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Magnetic gold nanoparticles (mGNP) have become a great interest of research for nanomaterial scientists because of their significant magnetic and plasmonic properties applicable in biomedical applications. Various synthetic approaches and surface modification techniques have been used for mGNP including the most common being the coprecipitation, thermal decomposition, and microemulsion methods in addition to the Brust Schiffrin technique, which involves the reduction of metal precursors in a two-phase system (water and toluene) in the presence of alkanethiol. The hybrid magnetic–plasmonic nanoparticles based on iron core and gold shell are being considered as potential theranostic agents. In this critical review, in addition to future works, we have summarized recent developments for synthesis and surface modification of mGNP with their applications in modern biomedical science such as drug and gene delivery, bioimaging, biosensing, and neuro-regeneration, neuro-degenerative and arthritic disorders. This review includes techniques and biological applications of mGNP majorly based on research from the previous six years. [ABSTRACT FROM AUTHOR]

Magnetic gold nanoparticles (mGNP) have become a great interest of research for nanomaterial scientists because of their significant magnetic and plasmonic properties applicable in biomedical applications. Various synthetic approaches and surface modification techniques have been used for mGNP including the most common being the coprecipitation, thermal decomposition, and microemulsion methods in addition to the Brust Schiffrin technique, which involves the reduction of metal precursors in a two-phase system (water and toluene) in the presence of alkanethiol. The hybrid magnetic–plasmonic nanoparticles based on iron core and gold shell are being considered as potential theranostic agents. In this critical review, in addition to future works, we have summarized recent developments for synthesis and surface modification of mGNP with their applications in modern biomedical science such as drug and gene delivery, bioimaging, biosensing, and neuro-regeneration, neuro-degenerative and arthritic disorders. This review includes techniques and biological applications of mGNP majorly based on research from the previous six years.

The rational design of complex nanostructures is of paramount importance to gain control over their chemical and physical properties. Recently, magnetic-plasmonic heterostructured nanocrystals have been recognized as key players in nanomedicine as multifunctional therapeutic-diagnostic tools and in catalysis. Here we show how the properties of gold-iron oxide heterostructured nanocrystals can be tuned by chemical doping of the magnetic subunit. The divalent cations in the iron oxide were substituted with cobalt and manganese to obtain a general formula Au-MFe2O4 (M = Fe, Co, Mn). Magnetic properties of the heterostructures could be tuned, while maintaining well-defined plasmon resonance signatures, confirming the dual magnetic-plasmonic functional capability of these nanostructures. [ABSTRACT FROM AUTHOR]

Cancer is the second leading cause of death attributed to disease worldwide. Current standard detection methods often rely on a single cancer marker, which can lead to inaccurate results, including false negatives, and an inability to detect multiple cancers simultaneously. Here, we developed a multiplex method that can effectively detect and classify surface proteins associated with three distinct types of breast cancer by utilizing gap-enhanced Raman scattering nanotags and machine learning algorithm. We synthesized anisotropic magnetic core-gold shell gap-enhanced Raman nanotags incorporating three different Raman reporters. These multicolor Raman nanotags were employed to distinguish specific surface protein markers in breast cancer cells. The acquired signals were deconvoluted and analyzed using classical least-squares regression to generate a surface protein profile and characterize the breast cancer cells. Furthermore, computational data obtained via finite-difference time-domain and discrete dipole approximation showed the amplification of the electric fields within the gap region due to plasmonic coupling between the two gold layers. Finally, a random forest classifier achieved an impressive classification and profiling accuracy of 93.9%, enabling effective distinguishing between the three different types of breast cancer cell lines in a mixed solution. With the combination of immunomagnetic multiplex target specificity and separation, gap-enhancement Raman nanotags, and machine learning, our method provides an accurate and integrated platform to profile and classify different cancer cells, giving implications for identification of the origin of circulating tumor cells in the blood system.

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.

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”.

Heterodimeric nanoparticles comprising materials with different functionalities are of great interest for fundamental research and biomedical/industrial applications. In this work, Fe3O4-Au nano-heterostructures were synthesized by a one-step thermal decomposition method. The hybrid nanoparticles comprise a highly crystalline 12 nm magnetite octahedron decorated with a single noble metal sphere of 6 nm diameter. Detailed analysis of the nanoparticles was performed by UV-visible spectroscopy, magnetometry, calorimetry and relaxometry studies. The cytotoxic effect of the nanoparticles in the human hepatic cell line Huh7 and PLC/PRF/5-Alexander was also assessed. These Fe3O4-Au bifunctional nanoparticles showed no significant cytotoxicity in these two cell lines. The nanoparticles showed a good theranostic potential for liver cancer treatment, since the r2 relaxivity (166.5 mM−1·s−1 and 99.5 mM−1·s−1 in water and HepG2 cells, respectively) is higher than the corresponding values for commercial T2 contrast agents and the Specific Absorption Rate (SAR) value obtained (227 W/gFe) is enough to make them suitable as heat mediators for Magnetic Fluid Hyperthermia. The gold counterpart can further allow the conjugation with different biomolecules and the optical sensing.

Abstract: Magnetic-plasmonic nanoparticles, combining magnetic and plasmonic components, are promising structures for use in life sciences. Optical properties of core-shell magnetite-gold nanostructures, such as the wavelength of the plasmon resonance, the extinction cross-section, and the ratio of scattering to absorption at the plasmon wavelength are critical parameters in the search for the most suitable particles for envisioned applications. Using Mie theory and the discrete dipole approximation (DDA), optical spectra as a function of composition, size, and shape of core-shell nanospheres and nanorods were calculated. Calculations were done using simulated aqueous media, used throughout the life sciences. Our results indicate that in the advantageous near-infrared region (NIR), although magnetic-plasmonic nanospheres produced by available chemical methods lack the desirable tunability of optical characteristics, magnetic-plasmonic nanorods can achieve the desired optical properties at chemically attainable dimensions. The presented results can aid in the selection of suitable magnetic-plasmonic structures for applications in life sciences. From the Clinical Editor: In this basic science study, magnetic-plasmonic nanoparticles are studied for future applications in life sciences. Optical properties of core-shell magnetite-gold nanostructures, such as the wavelength of the plasmon resonance, the extinction cross-section, and the ratio of scattering to absorption at the plasmon wavelength are critical parameters in the search for the most suitable particles for proposed future applications. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

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". [ABSTRACT FROM AUTHOR]

Heterodimeric nanoparticles comprising materials with different functionalities are of great interest for fundamental research and biomedical/industrial applications. In this work, Fe3O4-Au nano-heterostructures were synthesized by a one-step thermal decomposition method. The hybrid nanoparticles comprise a highly crystalline 12 nm magnetite octahedron decorated with a single noble metal sphere of 6 nm diameter. Detailed analysis of the nanoparticles was performed by UV-visible spectroscopy, magnetometry, calorimetry and relaxometry studies. The cytotoxic effect of the nanoparticles in the human hepatic cell line Huh7 and PLC/PRF/5-Alexander was also assessed. These Fe3O4-Au bifunctional nanoparticles showed no significant cytotoxicity in these two cell lines. The nanoparticles showed a good theranostic potential for liver cancer treatment, since the r2 relaxivity (166.5 mM−1·s−1 and 99.5 mM−1·s−1 in water and HepG2 cells, respectively) is higher than the corresponding values for commercial T2 contrast agents and the Specific Absorption Rate (SAR) value obtained (227 W/gFe) is enough to make them suitable as heat mediators for Magnetic Fluid Hyperthermia. The gold counterpart can further allow the conjugation with different biomolecules and the optical sensing. [ABSTRACT FROM AUTHOR]

A SERS-based aptasensor for ochratoxin A (OTA) is described. It is making use of Fe3O4@Au magnetic nanoparticles (MGNPs) and of Au@Ag nanoprobes modified with the Raman reporter 5,5-dithiobis-(2-nitrobenzoic acid; DTNB). Au-DTNB@Ag NPs were modified with the OTA aptamer (aptamer-GSNPs) and used as Raman signal probes. The SERS peak of DTNB at 1331 cm−1 was used for quantitative analysis. MGNPs modified with cDNA (cDNA-MGNPs) were used as capture probes and reinforced substrates. When the Au-DTNB@Ag-Fe3O4@Au complexes are formed through oligonucleotide hybridization, the Raman signal intensity of the Raman probe is significantly enhanced. If the OTA concentration in samples increases, more Raman signal probes (aptamer-GSNPs) will dissociate from the cDNA-MGNPs because more OTA aptamer is bound by OTA. This leads to a lower Raman signal after magnetic separation. Under the optimal conditions, the detection limit for OTA is 0.48 pg·mL−1 based on 3σ criterion. This is attributed to the multiple Raman signal enhancement and the good performance of the OTA aptamer. The good recovery and accuracy of the assay was confirmed by evaluating spiked samples of wine and coffee.Schematic of an aptamer based SERS assay for OTA by integrating Fe3O4@AuNPs (MGNPs) with Au-DTNB@Ag NPs with multiple signal enhancement. Aptamer modified Au-DTNB@Ag NPs are used as Raman probes, and MGNPs modified with cDNA are used as capture probes and reinforced substrates. [ABSTRACT FROM AUTHOR]