基于聚二甲基硅氧烷（PDMS）的柔性表面增强拉曼散射（SERS）衬底的制备及其超灵敏检测
Summary
该协议描述了一种用于表面增强拉曼散射的柔性基板的制造方法。该方法已成功用于检测低浓度的R6G和Thiram。
Abstract
本文介绍了一种用于表面增强拉曼散射（SERS）的柔性衬底的制备方法。通过硝酸银（AgNO3）和氨的络合反应合成了银纳米颗粒（AgNPs），然后使用葡萄糖还原。所得的AgNPs表现出均匀的尺寸分布，范围为20 nm至50 nm。随后，采用3-氨丙基三乙氧基硅烷（APTES）对已用氧等离子体表面处理的PDMS衬底进行改性。该过程有助于AgNPs在基板上的自组装。通过系统评估各种实验条件对衬底性能的影响，开发出具有优异性能和增强因子（EF）的SERS衬底。利用这种底物，R6G（罗丹明6G）的检测限为10-10 M，Thiram的检测限为10-8 M，令人印象深刻。该基质被成功用于检测苹果上的农药残留，结果非常令人满意。灵活的SERS基板在实际应用中显示出巨大的潜力，包括复杂场景中的检测。
Introduction
表面增强拉曼散射（SERS）作为拉曼散射的一种，具有灵敏度高、检测条件温和等优点，甚至可以实现单分子检测1,2,3,4。金属纳米结构，如金和银，通常用作SERS基板，以实现物质检测5,6。纳米结构表面的电磁耦合增强在SERS应用中起着重要作用。具有不同尺寸、形状、粒子间距离和成分的金属纳米结构可以聚集起来产生许多“热点”，由于局部表面等离子体共振而产生强烈的电磁场 7,8。许多研究已经开发了具有不同形态的金属纳米颗粒作为SERS底物，证明了它们在实现SERS增强方面的有效性9,10。
柔性SERS衬底具有广泛的应用，其纳米结构能够产生SERS效应沉积在柔性衬底上，便于在曲面上直接检测。柔性SERS底物用于检测和收集不规则、非平面或曲面上的分析物。常见的柔性SERS基材包括纤维、聚合物薄膜和氧化石墨烯薄膜11,12,13,14。其中，聚二甲基硅氧烷（PDMS）是应用最广泛的高分子材料之一，具有透明度高、拉伸强度高、化学稳定性高、无毒、附着力等优点15,16,17。PDMS具有较低的拉曼截面，因此其对拉曼信号的影响可以忽略不计18。由于PDMS预聚物是液态的，因此可以通过热或光固化，从而提供了高度的可控性和便利性。基于PDMS的SERS衬底是相对常见的柔性SERS衬底，在以前的研究中已被用于嵌入各种金属纳米颗粒，用于检测具有示范性性能的不同生化物质19,20。
在SERS衬底的制备中，纳米间隙结构的制备至关重要。物理沉积技术具有高扩展性、均匀性和可重复性等优点，但通常需要良好的真空条件和专用设备，限制了其实际应用21。此外，使用传统的沉积技术在几纳米尺度上制造纳米结构仍然具有挑战性22。因此，通过化学方法合成的纳米颗粒可以通过各种相互作用吸附到柔性透明薄膜上，从而促进金属结构在纳米尺度上的自组装。为了确保成功吸附，可以通过物理或化学修饰薄膜表面来改变其表面亲水性来调整相互作用23。与金纳米颗粒相比，银纳米颗粒表现出更好的SERS性能，但它们的不稳定性，特别是它们在空气中对氧化的敏感性，导致SERS增强因子（EF）迅速降低，影响底物性能24。因此，开发一种稳定的颗粒方法至关重要。
农药残留的存在引起了人们的极大关注，因此迫切需要能够快速检测和识别现场食品中各种危险化学品的可靠方法25,26。柔性SERS基材在实际应用中具有独特的优势，特别是在食品安全领域。本文介绍了一种通过将合成的葡萄糖包被银纳米颗粒（AgNPs）键合到PDMS底物上来制备柔性SERS底物的方法（图1）。葡萄糖的存在可以保护AgNPs，减轻空气中的银氧化。该底物表现出优异的检测性能，能够检测低至10-10 M的罗丹明6G（R6G）和低至 10-8 M的农药硫兰，具有良好的均匀性。此外，柔性基板可用于通过粘接和取样进行检测，具有众多潜在的应用场景。
Protocol
1. 纳米粒子的合成 硝酸银溶液的制备使用精密称量天平，测量 0.0017 g AR 级硝酸银（AgNO3，参见 材料表），并将其加入 10 mL 去离子 （DI） 水中。搅拌混合物以产生 10-3 mol/L AgNO3 溶液。 银-氨络合物的制备取 1 mL AR 级氨水 （NH3.H2O，见 材料表）使用注射器，并在搅拌的同时逐滴加入硝…
Representative Results
本研究利用APTES开发了一种由葡萄糖包裹的合成AgNPs组成的柔性SERS底物，并利用APTES在PDMS上自组装，在实际农药检测应用中实现了优异的检测性能。R6G 和 Thiram 的检出限分别达到 10-10 M 和 10-8 M，增强因子 （EF） 为 1 x 10 5。此外，基材表现出均匀性。 使用改进的 Tollens 方法合成包裹在葡萄糖中的 AgNP28,29。这?…
Discussion
本研究引入了一种柔性SERS底物，通过化学改性将AgNPs与PDMS键合，并取得了优异的性能。在颗粒合成过程中，特别是在银氨络合物合成（步骤1.2）中，溶液的颜色起着至关重要的作用。滴加过多的氨水会对AgNPs的合成质量产生不利影响，可能导致检测结果不成功。合成过程中应注意底物改性（步骤2.2）;否则，AgNP可能无法与PDMS正确结合，从而导致检测性能下降。
在实际制备中?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
该研究得到了国家自然科学基金（批准号61974004和61931018）以及国家重点研发计划（批准号：2021YFB3200100）的支持。该研究感谢北京大学电子显微镜实验室提供电子显微镜。此外，这项研究还感谢崔莹和北京大学地球与空间科学学院在拉曼测量方面的帮助。
Materials
| Ammonia (NH3.H2O, 25%) | Beijing Chemical Works | ||
| APTES (98%) | Beyotime | ST1087 | |
| BD-20AC Laboratory Chrona Treater | Electro-Technic Products Inc. | 12051A | |
| D-glucose | Beijing Chemical Works | ||
| Environmental Scanning electron microscope (ESEM) | FEI | QUANTA 250 | |
| Raman microscope | Horiba JY | LabRAM HR Evolution | |
| Rhodamine 6G | Beijing Chemical Works | ||
| Silicone Elastomer Base and Silicone Elastomer Curing Agent | Dow Corning Corporation | SYLGARD 184 | |
| Silver nitrate | Beijing Chemical Works | ||
| Thiram (C6H12N2S2, 99.9%) | Beijing Chemical Works |
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Cite This Article
Lin, G., Zhu, J., Wang, Y., Yang, B., Xiong, S., Zhang, J., Wu, W. Fabrication of polydimethylsiloxane (PDMS)-Based Flexible Surface-Enhanced Raman Scattering (SERS) Substrate for Ultrasensitive Detection. J. Vis. Exp. (201), e65595, doi:10.3791/65595 (2023).