A new dynamic in mass spectral imaging for biological systems

与宾夕法尼亚州立SIMS集团提出了一个合作项目，以利用曼彻斯特SIMS集团在2000年开发常规C60初级离子束技术所带来的ToF-SIMS的巨大进步。ToF-SIMS（飞行时间二次离子质谱法）通过用中等能量粒子轰击材料表面，从而去除和检测带电粒子（或离子）形式的分子和原子碎片，从而分析材料的表面化学。与之前使用的原子离子束轰击技术相比，C60光束相当温和地去除分子，确保分析物材料在去除过程中受到的破坏要小得多。C60还提供了更大的分子去除率（溅射），从而提高了灵敏度和分析效率。Winograd教授领导的宾夕法尼亚州立大学小组迅速认识到这一发展的重要性，并与曼彻斯特大学小组同时探索C60溅射和开发应用。最令人兴奋的进步是，由于C60能够去除表层而对底层的破坏很小，因此分子深度分析成为可能，更重要的是，具有良好的2D和3D空间分辨率的3D分子成像。仅在生物学研究方面的潜在应用就很多。两个小组都意识到，要开发这种新能力需要新的仪器概念。曼彻斯特小组得到了EPSRC的资助，与两家英国小公司一起开发一种新的仪器设计。这项工作已接近完成，初步结果表明，它将超出预期。宾夕法尼亚州立大学的研究小组已经获得了资金，将现有的商用质谱仪与C60源的几何形状有所不同。他们系统的产出也超出了预期。通过在国际会议上的讨论，很明显，充分实现这种SIMS分析方法的潜力的研究和开发要求几乎是相同的，但超过了每个小组最初资助工作时设想的水平。提出了PSU和UoM的协调工作计划，以实现新技术的全部力量。这将涉及博士和研究生研究人员的交流，以利用两个小组在两个重点工作领域的专业知识。第一个将涉及基本的溅射研究和分析协议的发展，以充分实现可靠的2和3 D分析和成像的潜力。基础研究将试图揭示和定义离子/材料相互作用和仪器参数影响可靠和可理解的2D和3D化学图像获取的程度。对这两种仪器进行平行研究对这项工作至关重要。另一个重要的操作参数是，这两种仪器都能非常快速地提供大量信息，而输出可能非常复杂。将研究计算方法来处理输出并快速提供可理解的信息，例如使用最新的3D可视化方法和使用MVA分析技术来提取真实的化学信息。灵敏度是质谱成像模式的核心问题，因为对提高空间分辨率水平的渴望意味着永远不可能有足够的离子产量。在大多数情况下，有机SIMS（以及其他解吸质谱，如MALDI和DESI）的当前电离概率小于10-5。将二次离子产率提高至少10倍，将对这一方法和其他质谱学带来巨大的好处。因此，第二个研究领域将研究机制和开发设备，以实现增强阳离子化，特别是生物分子的质子化，以寻求获得10倍以上的增长。

A collaborative project is proposed with the Penn State SIMS Group to capitalise on the dramatic advances in ToF-SIMS resulting from the development of routine C60 primary ion beam technology by the Manchester SIMS Group in 2000. ToF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) analyses the surface chemistry of materials by bombarding the surface with moderate energy particles and thereby removing and detecting molecular and atomic fragments in the form of charged particles (or ions). C60 beams remove molecules rather gently ensuring that the analyte materials are much less damaged in the removal process than under the atomic ion beam bombardment technology previously used. C60 also delivers a much larger molecular removal rate (sputtering) resulting in enhanced sensitivity and analytical efficiency. The Penn State Group under Professor Winograd, rapidly recognised the importance of this development and in parallel with the Manchester group has been exploring C60 sputtering and developing applications. The most exciting advance is that because C60 is able to remove surface layers with little damage to underlying layers, molecular depth profiling is possible and, of even more significance, 3D molecular imaging with good 2D and 3D spatial resolution. The potential applications in biological research alone are legion.Both groups have realized that to exploit this new capability requires new instrument concepts. The Manchester group has been funded by EPSRC to develop a new instrument design with two small UK companies. This is close to completion and initial results show that it will more than meet expectations. The Penn State group has been funded to adapt a current commercial mass spectrometer of somewhat different geometry with a C60 source to the same end. The outputs from their system are also beyond expectations. Through discussions at international meetings it is clear that the research and development requirements to fully realise the potential of this SIMS analysis approach are almost identical, but exceed the level envisaged when each groups' work was originally funded. A coordinated programme of work at PSU and UoM is proposed to realise the full power of the new technologies. This will involve the exchange of doctoral and post-graduate student researchers to harness the expertise of the two groups on two focused areas of work. The first will be concerned with fundamental sputtering studies and analysis protocol development to fully enable the potential for reliable 2 and 3 D analysis and imaging. Fundamental studies will seek to unravel and define the degree to which ion/material interactions and instrumental parameters influence the acquisition of reliable and understandable 2D and 3D chemical images. Parallel studies on the two instruments will be vital for this work. The other important operational parameter is that both instruments deliver vast amounts of information very rapidly and the outputs are potentially very complex. Computational methods will be researched to handle the outputs and deliver understandable information quickly, for example using the latest 3D visualisation methods and the use of MVA analysis techniques to extract real chemical information.Sensitivity is the central issue in mass spectrometry in the imaging mode because the desire for increasing levels of spatial resolution means there can never be enough ion yield. The current ionisation probability in organic SIMS (and indeed in other desorption mass spectrometries such as MALDI and DESI) is less than 10-5 in most cases. Increasing secondary ion yield by at least a factor 10 would be an enormous benefit to this and other mass spectrometries. The second area of research will therefore investigate mechanisms and develop equipment to implement enhanced cationisation and particularly protonation of bio-molecules to seek to obtain a more than 10-fold increase.