Magnetic Fe₃O₄‐Au core‐shell nanostructures for surface enhanced Raman scattering

Abstract

The synthesis, structural and optical characterization, and application of superparamagnetic and water‐dispersed Fe3O4‐Au core‐shell nanoparticles for surface enhanced Raman scattering (SERS) is reported. The structure of the nanoparticles was determined by scanning transmission electron microscopy (STEM) and high‐resolution transmission electron microscopy (HRTEM). STEM images of the Fe3O4‐Au core‐shell nanoparticles reveal an average diameter of 120 nm and a high degree of surface roughness. The nanoparticles, which display superparamagnetic properties due to the core Fe3O4 material, exhibit a visible surface plasmon resonance (SPR) peaked at 580 nm due to the outer gold shell. The nanoparticles are used as a substrate for surface enhanced Raman scattering (SERS) with rhodamine 6G (R6G) as a Raman reporter molecule. The SERS enhancement factor is estimated to be on the order of 106, which is ∼ 2 times larger than that of conventional gold nanoparticles (AuNPs) under similar conditions. Significantly, magnetically‐induced aggregation of the Fe3O4‐Au core‐shell nanoparticles substantially enhanced SERS activity compared to non‐magnetically‐aggregated Fe3O4‐Au nanoparticles. This is attributed to both increased scattering from the aggregates as well as “hot spots” due to more junction sites in the magnetically‐induced aggregates. The magnetic properties of the Fe3O4 core, coupled with the optical properties of the Au shell, make the Fe3O4‐Au nanoparticles unique for various potential applications including biological sensing and therapy.

Maximizing surface-enhanced Raman scattering sensitivity of surfactant-free Ag-Fe3O4 nanocomposites through optimization of silver nanoparticle density and magnetic self-assembly

“…28 Magnetically aggregated Fe 3 O 4 -Au core-shell nanostructures also demonstrated a higher SERS activity than that of conventional Au NPs under the same conditions. 29 Naturally, the size and density of metal NPs supported on individual microspheres largely affect the total number of "hot" spots formed either between neighboring nanoparticles supported on the same microsphere, or between nanoparticles locating within the contact area of two or more microspheres in the aggregated or self-assembled clusters. Therefore, controllable growth and distribution of noble metal NPs on Fe 3 O 4 microspheres or on more general magnetic templates is the key to maximizing the SERS sensitivity of such bifunctional composite nanostructures, but has been largely overlooked in previous studies.…”

“…Therefore, controllable growth and distribution of noble metal NPs on Fe 3 O 4 microspheres or on more general magnetic templates is the key to maximizing the SERS sensitivity of such bifunctional composite nanostructures, but has been largely overlooked in previous studies. [7][8][9][10][11][12][13][14][15][16]28,29 This is the second critical problem we are attempting to tackle in the present work.…”

SERS under magnetic control

“…Gold is advantageous over silver because gold is chemically more inert and aggregates of gold have plasmon bands red-shifted into the near-infrared, which is important for biological applications. The present work by Zhang et al [10] presents the synthesis, structural and optical characterization, and SERS performance of a novel paramagnetic Fe 3 O 4 -Au core-shell nanoparticle system for the fingerprint detection of rhodamine 6G. These nanoparticles display superparamagnetic properties due to the core Fe 3 O 4 material and a surface plasmon resonance peaked at 580 nm due to the outer gold shell.…”

SERS Detection of Penicillin G Using Magnetite Decorated with Gold Nanoparticles

“…The upgrade of such sorbents for simultaneous use in water purification and contaminant detection is a challenging task but of great practical interest for sensing applications, thus following current interest in developing multifunctional nanomaterials. In this context, the development of SERS-active magnetic nanomaterials has attracted much attention, because it provides innovative platforms that combine magnetic responsiveness and the ability for Raman monitoring within a single material [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. Penicillin G (PG) belongs to the β-lactam antibiotics family whose structure is composed of a five-membered sulfur-containing thiazolidine ring fused to a beta-lactam ring and a phenyl ring attached to the side chain ( Figure S1, Supporting Information).…”