Magnetic-plasmonic Nanoparticles Research Articles

Study on Magnetic and Plasmonic Properties of Fe3O4-PEI-Au and Fe3O4-PEI-Ag Nanoparticles.

Magnetic-plasmonic nanoparticles (NPs) have attracted great interest in many fields because they can exhibit more physical and chemical properties than individual magnetic or plasmonic NPs. In this work, we synthesized Au- or Ag-decorated Fe3O4 nanoparticles coated with PEI (Fe3O4-PEI-M (M = Au or Ag) NPs) using a simple method. The influences of the plasmonic metal NPs' (Au or Ag) coating density on the magnetic and plasmonic properties of the Fe3O4-PEI-M (M = Au or Ag) NPs were investigated, and the density of the plasmonic metal NPs coated on the Fe3O4 NPs surfaces could be adjusted by controlling the polyethyleneimine (PEI) concentration. It showed that the Fe3O4-PEI-M (M = Au or Ag) NPs exhibited both magnetic and plasmonic properties. When the PEI concentration increased from 5 to 35 mg/mL, the coating density of the Au or Ag NPs on the Fe3O4 NPs surfaces increased, the corresponding magnetic intensity became weaker, and the plasmonic intensity was stronger. At the same time, the plasmonic resonance peak of the Fe3O4-PEI-M (M = Au or Ag) NPs was red shifted. Therefore, there was an optimal coverage of the plasmonic metal NPs on the Fe3O4 NPs surfaces to balance the magnetic and plasmonic properties when the PEI concentration was between 15 and 25 mg/mL. This result can guide the application of the Fe3O4-M (M = Au or Ag) NPs in the biomedical field.

Novel Characterization Techniques for Multifunctional Plasmonic-Magnetic Nanoparticles in Biomedical Applications.

In the rapidly emerging field of biomedical applications, multifunctional nanoparticles, especially those containing magnetic and plasmonic components, have gained significant attention due to their combined properties. These hybrid systems, often composed of iron oxide and gold, provide both magnetic and optical functionalities and offer promising avenues for applications in multimodal bioimaging, hyperthermal therapies, and magnetically driven selective delivery. This paper focuses on the implementation of advanced characterization methods, comparing statistical analyses of individual multifunctional particle properties with macroscopic properties as a way of fine-tuning synthetic methodologies for their fabrication methods. Special emphasis is placed on the size-dependent properties, biocompatibility, and challenges that can arise from this versatile nanometric system. In order to ensure the quality and applicability of these particles, various novel methods for characterizing the magnetic gold particles, including the analysis of their morphology, optical response, and magnetic response, are also discussed, with the overall goal of optimizing the fabrication of this complex system and thus enhancing its potential as a preferred diagnostic agent.

Theoretical Investigation on the Metamaterials Based on the Magnetic Template-Assisted Self-Assembly of Magnetic-Plasmonic Nanoparticles for Adjustable Photonic Responses.

The assembly of artificial nano- or microstructured materials with tunable functionalities and structures, mimicking nature's complexity, holds great potential for numerous novel applications. Despite remarkable progress in synthesizing colloidal molecules with diverse functionalities, most current methods, such as the capillarity-assisted particle assembly method, the ionic assembly method based on ionic interactions, or the field-directed assembly strategy based on dipole-dipole interactions, are confined to focusing on achieving symmetrical molecules. But there have been few examples of fabricating asymmetrical colloidal molecules that could exhibit unprecedented optical properties. Here, we introduce a microfluidic and magnetic template-assisted self-assembly protocol that relies mainly on the magnetic dipole-dipole interactions between magnetized magnetic-plasmonic nanoparticles and the mechanical constraints resulting from the specially designed traps. This novel strategy not only requires no specific chemistry but also enables magnetophoretic control of magnetic-plasmonic nanoparticles during the assembly process. Moreover, the assembled asymmetrical colloidal molecules also exhibit interesting hybridized plasmon modes and produce exotic optical properties due to the strong coupling of the individual nanoparticle. The ability to fabricate asymmetrical colloidal molecules based on the bottom-up method opens up a new direction for the fabrication of novel microscale structures for biosensing, patterning, and delivery applications.

Magnetically-assembled multifunctional magnetic-plasmonic SERS substrate for low-concentration analyte detection

Multifunctional particles with combined magnetic and optical properties are promising materials for applications such as sensing and detection of analytes, and contrast agents for imaging techniques such as MRI, and photocatalysis. While the magnetic property allows for non-contact manipulation of the nanoparticles, optical properties can be harnessed for such sensing applications. We present the synthesis and large-scale assembly of inter-layered magnetic-plasmonic nanoparticles with graphene oxide (GO) spacer (Fe3O4@GO@Ag). The multifunctional composite particles were prepared using simple chemical methods and had an average size of 225 nm. The prepared samples were characterized using different techniques including powder XRD, FT-IR, Raman scattering, SEM, and TEM imaging. By using an external magnetic field, it is possible to form an assembly of these multifunctional particles on a large scale. Due to the chain-like formation in the presence of a magnetic field, such assemblies are good substrates for surface-enhanced Raman scattering (SERS). Here, we demonstrate the application of these magnetically-assembled particles for the detection of very low concentrations of analyte molecules (4-mercaptopyridine) using SERS. These multifunctional composite particles are good candidates for potential applications involving chemical detection, photocatalytic reactions, optoelectronic devices, and photothermal effects.

A Robust Nanoparticle-based Magnetic Separation Method for Intact Lysosomes.

Lysosome isolation is a preresiquite for identifying lysosomal protein composition by mass spectroscopic analysis, to reveal lysosome functions, and their involvement in some diseases. Magnetic nanoparticle-based fractionation has received great attention for lysosome isolation, owing to its high efficiency, purity, and preservation of lysosomal structures. Understanding the intracellular trafficking of magnetic probes is the key point of this technique, to determine the appropriate time for magnetic isolation of lysosomes, because this parameter changes depending on different cell lines used. The traditional magnetic probes, such as superparamagnetic iron oxide nanoparticles (SPIONs), require surface modification by fluorescent dyes to enable the investigation of their intracellular trafficking, which has some disadvantages, including the possible alternation of their bio-interaction, and the instability of fluorescence properties in the lysosomal environment. To overcome those limitations, we present a protocol that employs magnetic-plasmonic nanoparticles (MPNPs) to investigate intracellular trafficking using their intrinsic imaging capability, followed by quick lysosome isolation using a magnetic column. This protocol can be easily applied to isolate the intact lysosomes of any adherent cell lines. Graphical abstract.

Giant Faraday rotation, magnetic and nonlinearity of diamagnetic glass tailored by plasmonic-magnetic bimetallic Au-Ni NPs

Glass containing plasmonic-magnetic nanoparticles have presented striking potential for plasmonic and nonlinear properties. For the first time, we report the synthesis and the magnetic/magneto-optical characterization of plasmonic-magnetic bimetallic Au-Ni nanoparticles (NPs) in heavy metal oxide diamagnetic glasses through co-sputtering technique. The optimum parameters for deposition, diffusion and formation of AuNi NPs were determined and< 50 nm AuNi NPs were synthesized in glass. Compositional and chemical valence states analysis revealed that the NPs is metallic AuNi, oxidization occurred for temperature high than 380 °C. The incorporation of Au-Ni NPs endowed the diamagnetic glass intense SPR peaks and superior optical nonlinearities comparable to that of host and single Au incorporated glasses. The alloy of transition metal Ni contributed to remarkable ferromagnetic character to glasses with characteristic M-H and M-T relations. Giant Verdet constant were obtained for glass and influential reasons were investigated insight of SPR effect, optical energy band gap and magnetization. Glass having 42 nm-AuNi NPs treated at 380 °C for 6 h exhibited huge Verdet constant of 72.66 rad/T m, large third-nonlinear susceptibility of 8.14 × 10−11 esu and strong ferromagnetic moment. This glass will be promising for advanced optical nonlinear and magneto optical applications.

Reduced Self-Aggregation and Improved Stability of Silica-Coated Fe3O4/Ag SERS-Active Nanotags Functionalized With 2-Mercaptoethanesulfonate.

Nanocomposites combining magnetic and plasmonic properties are very attractive within the field of surface-enhanced Raman scattering (SERS) spectroscopy. Applications presented so far take advantage of not only the cooperation of both components but also synergy (enhanced properties), leading to multi-approach analysis. While many methods were proposed to synthesize such plasmonic-magnetic nanoparticles, the issue of their collective magnetic behavior, inducing irreversible self-aggregation, has not been addressed yet. Thus, here we present a simple and fast method to overcome this problem, employing 2-mercaptoethanesulfonate (MES) ions as both a SERS tag and primer molecules in the silica-coating process of the previously fabricated Fe3O4/Ag nanocomposite. The use of MES favored the formation of silica-coated nanomaterial comprised of well-dispersed small clusters of Fe3O4/Ag nanoparticles. Furthermore, adsorbed MES molecules provided a reliable SERS response, which was successfully detected after magnetic assembly of the Fe3O4/Ag@MES@SiO2 on the surface of the banknote. Improved chemical stability after coating with a silica layer was also found when the nanocomposite was exposed to suspension of yeast cells. This work reports on the application of 2-mercaptoethanesulfonate not only providing a photostable SERS signal due to a non-aromatic Raman reporter but also acting as a silica-coating primer and a factor responsible for a substantial reduction of the self-aggregation of the plasmonic-magnetic nanocomposite. Additionally, here obtained Fe3O4/Ag@MES@SiO2 SERS nanotags showed the potential as security labels for the authentication purposes, retaining its original SERS performance after deposition on the banknote.

Theoretical investigation of the microfluidic and magnetic field-assisted self-assembly of colloidal magnetic-plasmonic nanoparticles

Patterning a wide range of colloidal plasmonic nanoparticles into prescribed spatial arrangements, analogous to the formation of natural materials, enables the fabrication of functionalized structures with novel optical properties, such as Fano resonance, magneto-optical Kerr effect, negative refraction, etc. Currently, capillarity-assisted particle assembly is always utilized to place colloidal particles at predetermined positions by exploiting the capillary forces resulting from the motion of an evaporating droplet. However, this technique requires specialized equipment and the assembly process is always carried out in an open system, thereby introducing the risk of contamination and limiting its applications. Here, we present a microfluidic and magnetic field-assisted self-assembly of colloidal magnetic-plasmonic nanoparticles by utilizing magnetic dipole–dipole interactions resulting from the localized magnetic gradient field produced by an array of soft-magnetic elements and external magnetic bias field. The magnetized magnetic-plasmonic nanoparticles are controlled to deposit at the predesigned traps microfabricated onto the soft-magnetic elements. After deposition, the inlet velocity of the microchannel is improved to clear away the particles out of the traps, forming arrays of patterns with consistent structures. Furthermore, a Lagrangian–Eulerian model is introduced for the first time to predict the processing of the microfluidic and magnetic field-assisted self-assembly of colloidal magnetic-plasmonic nanoparticles by taking the magnetic and hydrodynamic forces and particle–fluid interaction into account. Our analysis demonstrates that the particle–fluid interaction not only plays a significant role in determining the final self-assembled nanostructures, but provides an opportunity to improve the consistency of the assembled nanostructures. The microfluidic and magnetic field-assisted self-assembly protocol proposed here enables the patterning of colloidal magnetic-plasmonic nanoparticles to be carried out in a controlled environment and also opens up a new direction for assembling complex structures.

Plasmonic colorimetric PCR for Rapid molecular diagnostic assays

• A plasmonic photothermal colorimetric biosensor is developed for molecular diagnostic assays. • Simple point-of-care system without the need of bulky and expensive instrumentation. • Fast (< 20 min) and highly sensitive (63.7 aM) colorimetric method for nucleic acid detection. • Colorimetric signals can be easily obtained with the naked eye and quantified by using a spectrophotometer and smart phone. The development of efficient and sensitive diagnostic method with no need for bulky and expensive instrumentation is of great importance in early detection and large-scale prevention of various infectious disease. Herein, we introduce a plasmonic photothermal colorimetric PCR (PPT-cPCR) for fast, sensitive, cheap, and simple nucleic acid detection. Our platform utilizes ultrafast PCR amplification based on the photothermal effect of plasmonic magnetic nanoparticles and color change by oxidation of chromogenic substrates caused by the photocatalytic activity of fluorescent dyes. PPT-cPCR has successfully shown that DNA targets ranging from 0.5 ng μL −1 to 3 fg μL −1 can be visually detected within 20 min with the naked eye. Additionally, the quantitative information can be easily obtained by using a spectrophotometer and smart phone, and the limit of detection (2.00 fg μL -1 , 63.7 aM) based on UV–vis absorbance is comparable with conventional PCR, however the assay time is about 2∼3 times shorter for the PPT-cPCR and the assay method is cost-effective. The strategy that combines PPT-based PCR and colorimetric analysis will open new horizons for point-of-care biosensor development.

Fast and sensitive immuno-PCR assisted by plasmonic magnetic nanoparticles

Immunoassay for quantitative protein detection is an important tool in biomedical and clinical researches. Various types of detection platforms have emerged from typical ELISA using chromogenic reporter to more advanced approaches including electric, electrochemiluminescent and fluorogenic reporters to create quantitative analysis. Among them, fluorescence-based immuno-polymerase chain reaction (iPCR) is regarded as one of the simplest and most sensitive strategy that combines the specificity of immunological recognition technology with the amplification power of PCR. However, most PCR-based immunoassays to date have relied on the costly and time-consuming Peltier block heating technology. Here, we introduce a plasmonic photothermal (PPT)-iPCR assay method based on plasmonic magnetic nanoparticles to reduce the required thermal cycling time of amplification without compromising the superior sensitivity of iPCR. PPT-iPCR is capable of sensitive and quantitative detection of tumor necrosis factor-α (TNF-α) proteins ranging from 0.1 pg/mL to 1000 pg/mL within 8 min. PPT-iPCR uses fast, energy-efficient and inexpensive LED-based devices and can be used with commercial kits without modification while achieving excellent sensitivity. Our strategy can be easily combined with mobile phones or micro-optics, thus laying the foundation for the development of inexpensive, highly mobile detection devices that can quickly and accurately analyze biomarkers in a variety of diagnostic applications.

Formation and Application of Core-Shell of FePt-Au Magnetic-Plasmonic Nanoparticles.

Monodispersed FePt core and FePt–Au core–shell nanoparticles (NPs) have been chemically synthesized in liquid solution and with controllable surface-functional properties. The NP size was increased from 2.5 nm for FePt to 6.5 nm for FePt–Au, which could be tuned by the initial concentration of gold acetate coated onto FePt seeding NPs via a seed-mediated formation of self-assembled core–shell nanostructures. The analyses of the interplanar spacing obtained from the high-resolution transmission electron microscopy (HRTEM), selective electron diffraction pattern (SAED), and x-ray diffraction (XRD) confirmed that both FePt core and Au shell belong to the face-centered cubic (fcc) structure. FePt–Au NPs have a surface plasmon resonance (SPR) peak at 528 nm in the visible optical band region, indicating the red shift compared with the typical theoretical value of 520 nm of pure Au NPs. The surface modification and ligand exchange of FePt–Au was using mercaptoacetic acid (thiol) as a phase transfer reagent that turned the NPs hydrophilic due to the functional carboxyl group bond on the surface of presented multifunctional magnetic–plasmonic NPs. The water-dispersible FePt-based NPs conjugated with biomolecules could reach the different biocompatibility requirements and also provide enough heating response that acted as a potential agent for magnetic fluid hyperthermia in biomedical engineering research fields.

Dark Field and Coherent Anti-Stokes Raman (DF-CARS) Imaging of Cell Uptake of Core-Shell, Magnetic-Plasmonic Nanoparticles.

Magnetic-plasmonic, Fe3O4-Au, core-shell nanoparticles are popular in many applications, most notably in therapeutics and diagnostics, and thus, the imaging of these nanostructures in biological samples is of high importance. These nanostructures are typically imaged in biological material by dark field scatter imaging, which requires an even distribution of nanostructures in the sample and, therefore, high nanoparticle doses, potentially leading to toxicology issues. Herein, we explore the nonlinear optical properties of magnetic nanoparticles coated with various thicknesses of gold using the open aperture z-scan technique to determine the nonlinear optical properties and moreover, predict the efficacy of the nanostructures in nonlinear imaging. We find that the magnetic nanoparticles coated with gold nanoseeds and thinner gold shells (ca. 4 nm) show the largest nonlinear absorption coefficient β and imaginary part of the third-order susceptibility Im χ(3), suggesting that these nanostructures would be suitable contrast agents. Next, we combine laser dark field microscopy and epi-detected coherent anti-Stokes Raman (CARS) microscopy to image the uptake of magnetic-plasmonic nanoparticles in human pancreatic cancer cells. We show the epi-detected CARS technique is suitable for imaging of the magnetic-plasmonic nanoparticles without requiring a dense distribution of nanoparticles. This technique achieves superior nanoparticle contrasting over both epi-detected backscatter imaging and transmission dark field imaging, while also attaining label-free chemical contrasting of the cell. Lastly, we show the high biocompatibility of the Fe3O4 nanoparticles with ca. 4-nm thick Au shell at concentrations of 10–100 µg/mL.

The Effects of a Varied Gold Shell Thickness on Iron Oxide Nanoparticle Cores in Magnetic Manipulation, T1 and T2 MRI Contrasting, and Magnetic Hyperthermia.

Fe3O4–Au core–shell magnetic-plasmonic nanoparticles are expected to combine both magnetic and light responsivity into a single nanosystem, facilitating combined optical and magnetic-based nanotheranostic (therapeutic and diagnostic) applications, for example, photothermal therapy in conjunction with magnetic resonance imaging (MRI) imaging. To date, the effects of a plasmonic gold shell on an iron oxide nanoparticle core in magnetic-based applications remains largely unexplored. For this study, we quantified the efficacy of magnetic iron oxide cores with various gold shell thicknesses in a number of popular magnetic-based nanotheranostic applications; these included magnetic sorting and targeting (quantifying magnetic manipulability and magnetophoresis), MRI contrasting (quantifying benchtop nuclear magnetic resonance (NMR)-based T1 and T2 relaxivity), and magnetic hyperthermia therapy (quantifying alternating magnetic-field heating). We observed a general decrease in magnetic response and efficacy with an increase of the gold shell thickness, and herein we discuss possible reasons for this reduction. The magnetophoresis speed of iron oxide nanoparticles coated with the thickest gold shell tested here (ca. 42 nm) was only ca. 1% of the non-coated bare magnetic nanoparticle, demonstrating reduced magnetic manipulability. The T1 relaxivity, r1, of the thick gold-shelled magnetic particle was ca. 22% of the purely magnetic counterpart, whereas the T2 relaxivity, r2, was 42%, indicating a reduced MRI contrasting. Lastly, the magnetic hyperthermia heating efficiency (intrinsic loss power parameter) was reduced to ca. 14% for the thickest gold shell. For all applications, the efficiency decayed exponentially with increased gold shell thickness; therefore, if the primary application of the nanostructure is magnetic-based, this work suggests that it is preferable to use a thinner gold shell or higher levels of stimuli to compensate for losses associated with the addition of the gold shell. Moreover, as thinner gold shells have better magnetic properties, have previously demonstrated superior optical properties, and are more economical than thick gold shells, it can be said that “less is more”.

Immunomagnetic Capture and Multiplexed Surface Marker Detection of Circulating Tumor Cells with Magnetic Multicolor Surface-Enhanced Raman Scattering Nanotags.

Circulating tumor cells (CTCs) have substantial clinical implications in cancer diagnosis and monitoring. Although significant progress has been made in developing technologies for CTC detection and counting, the ability to quantitatively detect multiple surface protein markers on individual tumor cells remains very limited. In this work, we report a multiplexed method that uses magnetic multicolor surface-enhanced Raman scattering (SERS) nanotags in conjunction with a chip-based immunomagnetic separation to quantitatively and simultaneously detect four surface protein markers on individual tumor cells in whole blood. Four-color SERS nanotags were prepared using magnetic-optical iron oxide-gold core-shell nanoparticles with different Raman reporters to recognize four different cancer markers with respective antibodies. A microfluidic device was fabricated to magnetically capture the nanoparticle-bound tumor cells and to perform online negative staining and single-cell optical detection. The level of each targeted protein was obtained by signal deconvolution of the mixed SERS signals from individual tumor cells using the classic least squares regression method. The method was tested with spiked tumor cells in human whole blood with three different breast cancer cell lines and compared with the results of purified cancer cells suspended in a phosphate buffer solution. The method, with either spiked cancer cells in blood or purified cancer cells, showed a strong correlation with purified cancer cells by enzyme-linked immunosorbent assay, suggesting the potential of our method for the reliable detection of multiple surface markers on CTCs. Combining immunomagnetic enrichment with high specificity, multiplexed targeting for the capture of CTC subpopulations, multicolor SERS detection with high sensitivity and specificity, microfluidics for handling rare cells and magnetic-plasmonic nanoparticles for dual enrichment and detection, our method provides an integrated, yet a simple and an efficient platform that has the potential to more sensitively detect and monitor cancer metastasis.

Design of Magnetic-Plasmonic Nanoparticle Assemblies via Interface Engineering of Plasmonic Shells for Targeted Cancer Cell Imaging and Separation.

Magnetic-plasmonic nanoparticles have received considerable attention for widespread applications. These nanoparticles (NPs) exhibiting surface-enhanced Raman scattering (SERS) activities are developed due to their potential in bio-sensing applicable in non-destructive and sensitive analysis with target-specific separation. However, it is challenging to synthesize these NPs that simultaneously exhibit low remanence, maximized magnetic content, plasmonic coverage with abundant hotspots, and structural uniformity. Here, a method that involves the conjugation of a magnetic template with gold seeds via chemical binding and seed-mediated growth is proposed, with the objective of obtaining plasmonic nanostructures with abundant hotspots on a magnetic template. To obtain a clean surface for directly functionalizing ligands and enhancing the Raman intensity, an additional growth step of gold (Au) and/or silver (Ag) atoms is proposed after modifying the Raman molecules on the as-prepared magnetic-plasmonic nanoparticles. Importantly, one-sided silver growth occurred in an environment where gold facets are blocked by Raman molecules; otherwise, the gold growth is layer-by-layer. Moreover, simultaneous reduction by gold and silver ions allowed for the formation of a uniform bimetallic layer. The enhancement factor of the nanoparticles with a bimetallic layer is approximately 107 . The SERS probes functionalized cyclic peptides are employed for targeted cancer-cell imaging and separation.

Janus Magnetic-Plasmonic Nanoparticles for Magnetically Guided and Thermally Activated Cancer Therapy.

Progress of thermal tumor therapies and their translation into clinical practice are limited by insufficient nanoparticle concentration to release therapeutic heating at the tumor site after systemic administration. Herein, the use of Janus magneto-plasmonic nanoparticles, made of gold nanostars and iron oxide nanospheres, as efficient therapeutic nanoheaters whose on-site delivery can be improved by magnetic targeting, is proposed. Single and combined magneto- and photo-thermal heating properties of Janus nanoparticles render them as compelling heating elements, depending on the nanoparticle dose, magnetic lobe size, and milieu conditions. In cancer cells, a much more effective effect is observed for photothermia compared to magnetic hyperthermia, while combination of the two modalities into a magneto-photothermal treatment results in a synergistic cytotoxic effect in vitro. The high potential of the Janus nanoparticles for magnetic guiding confirms them to be excellent nanostructures for in vivo magnetically enhanced photothermal therapy, leading to efficient tumor growth inhibition.

One-step synthesis of Fe–Au core–shell magnetic-plasmonic nanoparticles driven by interface energy minimization

The formation of core–shell (CS) nanoparticles (NPS) often requires complex procedures. Due to minimization of interface energy, we show that colloidal Fe–Au CS NPs are obtained in one step, by laser ablation of bimetallic thin films in liquid.

Theoretical study of the photothermal behaviour of self-assembled magnetic-plasmonic chain structures.

We study the field-directed self-assembly and photothermal behavior of one-dimensional (1D) chains of core-shell Fe3O4@Au magnetic-plasmonic nanoparticles. Monte Carlo analysis is used to predict the self-assembly of the nanoparticles when they are subjected to a uniform magnetic field and confined to a fluidic nanochannel. A coupled photonic and thermodynamic analysis is performed to analyze the optical and photothermal properties of the 1D chain structures. We show for the first time that the assembled chain structures exhibit a pronounced dip in their absorption spectrum at a wavelength that is strongly sensitive to changes in the refractive index of the surrounding medium. The plasmon enhanced features of these structures are well suited for a variety of theranostic modalities as we discuss.

Janus plasmonic-magnetic gold-iron oxide nanoparticles as contrast agents for multimodal imaging.

The design of compact nanoprobes for multimodal bioimaging is a current challenge and may have a major impact on diagnostics and therapeutics. Multicomponent gold-iron oxide nanoparticles have shown high potential as contrast agents in numerous imaging techniques due to the complementary features of iron oxide and gold nanomaterials. In this paper we describe novel gold-iron oxide Janus magnetic-plasmonic nanoparticles as versatile nanoprobes for multimodal imaging. The nanoparticles are characterized as contrast agents for different imaging techniques, including X-ray computed tomography (CT), T2-weighted nuclear magnetic resonance imaging (MRI), photoacoustic imaging (PA), dark-field and bright-field optical microscopy, transmission electron microscopy (TEM), and surface enhanced Raman spectroscopy (SERS). We discuss the effect of particle size and morphology on their performance as contrast agents and show the advantage of a Janus configuration. Additionally, the uptake of nanoparticles by cells can be simultaneously visualized in dark- and bright-field optical microscopy, SERS mapping, and electron microscopy. These complementary techniques allow a complete view of cell uptake in an artifact-free manner, with multiplexing capabilities, and with extra information regarding the nanoparticles' fate inside the cells. Altogether, the results obtained with these non-invasive techniques show the high versatility of these nanoparticles, the advantages of a Janus configuration, and their high potential in multipurpose biomedical applications.

Preparation of plasmonic magnetic nanoparticles and their light scattering properties

Fe3O4@SiO2@Au nanoparticles (NPs) that have plasmonic and magnetic properties were prepared by simple immobilization method of Au NPs to silica coated magnetic NPs.