Single Au Nanoparticles Research Articles

Enhanced Ferroelectric Polarization in Au@BaTiO3 Yolk-in-Shell Nanostructure for Synergistic Boosting Visible-Light- Piezocatalytic CO2 Reduction.

Developing efficient photo-piezocatalytic systems to achieve the conversion of renewable energy to chemical energy emerges enormous potential. However, poor catalytic efficiency remains a significant obstacle to future practical applications. Herein, a series of unique Au@BaTiO3 (Au@BT) yolk-shell nanostructure photo-piezocatalyst is constructed with single Au nanoparticle (Au NP) embedded in different positions within ferroelectric BaTiO3 hollow nanosphere (BT-HNS). This special structure showcases excellent mechanical force sensitivity and provides ample plasmon-induced interfacial charge-transfer pathways. In addition, the powerful piezoelectric polarization electric field induced by the enhanced ferroelectric polarization electric field via corona poling treatment in BT-HNS further promotes charge separation, CO2 adsorption and key intermediate conversion. Notably, BT with single Au NP encapsulated into hollow nanosphere shell with reinforced polarization (Au@BT-1-P) shows synergistically improved photo-piezocatalytic CO2 reduction activity for producing CO with a high production rate of 31.29 µmol g-1 h-1 under visible light irradiation and ultrasonic vibration. This work highlights a generic tactic for optimized design of high-performance and multifunctional nanostructured photo-piezocatalyst. Meanwhile, these yolk-in-shell nanostructures with single Au nanoparticle as an ideal model may hold great promise to inspire in-depth exploration of carrier dynamics and mechanistic understanding of the catalytic reaction.

In-situ and wavelength-dependent photocatalytic strain evolution of a single Au nanoparticle on a TiO2 film

Photocatalysis is a promising technique due to its capacity to efficiently harvest solar energy and its potential to address the global energy crisis. However, the structure–activity relationships of photocatalyst during wavelength-dependent photocatalytic reactions remains largely unexplored because it is difficult to measure under operating conditions. Here we show the photocatalytic strain evolution of a single Au nanoparticle (AuNP) supported on a TiO2 film by combining three-dimensional (3D) Bragg coherent X-ray diffraction imaging with an external light source. The wavelength-dependent generation of reactive oxygen species (ROS) has significant effects on the structural deformation of the AuNP, leading to its strain evolution. Density functional theory (DFT) calculations are employed to rationalize the induced strain caused by the adsorption of ROS on the AuNP surface. These observations provide insights of how the photocatalytic activity impacts on the structural deformation of AuNP, contributing to the general understanding of the atomic-level catalytic adsorption process.

Photothermophoretic Splitting of Gold Nanoparticles for Plasmonic Nanopores and Nanonets Sensing.

Optical processing of single plasmonic nanoparticles reinvents the way of high-density information storage, high-performance sensing, and high-definition displays. However, such laser-fabricated nanoplasmonics with well-defined hot spots remain elusive due to the diffraction limit of light. Here we show Au nanoparticle (NP) decorated nanopores can be facilely generated with photothermal splitting of single Au NPs embedded in a silica matrix. The extremely high local temperature induced by plasmonic heating renders gradients of the temperature and surface tension around the Au NP, which drives the nanoscale thermophoretic and Marangoni flow of molten Au/silica. As a result, a nanopore decorated with fragmented Au NPs is formed in the silica film, which presents much stronger surface-enhanced Raman scattering as compared to a single Au NP due to the emergence of hot spots. This strategy can be used to generate plasmonic nanopores of various sizes in the silicon nitride (SiNx) films, which further transforms into nanonets at ambient conditions via light-induced reconstruction of silicon nitride membrane. These nanonets can serve as a robust platform for single particle trapping and analysis.

Highly Chiral Light Emission Using Plasmonic Helicoid Nanoparticles

AbstractMaterials generating circularly polarized luminescence (CPL) have received increasing interest due to their potential applications in bioimaging, sensing, anticounterfeiting, and display technologies. The possibility of efficient CPL generation is explored for organic molecules, inorganic materials, and their hybrid systems. A chiral plasmonic nanostructure is one candidate for generating strong and highly dissymmetric CPL by coupling with the surrounding luminescent material. Here, the inherent luminescence of gold nanoparticles can produce CPL without using any secondary material is suggested. In this study, the generation of circularly polarized two‐photon‐induced photoluminescence (TPI‐PL) from chiral gold nanostructures is demonstrated. Measurements of TPI‐PL show that it has a strong dissymmetry factor of ≈0.7 for a single chiral Au nanoparticle. A theoretical simulation study showed that a local chiral electromagnetic field confined to the chiral gap structures contributes to the high degree of circular polarization in TPI‐PL. It is believed that this work provides a new route for novel CPL‐generating materials with strong dissymmetry and holds promise for various applications using CPL technology.

Thiol-functionalized mesoporous silica-embedded AuNPs with highly sensitive substrates for surface-enhanced Raman scattering detection

Surface-enhanced Raman spectroscopy (SERS) provides a fast, simple, and label-free approach that can directly detect various analytes attached to SERS substrates and provide qualitative and quantitative information based on the SERS spectra of the analyte. The signal enhancement provided by noble metal particles allows us to achieve high sensitivity and good stability even at low concentrations in water quality testing. Over the past decade, SERS has become increasingly popular in the detection field, highlighting its significant application potential. However, the signal enhancement of single AuNPs is inferior to that of AgNPs, but we can achieve an overall enhancement by uniformly arranging multiple AuNPs. The hot-spot effect, which is crucial for Raman signal enhancement, occurs only when NMNPs are within a specific distance. However, when noble metal particles come into contact with each other, the enhancement effect of the hot spot disappears. Therefore, in this study, AuNPs@MPS-SH substrates with surface-enhanced Raman scattering (SERS) activity were successfully synthesized by immobilizing AuNPs on thiol-functionalized mesoporous silica (MPS-SH). MPS nanospheres with tailored pore size and surface-bound -SH groups were synthesized for the controlled embedding of Au nanoparticles (AuNPs). By adjusting the ratio of reactants, uniform AuNP dispersion and strong MPS-AuNP interactions were achieved. This optimized structure creates localized surface plasmon resonance (LSPR) hotspots, significantly enhancing the surface-enhanced Raman scattering (SERS) effect for ultrasensitive analyte detection. Transmission electron microscopy (TEM) revealed that the average diameter of MPS nanoparticles is 260 nm, with a pore size of 8 nm. Optimal Raman enhancement was achieved at an AuNPs concentration of 2.6 × 1018 particles/mL. The lowest detection limit concentration for Rhodamine 6G was below 10−6 M, while for uremic toxin (urea) it was below 10−3 M. The ability to directly detect low concentrations by mixing with the analyte demonstrates the ultra-high sensitivity and label-free detection potential of this study in the fields of water quality and disease detection.

Design and performance of pH-responsive cyano-Raman label SERS probes based on single urchin Au nanoparticles.

A cyano-Raman label pH-responsive SERS probe was constructed by immobilizing 6-MPN molecules onto the surface of a single urchin Au nanoparticle (AuNP). The effects of different conditions on the synthetic materials were investigated and the optical properties of the single nanoparticles were evaluated. The peak-strength ratio of SERS probes at 1589 cm-1 and 2240 cm-1 exhibited a linear relationship in the pH range 4-7. The properties and stability of the probe were also verified by the acid-base cycle and ion interference tests.

Drop-cast gold nanoparticles are not always electrocatalytically active for the borohydride oxidation reaction

A collection of single Au nanoparticles (NPs) and NP clusters were individually tested for the borohydride oxidation reaction. Significant variation in the activity could not be attributed to NP size, and ∼67% of NP locations displayed no activity.

Dramatic Electrochemical Tuning of the Plasmonic Spectrum of a Metal Nanoparticle on a Mirror

Enhancement of electric fields in the nanometric gap between plasmonic nanostructures is widely exploited for sensing, enhanced spectroscopies and photochemistry. Plasmonic properties of nanostructures with ultrathin gaps, such as nanoparticles (NPs) positioned on a flat metal surface (a mirror), have attracted much attention in recent years [1]. We studied the effect of electrochemical control on the plasmonic properties of single Au and Ag NPs on a mirror. We found that the coupled plasmonic resonance could be reversibly tuned over a range of tenths of nanometers, more than an order of magnitude higher than expected based just on capacitive charging of the NPs.Our experimental system consisted of single Au or Ag NPs (50 nm – 100 nm) adsorbed on a self-assembled monolayer (SAM) of either polyelectrolytes, cysteamine (CEA) or ethanedithiol (EDT) deposited on an atomically flat 100nm thick Au electrode prepared by template stripping. The NPs were either bare (prepared by H2 reduction) or citrate-stabilized and the system was immersed in a basic solution.Coupling to the mirror electrode resulted in the appearance of several bands in the plasmonic spectrum of individual NPs, as measured by dark-field microspectroscopy (Fig. 1a), and the lowest-energy band could be attributed to the coupled plasmon. Variation of the electrode potential generated a giant, though reversi shift of the spectrum. A plot of the peak position of the coupled plasmon band displayed an S-shaped, phase-transition like behavior (Fig. 1b).This remarkable result could not be observed with individual NPs deposited on non-metallic surfaces, and can therefore be attributed to a dramatic modulation of the coupling between the particles and the mirror with electrode potential.Figure 1. Scattering spectra (a) and variation of the spectral position of the coupled plasmon peak (b) of bare AuNP (ca. 60 nm) on CEA/Au electrode. Inset in (a): Scheme of NP on the mirror.

Synthesis of Single Nanometer-Sized Au Nanoparticles Coated with Silica Toward X-Ray Contrast Agent

In this study, we proposed a method for fabricating diagnostic imaging nanoparticles composed of Au nanoparticles and silica shells (Au/SiO2). The proposed method consisted of two steps. The first step was the synthesis of Au nanoparticles. In sodium hydroxide (NaOH) solution, hydrogen tetrachloroaurate (III) trihydrate was reduced with tetrakis(hydroxymethyl)phosphonium chloride to synthesize Au nanoparticles with a diameter of 1.7 ± 0.3 nm. The Au nanoparticles were then coated with silica in the following step. The silica coating was achieved via a sol–gel reaction of tetraethyl orthosilicate in the presence of Au nanoparticles in water/ethanol dissolved in NaOH. The Au/SiO2 nanoparticles degraded faster in saline or phosphate-buffered saline than in water, and the X-ray imaging capability was retained.

MoS2/Au heterojunction nanostructures for electrochemical detection of trace Hg(II) in wastewater samples

In this study, a highly sensitive electrochemical sensor was developed for the detection of mercury ions in wastewater samples. The sensor was constructed using MoS2/Au heterojunction nanostructures, which involved depositing plasmonic Au nanoparticles onto MoS2 nanosheets on screen-printed carbon electrodes. The MoS2/Au-SPCE sensor demonstrated outstanding electrochemical sensing capabilities, attributed to the emergence of a mid-gap state across the Fermi level. This state arises from the interaction between the Au 5d (Au, +1 charge state) and Mo 3d (MoS2, +4 charge state) orbitals. This performance was superior to that of single Au nanoparticles and MoS2. The sensor showed high sensitivity in detecting Hg(II) ions with a wide linear range from 0.02 ppm to 0.0004 ppb and a LOD of 0.0004 ppb. The developed sensor was effectively applied for the detection of Hg(II) ions in factory wastewater and other samples. The MoS2/Au-SPCE sensor was successfully used to detect low concentrations of 565.0 ppb and 92.0 ppb Hg(II) in the investigated samples. This study introduces a new electrochemical sensor, leveraging the MoS2/Au heterostructures, meticulously crafted for the intricate sensing of Hg(II) ions

Cell-inspired design of cascade catalysis system by 3D spatially separated active sites

Cells possess isolated compartments that spatially confine different enzymes, enabling high-efficiency enzymatic cascade reactions. Herein, we report a cell-inspired design of biomimetic cascade catalysis system by immobilizing Fe single atoms and Au nanoparticles on the inner and outer layers of three-dimensional nanocapsules, respectively. The different metal sites catalyze independently and work synergistically to enable engineered and cascade glucose detection. The biomimetic catalysis system demonstrates ~ 9.8- and 2-fold cascade activity enhancement than conventional mixing and coplanar construction systems, respectively. Furthermore, the biomimetic catalysis system is successfully demonstrated for the colorimetric glucose detection with high catalytic activity and selectivity. Also, the proposed gel-based sensor is integrated with smartphone to enable real-time and visual determination of glucose. More importantly, the gel-based sensor exhibits a high correlation with a commercial glucometer in real samples detection. These findings provide a strategy to design an efficient biomimetic catalysis system for applications in bioassays and nanobiomedicines.

Triple strategy-enhanced immunochromatographic assay based on APCB and AIEFM for the ultrasensitive detection of AFM1

Aflatoxin M1 (AFM1) is highly toxic, widely distributed, and difficult to monitor, posing a serious threat to human health. Therefore, a highly sensitive, rapid, convenient, and low-cost detection method must be urgently established. In this study, a triple strategy-enhanced immunochromatographic assay (ICA) was developed to satisfy these detection requirements. First, a turn-on signal output mode of the fluorescence quenching ICA substituted the turn-off mode of the traditional ICA for sensitive response to trace AFM1, with the limit of detection (LOD) reduced by approximately 4.9-fold. Then, a novel Au and polydopamine (PDA) cogrowth chrysanthemum-like blackbody was prepared as the quenching probe to reduce the background signal. This probe combined the excellent properties of Au nanoparticles with PDA. Thus, its fluorescence quenching constant was higher than that of single Au and PDA nanoparticles by 25.8- and 4.9-fold, respectively. Furthermore, an aggregation-induced emission fluorescence microsphere with a 5.7-fold higher relative quantum yield than a commercial fluorescence microsphere was selected as the signal output carrier to improve the signal-to-noise ratio. The integration of the above triple strategies established a 53.4-fold sensitivity-enhanced fluorescence quenching ICA (LOD = 0.9 pg/mL) for detecting AFM1 in milk, providing a strong technical guarantee for the safety monitoring of milk products.

Current Lifetime of Single-Nanoparticle Electrochemical Collision for In Situ Monitoring Nanoparticles Agglomeration and Aggregation.

In situ monitoring of the agglomeration/aggregation process of nanoparticles (NPs) is crucial because it seriously affects cell entry, biosafety, catalytic performance of NPs, and so on. Nevertheless, it remains hard to monitor the solution phase agglomeration/aggregation of NPs via conventional techniques such as electron microscopy, which requires sample pretreatment and cannot represent native state NPs in solution. Considering that single-nanoparticle electrochemical collision (SNEC) is powerful to detect NPs in solution at the single-particle level, and the current lifetime, which refers to the time that current intensity decays to 1/e of the original value, is skilled in distinguishing different sized NPs, herein, a current lifetime-based SNEC has been developed to distinguish a single Au NP (d = 18 nm) from its agglomeration/aggregation. Based on this, the agglomeration/aggregation process of small-sized NPs and the discrimination of agglomeration vs aggregation have been carefully investigated at the single-particle level. Results showed that the agglomeration/aggregation of Au NPs (d = 18 nm) in 0.8 mM HClO4 climbed from 19% to 69% over two hours, whereas there was no visible granular sediment, and Au NPs tended to agglomerate rather than aggregate irreversibly under normal conditions. Hence, the proposed current lifetime-based SNEC could serve as a complementary method to in situ monitor the agglomeration/aggregation of small-sized NPs in solution at the single-particle level and provide effective guidance for the practical application of NPs.

Coexistence of Au single atoms and Au nanoparticles on NiAl-LDH for selective electrooxidation of benzyl alcohol to benzaldehyde.

Introducing different active sites into heterogeneous catalysts provides new prospects to address the challenges in single-atom catalysis. Herein, the Au single atoms together and the Au nanoparticles were loaded onto NiAl-LDH by a facile impregnation-reduction method for the first time, resulting in the formation of Au1+n-NiAl-LDH, in which abundant Au single atoms are located around the Au nanoparticles with ∼5 nm size. When applied in the electrocatalytic benzyl alcohol oxidation reaction (BAOR), the as-prepared Au1+n-NiAl-LDH exhibits a remarkable selectivity of 91% and 177.63 μmol for benzaldehyde in 5 hours, while in contrast examples using solely Au single atom loaded NiAl-LDH (Au1-NiAl-LDH) and solely Au nanoparticle loaded NiAl-LDH (Aun-NiAl-LDH) can only realize 87.36 μmol production (75% selectivity) and 48.90 μmol production (28% selectivity) of benzaldehyde, respectively. Such a dramatic difference can be attributed to the synergistic effects of Au single atoms and Au nanoparticles. DFT calculation results reveal that for Au1+n-NiAl-LDH, Au single atoms promote the dehydrogenation capacity of LDH laminates, while Au nanoparticles offer adsorption sites for the electrophilic attachment of benzyl alcohol.

Atom-dispersed Au combined with nano-Au on halloysite nanotubes with closo-dodecaborate promotes synergistic effects for enhanced photocatalysis

Au single atoms (Au SAs) and Au nanoparticles (Au NPs) were obtained on HNT@B12H12@Au catalysts. Experimental and theoretical calculations revealed that O–Au–B–Au SAs, O–Au SAs, B–Au SAs and Au NPs are involved in the reaction simultaneously.

Potentiometric Study of the Growth of a Single Au Nanoparticle

AbstractA single nanoparticle (NP) attached to a nanoelectrode is a very useful system in understanding the relationship between the size of nanoparticles and their electrochemical properties. In this study, a single Au NP was spontaneously formed on a Pt nanoelectrode. The potential measured on such a system can be employed to study the effect of size of an Au nanoparticle on the Nernst potential of the reaction, AuCl4− +3e → Au(s) +4Cl−. Moreover, the nucleation period and the growth period can be distinguished from the potential graph, and the nucleation rate of the spontaneously formed Au NP can be evaluated.

Fine Tuning the Optical Properties of Single Au Nanoparticles by Plasmon‐Driven Growth in Closed‐Loop Control

AbstractThe morphology and composition of metallic nanoparticles (NPs) determine their optical response, so finely controlling them at the single particle level is the key to achieve tailored functionalities. Here, the control of plasmon‐driven growth of Au NPs is studied by live monitoring their photoluminescence emission in a closed‐loop. It is found that the final emission maximum of single NPs can be tuned between 550 and 580 nm with a precision of 2–3 nm, and that the tuning is also reflected in their scattering maximum. In comparison to controlling the growth by irradiation time and/or reaction conditions, the closed‐loop control delivers superior reproducibility and a three to fourfold higher precision in the final properties of the NPs.

Fabrication and Characterization of Single and Bimetallic Non-Alloyed Nanoparticles

We have demonstrated the fabrication of single and bimetallic Au and Ag nanoparticles on SiO2 substrate for light trapping application. Those nanoparticles were obtained by depositing 6nm and 8nm Au while 8nm and 10nm of Ag on SiO2 substrate. Then, the dewetting process takes place at 600oC for Au and 500oC for Ag. The particle distribution is quite non-uniform, making the shifting effect unclear and different from the previous result. However, the absorption effect of the BNNPs can be observed in this work, where it shows significantly broader peak spectra compared to both single Au and Ag NPs. This makes the BNNPs is the best candidate for selective detection sensors.

(Invited) Ultrasensitive Detection of Nucleic Acid Molecules with Interferometric Plasmonic Microscopy

The detection of nucleic acid molecules plays important role in clinical diagnosis of diseases and fundamental biomedical research. The widely used polymerized chain reaction technique requires hours of amplification process, and is prone to aerosol pollution. Here, we presented the amplification-free digital sensing of nucleic acid molecules with the interferometric plasmonic microscopy (iPM). A sandwich assay was performed with the primary DNA probes coated on the plasmonic sensing surface and the secondary DNA probes tethered Au nanoparticles. Hybridization between DNA probes and single analyte molecules was monitored by the imaging of single Au nanoparticle with iPM system. By digitally counting the events of hybridization, the detection limit at the fM level could be achieved. Without amplification, this assay could be done within one hour. Furthermore, by analyzing the real-time binding behaviro during single hybridization event, non-specific bindings could be excluded from the specific ones, resulting in the improved specificity. This technique could be further improving by a careful design of the kinetic binding properties between DNA probes and analyte molecules.

Strong coupling of a plasmonic nanoparticle to a semiconductor nanowire

Abstract By placing a single Au nanoparticle on the surface of a cadmium sulfide (CdS) nanowire, we demonstrate strong coupling of localized surface plasmon resonance (LSPR) modes in the nanoparticle and whispering gallery modes (WGMs) in the nanowire. For a 50-nm-diameter Au-nanosphere particle, strong coupling occurs when the nanowire diameter is between 300 and 600 nm, with a mode splitting up to 80 meV. Using a temperature-induced spectral shift of the resonance wavelength, we also observe the anticrossing behavior in the strongly coupled system. In addition, since the Au nanosphere has spherical symmetry, the supported LSPR mode can be selectively coupled with transverse electric (TE) and transverse magnetic (TM) WGMs in the nanowire. The ultracompact strong-coupling system shown here may provide a versatile platform for studying hybrid “photon–plasmon” nanolasers, nonlinear optical devices, and nanosensors.