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.

Single-particle inductively coupled plasma mass spectrometry (spICP-MS) is used increasingly to characterize element-containing nanoparticles (NPs) in various samples, providing data on the number, concentration, size of particles, as well as the dissolved element concentration. Because there are currently only three examples of spICP-MS analysis of NPs in hydrocarbons in the literature. There is a clear need for hydrocarbon-based NP reference materials (RMs), available for analysts to develop and validate new methods. Here, an analysis of spICP-MS data is presented for two custom-developed gold NP RMs in toluene. The particle size data obtained by spICP-MS is compared with the total particle diameter obtained by transmission electron microscopy (TEM) and shows the excellent agreement among both techniques.

Pulsed laser (ms, 1064 nm) gold nanoparticle (GNP) heating has been used recently to achieve fast (>10 000 000 °C min-1) warming of vitrified droplets using gold nanorods (GNRs) as photon-absorbers. To maximize the viability of biomaterials in vitrified droplets, the droplets must be warmed as uniformly as possible. A potential approach to such warming is to use an appropriate combination of photon-absorption and -scattering to distribute heat more uniformly throughout a droplet. To investigate this, 2 plasmonic gold nanorods (GNRs), 1 hollow gold nanoshell, and 2 silica-core gold nanoshells (GNSs) were synthesized and characterized under 1064 nm laser irradiation in water, propylene glycol, and protein-rich (egg white) solutions. Using a modified cuvette laser calorimetry experiment with complementary Monte Carlo modeling, the GNSs were found to have higher per-particle absorption and scattering cross sections, while the GNRs had higher photothermal conversion efficiency, absorption efficiency, and Au mass normalized absorption cross sections. In the characterization, the GNSs with larger scattering-to-absorption ratios could have ∼30% over-estimation of photothermal conversion efficiency if scattering and reabsorption inside the solution were not considered, while GNRs with lower ratios were less impacted. Combined Monte Carlo and COMSOL simulations were used to predict the specific absorption rate (W m-3) and heating behavior of GNP-loaded hemispherical droplets, thereby demonstrating that the GNS case with higher scattering-to-absorption ratio achieved more uniform heating than the GNR case. Interestingly, further tuning of the scattering and absorption coefficients of the hemispherical GNP-loaded droplet within the model suggests the ability to obtain an optimal scattering-to-absorption ratio for uniform heating. These results show the importance of considering the reabsorption of scattered light to accurately characterize the photothermal conversion efficiency of GNP solutions during laser irradiation. We also show that the relative scattering and absorption properties of the nanoparticles can be designed to promote both rapid and uniform laser rewarming of vitrified droplets for application in cryopreservation.

Engineered iron oxide (Fe3O4) nanoparticles (NPs) were synthesized with a silica shell using a modified alkylsilane approach with o-xylene, as a hydrocarbon media, and transmission electron microscopy (TEM) and single-particle inductively coupled plasma mass spectrometry (spICP-MS) were used to determine the particle size of the Fe3O4 core diameter. In contrast, mass concentrations of the Fe3O4 particles were determined using spICP-MS, using helium (He) as a collision gas to control spectral interferences from ArO and CaO on Fe at m/z 56. Different cell gas flow rates (3, 3.5, and 4 mL/min) and NP’s solution dilution factors from 1:20,000 up to 1:60,000 were investigated; He flow rate of 4 mL/min and a dilution factor of 1:20,000 were found as optimum. The spICP-MS method was calibrated by using gold nanospheres (polystyrene-coated) in toluene as reference material. For the engineered Fe3O4 nanoparticles, TEM. Results gave a (63 ± 6 nm) value for the Fe2O3 core diameter, while spICP-MS was 61.1 ± 4.5 nm (n = 36), demonstrating the excellent agreement among methods. The method was applied for the analysis Fe oxide NPs in petroluem hydrocarbon materials and data compared with TEM. Two standard reference materials (SRMs); NIST 2717a sulfur in residual fuel oil and NIST 8505 vanadium in crude oil were selected. spICP-MS results agreed pretty well among these techniques. These findings suggest that spICP-MS could be useful to characterize Fe-containing particles in complex solution media, such as petroleum hydrocarbons. Graphical abstract

The combination of concentrating solar power and photovoltaic technologies in hybrid photovoltaics thermal systems have the potential of increasing the overall efficiency of solar energy by utilizing non-Photovoltaic wavelengths as dispatchable thermal energy for use as industrial process heat and/or electricity generation using a thermal engine. One way of achieving this requires a thermally-stable spectral filter capable of effectively transmitting photovoltaic radiation while absorbing non-Photovoltaic radiation. Here, we utilize indium tin oxide and gold nanoparticles in a silane-based heat transfer fluid capable of withstanding temperatures up to 340 degrees C while maintaining spectral transparency at photovoltaic wavelengths. To promote compatibility with the heat transfer fluid and achieve greater thermal stability of the nanoparticles, surface modifications were performed for both the indium tin oxide and the gold nanoparticles. It was found that the greatest solution stability was achieved with the use of a (6-7% aminopropylmethylsiloxane)-dimethylsiloxane copolymer surface ligand. Interestingly, when heating the nanoparticles, a spectral blue-shift was observed in the localized surface plasmon resonance peaks of both nanoparticles along with an increase in absorptivity for indium tin oxide. Analysis of the filter performance revealed that a filter optimized for c-Si photovoltaic receiver transmits 73% of bandgap radiation and absorbs 78% of sub-bandgap radiation. The increasing solar absorption properties of the nanoparticle at higher temperatures helped the filter maintained an ideal performance up to 250 degrees C, even with lower concentrations of nanoparticles. At 300 degrees C, however, the filter performance reduced due to the disappearance of the gold peak, which is attributed to the inferring free tin ions.

A nanoparticle fluid filter consisting of gold nanoparticles and indium tin oxide nanocrystals was fabricated and the optical properties were assessed. Results were integrated against the AM 1.5 solar spectrum to determine solar weighted efficiency of the filter for light energies transmitted above the bandgap to a photovoltaic cell for direct electrical generation while absorbing light below the bandgap that is converted to heat for thermal storage or processing. Temperature dependent bandgaps for both GaAs and cSi were used for optimization of the filter design. GaAs is preferred based upon its higher IR reflectivity, lower temperature coefficient, and greater high-temperature efficiency. However, cSi is significantly cheaper than current and projected GaAs costs. It was found that the experimental filter efficiency was 62% for GaAs and 56% for cSi which was within 6% of previous theoretical predictions.

We propose a design for a concentrating PV/T collector utilizing plasmonic nanoparticles directly suspended in the working fluid to spectrally filter the incoming solar flux. This liquid filter serves two purposes: the direct capture of thermal energy as well as filtering off of key portions of the spectrum before transmission to the PV cell. Our device builds upon the current Cogenra T14 system with a two-pass architecture: the first pass on the back side of the PV cell pre-heating the fluid from any thermalization losses, and the second pass in front of the PV cell to achieve the spectral filtering. Here we present details on the selection of plasmonic nanoparticles for a given cell bandgap as well as the impact to the overall system pumping power and cost.

Prior investigations into the synthesis of colloidal CdSe nanocrystals with a wurtzite crystal structure (wz-CdSe) have given rise to well-developed methods for producing particles with anisotropic shapes such as rods, tetrapods, and wires; however, the synthesis of other shapes has proved challenging. Here we present a seed-mediated approach for the growth of colloidal, shape-controlled wz-CdSe nanoparticles with previously unobserved morphologies. The synthesis, which makes use of small (2-3 nm) wz-CdSe nanocrystals as nucleation sites for subsequent growth, can be tuned to selectively yield colloidal wz-CdSe nanocubes and hexagonal nanoplatelets in addition to nanorod and bullet-shaped particles. We thoroughly characterize the morphology and crystal structures of these new shapes, as well as discuss possible growth mechanisms in the context of control over surface chemistry and the nucleation stage.

The optical, electrical, magnetic, and catalytic properties of colloidal nanocrystals are intimately tied to their form, in particular their physical size and shape. Synthetic techniques have been developed to produce metallic and semiconducting nanomaterials with well-controlled forms; however, characterization tools for describing shape have remained limited to small samples and lack the quantitative rigor necessary for a universal classification scheme. Here complex Fourier descriptors are shown to be a quantitative and high-throughput approach for classifying the shape of colloidal nanocrystals. Large, monodisperse, and polydisperse ensembles of CdSe nanocrystals are characterized with respect to shape and categorized as circles, triangles, squares, rods, and pentagonal or hexagonal platelets. These results suggest that classification of shape by Fourier descriptor analysis may in the near future be a powerful tool for continuous monitoring of synthesis, purification, or packaging/integration processes during industrial-scale production of nanomaterials.

We report the synthesis of monodisperse colloidal copper nanocrystals and subsequent solvent-dependent oxidation to form copper(I) oxide nanoparticles. The oxidation process was monitored by optical spectroscopy in the visible spectrum with the Cu nanocrystals exhibiting a surface plasmon feature that was replaced over time by an excitonic feature corresponding to the band gap of the Cu2O nanocrystals. The initial intensity of the copper plasmon was strongly dependent on the properties of the ! solvent used to form the nanocrystal dispersion; solvents with pi-bonds significantly reduced (by >3-fold) the plasmon intensity and this effect was attributed to electron sharing between the solvent and the copper surface. The damped plasmon only recovered to its solvent-independent intensity once the nanocrystal surface oxidized and eliminated the solvent-Cu surface interactions. Solvents without pi-bonds induced only a very small damping of the plasmon, and at longer time scales all solvents caused similar changes in the optical properties as oxidation converted the nanocrystals from metallic copper to semiconducting copper oxide.

AbstractDie Forschung über Nanokristalle hat unter anderem die Entwicklung experimenteller Verfahren zum Ziel, mit denen Zusammensetzung und Form von Nanokristallen über vielfältige Materialkombinationen hinweg gesteuert werden können. Wenn nanometergroße Domänen metallischer, halbleitender und magnetischer Materialien zu einzelnen “Hybrid”‐Nanopartikeln kombiniert werden können, eröffnen sich faszinierende Möglichkeiten für die Herstellung von Nanomaterialien mit mehreren Funktionalitäten oder verbesserten Eigenschaften einer einzelnen Domäne. In unserem Aufsatz diskutieren wir aktuelle Strategien für die Herstellung von Halbleiter/Metall‐Hybridnanopartikeln, neue Eigenschaften dieser Mehrkomponentenmaterialien sowie ihre möglichen Anwendungen.

One key goal of nanocrystal research is the development of experimental methods to selectively control the composition and shape of nanocrystals over a wide range of material combinations. The ability to selectively arrange nanosized domains of metallic, semiconducting, and magnetic materials into a single hybrid nanoparticle offers an intriguing route to engineer nanomaterials with multiple functionalities or the enhanced properties of one domain. In this Review, we focus on recent strategies used to create semiconductor-metal hybrid nanoparticles, present the emergent properties of these multicomponent materials, and discuss their potential applicability in different technologies.

Linear CdTe|CdSe|CdTe heterostructure nanorods are synthesized by using a colloidal sequential reactant injection technique [Shieh et al., J. Phys. Chem. B 2005, 109, 8538-8542]. The composition profiles of the individual nanorods are verified by using nanobeam elemental mapping by energy dispersive X-ray spectroscopy (EDS) and the photoluminescence emission spectra of the linear CdTe|CdSe|CdTe heterostructure nanorods are measured as a function of the temperature (down to 5 K). Photoluminescence is observed to occur from electron-hole recombination in both the CdSe core and across the heterojunction. Thermally activated trapping is found to influence both luminescence processes, thereby being more significant for the type II recombination across the CdSe|CdTe interface.

A hybrid Pt-CdSe nanoparticle system is prepared in aqueous media. displaying rod or nanonet structures depending on the pH. The new hybrids display morphology-dependent photocatalytic activity under visible light irradiation. Separation between photo generated charge carriers occurs at the metal/semiconductor interface (see figure), allowing redox reactions to take place at the nanoparticle surface.

Colloidal CdS nanorods with diameters near 4 nm and narrow size distributions ( approximately +/-10%) were synthesized up to 300 nm long by a sequential reactant injection technique that utilizes phosophonic acids as capping ligands. The phosphonic acid strongly passivates the nonpolar CdS surfaces and sequential reactant injection provides controlled CdS formation kinetics to enable heterogeneous and facet-selective CdS deposition on the more reactive {002} surfaces. With this process, the nanorod length can be systematically increased by increasing reactant addition to extend nanorod growth. The phosphonic acid concentration, however, is quite important, as "low" concentrations allow radial deposition and branching to occur. These high aspect ratio (>100) CdS nanorods luminesce with relatively high efficiencies of 10.8% quantum yield at room temperature. The luminescence, however, mostly arises from trap-related recombination, and the emission is significantly red-shifted from the absorption edge. Various surface passivation treatments were explored to eliminate trap emission and increase the luminescence quantum yield. Thiol and amine passivation both significantly reduced trap emission and enhanced band-edge emission, but the total luminescence quantum yields dropped significantly, with a maximum measured value of 1.5% for the amine-passivated CdS nanorods.