Tailored 鈥淪andwich鈥?Strategy in Surface Enhanced Raman Scattering: Case Study with para-Phenylenediamine and Application in Femtomolar Detection of Melamine
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- 作者：Sougata Sarkar ; Soumen Dutta ; Tarasankar Pal
- 刊名：Journal of Physical Chemistry C
- 出版年：2014
- 出版时间：December 4, 2014
- 年：2014
- 卷：118
- 期：48
- 页码：28152-28161
- 全文大小：509K
- ISSN：1932-7455
文摘
Herein, we have implemented a modified sandwich strategy for surface enhanced Raman scattering (SERS) studies aimed at the accomplishment of remarkably enhanced vibrational signatures from preferred Raman probes. Here, para-phenylenediamine (or PDA) has been selected as the test molecule which can concurrently bind to two metal surfaces with its two terminal amino (鈭扤H2) groups. We have deliberately placed this molecule in the nanogaps found in between a nanostructured silver film/island and gold core鈥搒ilver shell nanoparticles using a tailormade approach. The whole method of fabrication of this sandwich-type assembly follows a simple colloidal chemistry route. We observed highly enhanced and well resolved Raman signals from the PDA molecule in this sandwich (i.e., nanostructured Ag-film@PDA@Auc-Ags) assembly. The spectral characteristics were also compared with other modes of assembly/association of the molecule in different Raman active plasmonic environments, and from all these comparative outcomes, we reach the conclusion that this particular sandwich assembly offers the most enhanced SERS profiles for the molecule. It is believed that the generation of immense numbers of SERS active hot spots in the nanogaps of the sandwich assembly cause an exceedingly enhanced electromagnetic field which principally contributes in the observed enhancement. A comparative SERS study was also made with different excitation wavelengths (632.8 and 514 nm lasers, respectively). Finally, we employed this SERS active sandwich-based plasmonic platform for the analytical assay of a common infant and milk-product contaminant, melamine. For this, we have chosen melamine as the Raman probe instead of PDA and have designed a similar sandwich assembly. Then we carried out SERS measurements of melamine employing this sandwich assembly (nanostructured Ag-film@melamine@Auc-Ags). The SERS spectrum was individually recorded for four different concentrations of melamine, and ultimately we were able to detect its concentration down to the femtomolar level (i.e., limit of detection = 10鈥?5 M). Thus, the tailored sandwich-based SERS strategy offers a simple roadmap toward the achievement of highly enhanced SERS signatures from molecules even at trace level concentrations.