Akshay Hande

ORCID Identifier(s)

0000-0003-0104-4753

Graduation Semester and Year

2016

Language

English

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

First Advisor

Yaowu Hao

Abstract

Au nanoparticles (AuNPs) and superparamagnetic iron oxide nanoparticles (SPIONs), in various forms, are considered as biocompatible and are of great interest for diagnostic imaging and therapeutic applications. Biomedical applications of AuNPs originate from the surface plasmon resonance (SPR) effect. In order to tune the SPR wavelength to the near infrared (NIR) region which is required for deep light penetration for in vivo applications, various types of AuNPs such as nanorods, nanoprisms, nanoshells and nanocages have been developed and investigated. SPIONs have also been explored extensively for biomedical applications, including magnetic cell separation, contrast enhancement agents for magnetic resonance imaging (MRI), targeted drug and gene delivery, hyperthermia treatment, biophysical studies, and bio sensing. In recent years, combining SPIONs with Au to form a composite multifunctional nanoparticles has attracted considerable attention. However, the effort has been mostly limited on coating iron oxide particles with a thin layer of Au. By such an approach, it is difficult, if not impossible, to tune the SPR wavelengths to the NIR region. Reported core/shell particles usually have their SPR in the visible light range (from 500 nm to 600 nm), which limits their optical functions for in vivo applications. The Au-Co multilayered nanoparticles made in this study have the benefit of high magnetization, small remanence and SPR peak’s presence in the NIR spectrum range. These particles were made using template synthesis technique. Anodic aluminum oxide (AAO) membrane which possess ~80 nm through channels is used as template. AAO membranes are successfully fabricated using an anodization process. Multilayered Au/Co nanoparticles are electrodeposited into the channels following the electrodeposition of Cu rod which serve as sacrificial layer for releasing the multilayered particles into the solution. The magnetic and optical properties of multilayered nanoparticles are characterized, and compared with theoretical calculation and computer simulation. It has been found that the multilayered nanorods have a single peak at around 620 nm (disc like Co segments) and at 590 nm (rod like Co segments), which suggests a blue shift if the inter Au layer distance increases (i.e. increase in Co layer thickness). The easy axis was determined as along the rod axis and along the diameter for rod like and disc like Co segments by using VSM measurements which can be credited to their shape anisotropy. The remanence and coercivity (<100 Oe) in the measured hysteresis loops are very low which is beneficial for biomedical applications. The theoretical calculations confirmed lower values of shape anisotropy energy along their easy axes than along other axes. The FDTD simulation results for the nanorods, which were similar to experimental results, showed a single peak around 530nm when illuminated along the axis of the rod without considering water as surrounding medium. The rods with an extra Au and Co layer (rod with 11 layers) showed no noticeable difference for both SPR and magnetic properties when compared to rods with lesser Au and Co layers (i.e. rod with 9 layers). The multilayer nanorods have absorption peaks in NIR range which are tunable by changing individual layer thicknesses and they have very high magnetization with low remanence and coercivity which makes them suitable for biomedical applications such as MRI imaging, cancer therapy etc. Thus, multiple Au disc separated by alternate Co layers give dual properties (plasmonic and magnetic) in a single entity with benefit of easy tuning by a simple change of thickness.

Keywords

Plasmonics, Magnetics, Nanorods

Disciplines

Engineering | Materials Science and Engineering

Comments

Degree granted by The University of Texas at Arlington

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