Size Of Gold Nanoparticles Research Articles

The non-linear evolution of radiative properties of plasmonic nanofluid during light-induced vaporization process

The light-induced vaporization process of plasmonic nanofluid plays an essential role in solar energy harvesting. Under light illumination, metallic nanoparticles can be converted into ideal thermal sources at nanoscale and generate plasmonic nanobubbles (PNBs) at the localized surface plasmon resonance (LSPR) wavelength, Therefore, the radiative properties of nanofluid closely correlate with the evolution of PNB nucleation, growth, fusion, and dissipation. A model based on finite element modeling is developed to investigate the evolution of radiative properties. The effect of gold nanoparticle (AuNP) size, PNB size, and AuNP aggregation morphology on the extinction cross section, albedo, and LSPR peak wavelength of particle-bubble complexes (P-B complexes) during the evolution of PNB is determined. The results indicate that with the vaporization process of nanofluid, the evolution of PNBs makes the radiation properties exhibit an obvious non-linear evolution pattern. Specifically, the generation of PNB shifts the LSPR peak wavelength towards blue, while the aggregation of AuNPs shifts it towards red. In the presence of PNB, the variation of the LSPR peak wavelength depends on the competition between the blue-shifting effect of PNB growth and the red-shifting effect of AuNP aggregation. After PNB dissipation, the aggregation of AuNPs raises the aggregates’ albedo. An albedo lower than 0.5 indicates a strong absorption of incident light energy. The increase in AuNP size, PNB size, and the aggregation of AuNPs all contribute to the increase in the peak extinction cross section. When PNB is present, whether the albedo of P-B complexes exceeds 0.5 depends on the relative magnitude of the extinction cross section of AuNP aggregates and PNB. The increase in the number of AuNPs aggregation layers causes the blue-shifted LSPR peak wavelength of AuNP aggregates, the decreased peak extinction cross section, the increased LSPR peak width, and the potential for multiple extinction peaks.

Development of portable sensor for the detection of bacteria: effect of gold nanoparticle size, effective surface area, and interparticle spacing upon sensing interface

In this study, systematic development of a portable sensor for the rapid detection of Escherichia coli (E. coli) and Exiguobacterium aurantiacum (E. aurantiacum) was reported. A conductive glass was utilized as a substrate and developed the electrode patterns on it. Trisodium citrate (TSC) and chitosan-stabilized gold nanoparticles (AuNPs) (CHI-AuNP-TSC) and chitosan-stabilized AuNPs (CHI-AuNP) were synthesized and utilized as a sensing interface. The morphology, crystallinity, optical properties, chemical structures, and surface properties of immobilized AuNPs on the sensing electrodes were investigated. The sensing performance of the fabricated sensor was evaluated by using an electrochemical method to observe the current changes in cyclic voltammetric responses. The CHI-AuNP-TSC electrode has higher sensitivity toward E. coli than CHI-AuNP with a limit of detection (LOD) of 1.07 CFU/mL. TSC in the AuNPs synthesis process played a vital role in the particle size, the interparticle spacing, the sensor’s effective surface area, and the presence of CHI around AuNPs, thus enhancing the sensing performance. Moreover, post-analysis of the fabricated sensor surface exhibited the sensor stability and the interaction between bacteria and the sensor surface. The sensing results showed a promising potential for rapid detection using a portable sensor for various water and food-borne pathogenic diseases.

The Role of Functionalization and Size of Gold Nanoparticles in the Response of MCF-7 Breast Cancer Cells to Ionizing Radiation Comparing 2D and 3D In Vitro Models.

Gold nanoparticles (AuNPs), as an agent enhancing radiosensitivity, play a key role in the potential treatment of breast cancer (BC). Assessing and understanding the kinetics of modern drug delivery systems is a crucial element that allows the implementation of AuNPs in clinical treatment. The main objective of the study was to assess the role of the properties of gold nanoparticles in the response of BC cells to ionizing radiation by comparing 2D and 3D models. In this research, four kinds of AuNPs, different in size and PEG length, were used to sensitize cells to ionizing radiation. The in vitro viability, uptake, and reactive oxygen species generation in cells were investigated in a time- and concentration-dependent manner using 2D and 3D models. Next, after the previous incubation with AuNPs, cells were irradiated with 2 Gy. The assessment of the radiation effect in combination with AuNPs was analyzed using the clonogenic assay and γH2AX level. The study highlights the role of the PEG chain in the efficiency of AuNPs in the process of sensitizing cells to ionizing radiation. The results obtained imply that AuNPs are a promising solution for combined treatment with radiotherapy.

Biosafety risk assessment of gold and aluminum nanoparticles in tumor-bearing mice.

To improve the biosafety of the nanodelivery system, this study developed novel monodisperse spherical aluminum nanoparticles (Al NPs) and evaluated their cytotoxicity in vitro and distribution and biotoxicity in vivo. Compared with gold nanoparticles of the same size, Al NPs not only had low cytotoxicity in vitro but also did not cause accumulation in major organs in vivo after intravenous injections. No significant abnormalities were observed in the serum biochemical indices of mice injected with Al NPs. Additionally, no substantial changes occurred in the histopathology of major organs, and no apparent biological toxicity was measured after consecutive injections of Al NPs. These results indicate that Al NPs have a good biological safety and provide a new method for developing low-toxicity nanomedicine.

An acetylcholinesterase-based biosensor for isoprocarb using a gold nanoparticles-polyaniline modified graphite pencil electrode.

An analysis tool for isoprocarb has been successfully developed as a biosensor system based on enzymatic inhibition of acetylcholinesterase (AChE) by isoprocarb. A gold nanoparticles-polyaniline modified graphite pencil electrode (AuNPs-PANI-GPE) was utilized to detect the change of thiocholine in the presence of isoprocarb. This electrode was prepared by two cyclic voltammetry steps, including the electro-polymerization of aniline on a graphite pencil and the electro-deposition of gold nanoparticles on the polyaniline surface. Characterization performed by SEM-EDX indicates that 8-80nm size of gold nanoparticles could be deposited on the surface of polyaniline-modified graphite pencil (PANI-GPE). Electrochemical characterization using cyclic voltammetry suggested that the active surface area of the prepared electrode was 0.17019 cm2, which was about 4 times higher than (PANI-GPE) and 13 times higher than the unmodified GPE. Furthermore, an oxidation peak of thiocholine could be observed at the modified GPE at a potential of + 0.675V (vs. Ag/AgCl), formed by an enzymatic reaction of AChE in the presence of acetylthiocholine. This peak current was found to linearly increase with acetylthiocholine concentrations, while in the presence of isoprocarb in a constant concentration of AChE and acetylthiocholine the peak linearly decreases. At the optimum condition of 0.1M phosphate buffer solution pH 7.4 containing 0.1M KCl; 100mU/ml AChE; and 1mM acetylthiocholine chloride in an inhibition and contact time of 25 and 15min, respectively, a linear calibration curve of isoprocarb in the concentration range of 0.05-1.0μM could be provided. Estimated limits of detection and quantifications of 0.1615nM and 0.5382nM, respectively, with a sensitivity of 1.7771 μA/μM.mm2 could be achieved. Furthermore, an excellent stability for 8 times measurements was observed with an RSD of 4.87%, suggesting that the developed tool is promising for the real detection of isoprocarb.

Theory and simulations of angular momentum transfer from swift electrons to spherical nanoparticles in scanning transmission electron microscopy

Electron beams in scanning transmission electron microscopy (STEM) exert forces and torques on study samples, with magnitudes that allow the controlled manipulation of nanoparticles (a technique called electron tweezers). Related theoretical research has mostly focused on the study of forces and linear momentum transfers from swift electrons (like those used in STEM) to nanoparticles. However, theoretical research on the rotational aspects of the interaction would benefit not only the development of electron tweezers, but also other fields within electron microscopy such as electron vortices. Starting from a classical-electrodynamics description, we present a theoretical model, alongside an efficient numerical methodology, to calculate the angular momentum transfer from a STEM swift electron to a spherical nanoparticle. We show simulations of angular momentum transfers to aluminum, gold, and bismuth nanoparticles of different sizes. We found that the transferred angular momentum is always perpendicular to the system's plane of symmetry, displaying a constant direction for all the cases considered. In the simulations, the angular momentum transfer increased with the radius of the nanoparticle, but decreased as the speed of the electron or the impact parameter increased. Also, the electric contribution to the angular momentum transfer dominated over the magnetic one, being comparable only for high electron's speeds (greater than 90% of the speed of light). Additionally, for nanoparticles with 1 nm radius of the studied materials, we found validity criteria for the small-particle approximation (in which the nanoparticle is modeled as an electric point dipole). We believe that these findings contribute to the understanding of rotational aspects present in STEM experiments, and might be useful for further developments in electron tweezers and other electron microscopy related techniques.

Effect of gold-nanoparticle size on microfiber saturable absorber for mode-locked erbium-doped fiber lasers

The optical performance of passively mode-locked erbium-doped fiber laser incorporating gold-nanoparticles (Au-NPs) of different sizes as saturable absorbers (SAs) was compared. A composite of Au-NPs with polydimethylsiloxane was spin coated on the surface of a microfiber waveguide. The fabricated Au-NP-based SA was deployed in a ring cavity erbium-doped fiber laser and its lasing performance was evaluated by comparing SA characteristics as well as pulse qualities among the different Au-NP sizes. The optimum pulse performance was realized when the SA was fabricated with 20 and 40 nm Au-NP size. For the former, time-bandwidth product of 0.34 was demonstrated which was the closest to its bandwidth-limited pulse. As for the latter, the fabricated SA exhibited 4.0% modulation depth and an average pulse duration of 886.7 fs. The research work has demonstrated the functionality of Au-NPs as a saturable absorption material for ultrashort pulses generation. In addition, the influence of nanomaterial size towards the characteristics of saturable absorbers, ergo the quality of laser pulse, was verified. This finding is also valuable in customizing ultrashort pulse output that can effectively suit system performance need.

Nanoplasmonic assay platforms for reproducible SERS detection of Alzheimer's disease biomarker

AbstractWith the recent developments in high‐sensitivity optical detection technologies, many studies have been conducted to accurately detect biomarkers with low concentrations of 1.0 pM or less as well as apply them to in vitro diagnostics. The tubulin‐associated unit (tau‐381) protein, a biomarker of Alzheimer's disease, is one such representative example, and its cut‐off value reported in clinical practice is 5.5 fM. Therefore, a robust sensing technology that can stably detect such low concentrations of biomarkers is needed. In this study, tau‐381 was detected with high sensitivity and reproducibility by a plasmonic Au nanopopcorn substrate fabricated via thermal evaporation. Here, aptamer DNAs labeled with Raman reporters on the terminal were used as the receptors. The plasmonic nanopopcorn substrate used in this study is composed of uniform gold nanoparticles (AuNPs) of average size 64 nm. The reproducibility was significantly improved through more uniform nanogaps than those formed by aggregation of AuNPs in solution. An assay was conducted by first reacting tau‐381 with the corresponding aptamers, and the remaining aptamer DNAs were then reacted with capture DNAs immobilized on the surface of the Au substrate. The assay results for tau‐381 showed a limit of detection value of 2.2 fM, which is below the cut‐off value (5.5 fM).

Nanoparticles separation by different conditions at asymmetric flow field-flow fractionation

Abstract As semiconductor manufacturing enters the era of sub-10 nm and 3D stacking, “cleanliness” in the process becomes a crucial factor for process yield. The measurement of nanoparticle concentration, size, and shape in various solutions that may cause contamination during the manufacturing process is currently an important research topic. Although there are various nanoparticle measurement techniques available, further technological development and breakthroughs are still needed for measuring low concentrations and complex mixtures of nanoparticles. Therefore, in this study, we attempted to address the measurement challenges posed by mixed particles by applying asymmetric flow field-flow fractionation in combination with dynamic light scattering and ultraviolet. The strategy involved separating the samples before measurement. For a nanomixture containing five different sizes of gold nanoparticles with diameters of 20, 40, 60, 80, and 100 nm, three different methods were employed to control the driving force for particle separation during the elution stage: constant cross flow rate, linearly decreasing cross flow rate, and exponentially decreasing cross flow rate. The results demonstrated that different flow rate control methods indeed yielded variations in nanoparticle separation, with the constant flow rate method showing the best separation efficiency. Additionally, it was observed that the thickness of the experimental chamber played a significant role in affecting the retention time of the nanoparticles during separation.

SERS Reveals the Presence of Au–O–O–H and Enhanced Catalytic Activity of Electrochemically Dealloyed AgAu Nanoparticles

Due to their high surface-to-volume ratio and large proportion of low coordinated surface atoms, dealloyed nanoparticles have gained increasing attention as porous catalysts for the electrochemical oxygen evolution reaction (OER). Here, we characterize and rationalize the physical and chemical properties of operando gold-enriched porous nanoparticles fabricated by electrochemical dealloying of citrate-capped silver gold alloy nanoparticles in 250 mM KNO3. We combine surface-enhanced Raman spectroscopy (SERS) with electrochemistry for catalyst tracking. With SERS, we observe at 1.05 V (vs platinum quasi-reference electrode) the formation of Au–O–O–H species, a known intermediate of OER, while this is not observed for monometallic gold nanoparticles or bare electrodes. In agreement, qualitative measurements of the catalytic activity prove that appreciable OER currents are detected at lower potentials for gold-enriched porous nanoparticles compared to gold nanoparticles of the same size. Our results pave the way for the application of dealloying-derived nanoparticles as promising catalyst materials.

On the Photo-Eradication of Methicillin-Resistant Staphylococcus aureus Biofilm Using Methylene Blue.

This work compared the effectiveness of several Methylene Blue (MB)-based protocols for photo-eradication of biofilms formed on the surface of the glass and stainless steel discs by S. aureus MRSA isolates using a diode laser (λ = 665 nm; output power 40 mW; energy fluence was 189 J cm-2). The results obtained showed that MB alone, up to a concentration of 62.5 mgL-1, had limited photo-bactericidal activity. It was possible to enhance the activity of MB using two types of spherical gold nanoparticles of similar sizes, 15 ± 3 nm/20 ± 3 nm, but differing in the method of their synthesis and stabilization. The enhancement of the photodestruction effect was related to the increased production of hydroxyl radicals by the MB+gold nanoparticles mixture, and this mixture showed dark cytotoxicity against the cocci studied. Effective destruction (mortality above 99.9%) of the biofilms formed by MRSA isolates was also possible without the use of gold nanoparticles, but the concentration of MB had to be at least 125 mgL-1. A highly efficient protocol of photodestruction of biofilms, consisting of triple exposure of biofilms to laser light in the presence of MB alone, combined with the removal of dead bacteria protecting deep layers of pathogens against photosensitization, was also described.

Nephrotoxicity induced by different diameters of sphere gold nanoparticles with special emphasis on the nephroprotective role of quercetin.

Although, gold nanoparticles (GNPs) are attracting more and more attention due to their ease of synthesis, modification, and great potential value in biomedical applications, exhibited harmful effects on human health and other living species. Quercetin (Qur) clarifies diverse pharmacological effects, especially anti-inflammatory, antiapoptotic, and antioxidant ones. This study aimed to evaluate the probable nephrotoxicity induced by different diameters of sphere GNPs, as well as the nephroprotective role of Qur. A total of 54 healthy mature male albino rats were grouped and treated with or without sphere GNPs; 10, 20, and 50 nm and Qur (200 mg/kg b.wt.). The effects of GNPs and Qur were estimated through the collection of blood and kidney samples from euthanized rats and performed biochemical, histopathological, and immunohistochemical investigations. In comparison between different diameters of GNPs, the 10 nm GNPs revealed more significant elevations in all renal function parameters: creatinine, urea, blood urea nitrogen, and uric acid followed by 20 nm then 50 nm. Pre-cotreatment with Qur decreased all renal functional values. Histopathologically, 10 nm revealed the most potent renal pathological changes represented in the renal cortex with cloudy swelling of renal tubules, hypercellularity of some glomeruli, severe congestion of renal blood vessels, focal inter tubular edema, and vascular endotheliosis (degeneration of endothelium). In addition, the renal medulla revealed perivascular inflammatory cellular infiltration, perivascular fibrosis, intra tubular glycogen deposition, and casts deposition of mainly cellular casts. On the other hand, the Qur treatment ameliorated most of these pathological changes. The size of GNPs is pivotal in their pathological effect on renal tissues where the small-sized GNPs; 10 nm have more potent cytotoxic, inflammatory, and apoptotic effects rather than the larger ones. Otherwise, Qur clarified a significant mitigating role against the nephrotoxicity of the GNPs.

3-Aminophenylboronic Acid Conjugation on Responsive Polymer and Gold Nanoparticles for Qualitative Bacterial Detection.

Because of their sensitive and selective responses to a wide variety of analytes, colorimetric sensors have gained widespread acceptance in recent years. Gold nanoparticles (AuNPs) are widely employed in visual sensor strategies due to their high stability and ease of use. Combining AuNPs with a responsive polymer can result in distinct surface plasmon resonance (SPR) changes that can be utilized as colorimetric biosensors. The purpose of this research is to develop a colorimetric-based sensor through the utilization of the optical properties of gold nanoparticles (AuNPs) crosslinked with pH-responsive polymers poly (acrylic acid) (PAA) conjugated to 3-aminophenyl boronic acid (APBA). The polymer (PAA) was synthesized via RAFT polymerization. The inversed Turkevic method was used to produce AuNPs, which were subsequently used in a self-assembly process using poly (acrylic acid)-aminophenyl boronic acid (PAA-APBA) to create the self-assembled AuNPs-APBA-PAA. The particle size, zeta potential, and reversibility of the polymer-modified gold nanoparticles were determined using a transmission electron microscope (TEM), a particle size analyzer (PSA), and an Ultraviolet-Visible spectrophotometer (UV-Vis spectrophotometer). Visual, UV-Vis spectrophotometer and TEM observations confirmed the system's ability to identify bacteria. Statistical analysis was performed using a one-way analysis of variance using Excel software. Using UV-Vis spectrophotometry, the particle size of AuNPs was determined to be 25.7 nm, and the maximum absorbance occurred at 530 nm. AuNPs PAA APBA colloid exhibited an absorbance maximum of 532 nm, a zeta potential of -41.53, and a pH transition point between 4 and 5. At E. coli concentrations of 4.5 x 107 CFU/mL, the color of the system sensors changed from red to blue after 15 hours of incubation, whereas at S. aureus concentrations of 1.2 x 109 CFU/mL, the color changed to purple immediately after mixing. The TEM confirmed that the detection mechanism is based on the boronate-polyol bonding of saccharides on the outer membranes of Escherichia coli and Staphylococcus aureus. The use of APBA in conjunction with pH-responsive PAA polymers containing AuNPs to detect E. coli and S. aureus bacteria induces a maximum wavelength transition, followed by a color change from red to blue. By the process of de-swelling of the responsive polymer, which induces the aggregation of the AuNPs, the established sensor system is able to alter the color. The conjugated polymer and gold nanoparticle-based sensor system demonstrated a promising method for bacterial detection.

In situ decrypting plasmonic nanoparticle size-controlled phosphorylation of epidermal growth factor receptor in living cells.

Recently, interaction between epidermal growth factor receptor (EGFR) and EGFR-targeted nanoprobes is a hot topic. Here, we use dark field microscope (DFM) observe different aggregations of EGFR-targeted nanoprobes in diverticulum. Different aggregation states are related to phosphorylation of EGFR. EGFR phosphorylation can be adjusted by gold nanoparticles (GNPs) size.

A simple strategy based on combinatorial gold nanoparticle sizes for enhanced sensitivity in colorimetric bioanalysis.

Taking advantage of salt-induced aggregation, gold nanoparticles (AuNPs) have been intensively employed in non-cross-linking strategies (NCLs) for colorimetric bioanalysis. Such a classical method is popular due to its simplicity and cost-effectiveness, but it still suffers from poor sensitivity in analytical practice. To address this issue, we simply mixed the four sizes of non-functional AuNPs (10 nm/20 nm/30 nm/40 nm) to establish a highly sensitive combinatorial system in a non-cross-linking strategy (cNCL). For comparison, we also designed four independent systems with individual sizes of AuNPs (10 nm, 20 nm, 30 nm and 40 nm, respectively) as typical non-cross-linking strategies (tNCLs). Interestingly, the cNCLs were found to have significantly enhanced sensitivity compared to each of the tNCLs in analytical performance. TEM and theoretical calculation were employed to explore this phenomenon, and it is indicated that the aggregation behaviours of cNCLs show more compact morphology by particle-to-particle stacking. We then tuned the size proportions of various AuNPs in cNCLs to evaluate the contribution of each size of the AuNPs. It appears that 10 nm AuNPs are mainly responsible for minimizing background intensity, and 40 nm AuNPs for maximizing signal intensity. Moreover, with the well-studied effect of combinatorial AuNP sizes in cNCLs, an excellent signal-to-background (S/B) ratio can be obtained, achieving at least 500-fold and 2.5-fold improvement in the aspects of optical and visual sensitivity, respectively. Such a combinatorial AuNP size-based NCL (cNCL) strategy is modification-free towards AuNPs, and the whole process can be accomplished within 10 min. The aggregation behaviour significantly impacts the optical properties and morphology, and therefore improves analytical sensitivity. With these findings, valuable insight is provided in developing sensitive and versatile colorimetric assays based on classic AuNP aggregation.

The application of gold nanoparticles in biomedicine

In the past few years, nano particles are one of the most popular scientific research fields. It has been widely used in biomedical, optics, electronics and other areas. Gold nanoparticles are quite different from other nanoparticles. Their practical application has a very long history, which has been recorded in ancient Rome. By using their scattering property, gold nanoparticles are added to glass products to make them not only have various colors, but also have photochromic effect. With the development of related fields such as new organic metal chemistry, nanotechnology, and complex research, gold nanoparticles are listed as an important research object in biomedical applications. The shape and size of gold nanoparticles have a direct impact on their optical properties and applications. Therefore, exploring the preparation method to achieve controllable preparation is of great significance for the research of gold nanoparticles. Moreover, the application research of nano gold in biomedicine filed has developed rapidly, especially in recent years. Gold nanoparticles play an increasingly important role in disease detection, targeted therapy, drug detection, enhanced device performance, and imaging. This work mainly discusses the preparation method of gold nanoparticles and its applications in biomedicine field.

Time-Dependent Size and Shape Evolution of Gold and Europium Nanoparticles from a Bioproducing Microorganism, a Cyanobacterium: A Digitally Supported High-Resolution Image Analysis

Herein, the particle size distributions (PSDs) and shape analysis of in vivo bioproduced particles from aqueous Au3+ and Eu3+ solutions by the cyanobacterium Anabaena sp. are examined in detail at the nanoscale. Generally, biosynthesis is affected by numerous parameters. Therefore, it is challenging to find the key set points for generating tailored nanoparticles (NPs). PSDs and shape analysis of the Au and Eu-NPs were performed with ImageJ using high-resolution transmission electron microscopy (HR-TEM) images. As the HR-TEM image analysis reflects only a fraction of the detected NPs within the cells, additional PSDs of the complete cell were performed to determine the NP count and to evaluate the different accuracies. Furthermore, local PSDs were carried out at five randomly selected locations within a single cell to identify local hotspots or agglomerations. The PSDs show that particle size depends mainly on contact time, while the particle shape is hardly affected. The particles formed are distributed quite evenly within the cells. HR-PSDs for Au-NPs show an average equivalent circular diameter (ECD) of 8.4 nm (24 h) and 7.2 nm (51 h). In contrast, Eu-NPs preferably exhibit an average ECD of 10.6 nm (10 h) and 12.3 nm (244 h). Au-NPs are classified predominantly as "very round" with an average reciprocal aspect ratio (RAR) of ~0.9 and a Feret major axis ratio (FMR) of ~1.17. Eu-NPs mainly belong to the "rounded" class with a smaller RAR of ~0.6 and a FMR of ~1.3. These results show that an increase in contact time is not accompanied by an average particle growth for Au-NPs, but by a doubling of the particle number. Anabaena sp. is capable of biosorbing and bioreducing dissolved Au3+ and Eu3+ ions from aqueous solutions, generating nano-sized Au and Eu particles, respectively. Therefore, it is a low-cost, non-toxic and effective candidate for a rapid recovery of these sought-after metals via the bioproduction of NPs with defined sizes and shapes, providing a high potential for scale-up.

Chronoamperometry-based controllable fabrication of gold nanoparticle monolayers and their hydrophobic force-induced movement on indium tin oxide glass substrate

Owing to their unique plasmonic properties, noble metals have been the materials of choice for photovoltaics, photocatalysis and sensors. Here, we demonstrate novel gold(Au) monolayers with tailorable particle diameters and optical property on transparent indium tin oxide (ITO) using a simple electrochemical deposition. The nanoparticles on ITO are spherical and isolated, and are identified as Au0 nanoparticles. The gold nanoparticles are uniformly distributed on ITO surface, but the gold nanoparticle sizes increase and the particle population densities decrease at lower current densities, resulting in higher light scattering. There is a positive correlation between mean particle size and maximum extinction wavelength of gold nanoparticles prepared with different current densities under a fixed total charge, whereas the maximum extinction wavelength of gold nanoparticles does not change with the total charge under the fixed current densities. The localized surface plasmon resonance change of Au nanoparticles on ITO can be effectively tuned by regulating deposition current density. With the existence of alkanethiols on Au monolayers surface, the original pink color of gold monolayers changed to blue after immersion in toluene for 30 min, indicating hydrophobic force produced by oil-in-water (O/W) or water-in-oil (W/O) phenomenon caused gold nanoparticles to migrate and produce a color change.

Fabrication of gold nanoparticle decorated surfaces for controlled nucleation of plasmonic microbubbles

Plasmonic bubbles produced by water-immersed gold nanoparticles (GNPs) under a laser irradiation are of great relevance in numerous applications. Normally, plasmonic bubbles are produced on a well-fabricated GNP decorated sample surfaces, which rely on expensive devices and complex fabrication processes. In this study, we systematically investigate the fabrication of GNP decorated sample surfaces for optimized production of plasmonic bubbles. Sample surfaces are fabricated by thermal dewetting of a gold film coated on fused silica substrates under an annealing temperature up to 1200 °C. Both the size and density of GNPs can be well tuned by adjusting gold film thickness and annealing temperature. The optical absorption of sample surfaces is also experimentally and numerically investigated, from which the optimal parameters of fabrication are determined. More importantly, for the first time, we find that the high annealing temperature leads to the formation of nanoindents beneath GNPs, resulting in the partial enwrapment of GNPs into fused silica substrates. This helps to stabilize GNPs on sample surfaces. With the fabricated sample surfaces, the nucleation and growth dynamics of giant initial bubbles and ordinary plasmonic bubbles can be well tuned. No apparent damage has been observed on the sample surfaces after the violent bubble nucleation. The increased stability of GNPs is important for plasmonic bubble related applications.

Size effect of gold nanoparticles in bimetallic ZIF catalysts for enhanced photo-redox reactions

It is well known that gold nanoparticles have been widely used in various photo-redox reactions because of the unique surface plasmon resonance effect and the excellent internal electron transfer ability. However, the essential factors of how the metal nanoparticles enhancing the activity of photocatalysts have not been fully revealed. In this paper, gold colloidal particles of different sizes were modified on the surface of the dodecahedral skeleton of ZIF-Co/Zn. The photocatalytic activity of Au@ZIF-Co/Zn was investigated under simulated visible light for treating Rhodamine B/Cr(VI) mixture solutions (RhB/Cr(VI) 20 mg/L) and 4-nitrophenol solution (4-NP 20 mg/L). The results indicate that the size of gold nanoparticles could affect the surface plasmon resonance effect observably, internal electron transfer capacity and carrier density change. Photoelectric chemistry experiments and radical quenching experiments were performed to reveal the charge-transfer photocatalytic mechanism and size influence of gold nanoparticles in composite photocatalysts. This work may provide a novel strategy for the construction of metal–organic frameworks for the purification of wastewater mixed with heavy metal ions, organic pollutants and pharmaceutical intermediates.