Optical Properties of Au-Ag Bimetallic Nanoparticles of Different Shapes for Making Efficient Bimetallic-Photonic Whispe
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Optical Properties of Au-Ag Bimetallic Nanoparticles of Different Shapes for Making Efficient Bimetallic-Photonic Whispering Gallery Mode Hybrid Microresonators Pragya Tiwari 1 & Gour Mohan Das 1 & Venkata Ramanaiah Dantham 1 Received: 16 October 2019 / Accepted: 17 February 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract For the first time, we propose a bimetallic-photonic whispering gallery mode (WGM) hybrid microresonator for the detection and sizing of single protein molecules in real time. To optimize the sensitivity of hybrid microresonators, theoretical simulations have been carried out to understand the optical properties of different types of Au-Ag bimetallic nanoparticles such as solid nanospheres, dielectric core-bimetallic nanoshells, nanostars, and nanoprisms using Lorenz-Mie theory, Aden-Kerker theory, and finite element method (FEM). The role of size and Au-Ag ratio on the optical properties of the nanospheres and nanoshells has been studied. In addition, the effect of the Au-Ag ratio on the optical properties of nanostars and nanoprisms has been investigated. The local electric field intensity enhancement values of bimetallic nanostructures of different shapes have been estimated using the FEM. Finally, the advantages of the bimetallic-WGM hybrid microresonator as compared to the monometallic-WGM hybrid microresonator have been explained in detail. Keywords Near-field scattering . Localized surface plasmon resonance . Finite element method . Whispering gallery mode . Bimetallic nanoparticles . Hybrid microresonator
Introduction The diagnosis of diseases at an early stage is one of the main interests of researchers working in the field of biosensing. At the early stage of any disease, viruses/protein markers (molecules) appear in the bodily fluids in ultra-low concentration (~ fM). Due to the low concentration of the protein molecules and their tiny size, it becomes difficult to detect the protein markers [1, 2]. The detection of single protein molecules can be achieved using a microresonator with high sensitivity and resolution [3]. Dantham et al. reported the detection of single thyroid cancer and bovine serum albumin (BSA) proteins in real time with the help of a monometallicwhispering gallery mode (WGM) hybrid microresonator [4]. However, the S/N of the experimental data for the BSA proteins was poor due to its smaller size than the thyroid cancer proteins. The sensitivity of the hybrid microresonator strongly depends upon the size, shape, and electric permittivity of the * Venkata Ramanaiah Dantham [email protected] 1
Department of Physics, Indian Institute of Technology Patna, Patna, Bihar 801103, India
nanoparticle, electric permittivity of the surrounding medium, and orientation of the nanoparticle with respect to the direction of the incident electric field. Therefore, researchers have been trying to improve the sensitivity of the hybrid microresonators using different shapes of monometallic nanoparticles. In contrast, we propose a bimetallic-WGM hybri
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