Bio-Magnetoplasmonics, Emerging Biomedical Technologies and Beyond

Abstract

similar manner, it merges bio-nanoplasmonics where biological samples are made to interact with surface plasmonic wave fields, also referred to as evanescent radiation fields. The circle with big arrows (clockwise) shows a process involved in creating new MP material through innovative design, modeling, simulation and verification of these designs through nanofabrication, optical and magnetic characterization and data fitting. The outer circle (clockwise) shows the various functionalities of MPs-including biosensing, bio-imaging, Immunoassays monitoring of environmental problems, thermal therapy, space exploration, biophysics and photovoltaics. Schematic of essential characteristics of nanoparticles used in magnetoplasmonic is shown in the top right and that of multilayered nanostructure in the bottom right. Surface plasmons (SPs) are oscillating charge density waves and are created on the surface of the materials when excited by electromagnetic (EM) radiation. Surface plasmon resonance (SPR) occurs when the wave-vector of the incident optical radiation matches that of the wave vector of the surface plasmons [10-15]. Much in the same way as the SPR, in magnetoplasmonics, in the presence of magnetic materials or external magnetic fields a. Plasmonics is used to enhance the magnetic response (e.g. Kerr effect) and b. Magnetism is used as a way to make plasmonics tunable with a modest external magnetic field or direction sensitive. When the plasmon waves are coupled with the incident optical radiation, the effect arises due to the spin-orbit interaction and Lorenz force drift as H fields are introduced. Depending on the device geometry and sizes, there are two types of SPs. One is the localized surface plasmons (LSPs), which are non-propagating excitation of the plasmons coupled to the EM fields and confined within the nanostructures such as metallic nanoparticles, nanorods, nanodisks, nanowires, etc., whose dimensions are smaller than the wavelength of the incident optical radiation [5,11,15-19]. The other type is the surface plasmon polaritons (SPP), which arises from the coupling of the electrons at the interface between the materials with negative and positive permittivity (which is the case for metal and dielectric layers) and incident EM waves produces oscillations of electron plasma on the metallic surface that in turn generates confined two-dimensional transverse EM waves at the interface [2,20-25]. These waves decay exponentially in the direction perpendicular to the interface and practically vanish at both sides of the interface. Unlike the LSPs, the SPP arises from the layered nano structured configurations where the lateral size of the nanostructure is greater than the wavelength of the optical radiation such as, multilayers of dielectric/ferromagnetic, dielectric/oxides and dielectric/plasmonic metals. Commonly available and most popular materials used in plasmonic studies for SPR phenomena are non-magnetic (NM) noble metals such as, Au, Cu and Ag. However, being purely NM, the optical properties are determined in an extended spectral range by the conduction electron and as determined by the Drude's theory of conduction of electron in metals, they exhibit small magneto-optical (MO) effects. The 3-d transition ferromagnetic (FM) metals such as Co, Fe and Ni and ferri-magnetic metals and their alloys and multilayers are excellent candidates for the study of MO surface plasmon resonance (MO-SPR); primarily because they offer excellent MO and optical properties such as enhanced permittivity and electromagnetic coupling and these can be controlled using both optical radiation and H fields. It is a well established fact that FM of Fe, Co and Ni offer large MO effects (e.g., MO effects in Co is ~1000 times larger than in NM metals such as Au). The propagation length of SPP calculated