dependent. The molecular ion yield of the bradykinin was maximized by using 30 keV Bi3 (+) primary ions in a DHB matrix but in the HCCA matrix, the maximum molecular ion yield was obtained by using 30 keV Bi7 (+) primary ions. In contrast, the molecular ion yield for melittin in both matrices was greatest using 20 keV Ar2000 (+) primary ions. Improvements in the molecular ion yield were only loosely correlated with a decrease in small fragment ions. The data indicate a complex interplay between desorption processes and ion formation processes which mean that the optimal analytical conditions depend on both the target analyte and the matrix.
飞行时间二次离子质谱（ToF-SIMS）是一种用于生物样品纳米分析的强大技术，但为了在生理浓度下在单个细胞水平检测大生物分子（如肽），还需要提高灵敏度。提高SIMS对大肽灵敏度的两个有前景的选择是使用簇状一次离子来增加完整分子的解吸，或使用基质辅助激光解吸/电离（MALDI）基质来增加电离概率。在本文中，作者将这两种方法结合起来，以增进对电离和碎片化过程之间相互作用的理解。将缓激肽和蜂毒肽制备成硅上的纯单层、葡聚糖-40基质以及两种常见MALDI基质（2,5-二羟基苯甲酸（DHB）和α-氰基-4-羟基肉桂酸（HCCA））中的样品。使用一系列小的Bi簇状一次离子和大的Ar簇状一次离子收集这些样品的ToF-SIMS光谱。在分子离子产率以及M+H/C4H8N(+)比值方面观察到的随一次离子簇大小变化的趋势取决于样品体系。在DHB基质中使用30 keV Bi3(+)一次离子时，缓激肽的分子离子产率达到最大值，但在HCCA基质中，则通过使用30 keV Bi7(+)一次离子获得最大分子离子产率。相比之下，在两种基质中，使用20 keV Ar2000(+)一次离子时蜂毒肽的分子离子产率最高。分子离子产率的提高与小碎片离子的减少只是松散相关。数据表明解吸过程和离子形成过程之间存在复杂的相互作用关系，这意味着最佳分析条件取决于目标分析物和基质。
