Synthesis and Properties of Magnetic-Optical Core-Shell Nanoparticles

Abstract

Due to their high integrity, facile surface chemistry, excellent stability, and dual properties from the core and shell materials, magnetic-plasmonic core-shell nanoparticles are of great interest across a number of science, engineering and biomedical disciplines. They are promising for applications in a broad range of areas including catalysis, energy conversion, biological separation, medical imaging, disease detection and treatment. The technological applications have driven the need for high quality nanoparticles with well controlled magnetic and optical properties. Tremendous progress has been made during past few decades in synthesizing and characterizing magnetic-plasmonic core-shell nanoparticles, mainly iron oxide-gold core-shell nanoparticles. This review introduces various approaches for the synthesis of spherical and anisotropic magnetic-plasmonic core-shell nanoparticles focusing on iron oxide-gold core-shell nanoparticles. Growth mechanisms are discussed to provide understanding of the key factors controlling shape-controlled synthesis. Magnetic and optical properties are summarized from both computational and experimental studies.

Keywords: Synthesis; core-shell nanoparticles; gold; iron oxide; magnetic-plasmonic; optical properties.

Figure 1

Synthesis of IO-Au core-shell NPs by the direct deposition method. (A) Synthesis of IO-Au core-shell NPs by iterative hydroxylamine seeding. Top: Schematic of the preparation procedure. Bottom: TEM images of IO-Au core-shell NPs with zero, one, three, and five times of deposition of Au atoms via reduction of Au³⁺ with hydroxylamine, respectively. Scale bar: XX nm. Reprinted with permission from ref . Copyright (2009) American Chemical Society. (B) Synthesis of IO-Au core-shell NPs by hydroxylamine reduction of Au precursor on the surface of polymer-coated IO NPs. Left: Schematic of the preparation procedure. Right: TEM image of Fe₃O₄ NPs and Fe₃O₄-Au core-shell NPs. Reprinted by permission from Macmillan Publishers Ltd: [Nature Communications] (ref 44), copyright (2010).

Figure 2

Synthesis of IO-Au core-shell NPs via Au-seeded growth methods. (A) APTMS and (B) PEI are used as the anchor agent for the adsorption of Au seeds on IO NPs. (A) is reprinted with permission from ref . Copyright (2007) American Chemical Society. (B) is reprinted with permission from ref . Copyright (2009) American Chemical Society.

Figure 3

Synthesis of IO-Au core-shell nanorices via an Au-seeded growth method. (A) Schematic of the preparation of IO-Au core-shell nanorices. (B–E) SEM (left) and TEM (right) images of IO-Au core-shell nanorices at different preparation steps. (B) The IO nanorices. (C) Au-seeded IO nanorices. (D) IO-Au core-shell nanorices with thin shells (~13 nm). (E) IO-Au core-shell nanorices with thick shells (~28 nm). Reprinted with permission from ref . Copyright (2006) American Chemical Society.

Figure 4

Synthesis of IO-Au core-shell NSTs. (A) Synthesis of IO-Au core-shell NSTs from small IO-Au core-shell nanospheres. (Top) Schematic of the preparation procedure. (Bottom) TEM image of IO NPs (left), HRTEM image of a tip (middle), and TEM image of IO-Au NSTs. Reprinted with permission from ref . Copyright (2010) American Chemical Society. (B) Synthesis of IO-Au core-shell NSTs by the Au-seeded growth method. (Top) Schematic of the preparation procedure. (Bottom) TEM images of IO NPs (left), Au-seeded IO NPs (middle) and IO-Au NSTs. Reprinted with permission from ref . Copyright (2016) American Chemical Society.

Figure 5

Computational studies on growth mechanisms of IO-Au core-shell nanospheres, nanopopcorns, and nanostars. (A–C) TEM images of IO-Au core-shell nanospheres, nanopopcorns, and nanostars. (D–F) The adsorption of Ag on the Au (100) surface (D), Au (110) surface (E), and Au (111) surface (F). (G) Schematic of the proposed geometry of the tip of the nanostar. (H) HRTEM image of a tip of the nanostar. The inset shows an enlarged view of the lattice, where the position of each atom is visible. (I) The positions of atoms according to the proposed model in (G), which is viewed from the [1–10] direction. (J–L) The growth mechanism of Au nanospheres (J), nanopopcorn (K), and nanostars (L). Reprinted with permission from ref . Copyright (2016) American Chemical Society.

Figure 6

Magnetic properties of IO-Au core-shell NPs. (A–B) Magnetization as a function of applied field at 100 K and 250 K for uncoated and Au coated tetracubic IO NPs. Reprinted with permission from ref . Copyright (2009) American Chemical Society. (C) Magnetization as a function of applied field at 10 K for IO-Au core-shell nanopopcorns of three different sizes. Reprinted with permission from ref . Copyright (2016) American Chemical Society. (D) Magnetization as a function of applied field at 10 K and 300 K for bare IO NPs (sample A), IO-Au core-shell NPs with low Au (sample B) and high Au (sample C). Reprinted with permission from ref . Copyright (2011) American Chemical Society.

Figure 7

Calculated optical properties of Fe₃O₄-Au core-shell NPs. (A) Extinction spectrum of Fe₃O₄-Au core-shell NPs in comparison with other core-shell NPs and solid Au NPs with the same diameter Dtotal=50nm of NPs and a shell thickness of 5nm. (B) Extinction spectra of core-shell NPs with varied core refractive indices. (C) Extinction spectra of Fe₃O₄-Au core-shell NPs with different shell thickness with fixed total particle size. D_total = 50 nm. (D) Fractional shifts (Δλ/λ0) of the LSPR peak maximums of the IO-Au NPs from (C). (E) Extinction spectra of Fe₃O₄-Au core-shell NPs with different shell thickness with fixed IO core size. D_core = 15 nm. (F) Fractional shifts (Δλ/λ0) of the LSPR peak maximums of the IO-Au NPs from (E). Reprinted with permission from ref . Copyright (2014) American Chemical Society.

Figure 8

NIR absorbing IO-Au core-shell NPs. (A) Absorption spectra of Fe₃O₄-Au core-shell NPs with different shell thickness. D core = 25 nm. Reprinted by permission from Macmillan Publishers Ltd: [Nature Communications] (ref 44), copyright (2010). Calculated extinction spectra of IO-Au core-shell NRs with different aspect ratios. Reprinted with permission from ref . Copyright (2011) Elsevier. (C) Absorption spectra of Fe₃O₄-Au core-shell NPs with different shapes. The Fe₃O₄ core is octahedral with an edge length of 35 nm. Reprinted with permission from ref . Copyright (2016) American Chemical Society. (D) Calculated extinction spectra of IO-Au core-shell NSTs with different base size. The Fe₃O₄ core is octahedral with an edge length of 35 nm. Reprinted with permission from ref . Copyright (2016) American Chemical Society.