Polychlorinated biphenyls (PCBs) belong to a class of persistent organic pollutants, which can long-term residue and long-range migrate in the environment. This kind of chemical is lipophilic and bio-accumulating, showing hazardous effect to human and animals. In history, several PCBs-related chemical contamination events made severe consequences, arousing a universal public attention. In this sense, fast detection of trace PCBs can be helpful to the early warning and minimize the damage of PCBs' contaminations.
As we known, each molecule possesses an intrinsic Raman scattering fingerprint pattern. So, the identity of a chemical can be discriminated by measuring the Raman signals of target molecules. For trace analytes, the Raman signals are rather weak, which is difficult to detect directly using Raman spectroscopy. The surface-enhanced Raman scattering spectroscopy based on noble metallic nanostructures, is expected to realize rapid detection of trace pollutants. The key issues lie in the design and fabrication of plasmonic nanostructures with high SERS sensitivity, while adsorbing the target PCB molecules effectively. Recently, researchers from ISSP made improvements regarding the construction of SERS-active substrates toward PCBs.
For example, Doc. Zhu Chuhong designed a "nanosheet assembled microhemisphere" SERS-active substrate (Figure 1, left). It is shown that lots of sub-10 nm nanogaps are generated between the parallel Ag nanosheets, boosting strong electromagnetic coupling required for high Raman enhancement; also, the massive sharp edges around the nanosheet surface produce significant "antenna effect". Based on such nanostructures with high SERS activity, thiolated ¦Â-cyclodextrin (HS-¦Â-CD) was functionalized on the Ag nanosheet surface to further capture the PCBs molecuels, to achieve a sound guest-inclusion for PCB77 and high SERS response (Figure, right). The related achievements were publish on Journal of Materials Chemistry and Journal of Hazardous Materials ((J. Mater. Chem. 22, 2271-2278, 2012; J. Hazard. Mater. 211, 389-395, 2012).
Meanwhile, Doc. Tang Haibin fabricated a Ag nanoparticles decorated ZnO nanocone arrays as SERS substrates (Figure 2). The Ag nanoparticles decorated on the ZnO nanocones would produce three kinds of electromagnetic enhancement induced SERS "hot spots" (The upper image of Figure 2); also, the semiconductor ZnO nanocones contribute to the chemical enhancement of Raman signals. In addition, the three dimensional architecture of the Ag decorated ZnO nanocone arrays with a high specific surface area can be helpful to accumulate the target molecules. Laboratory tests indicate that the SERS substrate exhibit a high SERS sensitivity for PCB77. This study was published on "Advanced Functional Materials" (Adv. Funct. Mater. 22, 218-224, 2012).
These high SERS-active substrates establish a materials foundation for the SERS-based rapid detection of trace pollutants. These work were financially supported by the National Key Basic Research Program of China and the Natural Science Foundation of China.
Figure 1. (Left) The SEM image of Ag nanosheet assembled microhemispheres; (right) the SERS spectra of PCB77 with varied concentrations adsorbed on the Ag nanosheet assembled microhemishperes after the decoration of HS-¦Â-CD (curve¢ñ,¢ò and ¢ó corresponds to 3¡Á10-5, 10-6, and 3¡Á10-7 M PCB77, respectively).
Figure 2. Diagram showing the fabrication of Ag nanoparticle decorated ZnO nanocone arrays and the corresponding structural micro characterizations.
Figure 3. The SERS spectra of R6G with varied concentrations adsorbed on Ag decorated ZnO nanocone arrays