These metal layers are separated by an additional thin polymer-based protective layer. Two 0.6 mm thick polycarbonate (PC) layers act as a support for two reflective, mirror-like metal films with a thickness of 0.1 mm. Results and discussion Commercially available double-sided HD DVD disks present a sandwich-like structure consisting of different layers ( Fig. As a result, it could be demonstrated that HD DVD disks are attractive nanostructured materials for plasmonic applications due to the structural arrangement and dimensions of their encoding pits. We report here the fabrication of SERS substrates based on commercial HD DVDs, a theoretical discussion of the surface plasmon characteristics of the HD DVD structure based on finite element modelling (FEM) and finally demonstrate their capabilities for SERS application by the detection of vitamin A (retinol) and pro-vitamin A (β-carotene) as model substances. As a result, the modern CD/DVD industry reached excellent product quality not only for the conventional (CD and DVD) but also for the next-generation (HD DVD and Blue-Ray) disks. 8–10 In particular for the change from common CD to the DVD and later on to the HD DVD standard, the primary priority was the improvement of the molding processes to obtain nanometer precision as well as to establish the required quality controls. These optical storage disks are on one hand very low priced (production costs vary between $0.90 to $1.50 per HD DVD), since large scale production for the mass-market made them a widespread technological product, and are, on the other hand, high quality products regarding their encoded structure.
In the present study we suggest the utilization of a mass-produced commercial product as SERS-active substrates, which is well established in optical data storage technology namely HD-DVDs. Therefore, these fabrication methods need still to be improved before a high efficiency for SERS measurements can be achieved on a reproducible base. Alternatively, bottom-up fabrication methods provide cost-efficient and easily accessible nanostructures but have a limited control over their chemical purity, size and geometry. In general, the applicability of these substrates is limited by high production costs due to demanding technological requirements. Top-down fabrication techniques, including e.g., optical and electron-beam lithography 6,8 can provide SERS-active substrates with a high structural homogeneity and SERS signal reproducibility. Additionally, the Raman signal enhancement behavior should be sufficient for the desired application. One issue for the establishment of SERS tools is the availability of suitable substrates, which should provide nanostructured metallic surface features, that are, at the same time cost-efficient and preferably available in large quantities with a constant quality on a large scale. As a consequence, close to the nanostructured metal surface, Raman signals of molecules can be enhanced by several orders of magnitude compared to a conventional Raman measurement. This is based on the utilization of light interactions with metallic nanoparticles or nanostructures, which result in a strong electromagnetic field on the metal surface. SERS is a fast and easy to perform technique proving molecular fingerprint information of the sample. 3,4 Surface enhanced Raman Spectroscopy (SERS) 2,4–7 has been developed into a very powerful tool to address these issues. Sensitive detection down to the molecular level is one of the key issues, e.g., for the identification of different bacteria and the treatment of diseases which are induced by them, 1,2 as well as of low-molar mass substances in food-relevant matrices. Introduction The detection of trace contaminations and low concentrations of molecules represents an important area of research concerning sensing and diagnostic applications.
First tests of the developed SERS substrates demonstrated their excellent potential for detecting vitamin A and pro-vitamin A at low concentration levels.
The theoretical simulation predicted the formation of supermodes under optimized illumination conditions, which were verified experimentally. The study targets the simulation of the plasmonic structure of the substrates and presents an easily accessible fabrication process to obtain highly sensitive SERS active substrates. Commercial HD DVDs provide a characteristic structure of encoding pits which were utilized to fabricate cost efficiently large area SERS substrates for chemical analysis.
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