Shell-isolated nanoparticle-enhanced Raman spectroscopy: a review

Surface analysis of various materials (especially in in-situ conditions) is very important both from the economic and scientific points of view. Carrying out surface analysis is especially difficult for so-called buried interfaces; it means surfaces of the solid samples in the liquid or the high-pressure gas, a situation which occurs in very important from the practical point of view interfaces of various biological samples. Surfaces of biological objects have to be often studied in their “natural” environment because they are usually damaged after introducing to the vacuum. In 2010, Tian et al. reported a new relatively sensitive method of chemical analysis of various surfaces, which allows for analysis of biological samples in situ-developed method, was called shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). In SHINERS measurements, the surface of the investigated sample is covered with the layer of M@P nanoparticles, where M denotes plasmonic metal (e.g., silver or gold) and P denotes protecting layer (usually relatively inert oxide such as SiO2, MnO2, and TiO2, or various stable macromolecular organic species). Plasmonic cores of nanoparticles act as electromagnetic resonators, significantly enhancing the electric field of the incident electromagnetic radiation, and hence leading to a large increase in the efficiency of the generation of the Raman signal (the increase in the efficiency of Raman scattering is roughly proportional to the fourth power of the field enhancement). The ultrathin protecting layer does not damp significantly the surface electromagnetic enhancement, however, separates metallic cores of nanoresonators from the direct contact with the probed material and keeps them from agglomerating. This chapter is an attempt to provide an overview of the state of the art of SHINERS technique.