Rapid, Parallel Imaging in Surface Chemistry and Biochemistry

空间成像质谱是一种越来越重要的分析技术，具有广泛的令人兴奋的应用范围，从法医学，组织取样，到并行，高通量化学分析，并且越来越多地被应用于生物样品的表征。空间成像MS通常以两种方式之一进行，微探针或显微镜模式。在前者中，微探针模式，电离源，如离子流或激光辐射，被聚焦到样品上的一个小点，并在该精确位置记录质谱。如果采用离子束，该技术通常被称为二次离子质谱法或西姆斯。然后将样品或离子源移动到新的位置，并重复该过程，直到建立整个空间分辨质谱。相比之下，在显微镜模式下，整个表面被电离，通常是用强脉冲激光辐射，离子通常被记录在二维检测器上。应用快速成像传感器，与几十纳秒的时间分辨率，显微镜模式质谱成像将允许在每个实验周期中的所有质量峰的空间成像。由于可以同时探测到所有碎片，因此需要更少的激光发射和采集周期就可以获得一整套数据。我们在这一领域的概念验证实验已经取得了非常有前景的结果，目前我们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，非常热衷于在该项目的这方面进行合作，提供了一台经过特别改装的商用MALDI光谱仪LaserToF LT 2 Plus，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敏感检测器上。它们的分子量可以从各种分子离子的飞行时间计算出来。仪器的空间分辨率将由成像静电透镜中的球面像差、离子检测器的孔径和成像传感器的像素尺寸的组合来确定，并且原则上可以达到0.25微米。许多已建立的市场将受益于测量技术的这种改进，特别是在生物芯片测试行业中。生物芯片已经被开发用于高通量分析，并且在反相蛋白质微阵列的情况下，通常在小于5平方毫米的区域中点样约500个样品。它们目前是采用荧光或比色技术顺序读取的，这是昂贵的，并且可能不够灵敏。拟议的开发将大大改善使用生物芯片技术的并行测量，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品的需求。

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.