Houlne Michael P, Sjostrom Christopher M, Uibel Rory H, Kleimeyer James A, Harris Joel M
Department of Chemistry, University of Utah, Salt Lake City 84112-0850, USA.
Anal Chem. 2002 Sep 1;74(17):4311-9. doi: 10.1021/ac020325t.
Optical trapping of small structures is a powerful tool for the manipulation and investigation of colloidal and particulate materials. The tight focus excitation requirements of optical trapping are well suited to confocal Raman microscopy. In this work, an inverted confocal Raman microscope is developed for studies of chemical reactions on single, optically trapped particles and applied to reactions used in solid-phase peptide synthesis. Optical trapping and levitation allow a particle to be moved away from the coverslip and into solution, avoiding fluorescence interference from the coverslip. More importantly, diffusion of reagents into the particle is not inhibited by a surface, so that reaction conditions mimic those of particles dispersed in solution. Optical trapping and levitation also maintain optical alignment, since the particle is centered laterally along the optical axis and within the focal plane of the objective, where both optical forces and light collection are maximized. Hour-long observations of chemical reactions on individual, trapped silica particles are reported. Using two-dimensional least-squares analysis methods, the Raman spectra collected during the course of a reaction can be resolved into component contributions. The resolved spectra of the time-varying species can be observed, as they bind to or cleave from the particle surface.
对小结构进行光镊操作是用于操控和研究胶体及颗粒材料的一项强大工具。光镊对紧密聚焦激发的要求非常适合共焦拉曼显微镜。在这项工作中，开发了一种倒置共焦拉曼显微镜，用于研究单个光镊捕获颗粒上的化学反应，并应用于固相肽合成中使用的反应。光镊捕获和悬浮能使颗粒从盖玻片移开并进入溶液，避免来自盖玻片的荧光干扰。更重要的是，试剂向颗粒内的扩散不会受到表面的抑制，因此反应条件模拟了分散在溶液中的颗粒的反应条件。光镊捕获和悬浮还能保持光学对准，因为颗粒在光轴上横向居中且位于物镜的焦平面内，在此处光力和光收集都达到最大值。本文报道了对单个捕获的二氧化硅颗粒上的化学反应进行长达一小时的观察。使用二维最小二乘法分析方法，在反应过程中收集的拉曼光谱可以分解为各组分的贡献。可以观察到随时间变化的物种与颗粒表面结合或从颗粒表面裂解时的分辨光谱。
