Institute of Quality Standard and Testing Technology for Agro-products, Chinese Academy of Agricultural Sciences, Key Laboratory of Agro-food Safety and Quality, Ministry of Agriculture, Beijing, 100081, China; Beijing Titan Instruments Company, Limited, Beijing, 100015, China.
Institute of Quality Standard and Testing Technology for Agro-products, Chinese Academy of Agricultural Sciences, Key Laboratory of Agro-food Safety and Quality, Ministry of Agriculture, Beijing, 100081, China; College of Instrumentation & Electrical Engineering, Jilin University, Changchun, 130012, China.
Talanta. 2020 Aug 15;216:120942. doi: 10.1016/j.talanta.2020.120942. Epub 2020 Mar 20.
Liquid core waveguide (LCW) is well-known as an effective fiber enhanced approach for Raman spectroscopy with features of long optical path and small sampling size. However, inevitable air bubbles introduced in the LCW tube possibly caused light scattering, refraction and reflection so as to further hamper the quantitative analysis. In this work, to eliminate air bubbles, a novel negative pressure system combined with 3D printing was first utilized for the enhanced Raman spectroscopy on the principle of the gas permeability of LCW tube. After optimization, the LCW tube made of Teflon-AF was inserted into a D-shaped support with an internal channel manufactured by 3D printing to create a sealed space; then, air pressure outside the LCW tube was reduced to create a negative pressure via diaphragm pump and magnetic valve controlled by computer. Under adjustable negative pressure, not only can liquid sample be introduced into the LCW tube automatically, but air bubbles can also be removed through the tube wall simply and completely. For real samples, the assembled apparatus was employed as the small sampling system of Raman spectrometer to measure rhodamine B and ethanol in solutions, with the highest 82-fold (ethanol) enhancement of analytical sensitivity vs. the traditional colorimetric ware. The limit of detections (LODs) were 0.7 μg/mL rhodamine B and 0.03% (v:v) ethanol with only 250 μL sample consumption; their linear correlation coefficients (r) were 0.998 and 0.999 in the range from 2 μg/mL to 25 μg/mL (rhodamine B) and 0.1%-5% (ethanol), respectively. It is worth mentioning that the intraday stability and 7-days reproducibility can be both controlled within 7%, which is extremely superior to the previous enhanced Raman spectroscopy. For another, 3D printing enables the LCW detection system more integrated and easier to assemble. So, the proposed method proves many advantages, such as stability, sensitivity, and quickness, in addition of effective physical enhancement, low sample consumption, and long light path. Considering the flexibility of LCW tube, as a versatile module, the negative pressure LCW system should be further suitable to ultraviolet, fluorescence and other detectors, which reveals a favorable application prospect for the fast testing instruments.
液相芯光纤（LCW）作为一种有效的纤维增强拉曼光谱学方法，具有长光路和小采样尺寸的特点。然而，LCW 管中不可避免的气泡可能会引起光散射、折射和反射，从而进一步阻碍定量分析。在这项工作中，为了消除气泡，首次利用负压系统结合 3D 打印技术，根据 LCW 管的透气性原理，对增强拉曼光谱进行了研究。经过优化，将聚四氟乙烯-AF 制成的 LCW 管插入由 3D 打印制造的带有内部通道的 D 形支架中，形成密封空间；然后，通过计算机控制的隔膜泵和电磁阀将 LCW 管外的气压降低，形成负压。在可调负压下，不仅可以自动将液体样品引入 LCW 管，而且还可以通过管壁简单、彻底地去除气泡。对于实际样品，组装后的装置作为小型拉曼光谱仪的采样系统，用于测量溶液中的罗丹明 B 和乙醇，与传统的比色器皿相比，分析灵敏度的最高增强倍数达到 82 倍。罗丹明 B 的检出限（LOD）为 0.7μg/mL，乙醇的检出限（LOD）为 0.03%（v:v），样品消耗量仅为 250μL；在 2μg/mL 至 25μg/mL 范围内（罗丹明 B）和 0.1%-5%（乙醇）范围内，其线性相关系数（r）分别为 0.998 和 0.999。值得一提的是，日内稳定性和 7 天重现性均可控制在 7%以内，这比以前的增强拉曼光谱要好得多。此外，3D 打印使 LCW 检测系统更加集成，更容易组装。因此，该方法除了具有有效的物理增强、低样品消耗和长光路外，还具有稳定性、灵敏度和快速性等优点。考虑到 LCW 管的灵活性，作为一种通用模块，负压 LCW 系统应该进一步适用于紫外、荧光和其他探测器，这为快速检测仪器展示了良好的应用前景。
