Laser-Ablative Synthesis of Ultrapure Magneto-Plasmonic Core-Satellite Nanocomposites for Biomedical Applications

Exploring the impact of particle stability, size, and morphology on nanofluid thermal conductivity: A comprehensive review for energy applications

Recent advancements enhance the efficiency of energy conversion processes and leverage nanofluids-novel thermal fluids with nanoparticles (under 100 nm) suspended in conventional fluids. These nanofluids significantly alter thermophysical properties, notably thermal conductivity, which is crucial for evaluating their thermal performance. Despite three decades of intensive research, disagreements persist due to a lack of comprehensive data on how particle size, shape, stability, and others influence thermal conductivity. This review tries to fill this literature gap by critically reviewing how the characteristics that distinguish nanofluids from their micrometer-sized counterparts affect the stability and convective heat transfer. The study compares experimental results in a systemic way that addresses the reported inconsistencies and provides a general summary of the thermal behavior of nanofluids in energy systems. It has also pointed out the lack of reliable hybrid models considering all parameters affecting thermal conductivity. The current study assembles data from different analyses showing that a particle size within the 10-50 nm range may enhance thermal conductivity, depending on the base-fluid used. Likewise, the morphological options available, namely, spherical, ellipsoid, platelet, and blade-like, all have given promise for enhancing thermal conductivity, hence considering morphological issues. Finally, stability, defined by the zeta potential analyses, forms a vital criterion for the long-term sustainability of these enhancements. By consolidating experimental results across different research groups, this review highlights the variability and sometimes contradictory findings in thermal conductivity enhancements, ranging from negligible increases to over 50% improvement in specific nanofluids systems. The absence of reliable hybrid models encapsulating all influencing parameters for predicting thermal conductivity is critically addressed. It is concluded by identifying the main challenges in the field and offering recommendations for standardizing measurement techniques, which include the need for a unified model capable of predicting thermal conductivity enhancements with an accuracy of ±5%.

Time-Resolved Dynamics of Laser Ablation in Liquid with Gas-Evolving Additives: Toward Molding the Atomic Structure of Nonequilibrium Nanoalloys

Laser ablation in liquid (LAL) is a reference technique for the synthesis of multicomponent non-equilibrium nanomaterials which have potentially disruptive properties in photonics, nanomedicine, and catalysis. Yet, ablation dynamics is poorly understood regarding the multielement matter and, therefore, the remarkable potential of LAL for controlling the local atomic structure of metastable nanophases remains largely unexploited. Here, the dynamics of LAL are investigated with non-equilibrium gold-iron nanoalloys generated in the presence of gas-evolving additives, which drive the formation of different nanostructures. With analytical electron microscopy, the structure in the different conditions is properly identified through complete segregation into oxide-metal heterostructures, precipitation of nanoclusters within the nanoalloys, or ordered solid solutions. To elucidate the unforeseen effects of the solutes on the atomic structure of nanoalloys, the early and full dynamics of LAL is investigated with time-resolved experiments, leading to the pivotal evidence that alloying of metastable compounds with different chemical reactivity is favored by decreasing the pressure of the shockwave front. The resulting picture indicates LAL with gas-evolving additives as a strategy for molding the atomic structure of non-equilibrium nanoalloys, opening the way to the development of a library of advanced nanomaterials otherwise inaccessible.

Tungsten Diselenide Nanoparticles Produced via Femtosecond Ablation for SERS and Theranostics Applications

Due to their high refractive index, record optical anisotropy and a set of excitonic transitions in visible range at a room temperature, transition metal dichalcogenides have gained much attention. Here, we adapted a femtosecond laser ablation for the synthesis of WSe2 nanoparticles (NPs) with diameters from 5 to 150 nm, which conserve the crystalline structure of the original bulk crystal. This method was chosen due to its inherently substrate-additive-free nature and a high output level. The obtained nanoparticles absorb light stronger than the bulk crystal thanks to the local field enhancement, and they have a much higher photothermal conversion than conventional Si nanospheres. The highly mobile colloidal state of produced NPs makes them flexible for further application-dependent manipulations, which we demonstrated by creating substrates for SERS sensors.

A Review of Different Synthesis Approaches to Nanoparticles: Bibliometric Profile

Nanomaterials are currently one of the most popular emerging materials used in different applications such as drug delivery, water treatment, cancer treatment, electronic, food preservations, and production of pesticide. This is due to their interesting features including size-dependent properties, lightweight, biocompatibility, amphiphilicity and biodegradability. They offer wide possibilities for modification and are used in multiple functions with enormous possibilities. Some of them are medically suitable which has opened new opportunities for medical improvement especially for human health. These characteristics also make nanomaterials one of the pioneers in green materials for various needs, especially in environmental engineering and energy sectors. In this review, several synthesis approaches for nanoparticles mainly physical, chemical, and biological have been discussed extensively. Furthermore, bibliometric analysis on the synthesis of nanoparticles was evaluated. About 117,162 publications were considered, of which 92% are journal publications. RSC Advances is the most published outlet on the synthesis of nanoparticles and China has the highest number of researchers engaged in the synthesis of nanoparticles. It was noted in the evaluation of synthesis approach that biological approach is the savest method but with a low yield, while the chemical approach offers a high yield with some level of hazardous effect. Also, the bibliometric analysis revealed that the field of nanotechnology is a trending and hot ground for research.

Understanding mono- and bi-metallic Au and Ni nanoparticle responses to fast heating

Nanoparticle assembly, alloying and fragmentation are fundamental processes with significant implications in various fields such as catalysis, materials science, and nanotechnology. Understanding these processes under fast heating conditions is crucial for tailoring nanoparticle properties and optimizing their applications. For this, we employ molecular dynamics simulations to obtain atomic-level insights into nanoparticle behavior. The performed simulations reveal intricate details of sintering, alloying and fragmentation mechanisms shedding light on the underlying physical phenomena governing these processes. The calculation results help to visualize nanoparticle evolution upon undercritical and supercritical heating elucidating not only the role of temperature, but also of nanoparticle sizes and composition. In particular, it is shown that surface tension and surface energy play important roles not only in nanoparticle melting but also in its fragmentation. When the added energy exceeds a critical threshold, the nanoparticle begins to experience alternating compression and expansion. If the tensile stress surpasses the material's strength limit, fragmentation becomes prominent. For very small particles (with radius smaller than ∼10 nm), this occurs more rapidly, whereas sub-nano-cavitation precedes the final fragmentation in larger particles, which behave more like droplets. Interestingly, this effect depends on composition in the case of AuNi alloy nanoparticles, as expected from the phase diagrams and excess energy. The heating level required to overcome the mixing barrier is also determined and is shown to play an important role in the evolution of AuNi nanoparticles, in addition to their size. Furthermore, our findings provide insights into controlling nanoparticle synthesis for various applications in numerous nanotechnological domains, such as catalysis, sensors, material analysis, as well as deseas diagnostics and treatment. This study bridges the gap between experimental observations and theoretical predictions paving the way for designing advanced nanomaterials with enhanced functionalities.

Binary Proton Therapy of Ehrlich Carcinoma Using Targeted Gold Nanoparticles

Proton therapy can treat tumors located in radiation-sensitive tissues. This article demonstrates the possibility of enhancing the proton therapy with targeted gold nanoparticles that selectively recognize tumor cells. Au-PEG nanoparticles at concentrations above 25 mg/L and 4 Gy proton dose caused complete death of EMT6/P cells in vitro. Binary proton therapy using targeted Au-PEG-FA nanoparticles caused an 80% tumor growth inhibition effect in vivo. The use of targeted gold nanoparticles is promising for enhancing the proton irradiation effect on tumor cells and requires further research to increase the therapeutic index of the approach.

Cytotoxicity of Laser-Synthesized Nanoparticles of Elemental Bismuth

High X-ray absorption combined with photothermal properties make bismuth nanoparticles (Bi NP) a promising agent for multimodal cancer theranostics. However, the synthesis of Bi NP by the "classical" chemical methods has numerous limitations, including potential toxicity of the produced nanomaterials. Here we studied in vitro toxicity of laser-synthesized Bi NP coated with Pluronic F-127 on mouse fibroblast cell line L929. The survival of L929 cells decreased linearly with increasing the concentration of Bi NP in a concentration range of 3-500 μg/ml; the LC50 value was 57 μg/ml. The unique combination of functional properties and moderate toxicity of the laser-synthesized Bi NP makes them a new promising platform for sensitization of multimodal cancer theranostics.

Improving Sensitivity and Reproducibility of Surface-Enhanced Raman Scattering Biochips Utilizing Magnetoplasmonic Nanoparticles and Statistical Methods

Surface-enhanced Raman scattering (SERS) technology has been widely recognized for its remarkable sensitivity in biochip development. This study presents a novel sandwich immunoassay that synergizes SERS with magnetoplasmonic nanoparticles (MPNs) to improve sensitivity. By taking advantage of the unique magnetism of these nanoparticles, we further enhance the detection sensitivity of SERS biochips through the applied magnetic field. Despite the high sensitivity, practical applications of SERS biochips are often limited by the issues of stability and reproducibility. In this study, we introduced a straightforward statistical method known as "Gaussian binning", which involves initially binning the two-dimensional Raman mapping data and subsequently applying Gaussian fitting. This approach enables a more consistent and reliable interpretation of data by reducing the variability inherent in Raman signal measurements. Based on our method, the biochip, targeting for C-reactive protein (CRP), achieves an impressive detection limit of 5.96 fg/mL, and with the application of a 3700 G magnetic field, it further enhances the detection limit by 5.7 times, reaching 1.05 fg/mL. Furthermore, this highly sensitive and magnetically tunable SERS biochip is easily designed for versatile adaptability, enabling the detection of other proteins. We believe that this innovation holds promise in enhancing the clinical applicability of SERS biochips.

Cytotoxicity of PEG-Coated Gold and Gold-Iron Alloy Nanoparticles: ROS or Ferroptosis?

Nanomedicine relies on the exploitation of nanoscale constructs for therapeutic and diagnostic functions. Gold and gold-iron alloy nanoparticles (NPs) are two examples of nanomaterials with favorable features for use in nanomedicine. While gold NPs have been studied extensively in the last decades, they are not biodegradable. Nonetheless, biodegradation was recently observed in gold alloys with iron obtained using laser ablation in liquid (LAL). Hence, there is a significant interest in the study of the biological effects of gold and gold-iron alloy nanoparticles, starting from their tolerability and cytotoxicity. In this study, these two classes of NPs, obtained via LAL and coated with biocompatible polymers such as polyethylene glycol, were investigated in terms of their cytotoxicity in fibroblasts, prostate cancer cells (PC3) and embryonic kidney cells (HEK). We also explored the effects of different synthetic procedures, stabilizing additives, and the possible mechanisms behind cell mortality such as the formation of reactive oxygen species (ROS) or ferroptosis. NPs larger than 200 nm were associated with lower cell tolerability. The most tolerable formulations were pure PEG-Au NPs, followed by PEG-Au-Fe NPs with a hydrodynamic size < 50 nm, which displayed a toxicity of only 20% in fibroblasts after 72 h of incubation. In addition, tumor cells and highly proliferating HEK cells are more sensitive to the NPs than fibroblasts. However, a protective effect of catalase was found for cells incubated with PEG-Au-Fe NPs, indicating an important role of hydrogen peroxide in alloy NP interactions with cells. These results are crucial for directing future synthetic efforts for the realization of biocompatible Au NPs and biodegradable and cytocompatible Au-Fe alloy NPs. Moreover, the correlation of the cytocompatibility of NPs with ROS and ferroptosis in cells is of general interest and applicability to other types of nanomaterials.

Laser-Ablative Synthesis of Silicon-Iron Composite Nanoparticles for Theranostic Applications

The combination of photothermal and magnetic functionalities in one biocompatible nanoformulation forms an attractive basis for developing multifunctional agents for biomedical theranostics. Here, we report the fabrication of silicon-iron (Si-Fe) composite nanoparticles (NPs) for theranostic applications by using a method of femtosecond laser ablation in acetone from a mixed target combining silicon and iron. The NPs were then transferred to water for subsequent biological use. From structural analyses, it was shown that the formed Si-Fe NPs have a spherical shape and sizes ranging from 5 to 150 nm, with the presence of two characteristic maxima around 20 nm and 90 nm in the size distribution. They are mostly composed of silicon with the presence of a significant iron silicide content and iron oxide inclusions. Our studies also show that the NPs exhibit magnetic properties due to the presence of iron ions in their composition, which makes the formation of contrast in magnetic resonance imaging (MRI) possible, as it is verified by magnetic resonance relaxometry at the proton resonance frequency. In addition, the Si-Fe NPs are characterized by strong optical absorption in the window of relative transparency of bio-tissue (650-950 nm). Benefiting from such absorption, the Si-Fe NPs provide strong photoheating in their aqueous suspensions under continuous wave laser excitation at 808 nm. The NP-induced photoheating is described by a photothermal conversion efficiency of 33-42%, which is approximately 3.0-3.3 times larger than that for pure laser-synthesized Si NPs, and it is explained by the presence of iron silicide in the NP composition. Combining the strong photothermal effect and MRI functionality, the synthesized Si-Fe NPs promise a major advancement of modalities for cancer theranostics, including MRI-guided photothermal therapy and surgery.

Stimuli-responsive plasmonic core-satellite hybrid nanostructures with tunable nanogaps

Incorporating stimuli-responsive block copolymers to hierarchical metallic nanoparticles (MNPs) is of particular interest due to their tunable plasmonic properties responding to environmental stimuli. We herein report thermo-responsive plasmonic core-satellite hybrid nanostructures with tunable nanogaps as surface-enhanced Raman scattering (SERS) nanotags. Two different diblock copolymers with opposite charges, poly(acrylic acid-b-N-isopropylacrylamide) (p(AAc-b-NIPAM)) and poly(N,N-dimethylaminoethyl methacrylate-b-N-isopropylacrylamide) (p(DMAEMA-b-NIPAM)), were synthesized. The negatively charged p(AAc-b-NIPAM)s were bound to gold nanospheres (GNSs), while the positively charged p(DMAEMA-b-NIPAM)s were conjugated to gold nanorods (GNRs) via gold-sulfur bonds. When p(AAc-b-NIPAM)-GNSs and p(DMAEMA-b-NIPAM)-GNRs were electrostatically complexed, plasmonic hybrid nanostructures consisting of both GNS satellites and a GNR core were formed. Dynamic tuning of electromagnetic coupling of their nanogaps was achieved via a temperature-triggered conformational change of p(NIPAM) blocks. Furthermore, a sandwich-type immunoassay for the detection of immunoglobulin G was performed to demonstrate these core-satellites as potential SERS nanotags. Our results showed that these plasmonic core-satellites with stimuli-responsiveness are promising for SERS-based biosensing applications.

Hybrid Plasmonic Nanostructures and Their Applications

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Laser Synthesized Core-Satellite Fe-Au Nanoparticles for Multimodal In Vivo Imaging and In Vitro Photothermal Therapy

Hybrid multimodal nanoparticles, applicable simultaneously to the noninvasive imaging and therapeutic treatment, are highly demanded for clinical use. Here, Fe-Au core-satellite nanoparticles prepared by the method of pulsed laser ablation in liquids were evaluated as dual magnetic resonance imaging (MRI) and computed tomography (CT) contrast agents and as sensitizers for laser-induced hyperthermia of cancer cells. The biocompatibility of Fe-Au nanoparticles was improved by coating with polyacrylic acid, which provided excellent colloidal stability of nanoparticles with highly negative ζ-potential in water (−38 ± 7 mV) and retained hydrodynamic size (88 ± 20 nm) in a physiological environment. The ferromagnetic iron cores offered great contrast in MRI images with r₂ = 11.8 ± 0.8 mM⁻¹ s⁻¹ (at 1 T), while Au satellites showed X-ray attenuation in CT. The intravenous injection of nanoparticles enabled clear tumor border visualization in mice. Plasmonic peak in the Fe-Au hybrids had a tail in the near-infrared region (NIR), allowing them to cause hyperthermia under 808 nm laser exposure. Under NIR irradiation Fe-Au particles provided 24.1 °C/W heating and an IC₅₀ value below 32 µg/mL for three different cancer cell lines. Taken together, these results show that laser synthesized Fe-Au core-satellite nanoparticles are excellent theranostic agents with multimodal imaging and photothermal capabilities.