Metal Nanoparticles Research Articles

Investigations on the microbial activity and anti-corrosive efficiency of nickel oxide nanoparticles synthesised through green route

Abstract Researchers have shown considerable interest in the environmentally friendly synthesis of several nanoparticles particularly metal nano particles due to their multifaceted applications. The target of the current research includes the synthesis of nickel oxide nanoparticles (NiO-NPs) through the green route using the bark extract from Acacia Nilotica, and analyzed their chemical and surface morphological features using XRD, SEM, EDX, IR, UV–vis and photoluminescence spectroscopy. In addition, the corrosion inhibition ability and antimicrobial activity of the extract were also studied. The XRD analysis indicated that the NiO exist in the form of nanoparticles. It showed the formation of pure cubic NiO-NP with a prominent peak at 43.28° reflected from the plane (200). The crystallite size was found to be 15.83 nm. The SEM micrographs revealed that NiO-NPs appeared to be a bulk cluster-like structure on their surface.The EDX analysis displayed the presence of Ni and oxygen atoms. The photoluminescence spectrum demonstrated that the green synthesized metal oxide nanoparticles have a modified emission band due to the presence of oxygen deficiencies and induced surface imperfections. The Fourier transform infrared spectroscopy (FTIR) confirmed the association of peaks with the C–H and Ni–O bonds. The UV–vis study showed a maximum absorption at 264 nm. A study on the inhibition efficiency towards microbes confirmed that the prepared NiO-NPs have a good inhibition against selected microbes such as S. aureus, E. coli, Candida albicans, A. Niger. The mass loss system showed restraint 93.68 % effectiveness in the mild steel, and the electrochemical study supported the formation of a defensive protective layer on the cathodic locales of the carbon steel surface inhibiting corrosion.

Silica-coated liquid metal nanoparticles with different stiffness for cellular uptake-enhanced tumor photothermal therapy

Cells can sense the mechanical stimulation of nanoparticles (NPs) and then regulate the cellular uptake process. The enhanced endocytosis efficiency can improve the concentration of NPs in tumor cells significantly, which is the key prerequisite for achieving efficient biological performance. However, the preparation methods of NPs with flexible and tunable stiffness are relatively limited, and the impact of stiffness property on their interaction with tumor cells remains unclear. In this study, soft liquid metal (LM) core was coated with hard silica layer, the obtained core-shell NPs with a wide range of Young's modulus (130.5 ± 25.6 MPa - 1729.2 ± 146.7 MPa) were prepared by adjusting the amount of silica. It was found that the NPs with higher stiffness exhibited superior cellular uptake efficiency and lysosomal escape ability compared to the NPs with lower stiffness. The silica layer not only affected the stiffness, but also improved the photothermal stability of the LM NPs. Both in vitro and in vivo results demonstrated that the NPs with higher stiffness displayed significantly enhanced tumor hyperthermia capability. This work may provide a paradigm for the preparation of NPs with varying stiffness and offer insights into the role of the mechanical property of NPs in their delivery.

Second‐Order Topological Corner States in Square Lattice Plasmonic Metasurfaces with C4 and Glide Symmetries

Recently, plasmonic metasurfaces have emerged as a platform for topological photonics, exhibiting both advantages of plasmon‐induced tight confinement of local field and topological robustness. Most previous works regarding plasmonic systems are limited to the first‐order topologies and only a few studies dealt with higher‐order topological states in honeycomb lattices. Moreover, second‐order topologies of square lattice plasmonic systems have not yet been studied. This work presents second‐order topological corner states in the square lattices of metallic nanoparticles (NPs) with various symmetries, taking two different C4 and glide symmetries as examples. Their unit cells are obtained from nonprimitive cells, consisting of four equal spheroidal NPs, by expanding (or shrinking), rotating, and resizing. Bulk bands and spectral functions of the unit cells calculated by using the coupled dipole method well agree with COMSOL simulation results, revealing the accuracy of the numerical calculations as well as the experimental realizability of the systems. Second‐order topological corner states and their robustness against structural disorder are numerically shown for three different square lattices. This work will trigger extensive investigations to open a new realm of topological metasurfaces with promising applications.

Engineering of uniform dispersed Ni nanoparticles supported on carbon nanosheets for reduction of Nitroarenes to Aminoarenes

Facile synthesis of uniform supported metal catalysts is of great significance yet remains challenging for sustainable catalysis. Herein, a nanopore confinement strategy is developed to efficiently anchor metal ions in suitably sized polymer nanopores via strong coordinate bonds and ensure successful fabrication of uniform carbon-supported metal nanoparticles. Specifically, Ni2+-coordinated polydopamine (PDA) mesoporous layer was coated on GO nanosheets for the confinement of the nickel atoms (GO@PDA-Ni-x, x means pore size of PDA layer), resulting Ni@C-x nanosheets catalysts with uniformly dispersed Ni nanoparticles after pyrolysis in H2/Ar atmosphere. Characterization methods including SEM, TEM, and XPS reveal the intrinsic formation mechanism and physicochemical details. In the catalytic reaction of NaBH4-mediated hydrogenation of 4-nitrophenol (4-NP), the obtained Ni/C-10 exhibits exceptional catalytic performance with a rapid rate constant (0.686 min−1), outperforming many previously reported metal catalysts. Moreover, the catalytic activity remains almost unchanged after being recycled five times, proving the prominent stability. This work opens up an innovative avenue for rational design and synthesis of supported catalysts with controllable size for broad catalytic applications.

Decoration of Ag nanoparticle on MXene sheets for SERS studies

MXene sheets with the unique electrical and optical properties show the excellent potential for surface-enhanced Raman spectroscopy (SERS) applications. In this study, we chose Ti3C2Tx, a type of MXene, to decorate silver nanoparticles (Ag NPs) on the ultrathin two-dimensional (2D) MXene sheets. The designed Ag-MXene substrates with SERS activity showed high sensitivity, high stability, and reproducibility. The SERS signal was enhanced by the synergistic contribution of both charge-transfer (CT) and surface plasmon resonance (SPR) involving the Ag NPs and the MXene sheets. Due to the strong interaction between the probe molecules and Ag NPs which provided the nanoscale gap, the substrate exhibited remarkable SERS performance. A novel experimental strategy was developed to facilitate the controlled synthesis of noble metal NPs and MXene sheets and provide insights for further improving the practical applications of these materials in SERS detection.

Carbonized cellulose microspheres loaded with Pd NPs as catalyst in p-nitrophenol reduction and Suzuki-Miyaura coupling reaction

Catalytic reduction of p-nitrophenol is usually carried out using transition metal nanoparticles such as gold, palladium, silver, and copper, especially palladium nanoparticles (Pd NPs), which are characterized by fast reaction rate, high turnover frequency, good selectivity, and high yield. However, the aggregation and precipitation of the metals lead to the decomposition of the catalyst, which results in a significant reduction of the catalytic activity. Therefore, the preparation of homogeneous stabilized palladium nanoparticles catalysts has been widely studied. Stabilized palladium nanoparticles mainly use synthetic polymers. Cellulose microspheres, as a natural polymer material with low-cost and porous fiber network structure, are excellent carriers for stabilizing metal nanoparticles. Cellulose microspheres impregnated with palladium metal nanoparticles were carbonized to have a larger specific surface area and highly dispersed palladium nanoparticles, which exhibited excellent catalytic activity in the catalytic reduction of p-nitrophenol. In this work, the cellulose carbon-based microspheres palladium (Pd@CCM) catalysts were designed and characterized by SEM, TEM, EDS, XRD, FTIR, XPS, TGA, BET, and so on. Furthermore, the catalytic performance of Pd@CCM catalysts was investigated via p-nitrophenol reduction, which showed high catalytic activity. This catalyst also exhibited excellent catalytic performance in the Suzuki-Miyaura coupling reaction. Linking aromatic monomer and benzene through Suzuki-Miyaura coupling was presented as an effective route to obtaining biaryls, and the synthesis method is low-cost and simple. In addition, Pd@CCM showed desirable recyclability while maintaining its catalytic activity even after five recycles. This work is highly suggestive of the design and application of the heterogeneous catalyst.

Chitosan-coated nanoparticles in innovative cancer bio-medicine.

In the recent decade, nanoparticles (NPs) have had enormous implications in cancer biomedicine, including research, diagnosis, and therapy. However, their broad application still faces obstacles due to some practical limitations and requires further development. Recently, there has been more interest in the coated class of nanoparticles to address those challenges. Chitosan-coated NPs are simple to produce, biodegradable, biocompatible, exhibit antibacterial activity, and have less cytotoxicity. This study provides an updated and comprehensive overview of the application of chitosan-coated NPs as a promising class of NPs in cancer biomedicine. Additionally, we discussed chitosan-coated lipid, metal, and polymer-based nanoparticles in biomedical applications. Furthermore, different coating methods and production/characterization procedures were reviewed. Moreover, the biological and physicochemical advantages of chitosan-coated NPs, including facilitated controlled release, greater physicochemical stability, improved cell/tissue interaction, and enhanced bioavailability of medications, were highlighted. Finally, the prospects of chitosan-coated NPs in cancer biomedicine were discussed.

Generalized Synthesis of Highly-Dispersed, Ultrafine Transition Metal Nanoparticles on Silica Spheres for Enhanced Optical Absorption.

Robust synthesis of ultrafine metal nanoparticles (ufMNPs) below 5nm with clean surfaces and strong optical absorption in the visible spectral range is challenging due to their instability originating from large surface-to-volume ratios. This work reports a general strategy involving two sequential steps: i) loading metal precursor ions onto the surface of silica nanospheres (SiOx NSs) by forming a uniform coating of metal oxyhydroxide [MOy(OH)z] through preferred surface acid-base reactions and ii) thermally reducing MOy(OH)z in forming gas at elevated temperatures to form ufMNPs evenly dispersed on the surface of SiOx NSs. The capability of this synthesis strategy is verified by loading ufMNPs of various transition metals and bimetallic combinations onto the SiOx NSs. The ufMNPs exhibit strong optical absorption enhanced by the optical scattering resonances in the SiOx NSs, which generate intense electric fields near the surface of the SiOx NSs. The SiOx NSs also support stabilizing the ufMNPs, which do not need additional organic capping reagents. The successful synthesis of SiOx-NS-supported ufMNPs with clean surfaces and enhanced optical absorption is promising for exploring the photocatalytic properties of ufMNPs.

Nanotechnology's Applications and Potential in Various Fields.

Since ancient times, several sorts of nanoparticles have been employed in the quickly expanding field of nanotechnology. These features include size, shape, and chemical as well as physical properties.Because of their small size and huge surface area, carbon-based nanoparticles, including fullerenes, carbon nanotubes, graphene, graphene oxide, and carbon-based quantum dots, have attracted a lot of attention in a variety of sectors, including biomedical applications. Lipid bilayers form the spherical vesicles known as liposomes. Magnetic resonance imaging (MRI) contrast agents are iron oxide nanoparticles. These materials are perfect for drug and delivery of genes, bioimaging, and bone repair because of their remarkable mechanical, electrical, visual, and chemical properties. However, concerns about potential asbestos-related diseases have arisen due to their length-to-width aspect ratio. Ceramic nanoparticles, on the other hand, are a common material in daily life and play a crucial role in bone repair, multiscale hybridisation, and aerospace structures. These nanoparticles can enhance osseointegration and bone development by mimicking the nanocomposition and nanoscale characteristics of bone tissue and enhance osteoconductive and osteoinductive capacities. Ceramic nanoparticles, however, have the potential to generate oxidative stress, which can result in irritation of the reticuloendothelial system, cytotoxicity to the heart, liver, and lungs, as well as toxicity to the cells that are attached. Additionally, oxidative stress, cell damage, and genotoxicity might result from the generation of free radicals by ceramic nanoparticles. Metal nanoparticles exhibit linear optical properties similar to molecular systems but arise from a different physical process. Semiconductor nanocrystals (NCs) are made from various compounds, such as silicon and germanium. Polyandry nanoparticles are particles approximately 10 and 10000 nanometers (nm) in size that can contain active substances. They have applications in vaccine delivery, gene therapy, and polymer nanoparticles (nanomedicine) for therapeutic applications.

Impact of α-, β-, γ-cyclodextrins on recyclable catalytic reduction of silver nanoparticles loaded on cyclodextrin/alginate

Metallic nanoparticles (MNPs) synthesized through the ionotropic gelation mechanism using alginate (Alg) and cyclodextrins (CDs) have exhibited remarkable efficacy in physicochemical characterization and catalytic performance in the recent reports. This study delves into the impact of cyclodextrin structures on the synthesis, properties, and recyclable catalytic capabilities of nanocomposites containing silver nanoparticles (AgNPs) loaded onto CDs/Alg. The AgNPs were biogenically synthesized using an aqueous extract of Arctium lappa as a green reductant. Varying CDs led to AgNPs with mean sizes ranging from 7.0 to 18.0 nm within the nanocomposites. The crystalline structure of AgNPs was confirmed through HRTEM and SAED measurements. The recyclable catalytic potential of the nanocomposites was assessed for the reduction of toxic organic compounds, including 4-nitrophenol, methyl orange, and rhodamin B. Notably, the AgNPs@α-CD/Alg nanocomposite emerged as an outstanding catalyst, excelling in both catalytic performance and recyclability. These results underscore the substantial impact of cyclodextrin structure on the catalytic properties and efficiency of AgNPs-based nanocomposites.

Nanoarchitectonics of bimodal porous carbon nanosheet with NiO/Ni nanoparticles derived from nitrile-functionalized benzoxazine for a supercapacitor electrode material

Nitrile-functionalized benzoxazine was successfully synthesized as a precursor for porous carbon. NH4Cl was used as a template to generate the nanosheet morphology and mesopore structure, while nickel(II) chloride in the hydrate form was used as a nickel source. The results showed that carbon samples based on pristine nitrile-functionalized benzoxazine revealed the standard isotherm of type I, representing a microporous nature. This isotherm was altered to type IV, indicating a mesoporous nature after adding the NH4Cl template, and the morphology of the carbon sample was also transformed into a more nanosheet-like structure with increasing NH4Cl loading. The specific surface area, mesoporosity and pore volume of the as-prepared samples tended to increase when increasing NH4Cl template loading, with Ni-PCN5 (5 g of NH4Cl template) having the maximum mesoporosity of 88.7%. The maximum specific surface area and pore volume are 556 m2 g−1 for Ni-PCN5–350 and 0.71 cm3 g−1 for Ni-PCN5, respectively. In addition, the metallic nickel nanoparticles were successfully embedded in the carbon structure, which were further transformed into nickel oxide nanoparticles after an annealing process. This annealing process also resulted in carbon samples with the standard isotherm of type I. For electrochemical performance, Ni-PCN-300 also showed the highest value of the specific capacitance, as high as 181 F g−1 measured at a current density of 0.1 A g−1 in a 1 mol L−1 KOH aqueous electrolyte solution, with an excellent cycling stability of 96.5% over 2000 testing cycles. In short, this work demonstrates a facile, inexpensive and eco-friendly approach to rationally design and synthesize nickel/nickel oxide nanoparticles-embedded porous carbon nanosheets with a micro- and mesoporous structure, as a promising candidate for a supercapacitor electrode material.

Type-dependent hot carrier behavior in photoelectrochemical reduction and oxidation of Au/GaN junction photoelectrodes

In junctions with semiconductors, plasmonic metal nanoparticles (NPs) can be utilized to efficiently harness solar energy by collecting hot carriers. However, the behavior of hot carriers at the interfaces between semiconductors with opposite doping types is not fully elucidated. Here, Au NPs are attached to n-doped (Au/n-GaN) or p-doped gallium nitrides (Au/p-GaN) to examine the photoelectrochemical performance regarding hot carrier behavior. Direct surface potential measurements revealed that electrons are collected in n-type GaN (n-GaN) when illuminated, while hot holes remain in Au NPs for oxidation reactions via the plasmonic process. Conversely, holes are collected in p-type GaN (p-GaN), thereby promoting the reduction reaction by the electrons left in Au NPs. Specifically, the change in surface potential difference induced by green light illumination in Au/p-GaN is four times greater than that observed in Au/n-GaN. Conversely, the changes in open-circuit potential and photocurrent density under light illumination are approximately six times more significant in Au/n-GaN compared to Au/p-GaN. This difference in efficiency can be attributed to the more favorable oxidation reaction occurring in Au NPs at the interface with GaN materials, as opposed to the reduction reaction, due to the difference in band alignment between the Au/GaN junction systems.

Delineating cathodic extracellular electron transfer pathways in microbial electrosynthesis: Modulation of polarized potential and Pt@C addition

Microbial electrosynthesis (MES) is an innovative technology that employs microbes to synthesize chemicals by reducing CO2. A comprehensive understanding of cathodic extracellular electron transfer (CEET) is essential for the advancement of this technology. This study explores the impact of different cathodic potentials on CEET and its response to introduction of hydrogen evolution materials (Pt@C). Without the addition of Pt@C, H2-mediated CEET contributed up to 94.4 % at −1.05 V. With the addition of Pt@C, H2-mediated CEET contributions were 76.6 % (−1.05 V) and 19.9 % (−0.85 V), respectively. BRH-c20a was enriched as the dominated microbe (>80 %), and its relative abundance was largely affected by the addition of Pt@C NPs. This study highlights the tunability of MES performance through cathodic potential control and the addition of metal nanoparticles.

Green energy breakthroughs: Harnessing nano-catalysts and enzymatic catalysts for bioenergy generation

Microbial fuel cells and anaerobic digestion are promising bioenergy methods but inefficient and scalable. With its exceptional surface area-to-volume ratio, nano-catalysts are revolutionizing this field. Researchers have improved energy conversion efficiency by immobilizing or embedding nanoparticles on electrodes or catalytic supports to promote electron transport. Nanomaterials like graphene-based catalysts and metal nanoparticles speed up organic matter breakdown and make bioenergy systems more profitable. Researchers are working harder to find new bioenergy-generating methods to address environmental concerns and the demand for sustainable energy. The study discusses how nano-catalysts and enzymatic catalysts are revolutionizing bioenergy production in green energy. Additionally, enzymatic catalysts are the best bioenergy catalysts. Highly specialized, biocompatible, and renewable enzymes provide unrivaled biofuel production potential. Protein engineering and immobilization have improved enzymes for bioenergy systems. Enzymatic catalysts enable biofuel generation from more feedstocks without harsh chemical procedures by controlling biological reactions quickly and precisely. Combining nano- and enzymatic catalysts is promising. Nano-catalysts improve enzymatic processes by creating a favorable microenvironment, enhancing surface binding sites, and enabling substrate transport. This combination may maximize bioenergy systems' biofuel output and wastewater treatment capabilities. According to this study, integrating nano- and enzymatic catalysts is a green energy breakthrough. These advances will improve bioenergy generation by overcoming current techniques, opening new sustainable energy production prospects, and expediting our transition to a greener, more sustainable future.

Molecular mechanism of nanomaterials induced liver injury: A review.

The unique physicochemical properties inherent to nanoscale materials have unveiled numerous potential applications, spanning beyond the pharmaceutical and medical sectors into various consumer industries like food and cosmetics. Consequently, humans encounter nanomaterials through diverse exposure routes, giving rise to potential health considerations. Noteworthy among these materials are silica and specific metallic nanoparticles, extensively utilized in consumer products, which have garnered substantial attention due to their propensity to accumulate and induce adverse effects in the liver. This review paper aims to provide an exhaustive examination of the molecular mechanisms underpinning nanomaterial-induced hepatotoxicity, drawing insights from both in vitro and in vivo studies. Primarily, the most frequently observed manifestations of toxicity following the exposure of cells or animal models to various nanomaterials involve the initiation of oxidative stress and inflammation. Additionally, we delve into the existing in vitro models employed for evaluating the hepatotoxic effects of nanomaterials, emphasizing the persistent endeavors to advance and bolster the reliability of these models for nanotoxicology research.

Multifunctional (4-in-1) Therapeutic Applications of Nickel Thiocyanate Nanoparticles Impregnated Cotton Gauze as Antibacterial, Antibiofilm, Antioxidant and Wound Healing Agent.

The wounds, arises from accidents, burns, surgeries, diabetes, and trauma, can significantly impact well-being and present persistent clinical challenges. Ideal wound dressings should be flexible, stable, antibacterial, antioxidant and anti-inflammatory in nature, facilitating a scarless rapid wound healing. Initiatives were taken to create antibacterial cotton fabrics by incorporating agents like antibiotics and metallic nanoparticles. However, due to a lack of multifunctionality, these materials were not highly effective in causing scarless and rapid wound healing. In this article, nickel thiocyanate nanoparticle (NiSCN-NPs) impregnated cotton gauze wound dressing (NiSCN-CG) was developed. These nanoparticles were non-toxic to normal human cell lines till 1 mg/mL dose and did not cause skin irritation in the rat model. Further, NiSCN-NPs exhibited antimicrobial, antibiofilm and antioxidant activities confirmed using different in vitro experiments. In vivo wound healing studies in rat models using NiSCN-CG demonstrated rapid scarless wound healing. The nickel thiocyanate impregnated cotton gauze presents a novel approach in scarless wound healing, and as an antimicrobial agent, offering a promising solution for diverse wounds and infections in the future.

Cutting-edge Nanotechnology Approaches in Peptic Ulcer Therapy

Abstract: The ulcer is a chronic disease that penetrates the gastrointestinal tract and produces a deep lesion. One type of ulcer is peptic ulcer, which leads to the development of a lesion on the lining (mucosa) of the digestive tract. Various drugs are used for the treatment, including antibiotics, but don't provide correct eradication, so for the excellence in therapeutic value and decreasing side effects, nanotechnology is being used. Nanotechnology is a technique that is nowadays used in trend because of its outstanding efficacy and also its effect at both cellular and molecular levels. Based on this technology, nanoparticles are used for the treatment of peptic ulcers. This review focuses on the treatment approaches for peptic ulcers by using nanotechnology. Some nanoparticles used in the treatment of Helicobacter pylori (H. pylori) are metallic nanoparticles, polymeric nanoparticles, targeting nanoparticles, and a new technology arrived is membrane coated nanoparticles, which are very advantageous for H. pylori treatment. The purpose of this review is to overview and gain attention to the limitations in treatment (like antibiotic resistance) and also the new strategies to overcome them and enhance the properties of nanoparticles to produce the anti-bacterial effect. This development helps in the treatment of H. pylori.

Scaling-Up Microwave-Assisted Synthesis of Highly Defective Pd@UiO-66-NH2 Catalysts for Selective Olefin Hydrogenation under Ambient Conditions.

The need to develop green and cost-effective industrial catalytic processes has led to growing interest in preparing more robust, efficient, and selective heterogeneous catalysts at a large scale. In this regard, microwave-assisted synthesis is a fast method for fabricating heterogeneous catalysts (including metal oxides, zeolites, metal-organic frameworks, and supported metal nanoparticles) with enhanced catalytic properties, enabling synthesis scale-up. Herein, the synthesis of nanosized UiO-66-NH2 was optimized via a microwave-assisted hydrothermal method to obtain defective matrices essential for the stabilization of metal nanoparticles, promoting catalytically active sites for hydrogenation reactions (760 kg·m-3·day-1 space time yield, STY). Then, this protocol was scaled up in a multimodal microwave reactor, reaching 86% yield (ca. 1 g, 1450 kg·m-3·day-1 STY) in only 30 min. Afterward, Pd nanoparticles were formed in situ decorating the nanoMOF by an effective and fast microwave-assisted hydrothermal method, resulting in the formation of Pd@UiO-66-NH2 composites. Both the localization and oxidation states of Pd nanoparticles (NPs) in the MOF were achieved using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), respectively. The optimal composite, loaded with 1.7 wt % Pd, exhibited an extraordinary catalytic activity (>95% yield, 100% selectivity) under mild conditions (1 bar H2, 25 °C, 1 h reaction time), not only in the selective hydrogenation of a variety of single alkenes (1-hexene, 1-octene, 1-tridecene, cyclohexene, and tetraphenyl ethylene) but also in the conversion of a complex mixture of alkenes (i.e., 1-hexene, 1-tridecene, and anethole). The results showed a powerful interaction and synergy between the active phase (Pd NPs) and the catalytic porous scaffold (UiO-66-NH2), which are essential for the selectivity and recyclability.

Development of Au Nanoparticle Two-Dimensional Assemblies Dispersed with Au Nanoparticle-Nanostar Complexes and Surface-Enhanced Raman Scattering Activity.

We recently found that polyvinylpyrrolidone (PVP)-protected metal nanoparticles dispersed in water/butanol mixture spontaneously float to the air/water interface and form two-dimensional assemblies due to classical surface excess theory and Rayleigh-Bénard-Marangoni convection induced by butanol evaporation. In this study, we found that by leveraging this principle, a unique structure is formed where hetero gold nanospheres (AuNPs)/gold nanostars (AuNSs) complexes are dispersed within AuNP two-dimensional assemblies, obtained from a mixture of polyvinylpyrrolidone-protected AuNPs and AuNSs that interact electrostatically with the AuNPs. These structures were believed to form as a result of AuNPs/AuNSs complexes formed in the water/butanol mixture floating to the air/water interface and being incorporated into the growth of AuNP two-dimensional assemblies. These structures were obtained by optimizing the amount of mixed AuNSs, with excessive addition resulting in the formation of random three-dimensional network structures. The AuNP assemblies dispersed with AuNPs/AuNSs complexes exhibited significantly higher Raman (surface-enhanced resonance Raman scattering: SERRS) activity compared to simple AuNP assemblies, while the three-dimensional network structure did not show significant SERRS activity enhancement. These results demonstrate the excellent SERRS activity of AuNP two-dimensional assemblies dispersed with hetero AuNPs/AuNSs complexes.

Wet Chemical Engineering of Nanostructured GRIN Lenses

AbstractGradient‐index (GRIN) lenses have long been recognized for their importance in optics as a result of their ability to manipulate light. However, traditional GRIN lenses are limited on a scale of tens of microns, impeding their integration into nanoscale optical devices. This study presents a groundbreaking self‐assembled method that overcomes this limitation, allowing for constructing GRIN lenses at an extremely small dimension. The self‐assembly process offers several advantages, including creating highly precise, scalable, cost‐effective, and complex structures that eliminate the need for intricate and time‐consuming manual assembly. By engineering densely packed arrays of metallic nanoparticles, exceptional control over the local refractive index has been achieved. This is accomplished by layer‐by‐layer assembly of gold nanoparticles of different sizes over silica beads. A GRIN lens light‐sink is built where light is preferentially directed toward the center, which is corroborated by measuring the fluorescence of Rhodamine B (RhB) in the inside. Unlike traditional bulky macroscopic GRIN lenses, light‐sinks boast a size under 2.5 µm. Notably, the self‐focusing effects of this design allowed us to track the growth of single‐nanoparticle layers using SERS (Surface‐Enhanced Raman Spectroscopy). These results pave the way for designing and developing lens‐like devices at the nanoscale, allowing unprecedented light manipulation.