基于咖啡环效应和表面增强拉曼光谱技术的砷形态分析

Arsenic is found widely in the ecosystem and arsenic speciation is the key to accurately evaluate its toxicity and bioavailability. The regular arsenic speciation depends on bulky lab facilities and suffers from incapability of field studies and potential degradation of arsenic species during analytical processes, therefore, it is urged to develop a fast and convenient analytical method. Surface-enhanced Raman spectroscopy (SERS), being advanced in fast and non-destructive detection, is promising in elemental speciation. However, SERS measurements of different species may suffer from signal interference and background signal disturbance, separation is an efficient approach to reduce signal interference. In this project, SERS coupled with a double-ring coffee ring effect is proposed for the speciation of four commonly existing arsenic species in biological matrices. With reduced surface tension of a droplet and enhanced capillary action at the edge of a droplet, solution in the droplet migrates into peripheral region, which carries arsenicals moving outwards. Since arsenic species’ significant differences in deprotonation and migration capability, arsenic species are expected to have different interactions (electrostatic/adsorptive) with the film and the efficient separation of different arsenicals has a great possibility to be achieved during the outward migration. Once the proposed approach is successful, the separation of arsenicals could be performed by merely evaporating of one droplet on silver nanofilm, and it can be evolved into a brand new simple and fast separation technique, which has bright application prospects in environmental monitoring and food safety.

砷元素广泛存在于生态系统中，砷的形态分析是准确评估其毒性和生物利用率的关键。常用的砷形态分析方法依赖大型设备、无法进行现场分析且砷物质形态在分析过程中可能被破坏，亟需发展快捷的分析方法。表面增强拉曼光谱（SERS）检测技术具有快速无损的优点，在元素形态中有好的应用前景，但多种形态待分析物之间存在信号/背景的相互干扰，分离是解决信号干扰的有效途径。本项目提出结合SERS和双层咖啡环效应来对生物体内常见的四种形态砷物质进行形态分析。拟通过降低液滴的表面张力和增强液滴表面的毛细管作用，使液滴中的溶液能进入液滴外并并继续迁移；利用砷物质差异的电离/迁移能力仅通过一个液滴在纳米银膜上的蒸发来实现不同形态砷的分离。本项目有望成功，成为一种简便快速的新型分离技术，在环境监测和食品安全等领域具有很好的应用前景。

咖啡环效应是一种普遍的现象，在分析化学中研究人员经常将其作为一种特殊的样品富集方法，但是近期一种特殊的双层咖啡环效应描述了其还具有一定的小分子分离能力，但具体的分离机理尚不明晰。在本研究中两种性质差异较大的砷物质被选择作为研究对象，用于调查在双层咖啡环效应下小分子物质分离/迁移的控制因素。结果表明位于纳米银膜上的砷物质在迁移过程中，砷物质和银膜表面的相互作用起关键地位，包括静电作用和极性作用，其中静电作用影响相对更大。咖啡环效应在分析化学有大量应用，但是目前对这一领域的总结较少，因此我们对这一领域开展调查。通过文献调研，首先我们对咖啡环产生的机理进行了总结分析，发现液滴和表面的相互作用以及液滴内部液体流动对咖啡环的形成起关键作用。液滴的表面张力可以有效调控液滴在表面的接触角大小，进而影响咖啡环大小；液滴内部流动包含毛细管流动和马兰戈尼流动对液滴内部物质移动影响很大。随后我们根据咖啡环在分析化学应用中的关键因素对文献进行分类总结，并对咖啡环在分析化学领域的发展进行了展望。