Rapid, Parallel Imaging in Surface Chemistry and Biochemistry

空间成像质谱学是一种越来越重要的分析技术，具有从取证、组织采样到并行、高通量化学分析等广泛的令人兴奋的应用，并越来越多地被应用于生物样品的表征。空间成像MS通常以两种方式中的一种进行，即微探头或显微镜模式。在前者的微探针模式中，电离源，如离子流或激光辐射，被聚焦到样品上的一个小点上，并在该精确位置记录质谱图。如果使用离子束，这种技术通常被称为二次离子质谱仪，简称SIMS。然后，样品或离子源被移动到一个新的位置，重复这个过程，直到建立起整个空间分辨的质谱图。相比之下，在显微镜模式下，整个表面被电离，通常伴随着强烈的激光辐射脉冲，离子通常被记录在二维探测器上。将具有数十纳秒时间分辨率的快速成像传感器应用到显微镜模式的质谱学成像中，将允许在每个实验周期中对所有质量峰进行空间成像。由于可以同时检测所有碎片，因此需要更少的激光发射和采集周期来采集完整的数据集。我们在这一领域的概念验证实验已经取得了非常有希望的结果，我们目前正在努力提高我们的空间和质量分辨率，以及样品制备技术。SAI是一家英国基质辅助激光解吸/电离(MALDI)仪器制造商，该公司非常热衷于在该项目的这方面进行合作，提供一种经过特殊改装的商用MALDI光谱仪LaserToF LT2Plus，可以在其上测试快速成像传感器。在新仪器中，各种分子离子的释放位置将被保存并忠实地映射到位置灵敏探测器上。然后，可以根据各种分子离子的飞行时间来计算它们的分子量。仪器的空间分辨率将由成像静电透镜的球差、离子探测器的孔径和成像传感器的像素大小共同决定，原则上可以达到0.25微米。一些成熟的市场将从测量技术的改进中受益，特别是在生物芯片测试行业。生物芯片已被开发用于高通量分析，在反相蛋白质微阵列的情况下，大约500个样本通常被发现在不到5平方毫米的面积内。它们目前是顺序读取的，使用荧光或比色技术，这是昂贵的，可能不够灵敏。拟议的发展将极大地改进使用生物芯片技术的平行测量，产生更快的分析时间和更高的精度，同时消除对昂贵的光化学物质的需求。

Spatial imaging mass spectrometry is an analytical technique of growing importance, with a wide range of exciting applications ranging from forensics, tissue sampling, to parallel, high throughput chemical analysis, and is increasingly being applied to the characterization of biological samples. Spatial imaging MS is usually performed in one of two ways, microprobe or microscope mode. In the former, microprobe mode, an ionization source, such as a stream of ions or laser radiation, are focused to a small point on the sample and a mass spectrum is recorded at that precise location. If an ion beam is employed, the technique is usually referred to as secondary ion mass spectrometry, or SIMS. The sample or the ion source is then moved to a new position, and the process repeated until an entire spatially resolved mass spectrum is built up. By contrast, in microscope mode the entire surface is ionized, usually with an intense pulse of laser radiation, and the ions are typically recorded on a two-dimensional detector. Application of fast imaging sensors, with tens of nanosecond timing resolution, to microscope mode mass spectrometric imaging will allow the spatial imaging of all mass peaks in each experimental cycle. As all fragments can be detected simultaneously, far fewer laser shots and acquisition cycles are required for a full set of data to be acquired. A smaller amount of sample is required, samples suffer less degradation, and overall collection times are reduced.Our proof-of-concept experiments in this area have yielded extremely promising results, and we are currently working to improve our spatial and mass resolution, and sample preparation techniques. SAI, a UK manufacturer of matrix-assisted laser desorption/ionization (MALDI) instruments, is very keen to collaborate on this aspect of the project, providing a specially modified commercial MALDI spectrometer, LaserToF LT2Plus, on which the fast imaging sensors can be tested. In the new instrument, the positions of release of the various molecular ions will be preserved and faithfully mapped onto a position sensitive detector. Their molecular weights can then be calculated from the time of flight of the various molecular ions. The spatial resolution of the instrument will be determined by a combination of the spherical aberration in the image forming electrostatic lens, the pore size of the ion detector, and the pixel size of the imaging sensor, and could in principle achieve 0.25 microns.A number of established markets would benefit from this improvement in the measurement technology, in particular in the biochip testing industry. Biochips have been developed for high throughput analysis, and, in the case of reverse phase protein micro-arrays, some 500 samples are typically spotted in an area of less than five square millimetres. They are currently read sequentially, employing florescence or colorimetry techniques, which is costly and could be insufficiently sensitive. The proposed development will dramatically improve parallel measurements using biochip technology, yielding much faster analysis times and higher precision, whilst at the same time elimination the need for expensive photo-chemicals.