Probing the effect of charge transfer enhancement in off resonance mode SERS via conjugation of the probe dye between silver nanoparticles and metal substrates
Probing the effect of charge transfer enhancement in off resonance mode SERS via conjugation of the probe dye between silver nanoparticles and metal substrates
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DOI：
10.1039/c3cp51646f
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发表时间：
2013-01-01
影响因子：
3.3
通讯作者：
Bhargava, Suresh K.
中科院分区：
文献类型：
--
作者：
Selvakannan, P. R.;Ramanathan, Rajesh;Bhargava, Suresh K.
在非共振条件下研究了部分极化的银纳米粒子和光学光滑的金银基底之间化学共轭的结晶紫（CV）分子的电荷转移介导的表面增强拉曼散射（SERS）。酪氨酸分子被用作还原剂，将银离子转化为银纳米颗粒，其中氧化的酪氨酸用其半醌基团覆盖银纳米颗粒表面。这种通过醌基团的结合促进了电荷转移并导致部分氧化的银。这在银纳米颗粒和 CV 分子之间建立了化学联系，其中 CV 分子带正电的中心碳可以与氧化酪氨酸分子的末端羧酸根阴离子结合。在滴铸银纳米颗粒与 CV 分子结合后，发现游离末端胺基倾向于与下面的基材结合。值得注意的是，只有那些在部分极化的银纳米粒子和下面的金或银基底之间化学共轭的 CV 分子才被发现在非共振条件下显示出 SERS。通过使用以类似方式制备的金纳米颗粒，证实了纳米颗粒/封端剂界面处的部分电荷转移以及由此产生的 CV 分子共轭对共振 SERS 效应的重要性。在这种情况下，封端剂通过胺基团与纳米颗粒结合，胺基团不利于金纳米颗粒的电荷转移，并且在这些条件下，没有观察到夹层结构中的SERS增强。
The charge transfer-mediated surface enhanced Raman scattering (SERS) of crystal violet (CV) molecules that were chemically conjugated between partially polarized silver nanoparticles and optically smooth gold and silver substrates has been studied under off-resonant conditions. Tyrosine molecules were used as a reducing agent to convert silver ions into silver nanoparticles where oxidised tyrosine caps the silver nanoparticle surface with its semiquinone group. This binding through the quinone group facilitates charge transfer and results in partially oxidised silver. This establishes a chemical link between the silver nanoparticles and the CV molecules, where the positively charged central carbon of CV molecules can bind to the terminal carboxylate anion of the oxidised tyrosine molecules. After drop casting Ag nanoparticles bound with CV molecules it was found that the free terminal amine groups tend to bind with the underlying substrates. Significantly, only those CV molecules that were chemically conjugated between the partially polarised silver nanoparticles and the underlying gold or silver substrates were found to show SERS under off-resonant conditions. The importance of partial charge transfer at the nanoparticle/capping agent interface and the resultant conjugation of CV molecules to off resonant SERS effects was confirmed by using gold nanoparticles prepared in a similar manner. In this case the capping agent binds to the nanoparticle through the amine group which does not facilitate charge transfer from the gold nanoparticle and under these conditions SERS enhancement in the sandwich configuration was not observed.