State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Science, Graduate School of the Chinese Academy of Sciences, Changchun 130022, Jilin, PR China.
Nanoscale. 2012 Sep 28;4(19):5902-9. doi: 10.1039/c2nr31410j. Epub 2012 Aug 17.
Mercury which is a very important pollutant has drawn significant attention in recent research. So far, among the various detection methods, the strategies based on surface-enhanced Raman scattering (SERS) are quite attractive because of the high sensitivity, and especially as it is reported that Hg(2+) can be directly detected by SERS without tagging. However, the procedure for the direct SERS detection of mercury is still unclear with little experimental evidence, limiting further development of Hg(2+) detection by SERS. Herein, we performed a simple method based on SERS for the detection of mercury ions in water without tagging. It is established that in only 2 min, low concentration of Hg(2+) can be recognized based on the decrease of SERS intensity. The detection procedure is investigated by multiple characterizations and the mechanism proven by the obtained data provides a practical way to further improve the sensitivity of the SERS detection. It is demonstrated that the interaction between Hg(2+) and Ag nanoparticles (Ag NPs) could occur in a short time, which includes the complexation of Hg(2+) with citrate and the formation of amalgam due to the reduction of Hg(2+). This interaction influences the surface plasmon resonance (SPR) property of Ag NPs and thereby decays the electromagnetic enhancement of Ag NPs; meanwhile the interaction also causes the zeta potential decrease of Ag NPs and accordingly affects the adsorption of Raman reporter molecules on the surface of Ag NPs. Therefore, the weakness of SERS intensity in the presence of Hg(2+) should be mainly attributed to the interaction between Hg(2+) and Ag NPs. From the mechanism demonstrated, it can be speculated that using fewer Ag NPs in the detection could improve the sensitivity, because at low Hg(2+) concentration the interaction becomes stronger since every Ag nanoparticle acts with more Hg(2+) ions. Accordingly, we establish that 90.9 pM (18.2 ppt) Hg(2+) is detected in 18 μM Ag NPs, which is much lower than that in reported papers.
汞是一种非常重要的污染物，在最近的研究中引起了广泛关注。到目前为止，在各种检测方法中，基于表面增强拉曼散射（SERS）的策略因其高灵敏度而非常有吸引力，特别是因为据报道，Hg(2+)可以通过 SERS 直接检测，而无需标记。然而，Hg(2+)的直接 SERS 检测程序仍不清楚，实验证据很少，限制了 SERS 对 Hg(2+)检测的进一步发展。在此，我们提出了一种简单的基于 SERS 的方法，用于在不标记的情况下检测水中的汞离子。结果表明，仅需 2 分钟，即可通过 SERS 强度的降低识别低浓度的 Hg(2+)。通过多种特性研究了检测程序，并通过获得的数据证明了该机制为进一步提高 SERS 检测的灵敏度提供了一种实用方法。结果表明，Hg(2+)与 Ag 纳米颗粒（Ag NPs）之间的相互作用可以在短时间内发生，这包括 Hg(2+)与柠檬酸盐的络合以及由于 Hg(2+)的还原而形成汞齐。这种相互作用会影响 Ag NPs 的表面等离子体共振（SPR）性质，从而使 Ag NPs 的电磁增强衰减；同时，这种相互作用还会导致 Ag NPs 的 zeta 电位降低，从而影响拉曼报告分子在 Ag NPs 表面的吸附。因此，存在 Hg(2+)时 SERS 强度的减弱主要归因于 Hg(2+)与 Ag NPs 之间的相互作用。从所证明的机制可以推测，在检测中使用更少的 Ag NPs 可以提高灵敏度，因为在低 Hg(2+)浓度下，由于每个 Ag 纳米颗粒与更多的 Hg(2+)离子相互作用，相互作用变得更强。因此，我们确定在 18 μM 的 Ag NPs 中检测到 90.9 pM（18.2 ppt）的 Hg(2+)，这远低于已报道的文献值。
