The Effect of Bumpy Structure on Optical Properties of Bimetallic Nanoshells Maryam Saliminasab 1,2 & Marzieh Afkhami Garaei 3 & Rostam Moradian 1,2 & Hamid Nadgaran 3 Received: 11 June 2016 /Accepted: 8 August 2016 # Springer Science+Business Media New York 2016 Abstract In this paper, a sensitive bumpy bimetallic nano- shell for detection of thyroid cancer market (Thyroglobulin, Tg) and bovine serum albumin (BSA) proteins is reported. The physical origin of plasmonic properties of bimetal nano- shells is described by plasmon hybridization theory which indicates three intense and clearly separated plasmon modes. The electric field intensity enhancement of the bumpy bimetal nanoshell increases by ~559 %, at the surface of the bump in comparison with a smooth shell. The presence of bumpy structure on the nanoshell surface provides a high enhance- ment of the resulting Raman signal through an electromagnet- ic field of the order of 10 7 which leads to an increase in sen- sitivity detection of Tg and BSA proteins. In addition, a re- fractive index (RI) sensitivity of 332.54 nm/RIU is achieved for this bumpy bimetallic nanoshell. Keywords Bimetallic nanoshell . Field enhancement . Localized surface plasmon resonance Introduction Noble metal nanostructures have received extensive interests due to their unique optical properties. The ability of such nanostructures to sustain coherent oscillations of conductive electrons, known as localized surface plasmon resonance (LSPR), leads to large electromagnetic field confined near the surface of metal nanoparticles. The LSPR frequency de- pends on size, shape, material, structure, and composition of the nanoparticles and can be varied over a wide range by changing these parameters [1]. At the frequency close to the LSPR frequency, the local electric field near the metal nano- particles enhances greatly, which is responsible for surface enhanced Raman scattering (SERS) [2], improved fluores- cence emission, [3] and so on. This enhancement has been attributed to the random formation of localized plasmons or “hot spots” at the junctions between nanoparticles, giving rise to great enhancement that enable SERS detection near a vari- ety of molecules adsorbed on a rough metal surface [2, 4]. Metal core-shells have attracted significant research attention due to their special optical properties, which comes from surface Plasmon resonance (SPR) induced resonance light scattering and absorption and also local electric field enhancement. Quasi-static theory is the most common theory for analyzing the optical properties of the core-shell nanoparticles, which gives the exact solution of Maxwell’ s equations in spherical coordinates with boundary conditions appropriate for a spherical particle. Besides, plasmon hybridization theory [5] has been developed to characterize plasmon resonance of metal nanoshells. Among the various metal nanoparticles, silver and gold nanoparticles have been considered as suitable SERS sub- strates for the sensitive detection of target molecules due to the electromagnetic field enhancement near the nanoparticles. In particular, silver nanoparticles exhibit 10 to 1000 times larger than Raman enhancement and have a higher tendency to form rough surface morphologies than gold ones in nano- shell structures [6–8]. * Rostam Moradian moradian.rostam@gmail.com 1 Department of Physics, Razi University, Kermanshah 67144-15111, Iran 2 Nano-Science and Nano-Technology Research Center, Razi University, Kermanshah 67144-15111, Iran 3 Department of Physics, College of Science, Shiraz University, Shiraz 71454, Iran Plasmonics DOI 10.1007/s11468-016-0355-6