Department of Chemistry , Wabash College , Crawfordsville , Indiana 47933 , United States.
Anal Chem. 2019 Sep 17;91(18):11723-11730. doi: 10.1021/acs.analchem.9b02304. Epub 2019 Aug 30.
A low-cost second harmonic generation (SHG) microscope was constructed, and, for the first time, SHG microscopy was used for imaging agrochemical materials directly on the surface of common commercial crop leaves. The microscope uses a chromatically fixed (1560 nm) femtosecond fiber laser, a commercial 2D galvanometer mirror system, and a PCIe digital oscilloscope card, which together kept total instrument costs under $40 000 (USD), a significant decrease in cost and complexity from common systems (commercial and home-built) using tunable lasers and faster beam-scanning architectures. The figures of merit of the low-cost system still enabled a variety of measurements of agrochemical materials. Following confirmation of largely background-free SHG imaging of common crop leaves (soybean, maize, wheatgrass), SHG microscopy was used to image active ingredient crystallization after solution-phase deposition directly on the leaf surface, including at industrially relevant active ingredient concentrations (<0.05% w/w). Crystallization was also followed in real-time, with differences in crystallization time observed for different application procedures (spraying vs single droplet deposition). A strong dependency of active ingredient crystallization on the substrate was found, with an increased crystallization tendency observed on leaves vs on glass slides. Different crystal habits for the same active ingredient were also observed on different plant species. Finally, a model extended-release formulation was prepared, with a decrease in active ingredient crystallinity observed vs solution-phase deposition. These collective results demonstrate the need for making diagnostic measurements directly on the leaf surface and could help inform the next generation of pesticide products that ensure optimized agricultural output for a growing world population.
构建了低成本的二次谐波（SHG）显微镜，并首次将 SHG 显微镜用于直接在常见商业作物叶片表面成像农用化学品材料。该显微镜使用固定（1560nm）飞秒光纤激光器、商用 2D 振镜系统和 PCIe 数字示波器卡，总成本低于 40000 美元（USD），与使用可调谐激光器和更快光束扫描架构的常见系统相比，大大降低了成本和复杂性。低成本系统的优点仍然可以实现各种农用化学品材料的测量。在确认了常见作物叶片（大豆、玉米、小麦草）的基本无背景 SHG 成像之后，SHG 显微镜用于直接在叶片表面成像溶液相沉积后的活性成分结晶，包括在工业相关的活性成分浓度（<0.05%w/w）下。还实时跟踪了结晶过程，观察到不同的应用程序（喷雾与单滴沉积）之间结晶时间的差异。发现活性成分结晶强烈依赖于基质，与玻璃载玻片相比，在叶片上的结晶趋势增加。还观察到同一活性成分在不同植物物种上的不同晶体习性。最后，制备了模型控释制剂，与溶液相沉积相比，观察到活性成分结晶度降低。这些综合结果表明需要直接在叶片表面进行诊断测量，并有助于为不断增长的世界人口提供优化的农业产出，为下一代农药产品提供信息。
