Synthesis and Single‐Particle Optical Detection of Low‐Polydispersity Plasmonic‐Superparamagnetic Nanoparticles

Abstract

Both magnetic and plasmonic particles are of increasing interest for biomedical applications. Magnetic particles are currently used for magnetic separation, to collect tagged cells or DNA sequences, [1][2][3] and for magnetically guided drug delivery. [4][5][6] A key advantage of magnetism lies in the ability to control motion at a distance without perturbing the biological system, as would occur with a large electric field. Noble-metal nanostructures are beneficial not only because of their relative ease of biofunctionalization, but also for plasmonic biosensing. [7][8][9][10] Unlike quantum dots, [11] these particles do not show optical bistability or blinking making them competitive with fluorophores for quantifying the number of cell surface markers. [12,13] The main advantages of plasmonic particles are their extremely large molar extinction coefficients and resonant Rayleigh scattering efficiencies, [8] and the exceptional sensitivity of the surface plasmon resonance peak wavelength to changes in the local dielectric environment. Individual plasmonic nanoparticles and nanorods have been detected by using dark field optical microscopy. [13][14][15][16][17] In fact, by using nonmagnetically responsive gold-coated silica particles ($150 nm), Halas and co-workers have demonstrated the capability of gold-shell nanoparticles in detecting low concentrations of analytes in whole blood within minutes without any sample preparation.[18]Here we describe the preparation of iron oxide/gold core/ shell nanoparticles that can be moved magnetically and imaged optically. The synthesis of large-diameter ($150 nm) magnetic plasmonic three-layer composite particles has previously been reported, [19] but our focus here is on smaller particles. The small size of these nanoparticles approaches that of cellmembrane-bound antigens, and is in a range in which particles can be spontaneously internalized by endocytosis. We expect that the combination of magnetic responsiveness, facile bioconjugation, and a localized surface plasmon resonance in these smaller nanoparticles will open new possibilities for in vitro molecular and cell biological applications, including intracellular mechanical and chemical composition analyses, and magnetophoretic cell sorting according to the expression level of cell surface receptors. The magnetic forcẽ F m ¼ ðm pt Á rÞB * that can be applied to a particle depends on the particle magnetic moment m pt . Since m pt ¼ M s V pt , where M s is the saturation magnetization of the material and V pt is the particle volume, a larger size is generally preferable for a strong magnetic response. Thus there is a compromise between large magnetic moments and the desirability of small sizes for new applications.Gold, silver, and SiO 2 core/Au shell particles have been used for plasmonic sensing, where the surface plasmon peak wavelength shifts in response to small changes in the dielectric environment near the particle surface. A core/shell structure with the noble metal in the shell enables the surface plasmon resona...

Composite Fe3O4@Au Core-Shell Nanoparticle: Tunable and Enhancement of Optical Absorption Property

“…Therefore, the intense research in the development of nanoparticles (NPs) that combine multiple functions or properties not obtainable in individual materials is motivated by the scientists to obtain new materials in order to further many applications. Also, nanoparticles composed of a Fe 3 O 4 core, well known as magnetic properties, and continuous plasmonic (Au or Ag) shell layers, non-magnetic material but shown SP properties, for example, are of increasing interest for biomedicine application [9][10][11][12] . This article the only optical absorption property in multicomponent Fe 3 O 4 @Au core-shell nanoparticle embedded in water will be theoretically investigated.…”

Targeting T₁ and T₂ dual modality enhanced magnetic resonance imaging of tumor vascular endothelial cells based on peptides-conjugated manganese ferrite nanomicelles

“…In order to transfer the prepared NPs into water, hydrophobic MnFe 2 O 4 NPs were treated with TMAH. 39 Briefly, 10 mL of NPs suspension in hexane was added into 20 mL of ethanol and the NPs were collected with a permanent magnet. After decanting the solvent, the NPs were redispersed in 25 mL of TMAH aqueous solution (10%, w/v) and sonicated for 10 minutes.…”

A BIO-INSPIRED POLYDOPAMINE APPROACH TO PREPARATION OF GOLD-COATED Fe3O4 CORE–SHELL NANOPARTICLES: SYNTHESIS, CHARACTERIZATION AND MECHANISM

“…Although these aqueous methods are simple and quick and the resulting nanoparticles are dispersed in water, direct coating of Fe 3 O 4 nanoparticles with gold is di±cult to control due to the dissimilar nature of the two surfaces. 29 Consequently, gold atoms either nucleate rapidly forming discrete nanoparticles in solution without coating the surface of Fe 3 O 4 , or they do not uniformly distribute on Fe 3 O 4 , giving a dense gold shell. 3,12,14 The synthesized samples therefore contain a mixture of coated and uncoated Fe 3 O 4 that is di±cult to separate.…”