DESI-MS: analysing ancient proteins from artefacts

吸附在考古文物上的有机残留物提供了适用于古代生活不同方面的宝贵信息来源。例如，对新石器时代到铁器时代陶瓷中脂质的分析正在改变我们对乳制品起源的看法。牛奶中含有蛋白质，尤其是α -酪蛋白，它很容易被陶瓷吸收，虽然不那么坚固，但就其来源的动物而言，它比脂质更具特异性。在我们之前的工作中，我们使用了人工制品的破坏性采样和免疫检测，这使我们能够识别被挤奶的物种。牛奶蛋白是双重有趣的，因为它们随着时间的推移而持续存在的证据与在陶瓷和石器上发现古代蛋白质的说法有关。我们越来越多地使用分析科学，特别是基于质谱仪器技术的方法，因为这些方法不仅能够识别蛋白质，而且能够深入了解蛋白质的保存。因此，当一种叫做解吸电喷雾质谱（DESI-MS）的新分析技术在两年前发明时，我们看到了它在考古学上的明显应用。该方法可以直接从蔬菜、水果、砖块和木材等多种材料的表面分析化合物，而无需任何样品制备。因此，我们为我们的质谱仪之一设计并构建了一个DESI接口，并表明可以使用它来检测和分析有机玻璃表面上的小块蛋白质。我们建议改进DESI-MS的设计，使其更易于使用并接受典型的考古样本。然后，我们将分析两种实验样品，其中一种是通过将未经巴氏消毒的牛奶煮沸并储存在无釉陶瓷罐中，并在地下埋藏1年、2年、4年和8年，另一种是来自印度古吉拉特邦（Gujarat）的陶器破碎样品，这些陶器用于制作牛奶多年，然后从垃圾堆中回收。如果我们能够使用DESI-MS检测到这些日益退化的样品中的酪蛋白，我们将最终在新石器时代到铁器时代的一系列遗址和时期的考古陶器上测试分析仪。

Organic residues sorbed to archaeological artefacts provide a valuable source of information applicable to different aspects of ancient life. For example, analysis of lipids from ceramics dating from the Neolithic to the Iron Age is changing our perception of the origins of dairying. Milk contains proteins, notably alpha-casein, that are readily absorbed onto ceramics and which although less robust, are more specific than lipids in terms of the animal from which they originate. In our previous work we have used destructive sampling of the artefact and immunological detection, which has enabled us to identify the species that was milked. Milk proteins are doubly interesting, because evidence of their persistence over time has relevance to claims for the detection of ancient proteins on both ceramics and stone tools. We are increasingly using analytical science, especially methods based on the instrumental technique of mass spectrometry, as these are able not only to identify proteins, but give insights into this protein preservation. Consequently when a new analytical technique called desorption electrospray ionisation mass spectrometry (DESI-MS) was invented two years ago, we saw obvious application to archaeology. The method makes it possible to analyse compounds directly from the surface of materials as diverse as vegetables or pieces of fruit, bricks, and wood, without any sample preparation. We therefore designed and built a DESI interface for one of our mass spectrometers and showed that it was possible to use it to detect and analyse small pieces of protein on a Perspex surface. We propose to improve the design of our DESI-MS so that it is both easier to use and accepts typical archaeological samples. We will then analyse both experimental samples that were prepared by boiling and storing unpasteurized cow's milk in unglazed ceramic pots and buried in the ground for 1, 2, 4 and 8 years, as well as broken samples of pottery from Gujarat (India) used for many years to prepare milk and then recovered from a refuse heap. If we can detect casein on these increasingly degraded samples using DESI-MS, we will finally test the analyser on archaeological pottery from a range of sites and periods from Neolithic to Iron Age.