Elucidation of Electrostatic Interaction between Cationic Dyes and Ag Nanoparticles Generating Enormous SERS Enhancement in Aqueous Solution
Elucidation of Electrostatic Interaction between Cationic Dyes and Ag Nanoparticles Generating Enormous SERS Enhancement in Aqueous Solution
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DOI：
10.1021/jp110146y
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发表时间：
2011-04-07
影响因子：
3.7
通讯作者：
Yajima, Toru
中科院分区：
文献类型：
--
作者：
Futamata, Masayuki;Yu, Yingying;Yajima, Toru
将微量的阳离子三苯甲烷(TPM+)染料加入到水溶液中分离的银纳米颗粒中，可得到由几个紧密相邻的悬浮纳米颗粒组成的银絮凝体。在600-800 nm处出现的耦合LSP峰证明了这一变化。然而，中性对罗桑胺(p-RA)分子和中性罗丹明123与它们的阳离子相反，并没有引起银的絮凝，这表明阳离子染料与带负电的银表面之间的静电相互作用对银的絮凝起着至关重要的作用。相应地，阳离子染料分子位于紧密相邻的银纳米颗粒之间的纳米间隙中，这引发了巨大的SERS强度。TPM染料中氨基-NH2、-N(CH3)(2)和-N(C2H5)(2)对空间位阻不敏感。这与静电相互作用的主导作用是一致的。然而，根据共面和螺旋式苯环等分子结构的不同，荧光峰发生了明显的红移，这表明TPM染料在通过氨基吸附时处于微扰的电子态。
Addition of a trace quantity of cationic triphenylmethane (TPM+) dyes to isolated Ag nanoparticles in an aqueous solution yielded Ag flocculates composed of a few closely adjacent suspended nanoparticles. This change was evidenced by coupled LSP peaks emerged at 600-800 nm. However, neutral para-rosaniline (p-RA) molecules as well as neutral rhodamine 123 did not cause the Ag flocculation in contrast to their cations, indicating a crucial role of electrostatic interaction between cationic dyes and negatively charged Ag surfaces for the flocculation. Accordingly, cationic dye molecules are located in the nanogap between closely adjacent Ag nanoparticles which evoked enormous SERS intensity. The formation of the Ag flocculates was insensitive to steric hindrance by different amino groups -NH2, -N(CH3)(2), and -N(C2H5)(2) in TPM dyes. This observation is consistent with dominant role of the electrostatic interaction. Nevertheless, distinct red shifts of fluorescence peaks were observed depending on the molecular structures such as coplanar and propeller phenyl rings, suggesting perturbed electronic states of TPM dyes upon adsorption through the amino groups.