基于等离子体腔表面增强拉曼效应的研究

金属离子水滴与液态聚二甲基硅氧烷（PDMS）自发形成的等离子体腔作为一种新型的表面增强拉曼（SERS）基底将等离子体纳米颗粒整合到光学装置中，提高了SERS检测的实用性与可靠性，然而，与其他基底相比，对其最佳生长条件的研究很少。在此，用禁用兽药孔雀石绿（MG）作为探测分子，检验不同生长条件下等离子体腔的特性，包括生长温度和金属离子浓度，以研究等离子体腔的最佳生长条件。金属离子水溶液滴加到互不相容的液态PDMS上时，在表面张力和重力的共同作用下自发形成带开口的球形腔体。同时金属离子扩散到未固化的PDMS中并与残留的Si-H基团反应，金属离子逐渐还原成金属纳米颗粒，并随着PDMS的固化过程在腔体表面逐渐累积，最终形成等离子体腔。其不但能作为角度反射器将入射光限制在腔体中，而且可作为纳米级光子源将吸收的光散射到腔体中，这两个功能共同作用可在基底原本增强作用的基础上进一步提高对MG的拉曼增强效果。较高的生长温度在加快金属离子生长的同时也会加速PDMS的固化，以至于提前结束金属纳米粒子的生长过程。离子浓度越高，形成的金属离子颗粒越大，然而颗粒直径过大，等离子体腔表面的热点数量反而会减少，MG的拉曼增强减弱，因而，必定存在最优化的等离子体腔制备条件使基底对MG的增强效果达到最佳。设置了15，20，25和30 ℃的生长温度以及0.05，0.5，5和50 μg·mL-1的离子浓度，结果表明，在温度为25 ℃，0.5 μg·mL-1的生长条件下等离子体腔实现了对MG的最佳拉曼增强。对等离子体腔生长条件的优化，可为提高该类型基底的SERS增强效果，及可重复制备奠定基础。

Research on Surface Enhanced Raman Effect Based on Plasma Cavity

The plasma cavity formed by metal ion droplets and liquid polydimethylsiloxane (PDMS) as a novel surface-enhanced Raman (SERS) substrate integrates plasmonic nanoparticles into optical devices, improving SERS detection, practicality and reliability, however, there are few studies on their optimal growth conditions compared to other substrates. Here, we used the banned veterinary drug Malachite Green (MG) as a probe molecule to examine the characteristics of the plasma chamber under different growth conditions, including growth temperature and metal ion concentration, to study the optimal growth conditions of the plasma chamber. When the aqueous metal ion solution is dropped onto the mutually incompatible liquid PDMS, a spherical cavity with an opening is spontaneously formed by the combination of surface tension and gravity. At the same time, the metal ions diffuse into the uncured PDMS and react with the residual Si-H groups. The metal ions are gradually reduced to metal nanoparticles, and gradually accumulate on the surface of the cavity as the PDMS solidifies, eventually forming a plasma chamber. It can not only be used as an angle reflector to confine the incident light in the cavity, but also can be used as a nano-scale photon source to scatter the absorbed light into the cavity. These two functions work together to further enhance the Raman enhancement of MG based on the original enhancement of the substrate. The higher growth temperature accelerates the growth of the PDMS while accelerating the growth of the metal ions, so that the growth process of the metal nanoparticles is terminated prematurely. The higher the ion concentration, the larger the metal ion particles formed. However, the particle diameter is too large, the number of hot spots on the surface of the plasma chamber will decrease, and the Raman enhancement of MG will be weakened. Therefore, there must be optimized plasma chamber preparation conditions to maximize the enhancement of the substrate to MG. We set the growth temperature of 15, 20, 25, 30 ℃ and the ion concentration of 0.05, 0.5, 5, 50 μg·mL-1. The results show that the plasma chamber achieves the best Raman enhancement of MG at a temperature of 25 ℃ and 0.5 μg·mL-1 growth conditions. The optimization of plasma chamber growth conditions can lay a foundation for improving the SERS enhancement effect of this type of substrate and repeatable preparation.