Plasmon-Resonant Nanoparticles and Nanostars with Magnetic Cores: Synthesis and Magnetomotive Imaging

Abstract

Plasmon-resonant gold nanostars (NSTs) with magnetic cores were synthesized by a multistep sequence from superparamagnetic Fe3O4 nanoparticles (NPs), and evaluated as optical contrast agents under magnetomotive (MM) imaging conditions. Core–shell Fe3O4@Au NPs were prepared in nonpolar organic solvents with nanometer control over shell thickness, and with good epitaxy to the Fe3O4 surface. Anisotropic growth was performed in micellar solutions of cetyltrimethylammonium bromide (CTAB) under mildly reducing conditions, resulting in NSTs with physical features similar to those produced from colloidal gold seeds. NSTs could be produced below 100 nm from tip to tip but seed size had a significant impact on growth habit, with larger seed particles producing submicron-sized “morning stars.” Both NSTs and aggregated core–shell NPs are responsive to in-plane magnetic field gradients and can provide enhanced near-infrared (NIR) contrast under MM conditions, but do so by different mechanisms. NSTs can modulate polarized NIR scattering with minimal translational motion, giving the appearance of a periodic but stationary “blinking,” whereas core–shell NP aggregates require lateral displacement for signal modulation. The polarization-sensitive MM imaging modality offers the dual advantage of enhanced signal quality and reduced background signal, and can be applied toward the detection of magnetomotive NSTs in heterogenous biological samples, as illustrated by their detection inside of granular cells such as macrophages.

Nanostructured Fe3O4 satellite gold nanoparticles to improve biomolecular detection

“…The XRD pattern of Fe 3 O 4 @Au satellite nanoparticle has low intensity in the peaks when compared to the crystalline structure of Fe 3 O 4 due the diffractions of the heavy atoms of gold in the surface of this structure. The results showed Au Nps coating around the Fe 3 O 4 NPs surface without altered their crystalline structure, which is in accordance with the literature [37][38][39].…”

Improved Imaging of Magnetically Labeled Cells Using Rotational Magnetomotive Optical Coherence Tomography

“…As an alternative to further enhance the sensitivity of rotational magnetomotive measurements, particles with potentially increased anisotropy such as magnetic nanostars [16,17] could be applied. Moreover, for future in vivo application, faster imaging is desired.…”

Synthesis of Immunotargeted Magneto-plasmonic Nanoclusters

“…The combination of plasmonic and magnetic properties in a single nanoparticle is of particular interest because it provides a very strong light scattering and absorption cross-sections associated with plasmon resonances and responsiveness to a magnetic field. For example, magneto-plasmonic nanoparticles were used to increase contrast in dark-field imaging of labeled cells by applying a temporal signal modulation via an external electromagnet [3][4][5] . More recently, a similar principle was applied in development of a new imaging modality -magneto-photoacoustic imaging, where magneto-plasmonic nanoparticles enable great improvements in contrast and signal-to-background ratio 6,7 .…”

“…For example, Yu et al utilized decomposition and oxidation of Fe(CO) 5 on gold nanoparticles to form dumbbell-like bifunctional Au-Fe 3 O 4 nanoparticles 11 . Wang et al have synthesized goldcoated iron oxide nanoparticle by using thermal decomposition method 12 .…”