Formation Of Au Nanoparticles Research Articles

Gold Nanoparticles in Porous Silicon Nanotubes for Glucose Detection

Silicon nanotubes (Si NTs) have a unique structure among the silicon nanostructure family, which is useful for diverse applications ranging from therapeutics to lithium storage/recycling. Their well-defined structure and high surface area make them ideal for sensing applications. In this work, we demonstrate the formation of Au nanoparticles (NPs) functionalized with 4-Mercaptophenylboronic acid (MPBA) on porous Si NTs (pSi NTs) fabricated using ZnO nanowires as a template. The system was characterized, and the proposed structure was confirmed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Varying glucose concentrations in phosphate-buffered saline (PBS) (0.5–80 mM) were introduced to the Si NT nanocomposite system. The glucose is detectable at low concentrations utilizing surface-enhanced Raman spectroscopy (SERS), which shows a concentration-dependent peak shift in the benzene ring breathing mode (~1071 cm−1) of MPBA. Complementing these measurements are simulations of the Raman hot spots associated with plasmonic enhancement of the Au NPs using COMSOL. This biocompatible system is envisioned to have applications in nanomedicine and microfluidic devices for real-time, non-invasive glucose sensing.

Self-assembly of a AuNPs/Ti3C2 MXene hydrogel for cascade amplification of microRNA-122 biosensing.

A three-dimensional (3D) self-assembled AuNPs/Ti3C2 MXene hydrogel (AuNPs/Ti3C2 MXH) nanocomposite was prepared for the fabrication of a novel microRNA-122 electrochemical biosensor. The 3D hydrogel structure was gelated from two-dimensional MXene nanosheets with the assistance of graphite oxide and ethylenediamine. MXene hydrogels supported the in situ formation of Au nanoparticles (AuNPs) that predominantly exploring the (111) facet, and these AuNPs are utilized as carriers for hairpin DNA (hpDNA) probes, facilitating DNA hybridization. MXene acted as both a reductant and stabilizer, significantly improving the electrochemical signal. In addition, the conjugation of PAMAM dendrimer-encapsulated AuNPs and H-DNA worked as an ideal bridge to connect targets and efficient electrochemical tags, providing a high amplification efficiency for the sensing of microRNA-122. A linear relationship between the peak currents and the logarithm of the concentrations of microRNA-122 from 1.0 × 10-2 to 1.0 × 102 fM(I = 1.642 + 0.312 lgc, R2 = 0.9891), is obtained. The detection limit is 0.8 × 10-2 fM (S/N = 3). The average recovery for human serum detection ranged from 97.32 to 101.4% (RSD < 5%).

Evolution of Au nanoparticles in c-plane GaN under the heavy ion implantation and their optical properties

The modification of GaN with Au nanoparticles is a promising way for manipulating optical properties in optoelectronics and enhancing the sensitivity of GaN-based substrates used in Surface Enhanced Raman Spectroscopy. Ion implantation is an attractive method for the preparation of high-purity metal nanoparticles on the surface or within the bulk of solids, although this process in crystals is not yet fully understood. Here we study the specific stages of Au nanoparticle formation in c-plane GaN crystals implanted with 1.85 MeV Au ions to the fluence range of 1.5×1016 - 7×1016 cm−2. The implanted samples were annealed at 800 °C in an ammonia atmosphere for 20 minutes to support the nucleation of Au nanoparticles and prevent surface decomposition. The structural and optical properties of the samples were investigated by a combination of Rutherford backscattering spectroscopy in channeling mode (RBS-C), Transmission Electron Microscopy (TEM), Raman spectroscopy, photoluminescence (PL) and diffuse-reflectance spectroscopy (DRS). The two damaged regions, namely at the depth and at the surface, were identified. The depth region exhibits saturation of damage, unlike the surface region reaching an amorphous state for the highest implantation fluence. RBS-C revealed multimodal Au depth profiles for higher ion fluences, which were subsequently redistributed after thermal annealing due to the formation of Au nanoparticles, as confirmed by TEM. Au nanoparticles with fcc structure have been successfully synthesized with the Au-ion implantation fluence of 5×1016 cm−2 with the sizes mostly of 4 – 20 nm resulting in increased optical scattering and absorption within the spectral range of 500 – 700 nm associated with surface plasmon resonance (SPR) and the emergence of blue (2.8 eV) and red (2 eV) photoluminescence bands linked to the combined effect of SPR and implantation-induced defects.

Sub-millisecond microfluidic mixers coupled to time-resolved in situ photonics to study ultra-fast reaction kinetics: the case of ultra-small gold nanoparticle synthesis.

We report a continuous microreactor platform achieving sub-millisecond homogeneous reagent mixing (∼300 μs) for a time-resolved study on the synthesis of ultra-small gold nanoparticles (NPs). The microreactor (coupled with small angle X-ray scattering, UV-vis, and X-ray absorption spectroscopy for in situ and in operando characterizations), operates within mixing time frames below system characteristic times, providing a unique opportunity to deepen the comprehension of reaction and phase transition pathways with unprecedented details. The microreactor channel length can be approximated to a given reaction time when operated in continuous mode and steady state. As a result, the system can be statically investigated, eliminating technique-dependent probing time constraints and local inhomogeneities caused by mixing issues. We have studied Au(0) NP formation kinetics from Au(III) precursors complexed with oleylamine in organic media, using triisopropylsilane as a reducing agent. The existence of Au(III)/Au(I) prenucleation clusters and the formation of a transient Au(I) lamellar phase under certain conditions, before the onset of Au(0) formation, have been observed. Taking advantage of the high frequency time-resolved information, we propose and model two different reaction pathways associated with the presence or absence of the Au(I) lamellar phase. In both cases, non-classical pathways leading to the formation of NPs are discussed.

Electrodeposition of Au and AgAu Nanoparticles from Reverse Micelles – Tuning Particle Properties and Understanding Solvent and Confinement Effects by Ensemble and Single Entity Approaches

The synthesis and reactivity of nanoparticles (NPs) has vastly been studied for years,[1-3] yet still there are several open questions about how a synthesis method and its parameters influence the final properties of the obtained NPs. In the classical wet-chemical synthesis, capping agents are widely used to adjust the morphology and size, preventing further growth of NPs. However, their presence can be disadvantageous for some applications, e.g. electrocatalysis, where they decrease reaction kinetics. To overcome this issue, we use electrodeposition as synthetic route, and the size of the obtained NP is tuned by the amount of precursor that is loaded inside a reverse micelle. The NP formation is induced by applying a suitable potential to reduce the entrapped precursor at the electrode. This deposition can be done by ensemble or single entity approaches.Experimentally speaking, both approaches consist of an electrode immersed in a media with suspended precursor-loaded reverse micelles. However, for ensemble electrodeposition a macroelectrode is used, a standard chronoamperometry is recorded and average information about the system is provided. On the other hand, single entity approach relies on random collision of reverse micelles at a micro- or nanoelectrode, which appears as spikes on the chronoamperometric response, and data can be determined based on statistical analysis of single particle events.[4,5] It has been used to characterize different types of NPs, their size, composition and kinetic reaction parameters.[6,7] Focusing on the electrosynthesis, this work investigates the formation of Au and AgAu NPs by both ensemble and single entity approaches. Besides the synthesis method, the effect of the solvent and the 0D confinement is also under evaluation to better understand how one can tune NPs’ shape and structure, i.e. core-shell vs alloy arrangements. The solvent effect is investigated by using room temperature ionic liquid or organic solvents during electrodeposition. The reverse micelles act as a nanoreactor cage, confining the precursors, and therefore changing the type of this cage helps us to understand the influence of the 0D confinement. For this, reverse micelles of two different materials were used: SDS (sodium dodecyl sulphate) and PS-P2VP (polystyrene-b-poly(2-vinylpyridine)), with the former forming nanodroplets of an aqueous phase protected by a thin wall, and the latter assembling to a sphere with a polymeric core, completely binding the precursor.The resulting NPs were imaged by AFM, SEM and TEM and their composition resolved by EDX. Initial catalytic CV and LSV measurements towards hydrogen evolution reaction were done to provide further insights about the NPs’ properties. From these characterizations of the NPs, it has been demonstrated that the synthesis approach, the applied potential, the solvent, and the type of RM influence the final NPs’ properties. Hence, the size, composition, structure and catalytic activity of the resulting NPs can by tuned by electrochemical parameters, avoiding the necessity to select different capping and reducing agents as done in wet-chemical synthesis.[1] D. V. Talapin, E. V. Shevchenko. Chem. Rev. 2016, 116, 18, 10343–10345. doi: 10.1021/acs.chemrev.6b00566.[2] H. Duan, D. Wang, Y. Li. Chem. Soc. Rev., 2015, 44, 5778-5792. doi: 10.1039/C4CS00363B.[3] M. Grzelczak, J. Pérez-Juste, P. Mulvaney, L. M. Liz-Marzán. Chem. Soc. Rev., 2008, 37, 1783-1791. doi: 10.1039/B711490G[4] K. J. Stevenson, K. Tschulik. Curr. Opin. Electrochem. 2017, 6, 38–45. doi:10.1016/j.coelec.2017.07.009.[5] M. V. Evers, M. Bernal, B. Roldán Cuenya, K. Tschulik. Angew. Chem. 2019, 58, 8221-8225. doi: 10.1002/anie.201813993[6] E. N. Saw, M. Kratz, K. Tschulik. Nano Res. 2017, 10, 3680–3689. doi:10.1007/s12274-017-1578-3.[7] K. Shimizu, K. Tschulik, R. G. Compton. Chem. Sci. 2016, 7, 1408–1414. doi:10.1039/C5SC03678J.

Amorphous TiO2-Au thin film composites synthesized by pulsed laser deposition

TiO2 has been widely studied and synthesized by various methods due to its excellent optoelectronic properties. It is possible to modify the optical properties of TiO2 by incorporating noble metal nanoparticles in order to improve its photoresponse. In this work, TiO2-Au thin film composites were grown by pulsed laser deposition technique. Ti and Au targets were simultaneously ablated in order to produce combined plasmas under a reactive atmosphere containing oxygen at a pressure of 2×10-2 Torr. The plasmas were analyzed individually by means of a planar Langmuir probe in order to calculate their mean kinetic ion energy and plasma density. Ti plasma parameters were kept constant at 196 eV and 2.06×1013 cm-3 while the Au plasma density was varied from 2.65×1012 cm-3 to 22.4×1012 cm-3. The samples were characterized by UV-Vis spectroscopy and scanning electron microscopy. The band gap of the films was determined by means of the Tauc method, which decreased from 2.36 to 1.54 eV as the Au plasma density increased. The resultant morphology of the films shows the formation of spherical Au nanoparticles, whose average sizes increases as the Au plasma density increased, resulting in values ranging from 15 to 72 nm.

Defects Healing of the ZnO Surface by Filling with Au Atom Catalysts for Efficient Photocatalytic H2 Production.

Healed defects on photocatalysts surface and their interaction with plasmonic nanoparticles (NPs) have attracted attention in H2 production process. In this study, surface oxygen vacancy (Vo ) defects are created on ZnO (Vo -ZnO) NPs by directly pyrolyzing zeolitic imidazolate framework. The surface defects on Vo -ZnO provide active sites for the diffusion of single Au atoms and as nucleation sites for the formation of Au NPs by the in situ photodeposition process. The electronically healed surface defects by single Au atoms help in the formation of a heterojunction between the ZnO and plasmonic Au NPs. The formed Au/Vo -Au:ZnO-4 heterojunction prolongs photoelectron lifetimes and increases donor charge density. Therefore, the optimized photocatalysts of Au/Vo -Au:ZnO-4 has 21.28 times higher H2 production rate than the pristine Vo -ZnO under UV-visible light in 0.35m Na2 SO4 and 0.25m Na2 SO3 . However in 0.35m Na2 S and 0.25m Na2 SO3 , the H2 production rate is 25.84 mmole h-1 g-1 . Furthermore, Au/Vo -Au:ZnO-4 shows visible light activity by generating hot carries via induced surface plasmonic effects. It has 48.58 times higher H2 production rate than pristine Vo -ZnO. Therefore, this study infers new insight for defect healing mediated preparation of Au/Vo -Au:ZnO heterojunction for efficient photocatalytic H2 production.

Two-Step Electrochemical Au Nanoparticle Formation in Polyaniline.

In this work, we use a two-step cyclic electrochemical process to insert Au into polyaniline (PANI). It was suggested previously that this method would lead to the formation of atomic Au clusters with controlleds number of Au atoms without providing morphological proof. In each cycle, tetrachloroaurate anions (AuCl4-) are attached on the protonated imine sites of PANI, followed by a controlled reduction using cyclic voltammetry (CV). In contrast to previous work, we demonstrate that the reduction leads to the nucleation and growth of an Au nanoparticle (NP) whose density and size dispersion depend on the Au loading in PANI. Adding more deposition cycles increases the Au NP density and size. Transmission electron microscopy (TEM) and corresponding energy dispersive X-ray spectroscopy (EDS) indicate a homogeneous distribution of Au elements in the PANI matrix before CV reduction, while Au elements are aggregated and clearly localized in the NPs positions after CV reduction. We further use Rutherford backscattering spectrometry (RBS) to quantify the Au uptake in PANI. The Au distribution is verified to be initially homogeneous across the PANI layer whereas the increasing number of deposition cycles leads to a surface segregation of Au. We propose a two-step growth model based on our experimental results. Finally, we discuss the results with respect to the formation of atomic Au clusters reported previously using the same deposition method.

Tailored chitosan-based entrapped catalyst for dyes removal by highly active, stable, and recyclable nanoparticles toughened hydrogel

Functional catalytic hydrogels were a promising catalyst carrier with the advantages of low cost, high efficiency and environmental friendliness. However, conventional hydrogels suffered from mechanical defects and brittleness. Acrylamide (AM) and lauryl methacrylate (LMA) were used as raw materials, SiO2-NH2 spheres as toughening agents, and chitosan (CS) as stabilizers to form hydrophobic binding networks. p(AM/LMA)/SiO2-NH2/CS hydrogels exhibited superior stretchability and withstood strains up to 14,000 %. In addition, these hydrogels exhibited exceptional mechanical properties, including a tensile strength of 213 kPa and a toughness of 13.1 MJ/m3. Surprisingly, the introduction of chitosan into hydrogels showed excellent antibacterial activity against S. aureus and E. coli. At the same time, the hydrogel served as a template for the formation of Au nanoparticles. This resulted in high catalytic activity for methylene blue (MB) and Congo red (CR) on p(AM/LMA)/SiO2-NH2/CS-8 %-Au hydrogels with Kapp of 1.038 and 0.76 min−1, respectively. The catalyst was also found to be reusable for 10 cycles while maintaining an efficiency of over 90 %. Therefore, innovative design strategies can be used to develop durable and scalable hydrogel materials for catalysis in the wastewater treatment industry.

Nanoimaging of Facet-Dependent Adsorption, Diffusion, and Reactivity of Surface Ligands on Au Nanocrystals.

Analysis of the influence of dissimilar facets on the adsorption, stability, mobility, and reactivity of surface ligands is essential for designing ligand-coated nanocrystals with optimal functionality. Herein, para-nitrothiophenol and nitronaphthalene were chemisorbed and physisorbed, respectively, on Au nanocrystals, and the influence of different facets within a single Au nanocrystal on ligands properties were identified by IR nanospectroscopy measurements. Preferred adsorption was probed on (001) facets for both ligands, with a lower density on (111) facets. Exposure to reducing conditions led to nitro reduction and diffusion of both ligands toward the top (111) facet. Nitrothiophenol was characterized with a diffusivity higher than that of nitronaphthalene. Moreover, the strong thiol-Au interaction led to the diffusion of Au atoms and the formation of thiol-coated Au nanoparticles on the silicon surface. It is identified that the adsorption and reactivity of surface ligands were mainly influenced by the atomic properties of each facet, while diffusion was controlled by ligand-metal interactions.

INFLUENCE OF CeO2 ON THE FORMATION OF PLASMONIC Au NANOPARTICLES IN GLASSES OF THE ZnO–MgO–Al2O3–SiO2 SYSTEM

Using absorption spectroscopy, differential scanning calorimetry, and X-ray powder diffraction, we studied the effect of a small addition of CeO2 on the process of thermally stimulated formation of plasmonic Au nanoparticles in the glass of the ZnO–MgO–Al2O3–SiO2 system containing TiO2 and ZrO2 as nucleating agents. It is shown that when the glass is heated from temperatures slightly above Tg to temperatures in the region of the exothermic peak, the plasmon resonance band of Au nanoparticles undergoes a nonlinear shift; however, the addition of CeO2 significantly expands the the shift to the long wavelength region of the spectrum. We performed the computer simulation of the experimental optical absorption spectra, estimated the sizes of the formed nanoparticles and proposed the mechanism of the effect of the CeO2 addition on the formation of plasmonic Au nanoparticles.

Patterning of plasmonic Au nanoparticles on the surfaces of TiOx thin films by solid state thermal dewetting

It is essential to study the thermal dewetting behavior of as-deposited nano-films for large scale and high-throughput fabrication. We report here on the nucleation of Au nanostructures onto titanium dioxide (TiOx) thin films surfaces, which occurred in consecutive steps. First, TiOx thin films were grown on quartz substrates reactively by e-beam evaporator and then thermally annealed at different temperatures, starting from 300°C to 900°C. Subsequently, a nano-film of Au was deposited on the top of these TiOx surfaces. The stacked Au / TiOx samples were post-annealed using muffle furnace at a temperature of 600°C for 1 h, to study the thermal dewetting properties and the controlled growth of the different TiOx morphologies on the formation of Au nanoparticles (NP) and their plasmonic response. Such dual-structures were characterized accordingly to probe their topological, morphological, structural, and optical properties, by means of x-ray photoelectron spectroscopy, scanning electron microscope, atomic force microscopy, and ultra-violet–visible–near infrared characterization techniques. The thermal dewetting properties were found to improve at high temperatures (>500 ° C), where the Au NP size distribution was found to follow a Gaussian pattern centered around 30 nm. The average surface roughness also increased significantly with respect to the TiOx dewetting temperature, which is mainly attributed to the porosity of the films. Finally, the absorption peak for Au nanostructures has shown a localized surface plasmon resonance close to 520 nm, along with a broad shoulder peak with a strong tail thereby reflecting the wide distribution of the formed Au NP sizes.

Green synthesis, characterization, and biological evaluation of gold and silver nanoparticles using Mentha spicata essential oil

Green synthesis of bioactive nanoparticles (NPs) is getting more attractive in various fields of science including the food industry. This study investigates the green synthesizing and characterization of gold NPs (AuNPs) and silver NPs (AgNPs) produced using Mentha spicata L. (M. spicata) essential oil as well as their antibacterial, antioxidant, and in vitro cytotoxic effects. The essential oil was mixed with both Chloroauric acid (HAuCl4) and aqueous silver nitrate (AgNO3) solutions separately and incubated at room temperature for 24 h. The chemical composition of the essential oil was identified by gas chromatography coupled with a mass spectrometer detector (GC–MS). Au and Ag nanoparticles were characterized using UV–Vis spectroscopy, transmission electron microscopy, scanning electron microscopy, dynamic light scattering (DLS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR). The cytotoxicity of both types of nanoparticles was evaluated using MTT assay on cancerous HEPG-2cell line by exposing them to various concentrations of both NPs for 24 h. The antimicrobial effect was evaluated by the well-diffusion technique. The antioxidant effect was determined by DPPH and ABTS tests. According to the results of GC–MS analysis, 18 components were identified, including carvone (78.76%) and limonene (11.50%). UV–visible spectroscopy showed a strong absorption peak of 563 nm and 485 nm, indicating the formation of Au NPs and Ag NPs, respectively. TEM and DLS demonstrated that AuNPs and AgNPs were predominantly spherical shaped with average sizes of 19.61 nm and 24 nm, respectively. FTIR analysis showed that biologically active compounds such as monoterpenes could assist in the formation and stabilization of both types of NPs. Additionally, XRD provided more accurate results, revealing a nano-metal structure. Silver nanoparticles exhibited better antimicrobial activity against the bacteria than AuNPs. Zones of inhibition ranging 9.0–16.0 mm were recorded for the AgNPs, while zones of 8.0–10.33 mm were observed AuNPs. In the ABTS assay, the AuNPs and AgNPs showed a dose-dependent activity and synthesized nanoparticles exhibited higher antioxidant activity than MSEO in both assays. Mentha spicata essential oil can be successfully used for the green production of Au NPs and Ag NPs. Both green synthesized NPs show antibacterial, antioxidant, and in vitro cytotoxic activity.

Laser-textured Pd-Au hierarchical superhydrophobic micro-arrays for ultralow SERS detection

Ultra-trace identification of the limited quantity of diluted analyte solutions requires the condensation of target analytes utilizing the superhydrophobic analyte enrichment effect and are extremely desirable for improving the detection sensitivity. Herein, the identification of ultra-trace analyte concentrations employing laser-textured palladium-gold (Pd-Au) hierarchical superhydrophobic micro-arrays as surface-enhanced Raman sensors (SMA-SERS) is reported. The double ns-laser fast scanning strategy produces hierarchically arranged micro-strip and micro-pyramidal arrays over the large surface areas composed of nano-scale inter-particle gaps, enabling the numerous three-dimensional plasmonic hot-spots due to the uniform formation of Au nanoparticles' aggregates/clusters. Under the optimized fabrication parameters, the resultant hybrid SMA-SERS sensors exhibit periodic micro-pyramidal arrays with excellent inherent superhydrophobicity (Contact angle, CA∼171°) and consequently superior SERS performance with uniform (RSD∼10%) signal detectability down to the ∼34.2 fM (3.42×10−14 M) MB molecules utilizing analyte enrichment effect. The accumulation of analytes within the smaller dried spots (Contact diameter, CD∼1.13 mm) results in increased spatial density of analytes and subsequently enables the ultra-low detectability of MGO, DTTCI, PA, AN, adenine, and l-tryp molecules down to ∼3.57 pM, 0.34 fM, 0.31 nM, 0.44 µM, 0.25 nM, and 97.7 nM concentrations, respectively. The multiplexed identification of target (AN and adenine) analytes is explored utilizing serial-deposition of analytes and depict the simultaneous detection of target analytes down to ∼10−7 M (AN) and 10−9 M (adenine) concentrations. The double ns-laser fast scanning strategy provides dual-scale surface roughness in the SMA-SERS substrates and offers ultrahigh sensitivity for the identification of the low amount of analytes utilizing the superhydrophobicity-induced analyte enrichment effect.

The Formation of Au Nanoparticles in SiO2–TiO2 Films by Local Electrochemical Reduction Using an Atomic Force Microscope Probe

The Formation of Au Nanoparticles in SiO2–TiO2 Films by Local Electrochemical Reduction Using an Atomic Force Microscope Probe

Locking Effect in Metal@MOF with Superior Stability for Highly Chemoselective Catalysis

Ultrasmall metal nanoparticles (NPs) show high catalytic activity in heterogeneous catalysis but are prone to reunion and loss during the catalytic process, resulting in low chemoselectivity and poor efficiency. Herein, a locking effect strategy is proposed to synthesize high-loading and ultrafine metal NPs in metal-organic frameworks (MOFs) for efficient chemoselective catalysis with high stability. Briefly, the MOF ZIF-90 with aldehyde groups cooperating with diamine chains via aldimine condensation was interlocked, which was employed to confine in situ formation of Au NPs, denoted as Au@L-ZIF-90. The optimized Au@La-ZIF-90 has highly dispersed Au NPs (2.60 ± 0.81 nm) with a loading amount around 22 wt % and shows a great performance toward 3-aminophenylacetylene (3-APA) from the selective hydrogenation of 3-nitrophenylacetylene (3-NPA) with a high yield (99%) and excellent durability (over 20 cycles), far superior to contrast catalysts without chains locking and other reported catalysts. In addition, experimental characterization and systematic density functional theory calculations further demonstrate that the locked MOF modulates the charge of Au nanoparticles, making them highly specific for nitro group hydrogenation to obtain 3-APA with high selectivity (99%). Furthermore, this locking effect strategy is also applicable to other metal nanoparticles confined in a variety of MOFs, and all of these catalysts locked with chains show great selectivity (≥90%) of 3-APA. The proposed strategy in this work provides a novel and universal method for precise control of the inherent activity of accessible metal nanoparticles with a programmable MOF microenvironment toward highly specific catalysis.

β-cyclodextrin functionalized gold nanoparticles as an effective nanocatalyst for reducing toxic nitroaromatics

We demonstrated the effective reduction of the organic pollutants, the nitroaromatics, via green sustainable chemistry using high efficacy of the catalytic materials, i.e., β-cyclodextrin (β-CD) functionalized Au nanoparticles (AuNPs). Eco-friendly and biocompatible techniques were employed to fabricate gold nanoparticles (AuNPs) from an Au precursor (HAuCl4) using β-CD that plays as both reducing and surface-functionalizing agents. Detailed investigation of β-CD AuNPs formation, their sizes with morphologies, the surface charge, and the hydrodynamic size in a colloidal medium were performed by ultraviolet–visible (UV–vis) absorbance spectroscopy, high-resolution transmission electron microscopy (HR-TEM), Zeta potential measurements, and the dynamic light scattering analysis, respectively. The plasmonic nanoparticle formation of the β-CD AuNPs led to the strong localized surface plasmon resonance peak at around the 520 nm wavelength. The catalytic activity of the β-CD AuNPs was evaluated using model reactions, including the catalytic conversion of nitroaromatics to the corresponding amino-aromatic compounds upon mixing sodium borohydride in a water medium. Chemical reactions of such catalytic reduction of nitroaromatics were tracked by UV–vis absorbance spectroscopy, showing high catalytic activity of β-CD AuNPs. We also provided a discussion on the possible pathways for the AuNPs-mediated catalytic reduction of nitroaromatics. The efficacy of the nanocatalysts presented to reduce nitroaromatics can hold a potential promise for detoxifying aquatic environments and their pharmaceutical applications.

Formation and Characterization of 2D Closely Packed Arrays of Bare Gold Nanoparticles without Aggregation.

Uniform 2D arrays of metal nanoparticles (NPs) have received significant attention in the field of molecular sensing using localized surface plasmon resonance. Generally, metal NPs bear organic surface-modifying molecules to prevent aggregation and form 2D metal NP arrays. However, surface-modifying molecules negatively affect molecular sensing. Previously, we developed a technique for forming a 2D bare metal NP array, denoted the sandwich (SW) technique. However, the formation mechanism of these 2D metal NP arrays remains unknown and therefore the experimental conditions of the SW technique are not optimized. Here, we observed the formation of a 2D Au NP (d: 60 nm) array using the SW technique with an optical microscope. Moderate drying conditions of the colloidal droplets sandwiched between two parallel substrates were necessary for forming 2D Au NP arrays. We then optimized the drying conditions and obtained a 2D Au NP array. This array was uniform, and the Au NPs were arranged at distances of 4.5 nm with hexagonal periodicity, without aggregation. Further, the 2D Au NP arrays exhibited excellent spot-to-spot reproducibility in surface-enhanced Raman scattering.

Structure Formation and Regulation of Au Nanoparticles in LiTaO3 by Ion Beam and Thermal Annealing Techniques.

The size uniformity and spatial dispersion of nanoparticles (NPs) formed by ion implantation must be further improved due to the characteristics of the ion implantation method. Therefore, specific swift heavy ion irradiation and thermal annealing are combined in this work to regulate the size and spatial distributions of embedded Au NPs formed within LiTaO3 crystals. Experimental results show that small NPs migrate to deeper depths induced by 656 MeV Xe35+ ion irradiation. During thermal annealing, the growth of large Au NPs is limited due to the reductions in the number of small Au NPs, and the migrated Au NPs aggregate at deeper depths, resulting in a more uniform size distribution and an increased spatial distribution of Au NPs. The present work presents a novel method to modify the size and spatial distributions of embedded NPs.

Tunable Reversal of Circular Dichroism in the Seed-Mediated Growth of Bichiral Plasmonic Nanoparticles.

Plasmonic nanoparticles with an intrinsic chiral structure have emerged as a promising chiral platform for applications in biosensing, medicine, catalysis, separation, and photonics. Quantitative understanding of the correlation between nanoparticle structure and optical chirality becomes increasingly important but still represents a significantly challenging task. Here we demonstrate that tunable signal reversal of circular dichroism in the seed-mediated chiral growth of plasmonic nanoparticles can be achieved through the hybridization of bichiral centers without inverting the geometric chirality. Both experimental and theoretical results demonstrated the opposite sign of circular dichroism of two different bichiral geometries. Chiral molecules were found to not only contribute to the chirality transfer from molecules to nanoparticles but also manipulate the structural evolution of nanoparticles that synergistically drive the formation of two different chiral centers. By deliberately adjusting the concentration of chiral molecules and other synthetic parameters, such as the reducing agent concentration, the capping surfactant concentration, and the amount of Au precursor, we have been able to fine-tune the circular dichroism reversal of bichiral Au nanoparticles. We further demonstrate that the structure of chiral molecules and the crystal structure of Au seeds play crucial roles in the formation of Au nanoparticles with bichiral centers. The insights gained from this work not only shed light on the underlying mechanisms dictating the intriguing geometric and chirality evolution of bichiral plasmonic nanoparticles but also provide an important knowledge framework that guides the rational design of bichiral plasmonic nanostructures toward chiroptical applications.