Aggregation Of Au Nanoparticles Research Articles

Analyte-triggered citrate-stabilized Au nanoparticle aggregation with accelerated peroxidase-mimicking activity for catalysis-based colorimetric sensing of arsenite

Arsenite is a well-known toxic species widely distributed in many matrices, and exploring reliable and facile methods for its detection is always desired for environmental analysis and food safety control. Here we propose a catalytic colorimetric assay of arsenite based on the analyte inducing the aggregation of citrate-stabilized Au nanoparticles (AuNPs) with promoted peroxidase-mimicking activity. Originally, highly dispersed AuNPs with a mean size of ∼20 nm show negligible enzyme-like activity. However, when a small amount of arsenite is added, it triggers the rapid aggregation of AuNPs via the interactions between the analyte and the stabilizer citrate on AuNP surface, and it is further observed that the formed AuNP agglomerate can exhibit significantly accelerated peroxidase-mimetic activity to catalyze the 3,3′,5,5′-tetramethylbenzidine chromogenic reaction with the participation of H2O2. Based on this phenomenon, a facile colorimetric strategy with catalytic signal amplification was established for the efficient sensing of arsenite. With the catalysis-based strategy, arsenite in a wide range (0.0111.67 mg/L) was linearly determined with a detection limit lower than the standard approved by the US EPA and the EEA. Stable and reliable measurement of the analyte in various water matrices was also verified, promising our assay’s great potential in practical applications.

Markedly improved performance of oxide-supported catalysts in hot basic water by three facile ways in synergy

Use oxide-supported catalyst in green solvent, hot water : Au is anchored on oxide via Au┄O-M interaction (M = Fe, Ti, etc). Basic aqueous catalytic system may destruct a part of O M bonds into oxygen vacancies and weaken Au/support interaction, causing leaching and aggregation of Au. Three simple methods synergistically improve reusability of catalyst. • Three facile ways synergistically improve catalyst reusability in green solvent, water. • They raise support stability and Au/support interaction to reduce leaching and aggregation of Au. • Nano supports interact with Au more strongly, and are more stable in hot basic water. • Nano TiO 2 is more stable due to the stronger surface Ti O bond, in line with BOLS theory. Obtaining reusable catalysts and using water as a green solvent still remain huge challenges. Various oxides are frequently used as the support, however, the aqueous catalytic systems, particularly in hot basic water, may decrease their stability and thus cause leaching or aggregation of the supported metal nanoparticles (NPs). In this work, three very simple methods in catalyst preparation are demonstrated to greatly improve the reusability of oxide-supported catalysts in 100 °C basic water, by systematically studying a series of oxides as well as carbons as support of gold (Au) NPs and employing Suzuki-Miyaura cross-coupling (SMCC) reaction as a probe. These methods are prerequisites for obtaining both excellent activity and recyclability. Absence of any of them will badly improve leaching or aggregation of Au NPs. The reasons for the synergistically improved reusability are also elucidated in details. Though it’s extremely hard to thoroughly overcome leaching in hot water, this work achieves the application of Au/oxide to SMCC reaction in water with higher utilization efficiency of Au than some reported work in organic solvent or with other supports. The present work can serve as supplementary strategies to assist in designing high-performance oxide-supported catalysts for varieties of similar aqueous systems.

Interaction of gold and phthalocyanines nanoparticles generated by laser radiation in water

Experimental results are presented on the interaction of gold nanoparticles (NPs) generated by laser ablation in water and nanoparticles of copper and aluminum phthalocyanine (PC) obtained by laser fragmentation in water. Such particles are characterized by chemical purity, in contrast to NPs synthesized using other techniques. It is found that addition of either AlPC or CuPC colloidal solutions to colloid of Au NPs causes the aggregation of Au NPs. This is confirmed by evolution of extinction spectra of colloids mixture and by Transmission Electron Microscopy. This effect is not observed under addition of the colloid of AlPC to Ag NPs also generated by laser ablation in water. Addition of PC colloids to the mixture of Au and Ag NPs leads to selective aggregation of only Au NPs. Possible mechanisms of aggregation of Au NPs upon mixing with PC NPs that have the dzeta-potentials of different signs are discussed.

Heat transfer and thermoregulation within single cells revealed by transient plasmonic imaging

Summary Cells, as the basic unit of life, undergo continuous heat transfer and dissipation during their metabolism, which is related not only to fundamental cellular functions but also massive applications. Unfortunately, thus far, we still know little about the heat transfer properties at the cellular or subcellular levels. Here, we demonstrated a transient microscopic method to measure the heat transfer in single cells. The thermal conductivity of different regions within a single cell shows a wide heterogeneity, and heat transfer in the region near the cell membrane is more active than the central region. However, the median values of thermal conductivity between different individual cells are quite close. A cellular-level heat regulation that responds to environmental temperature is observed in warm-blooded humans and chickens rather than in cold-blooded bullfrogs. According to the temperature-dependent cell metabolism, we proposed a hypothesis for cellular control of heat dissipation, which might be the cellular-level foundation of body thermoregulation.

Simple synthesis of gold-decorated silica nanoparticles by in situ precipitation method with new plasmonic properties

We describe a simple method for the preparation of gold-decorated silica (SiO2) nanoparticles (NPs) by the in situ precipitation method using simple BH4− ions reduction as a procedure, where BH4− ions are adsorbed onto PEI-functionalized SiO2 NPs for stabilizing and reducing gold ions onto PEI-SiO2 surface in water under ambient conditions. The result was 3-nm gold nanoshell NPs attached to SiO2 core (~ 75 nm) with a surface plasmon resonance (SPR) at ~ 680 nm. SPR band is associated with Au NP aggregates that arise from strong interparticle interaction. This is an alternative to the gold-seeding methods and the use of anionic gold species for the obtention of gold-decorated SiO2 NPs with an important red-shift in UV–Vis absorption and with potential applications in biosensors and photothermal therapy.

Dynamic motions and architectural changes in DNA supramolecular aggregates visualized via transmission electron microscopy without liquid cells.

In the last decade, breakthroughs in liquid-phase transmission electron microscopy (TEM) have enabled in situ visualization of the motion dynamics of nanostructures in liquid media with unprecedented detail. However, it remains a significant challenge to perform liquid-phase TEM due to the intricate preparation procedure of liquid cells to keep liquid from evaporating under ultrahigh vacuum conditions in TEM columns. In the present study, the nonvolatility and remarkable solvation property of ionic liquids (ILs) is exploited to image the dynamic processes of DNA supramolecular aggregates and Au nanoparticle (NP) aggregates encompassing Brownian motions, interactions among individual nanoobjects and changes in architecture at nanometer resolution. Significant differences in motion behaviors are observed between DNA supramolecular aggregates and Au NP aggregates. Moreover, the temperature and dose dependence of dynamic motions are also investigated. The findings provide insights into the dynamics of DNA supramolecular aggregates and Au NP aggregates in ILs and present an easily accessible approach for probing the dynamic processes of biomacromolecular and other soft matter aggregates with various kinds of ILs at the nanoscale level.

On-site, rapid and visual method for nanomolar Hg2+ detection based on the thymine-Hg2+-thymine triggered "double" aggregation of Au nanoparticles enhancing the Tyndall effect.

This work describes a new nanosensor for the simple, rapid, portable, colorimetric analysis of mercury(ii) (Hg2+) ions by combining the sensitive Tyndall effect (TE) of colloidal Au nanoparticles (AuNPs) with specific thymine–Hg2+–thymine (T–Hg2+–T) coordination chemistry for the first time. For the TE-inspired assay (TEA), in the presence of Hg2+ in a sample, the analyte can selectively mediate the hybridization of three types of flexible single-stranded DNAs (ssDNAs) to form stable rigid double-stranded DNAs (dsDNAs) via the T–Hg2+–T ligand interaction. Subsequent self-assembly of the dsDNAs with terminal thiol groups on the AuNPs' surfaces led to their “double” aggregation in addition to the lack of sufficient ssDNAs as the stabilizing molecules in a high-salt solution, resulting in a remarkably enhanced TE signal that positively relied on the Hg2+ level. The results demonstrated that such a TEA method enabled rapid naked-eye qualitative analysis of 625 nM Hg2+ within 10 min with an inexpensive laser pointer pen as an inexpensive handheld light source to generate the TE response. Making use of a smartphone for portable TE readout could further quantitatively detect the Hg2+ ions in a linear concentration range from 156 to 2500 nM with a limit of detection as low as 25 nM. Moreover, the developed equipment-free nanosensor was also used to analyze the Hg2+ ions in real samples including tap water, drinking water, and pond water, the obtained recoveries were within the range of 93.68 to 108.71%. To the best of our knowledge, this is the first report of using the AuNPs and functional nucleic acids to design a TE-based biosensor for the analysis of highly toxic heavy metal ions.

The chain-like Au/carbon dots nanocomposites with peroxidase-like activity and their application for glucose detection

The nanocomposites with highly synergistic effect show important potential application as nanozymes. Herein, the chain-like Au/carbon dots (CDs) (GCDs) nanocomposites were prepared by self-assembly method. The negatively charged Au nanoparticles (NPs) and positively charged CDs were connected by the electrostatic interaction. Then, the electron transfer between Au and CDs induces the strong catalytic effect of GCDs nanocomposites. The cross-linking reaction occurred between amino groups and carboxyl groups on the surface of CDs, which led to form the chain-like Au aggregation surrounded by carbon shells. By FDTD simulation, the aggregation of Au NPs may enhance the electromagnetic field so that the surface-enhanced Raman scattering (SERS) signal can be increased based on GCDs nanocomposites as substrate. Otherwise, the GCDs nanocomposites can also be used to catalyze the oxidation of colourless3,3',5,5′-tetramethylbenzidine (TMB) to blue oxTMB in the presence of H2O2, which displays the enhanced peroxidase-like activity compared with alone Au NPs or CDs. The obvious oxidation process of TMB molecules may be monitored by the change of SERS signal during the catalytic reaction. On this basis, GCDs nanocomposites can be further used for detection of glucose. The detection level of glucose is obtained as low as 5 × 10−7 M. Therefore, this provides a method to detect the glucose based on GCDs nanocomposites as an enzyme mimic.

Reusable Surface-Enhanced Raman Spectroscopy Membranes and Textiles via Template-Assisted Self-Assembly and Micro/Nanoimprinting.

Surface-enhanced Raman spectroscopy (SERS) has emerged as a powerful tool for ultrasensitive fingerprint recognition of molecules with considerable potential in wearable biochemical sensing. However, previous efforts to fabricate wearable SERS devices by directly treating fabrics with plasmonic nanoparticles have generated a nonuniform assembly of nanoparticles, weakly adsorbed on fabrics via van der Waals forces. Here, we report the creation of washing reusable SERS membranes and textiles via template-assisted self-assembly and micro/nanoimprinting approaches. Uniquely, we employ the capillary force driven self-assembly process to generate micropatch arrays of Au nanoparticle (NP) aggregates within hydrophobic microstructured templates, which are then robustly bonded onto semipermeable transparent membranes and stretchable textiles using the UV-resist based micro/nanoimprinting technique. A mild reactive ion etching (RIE) treatment of SERS membranes and textiles can physically expose the SERS hotspots of Au NP-aggregates embedded within the polymer UV resist for further improvement of their SERS performance. Also, we demonstrate that the semipermeable transparent SERS membranes can keep the moisture content of meat from evaporating to enable stable in situ SERS monitoring of biochemical environments at the fresh meat surface. By contrast, stretchable SERS textiles can allow the spreading, soaking, and evaporation of solution analyte samples on the fabric matrix for continuous enrichment of analyte molecules at the hotspots in biochemical SERS detection. Due to the mechanical robustness of the UV-resist immobilized Au NP aggregates, simple detergent-water washing with ultrasound sonication or mechanical stirring can noninvasively clean contaminated hot spots to reuse SERS textiles. Therefore, we envision that washing reusable SERS membranes and textiles by template-assisted self-assembly and micro/nanoimprinting fabrication are promising for wearable biochemical sensing applications, such as wound monitoring and body fluid monitoring.

Au Nanoparticles Decorated Mesoporous SiO2 -WO3 Hybrid Materials with Improved Pore Connectivity for Ultratrace Ethanol Detection at Low Operating Temperature.

Semiconducting metal oxides-based gas sensors with the capability to detect trace gases at low operating temperatures are highly desired in applications such as wearable devices, trace pollutant detection, and exhaled breath analysis, but it still remains a great challenge to realize this goal. Herein, a multi-component co-assembly method in combination with pore engineering strategy is proposed. By using bi-functional (3-mercaptopropyl) trimethoxysilane (MPTMS) that can co-hydrolyze with transition metal salt and meanwhile coordinate with gold precursor during their co-assembly with PEO-b-PS copolymers, ordered mesoporous SiO2 -WO3 composites with highly dispersed Au nanoparticles of 5nm (mesoporous SiO2 -WO3 /Au) are straightforward synthesized. This multi-component co-assembly process avoids the aggregation of Au nanoparticles and pore blocking in conventional post-loading method. Furthermore, through controlled etching treatment, a small portion of silica can be removed from the pore wall, resulting in mesoporous SiO2 -WO3 /Au with increased specific surface area (129m2 g-1 ), significantly improved pore connectivity, and enlarged pore window (>4.3nm). Thanks to the presence of well-confined Au nanoparticles and ε-WO3 , the mesoporous SiO2 -WO3 /Au based gas sensors exhibit excellent sensing performance toward ethanol with high sensitivity (Ra /Rg = 2-14 to 50-250ppb) at low operating temperature (150°C).

Influence of initial distance and heating rate on the aggregation of Cu and Au nanoparticles: a MD study

This paper investigates the effects of interparticle distance and heating rate on the aggregation characteristics of Cu/Au nanoparticles using molecular dynamics (MD) simulations, and focuses on discussing the effects of the two above-mentioned factors on the entire system. Our results suggested that the reduction in heating rate and increasing the initial distance of the particles would both contribute to raising the initial sintering temperature. However, when the particles’ initial distance was greater than the cut-off radius of the system, the initial sintering temperature was not increased any longer, but fluctuated within a certain range. Furthermore, the sintering force of the nanoparticles at the initial sintering temperature was investigated, and it was found that the heating rate made no obvious difference to it. Nonetheless, the sintering force varied under different initial distance of the particles (at the same heating rate) due to system energy changes.

Deactivation behavior and aggregation mechanism of supported Au nanoparticles in the oxidation of monoethanolamine to glycine

Deactivation behaviors of gold catalysts in the liquid-phase oxidation of monoethanolamine to glycine were revealed. Properties of the catalysts including Au loading, the valence distribution, and particle size of Au nanoparticles before and after batch reactions were investigated by BET, ICP, XRD, XPS, and TEM. It was found that the main reason for the catalytic deactivation was aggregation of Au nanoparticles. The Au aggregation mechanism of oxidative dissolution-reductive deposition in the reaction was proposed and this mechanism could help to understand the common aggregation of Au nanoparticles in the liquid-phase oxidation of alcohols.

Chitosan stabilization and control over hot spot formation of gold nanospheres and SERS performance evaluation

Au nanoparticles tend to aggregate in solution in the presence of several agents, specifically most adsorbates used in SERS experiments, such as rhodamine-6G (R6G). That tendency may be circumvented by stabilizing agents, usually based on modulating electrostatic interactions. The control over stability and formation of SERS hot spots are important factors for application in SERS-based biosensors. Among the stabilizing agents, chitosan (Chit), which is positively charged biopolymer, can provide stability to the AuNS system and control the formation of hot spots. In the present study, Au nanospheres (AuNS) were coated by Chit, which improved stability against KCl and ethanol. The decrease in R6 G SERS intensity relative to the unprotected AuNS was attributed to prevention of hot spots formation by the biopolymer coating; this last characteristic was partially reverted by aggregating with chloride before adding Chit. The AuNS + KCl + Chit system resulted in half R6 G SERS intensity compared to uncoated AuNS, but in an increase in 5 times compared to coating with Chit without the chloride-generated hot spots. Adding Chit improved the temporal stability of AuNS suspension for several weeks. The present study shows that Chit may both stabilize existing hot spots and stop the increase of aggregates, avoiding additional aggregation and agglomeration of Au nanoparticles even in presence of aggregating agents and still resulting in high SERS performance.

Core@Satellite Janus Nanomotors with pH-Responsive Multi-phoretic Propulsion.

We report core@satellite Janus mesoporous silica-Pt@Au (JMPA) nanomotors with pH-responsive multi-phoretic propulsion. The JMPA nanomotors first undergo self-diffusiophoretic propulsion in 3.0 % H2 O2 due to the isolation of the Au nanoparticles (AuNPs) from the PtNPs layer. Then the weak acidity of H2 O2 can trigger the disassembly and reassembly of the AuNPs, resulting in the Janus distribution of large AuNPs aggregates. Such reconstruction of JMPA leads to the contact between PtNPs and AuNPs aggregates, thus changing the propulsion mechanism to self-electrophoresis. The asymmetric and aggregated AuNPs also enable the generation of a thermal gradient under laser irradiation, which propels the JMPA nanomotors by self-thermophoresis. Such multi-phoretic propulsion offers considerable promise for developing advanced nanomachines with a stimuli-responsive switch of propulsion modes in biomedical applications.

Core@Satellite Janus Nanomotors with pH‐Responsive Multi‐phoretic Propulsion

AbstractWe report core@satellite Janus mesoporous silica‐Pt@Au (JMPA) nanomotors with pH‐responsive multi‐phoretic propulsion. The JMPA nanomotors first undergo self‐diffusiophoretic propulsion in 3.0 % H2O2 due to the isolation of the Au nanoparticles (AuNPs) from the PtNPs layer. Then the weak acidity of H2O2 can trigger the disassembly and reassembly of the AuNPs, resulting in the Janus distribution of large AuNPs aggregates. Such reconstruction of JMPA leads to the contact between PtNPs and AuNPs aggregates, thus changing the propulsion mechanism to self‐electrophoresis. The asymmetric and aggregated AuNPs also enable the generation of a thermal gradient under laser irradiation, which propels the JMPA nanomotors by self‐thermophoresis. Such multi‐phoretic propulsion offers considerable promise for developing advanced nanomachines with a stimuli‐responsive switch of propulsion modes in biomedical applications.

Double responsive analysis of carbaryl pesticide based on carbon quantum dots and Au nanoparticles

B, N-doped carbon quantum dots (CQDs) with an emission peak at 490 nm was prepared by a hydrothermal method. It was found that the fluorescence of CQDs could be effectively quenched by Au nanoparticles (AuNPs) with the absorption peak at 520 nm. Thiocholine (TC), which was produced from acetylcholine (ACh) hydrolysis catalyzed by acetylcholinesterase (AChE), could induce the aggregation of AuNPs along with a drop in the absorption at 520 nm and result in the recovery of quenched CQDs fluorescence. When carbaryl was introduced, which inhabited the catalytic activity of AChE, thus the aggregation of AuNPs and the recovery of CQDs fluorescence was decremented. On the basis of above phenomena, we established a colorimetric and fluorescent double reading method for carbaryl determination. Under the optimum conditions, the fluorescence response was strongly correlated with carbaryl concentration in the 0.20–150 μg/L range, and the absorbance response was linearly proportional to the concentration of carbaryl in the range of 0.2–20 μg/L. This method was used to the determination of carbaryl in tap and lake water samples with high precision and accuracy, indicating the potential of the method in practical applications with simple operation, good accuracy and high sensitivity.

Depositing Highly Uniform Au Nanoparticles on the Surface of High-Curvature Nanofibers for SERS Optophysiology

Nanofibers as biosensors have attracted great attention due to its facile removal from the biosystem after a period of intra- or extracellular measurements and site-specific measurement among others. The application of nanofibers covered with Au nanoparticles as SERS sensor circumvents the aggregation and accumulation of Au nanoparticles in vitro or in vivo, in addition to the greater Raman enhancement of signal than on planar surface. To achieve this, our group has reported a block copolymer-template method to deposit Au nanoparticles on the highly curved surface of nanofibers.[1] Here the versatility of this strategy is demonstrated by depositing nanoparticles with the different dimensions or shapes and varying the density of Au nanoparticles on the surface of the nanofibers. To the best of our knowledge, we believe this is the first work to show how to obtain such highly uniform distribution of anistropic nanoparticles on the surface of high-curvature nanofibers. Among all the nanosensors studied in this work, the label-free nanofibers covered with Au nanostars with shorter branches shows the biggest enhancement, which could detect neurotransmitter secretion such as dopamine with moderate laser power and low integration time. Furthermore, measurement of pH in the cell microenvironment and pH gradient in the cell medium can be realized by our biosensors as well. The rapid pH response to the external environment makes it very promising for the application of the dynamic pH measurement in vitro or in vivo. In addition to SERS sensing, these highly uniform nanosensors have other far-reaching implications, including medical diagnostics, therapeutics and so on.[1] Zhu, H., Lussier, F., Ducrot, C., Bourque, M. J., Spatz, J. P., Cui, W., Yu, L., Peng, W., Trudeau, L. E., Bazuin, C. G. and Masson, J. F., ACS Appl. Mater. Interfaces, 2019, DOI: 10.1021/acsami.8b19161. Figure 1

Noble metal nanoparticle superstructures via liquid/liquid interfacial mass transfer-assisted self-assembly

Organized assemblies of noble metal nanoparticles (NPs) exhibit unique optical, electronic and catalytic properties and potential applications in various areas. Many kinds of methods have been developed to fabricate such functional systems. In this work, we report a facile and novel method to fabricate the organized aggregates of Au and Ag NPs. Their freshly prepared hydrosols were used as upper phase, and the DMF/chloroform solutions of different fatty amines were used as bottom phases to form a planar liquid/liquid interface. The mass transfer across the interface occurred immediately, where the DMF droplets containing fatty amines entered into the hydrosols, leading to the formation of organized aggregates of NPs through a self-assembly process of amine molecules. It was found that several kinds of assemblies were generated, including ellipsoidal and spherical superstructures of spherical NPs, networks of spherical NPs and nanorods, and hierarchical structure of nanorods. In addition, networks composed of Au NPs/Ag skeleton satellite-core type nanorods were further constructed, which exhibited good catalytic performance and SERS property.

Tramadol, Methadone and Buprenorphine-AuNPs Kit Based on Chemometrics Tools and Software

The SPR of the AuNPs, synthesized by the reduction of gold ion with citrate and modified with L-cysteine was used as a novel analytical method for the detection and determination of drugs and species based on aggregation of Au-nanoparticles. However, multivariate calibration modeling of the SPR absorbance data by chemometrics method resulted in more accurate results out-comes so that the relative prediction errors were almost lower than 5%. In comparison with the available analytical methods for highly selective and sensitive ternary determination of tramadol, methadone and buprenorphine the proposed method is in need of lower amounts of reagents. Through increasing the concentration of the Opiate and Fluent material, a visible color change of AuNPs from wine red to blue was observed so the obvious color change was easily noticeable by naked eyes. However, multivariate calibration modelling and 3-d way methods that used for the SPR absorbance data by PARAFAC resulted in more accurate outcomes so that the software, as well as the chemometrics and the solvent kit, with great assurance our kit is unique. PARAFAC is a multi-way method originating from psychometrics. Due to various reasons such as high computational power, awareness of the method and its possibilities, the increased complexity complication of the data dealt with in science and industry, is gaining more attention in chemometrics and associated areas.

A Prototype Evanescent Wave-Coupled Cavity Ring-down Spectrometer for Probing Real-Time Aggregation Kinetics of Gold and Silver Nanoparticles.

We report on the development of a simple, linear optical cavity-based system combining evanescent wave (EW) with high-sensitive cavity ring-down spectroscopy (CRDS) technique using a diode laser at 644 nm and a right-angled prism for evanescent field generation on prism surface. We characterized the setup in detail and achieved an optimum ring-down time of 159.4 ns and a minimum absorption coefficient of αmin = 1.67 × 10-6 cm-1. We utilized this setup to investigate the salt-induced aggregation kinetics of gold (Au) and silver (Ag) nanoparticles (NPs) at the prism interface with high-sensitivity. We evaluated the extinction rates on the surface due to Au and Ag NPs aggregation and examined the variations due to their respective concentrations. To demonstrate the applicability of the developed EW-CRDS prototype setup to different molecular systems, we investigated the urease-bound aggregation kinetics of the Au and Ag NPs which has not been explored earlier by this linear cavity geometry. We finally illustrated the aggregation dynamics through surface imaging, thus demonstrating an alternative analytical approach to monitor interfacial phenomena using EW-CRDS technique.