Secondary Ion Mass Spectrometry with Massive Projectiles

德州农工大学的Emile Schweikert和Stanislav Verkhotrov教授在分析和表面化学项目的支持下，研究了金簇作为抛射物的使用，用于检测分析物的原子量，并用于识别亚微米距离内表面上的分子。实验过程是二次离子质谱（SIMS），有两个关键的区别：弹丸的性质和单个弹丸在时间和空间上分解的轰击模式。在之前nsf支持的工作中，该实验室使用了一种液态金属离子源，该离子源产生了各种各样的金簇，例如200个带+4电荷的金原子。这项工作将探讨与大质量金弹丸产生二次离子的效率有关的基本问题。PI还将开发使用金粒子的负离子质谱法来评估空间分辨率。间隔一毫秒的单个射弹序列集中在一个小的表面区域。发生的每一次撞击都通过发射的电子单独记录下来，并与从同一事件中检测到的次级离子的飞行时间数据相关联。这些数据应该允许编制化学图，给出分子的2D或3D分布，预计空间分辨率为25纳米。质谱作为一种化学显微技术的发展对于实现生物结构（如单细胞）的化学定位是非常重要的。这些图像将使我们更好地了解细胞是如何工作的以及如何与其他细胞相互作用的。具有纳米级分辨率的化学成像在表征纳米颗粒方面也非常有用。

Professors Emile Schweikert and Stanislav Verkhotrov of Texas A&M University are supported by the Analytical and Surface Chemistry program to investigate the use of gold clusters as projectiles for the detection of attomol amounts of analyte and for identifying molecules colocated on surfaces within submicron distances. The experimental procedure is secondary ion mass spectrometry (SIMS), with two key differences: the nature of the projectile and the mode of bombardment with individual projectiles resolved in time and space. In previous NSF-supported work, this lab worked with a liquid metal ion source which produces a wide range of gold clusters, e.g. 200 gold atoms with a +4 charge. This work will investigate the fundamental issues related to the efficiency of massive gold projectiles to generate secondary ions. The PI's will also develop negative ion mass spectrometry using the gold particles to assess spatial resolution. A sequence of individual projectiles spaced one millisecond apart is focused on a small surface area. The impacts which occur are each recorded individually via the emitted electrons and correlated with the time-of-flight data of the secondary ions detected from the same event. These data should allow compilation of a chemical map giving a 2D or 3D distribution of molecules with an anticipated spatial resolution of 25 nm. The development of mass spectrometry as a chemical microscopy is very important for achieving the goal of chemically mapping biological structures such as the single cell. These images will lead to a greater understanding of how the cell works and interacts with other cells. Chemical imaging with nanoscale resolution will also be very useful in characterizing nanoparticles.