Pure AuNPs Research Articles

Visual/quantitative SERS biosensing chip based on Au-decorated polystyrene sphere microcavity arrays

A microfluidic chip was designed and fabricated to achieve visual and quantitative sensing for the biomarker of Epstein-barr virus antibody (EBV IgG) based on TMB chromogenic unit and Raman detection unit. The biosensor was composed of polystyrene/Au nanoparticles (PS/AuNPs) microsphere arrays on a quartz substrate, where the initial SERS signal was amplified ten times than pure AuNPs through synergetic coupling between the optical field of PS whispering gallery microcavity and plasmon of AuNPs. Meanwhile, we introduced a signal probe by assembling horseradish peroxidase with high catalytic activity to TMB and Raman reporter rhodamine 6 G, in which TMB turned from colorless to blue and gradually deepened with increasing amount of EBV IgG being captured while the unique fingerprint information of rhodamine 6 G provided the accurate Raman signal for point-of-care testing of target. In sum, an integrated microchip that allows visual prediction under the assistance of TMB color as well as SERS responses with a wide dynamic linear range of 10−1∼105 pg·mL−1 and detection limit as low as 0.045 pg·mL−1 were obtained simultaneously, this lab-on-a-chip design offers a powerful model system for the early diagnosis of various cancer markers in peripheral blood.

Synergistic Antibacterial Activity of Green Gold Nanoparticles and Tannin-Based Derivatives

The development of composites with antibacterial activity represents an important strategy to avoid side effects such as increasing bacterial resistance to antibiotics. In particular, the green synthesis of metal nanoparticles avoids the use of hazardous chemical compounds and introduces the intrinsic beneficial properties of plant-derived compounds. Herein, the reduction of gold salt into metal nanoparticles was provided by the action of a cationic polymer derived from tannin (Tanfloc®). Comparative activity of antibacterial agents (pure Tanfloc and Au NPs—Tanfloc) at different concentrations were evaluated in terms of the antibiofilm activity, kill-time assays and inhibition haloes confirming the antibacterial activity of the Tanfloc that is reinforced by the incorporation of reduced gold nanoparticles, resulting in the complete elimination of S. aureus from an initial concentration of 108 CFU/mL after 120 min of reaction of Au NPs + Tanfloc solution in association with strong inhibition of the biofilm formation attributed to the Tanfloc.

Performance evaluation of rose bengal dye-decorated plasmonic gold nanoparticles-coated fiber-optic humidity sensor: A mechanism for improved sensing

Low-cost fiber-optic humidity sensors with fast response became demanding. Thus, well-dispersed pruned triangular plasmonic gold nanoparticles (AuNPs) of mean size 16.4 ± 7.3 nm were prepared in Rose Bengal dye (RBD) using pulsed laser ablation in liquid method at laser fluence of 7.9 ± 0.3 J/cm 2 . These stable RBD molecules-decorated AuNPs (RBD-AuNPs) showed enhanced fluorescence (lifetime decay ranged from 7.1 ± 0.9–6.4 ± 0.2 ns) and localized surface plasmon resonance absorption. The fabricated RBD-AuNPs-coated fiber-optic relative humidity sensor (FO-RHS) when tested against polyvinyl alcohol (PVA) at intensity modulation of 40–100 % RH) displayed higher sensitivity (0.08 a.u./%RH) and linearity (0.86 a.u./%RH) compared to the one coated with pure AuNPs. This improvement was mainly due to the adherence mechanism of –OH and COOH functional groups of RBD onto AuNPs surface, enabling in binding strongly the PVA molecules via hydrogen bonds. • Gold nanoparticles (AuNPs) were made in rose Bengal dye (RBD) medium by PLAL method. • These RBD-AuNPs showed improved fluorescence and LSPR absorption. • Fluorescence lifetime decay was varied from 7.1 to 6.4 ns. • Presence of –OH and –COOH groups on AuNPs surface enabled strong binding of PVA molecules by hydrogen bonding. • RBD-AuNPs-coated fiber-optic relative humidity sensor (FO-RHS) showed fast response. • Obtained FO-RHS displayed a good sensitivity (0.08 %) and linearity (0.86 %).

A robust nanofilm co-assembled from poly(4-vinylpyridine) grafted carbon nanotube and gold nanoparticles at the water/oil interface as highly active SERS substrate for antibiotics detection

The preparation of robust and uniform surface-enhanced Raman scattering (SERS) substrate with high sensitivity and good reproducibility for practical applications remains a challenge. In this work, we develop a general strategy to fabricate robust nanofilms co-assembled from poly(4-vinylpyridine)-grafted carbon nanotube (CNT-g-P4VP) and gold nanoparticles (AuNPs) at the water/oil interface. The prepared CNT-g-P4VP/AuNPs composite nanofilms exhibited better mechanical strength and higher SERS detection sensitivity with good reproducibility, as compared to the nanofilms prepared from pure AuNPs. Also, the CNT-g-P4VP/AuNPs nanofilm can be utilized in rapid SERS detection of two antibiotics (i.e., sulfamonomethoxine and enrofloxacin). Thus, the nanofilm reported here promises great practicality as a robust, efficient, reproducible, and simple-to-fabricate SERS platform.

Green synthesis of gold nanoparticles in Gum Arabic using pulsed laser ablation for CT imaging

Laser ablation synthesis in liquid solution (PLAL) is a green technique that allows for the physical formation of nanomaterials. This study indicates the preparation of stable gold nanoparticles (AuNPs) in Gum Arabic (GA) solution via laser ablation as a CT contrast agent. The optical properties were achieved using the absorption spectroscopic technique whereas the morphology and size distribution were investigated by TEM and ImageJ software. TEM image shows greater stability and spherical shape of GA-AuNPs with smaller size at 1.85 ± 0.99 nm compared to AuNPs without GA. The absorption spectrum of pure AuNPs has a lower absorption peak height in the visible range at λ = 521 nm, while the spectrum of GA-AuNPs has a higher plasmon peak height at λ = 514 nm with a blue shift towards lower wavelengths. The concentration of GA that dissolved in 10 mL of DI water via laser ablation is set at 20 mg. Increasing the number of pulses has only a minor effect on particle size distribution, which remains tiny in the nanometer range (less than 3 nm). For energies greater than 200 mJ, there is a blue shift toward shorter wavelengths. As the concentration of GA-AuNPs increases, the CT number is also increased indicating good image contrast. It can be concluded that there is a positive and significant influence of GA as a reducing agent for AuNPs, and a contrast agent for CT imaging which highlights its superiority in future medical applications.

In vivo bio-distribution and acute toxicity evaluation of greenly synthesized ultra-small gold nanoparticles with different biological activities

Ultra-small gold nanoparticles (Au-NPs) “≤ 10 nm diameters” have potent biomedical applications. Hence, the present study aimed to greenly synthesize ultra-small gold nanoparticles using Egyptian propolis extract. Different biological activities, in vivo bio-distribution and acute toxicity study were assessed. Results revealed that, Egyptian propolis extract can successfully synthesize the highly pure and stable ultra-small Au-NPs with average diameter 7.8 nm. In vitro antimicrobial and antimycobacterial activities revealed the powerful effect of the prepared Au-NPs. Moreover, the cytotoxic effect on human cancer cell lines revealed the potent inhibition of the cancer cells’ proliferation with high reactive oxygen species-mediated apoptosis induction. In vivo bio-distribution and acute toxicity studies were performed (10 and 100 mg/kg doses) in male albino rats. The ultra-small Au-NPs showed low or no toxicity upon using the Au-NPs low dose. The mean area accumulation (%) of the Au-NPs was higher in the liver, kidney, and brain tissues (4.41, 2.96, and 0.3 times, respectively) treated with high Au-NPs dosage compared to those treated with the low dose. Surprisingly, Au-NP accumulation in brain tissue was observed in the glial cells only. Accordingly, the low dose (10 mg/kg) of Au-NPs can be used safely in a variety of biomedical applications.

A theoretical approach on the ability of functionalized gold nanoparticles for detection of Cd2+

Cadmium (Cd) as a toxic element that is widely present in water, soil, and air has important effects on human health, therefore proposing an accurate and selective method for detection of this element is of importance. In this article, by employing full atomistic molecular dynamics (MD) simulations and density functional theory dispersion corrected (DFT-D3) calculations, the effects of 6-mercaptonicotinic acid (MNA) and l-cysteine (CYS) on the stability of gold nanoparticles (AuNPs) and their sensitivity against Cd2+ were investigated. The obtained results indicate that pure AuNPs are not stable in water, while functionalized AuNPs with CYS and MNA groups have considerable stability without aggregation. In other words, the functional groups on the surface of AuNPs elevate their resistance against aggregation by an increase in the repulsive interactions between the gold nanoparticles. Moreover, functionalized AuNPs have considerable ability for selective detection of Cd2+ in the presence of different metal ions. Based on the MD simulation results, MNA-CYS-AuNPs (functionalized AuNPs with both functional groups) have the maximum sensitivity against Cd2+ in comparison with MNA-AuNPs and CYS-AuNPs due to the strong electrostatic interactions. DFT-D3 calculations reveal that the most probable interactions between the metal ions and functional groups are electrostatic, and Cd2+ can aggregate functionalized AuNPs due to strong electrostatic interactions with MNA and CYS groups. Moreover, charge transfer and donor–acceptor analyses show that molecular orbital interactions between the functional groups and Cd2+ can be considered as the driving force for AuNPs aggregation. A good agreement between the theoretical results and experimental data confirms the importance of the molecular modeling methods as a fast scientific protocol for designing new functionalized nanoparticles for application in different fields.

Preparation and linear/nonlinear optical properties of a gold-terpyridine nanohybrid constructed through thiocyanate coordinating bridge

In this study, a gold-based nanohybrid was designed and prepared, which was constructed through interfacial coordination interaction between gold nanoparticals (Au NPs) and terpyridine-Zn (II) complexes (L-Zn(NCS)2, L = N,N-diphenyl-4-(2,2':6′,2″-tepyridin-4-yl)aniline) with thiocyanate unit as the coordination bridge. The optimized molar ratio of L-Zn(NCS)2 to chloroauric acid was selected as 1:15 through UV-vis absorption spectra. Compared with that of pure Au NPs or free L-Zn(NCS)2, the electron absorption of the nanohybrid was enhanced and the single photon excited fluorescence was weakened. Enhanced nonlinear optical properties and enlarged two-photon absorption cross section (δTPA = 21870.56 GM) were also captured. Furthermore, the nanohybrid exhibited excellent photothermal conversion performance, which was beneficial to be applied in phototherapy against living cancer cells. HeLa cells co-cultivated with the nanohybrid were gradually apoptotic within 10 min irradiation at 860 nm.

Plasmon-Enhanced Antibacterial Activity of Chiral Gold Nanoparticles and In Vivo Therapeutic Effect.

d-cysteine (d-cys) has been demonstrated to possess an extraordinary antibacterial activity because of its unique steric configuration. However, inefficient antibacterial properties seriously hinder its wide applications. Here, cysteine-functionalized gold nanoparticles (d-/l-Au NPs) were prepared by loading d-/l-cysteine on the surface of gold nanoparticles for the effective inhibition of Escherichia coli (E. coli) in vitro and in vivo, and the effects on the intestinal microflora in mice were explored during the treatment of E. coli infection in the gut. We found that the antibacterial activity of d-/l-Au NPs was more than 2–3 times higher than pure d-cysteine, l-cysteine and Au NPs. Compared with l-Au NPs, d-Au NPs showed the stronger antibacterial activity, which was related to its unique steric configuration. Chiral Au NPs showed stronger destructive effects on cell membrane compared to other groups, which further leads to the leakage of the cytoplasm and bacterial cell death. The in vivo antibacterial experiment illustrated that d-Au NPs displayed impressive antibacterial activity in the treatment of E. coli-infected mice comparable to kanamycin, whereas they could not affect the balance of intestinal microflora. This work is of great significance in the development of an effective chiral antibacterial agent.

Green synthesis of different ratios from bimetallic gold: Silver nanoparticles core@shell via laser ablation scattered in Chitosan-PVA matrix and its electrical conductivity behavior

Blend of Chitosan-PVA embeded by different ratios of gold/silver nanoparticles (AuNPs/AgNPs) have been synthesized using casting method. Gold and silver nanoparticles were synthesized using laser ablation in a Chitosan-PVA blend solution. This green method for the preparation of metal nanoparticles offers a unique tool for nanofabrication of nanoparticles. UV–Vis spectra of Chitosan-PVA doped by pure AgNPs and Chitosan-PVA doped by pure AuNPs show broad peaks at 407 and 529 nm that indicate the SPR peaks of Ag and Au NPs. XRD showed the absence of characteristic peaks for the embedded NPs which confirm the homogenous dispersion and the complete dissolution of prepared NPs within the Chitosan-PVA matrix. FT-IR data show a decrease in the peaks of O–H stretching, N–H bending and C–O stretching, which confirm the addition of AuNPs/AgNPs in Chitosan-PVA matrix. TEM images imply the successful preparation of Ag@Au NPs core@shell structure within Chitosan-PVA matrix. The influence of addition of different concentrations of Ag NPs and Au NPs on the optical and structural properties of chitosan composites films has been investigated. The electrical conductivity measurement was show increased in electrical conductivity.

Core/shell structural ultra-small gold and amyloid peptide nanocomposites with effective bacterial surface adherence and enhanced antibacterial photothermal ablation

The exploration of ultra-small gold nanoparticles (Au NPs) (<5 ​nm) based photothermal nanoagent is important for antibacterial photothermal therapy due to their high biosafety. However, the ultra-small Au NPs usually have low absorption in near infrared (NIR) region, presenting poor NIR-based photothermal conversion. In the present work, a novel core/shell structural gold and amyloid peptide Aβ25-35 nanocomposites (Au@Aβ NCs) were constructed with ultra-small Au NPs (ca. 4.0 ​nm) as the core and Aβ25-35 oligomer as the shell (ca. 3 ​nm thickness) through the facile peptide templated chemical reduction method. The Au@Aβ NCs display enhanced NIR absorption and photothermal conversion efficiency as compared to pure Au NPs due to the extinction of Aβ shell. In addition, the Au@Aβ NCs can strongly adhere to the bacterial surfaces and aggregate together by virtue of the intrinsic self-assembly property of amyloid peptide, which facilitates the local photothermal ablation of bacteria. Consequently, the Au@Aβ NCs can fast and completely kill the pathogenic bacteria under NIR laser irradiation. This work provides an alternative strategy to prepare highly efficient ultra-small Au NPs based photothermal nanoagent for enhancing the antibacterial photothermal ablation.

THE MODIFICATION AND DEVELOPMENT OF THE SPECTROSCOPIC PROPERTIES OF Cs/PVA BLEND INCORPORATED GOLD NANOPARTICLES (AuNPs) PREPARED BY PULSED LASER ABLATION IN LIQUIDS (PLAL)

In the present work, pure gold nanoparticles (AuNPs) were synthesis by pulsed laser ablation technique using Nd:YAG as a source of laser. Then, the prepared AuNPs was used with low concentrations to synthesis nanocomposite films by adding it to chitosan/polyvinyl alcohol (Cs/PVA) blend using the casting method. All peaks of pure AuNPs were recorded by X-ray diffraction with face center cubic (FCC) structure. No peaks of AuNPs were found at low concentrations in the doped nanocomposites because of the complete degradation of AuNPs within Cs/PVA matrix. The intensity of some IR bands was changed due to the chemical interaction between the components. The broad band at 3350 cm−1 was decreased due to the intermolecular interaction. Dielectric constant and dielectric loss were decreased as an increase in the frequency and temperature. The increases of direct conductivity (σdc) imply that the free charge density or of the charge mobility that results. The AuNPs addition assists the charge transfer complex (CTCs) formation in which charge transportation occurs by coulomb forces and electric field. The Cole-Cole plot shows semicircles that supports the relaxation processes were a non‐ Debye method.

A molecular dynamics study on the thermal properties of carbon-based gold nanoparticles.

Due to unique features in surface activity, thermal stability, electrical and thermal conductivity, and compatibility with biomolecules such as DNA and proteins, carbon-based nanoparticles are raised potential as a candidate for various applications such as catalytic processes, drug delivery, light, and electrical engineering. Based on this premise, thermodynamic features of pure, graphene, and carbon nanotube (CNT)-based gold nanoparticles (AuNPs) are investigated using molecular dynamics approach. Melting, heat capacity, thermal conductivity, contact angle of molten AuNPs, and phase transition are calculated as indicators of thermodynamic properties of pure and carbon-based AuNPs. Simulation results indicate that the presence of a carbon platform and its contact surface area has a significant role in the thermodynamic properties of AuNPs and leads the phononic heat capacity and thermal conductivity to decrease for AuNPs. The platform also causes the melting point temperature of AuNPs to increase. The melting of gold on the carbon base is of the first-order type. In addition, contact angle for molten AuNPs on the Graphene is significantly higher than the one on the CNT due to more contact area on the Graphene substrate.Graphical abstract .

One-step chemical synthesis of Ag–Au alloy nanoparticles for modulating the catalytic hydrogenation reaction

One-step chemical reduction approach is developed to synthesize nearly monodispersed Ag–Au alloy nanoparticles stabilized by CTAB molecules. By controlling the molar ratios of Ag(I) and Au(III), the surface plasmon resonance (SPR) band of alloy nanoparticles observe between 410 and 530 nm, which are the absorption maxima of silver and gold nanoparticles, respectively. The transmission electron microscope (TEM) shows that the obtained alloy nanoparticles are spherical in shape having size from 12 to 17 nm which provides high catalytic activity towards hydrogenation reactions. The catalytic efficiency of Ag NPs are less compared to pure Au NPs, whereas their activity can be modulated in between these two by appropriately controlling their molar ratio in the resultant Ag–Au alloy NPs. Moreover, with regards to high stability and recyclability, Ag–Au alloy NPs shows ~ 100% conversion efficiency up to five consecutive reaction cycles while monometallic nanoparticle are incapable. Thus, it is possible to modulate and enhance the catalytic activity of Ag NPs by making an alloy with Au NPs of desired composition.

Spontaneous Formation of Gold Nanoparticles on Graphene by Galvanic Reaction through Graphene.

We demonstrate an effective and facile method for the deposition of gold nanoparticles (AuNPs) on graphene by using spontaneous galvanic reaction. Despite the interest and importance of the hybrid structure of noble metal-deposited graphene has been considerably increased for its fundamental knowledge in chemical and physical sciences and for its various applications, the progress of this subject is very slow mainly because of the lack of synthetic methods for such structures, especially that are not free from chemical contamination and usage of complex and expensive equipment. Therefore, we developed a new method allowing chemically pure AuNPs/graphene hybrid structures employing galvanic reaction. The spontaneous galvanic reaction was derived from reductant/graphene/oxidant sandwich structures, such as Au ions/graphene/Ge wafer and Au ions/graphene/copper foil, by placing Au ion solution droplets on graphene transferred on a germanium wafer or as made graphene on Cu foil, respectively. According to scanning electron microscopy and atomic force microscopy results, it was confirmed that AuNPs were successfully formed on the graphene surface. This result implies two important points. One is that the formation of pure AuNPs on graphene is possible without using other chemicals frequently required for conventional NP preparation. The other one is that it was experimentally demonstrated that there are electronic communications between the oxidant and reductant that are separated by graphene, through which electrons can pass freely.

Microplasma assisted synthesis of gold nanoparticle/graphene oxide nanocomposites and their potential application in SERS sensing

This is the first study on the deployment of direct current atmospheric pressure microplasma technique for the single step synthesis of gold nanoparticle/graphene oxide (AuNP/GO) nanocomposites. The nanocomposites were characterized using ultraviolet–visible spectroscopy (UV–vis), x-ray diffraction and x-ray photoelectron spectroscopy and their formation mechanisms have been discussed in detail. Our AuNP/GO nanocomposites are highly biocompatible and have demonstrated surface enhanced Raman scattering (SERS) properties as compared to pure AuNPs and pure GO. Their potential as SERS substrate has been further demonstrated using probe molecules (methylene blue) at different concentrations.

Facile synthesis of Au nanoparticles with different shapes in a soluble starch-hydroquinone system and their SERS activity

Abstract A simple soluble starch-hydroquinone system was explored, in which flower-like and star-like gold nanoparticles (Au NPs) could be individually synthesized only by adjusting the injection rate of the precursor solution. Meanwhile, their size could be easily tuned just by changing the molar ratio of Au3+ ions and Au seeds in the precursor solution. As-prepared samples were proved to be polycrystalline, pure and stable Au NPs by means of various characterization techniques. Clearly, the novel and facile method to control the shape (morphology and size) can provide a unique perspective for the shape control of other metal NPs. In addition, obtained Au NPs showed distinct shape-determined surface-enhanced Raman scattering (SERS) activity towards Rhodamine 6G molecules, implying their potential for applications in SERS-based detections and analysis.

A molecular approach on the ability of functionalized gold nanoparticles for selective sensing of Hg2+

Mercury detection due to harmful effects on the environment and human health is of importance. Among the reported methods, functionalized gold nanoparticles (AuNPs) due to their interesting ability for selective detection of Hg2+ have been considered. In this article, by employing full atomistic molecular dynamic (MD) simulations and quantum mechanic calculations, dynamical behavior and aggregation mechanism of the pure and 11-mecaptoundecanoic acid (MCA) functionalized gold nanoparticles (MCA-AuNPs) were investigated. MD simulation results indicate that pure AuNPs are not stable in water and aggregate due to van der Waals interactions. On the other hand, MCA groups increase the stability of AuNPs and their resistance against aggregation by elevating the repulsive interactions of the AuNPs. Moreover, MCA-AuNPs have the considerable ability for selective detection of Hg2+ in the presence of different metal ions, such as Zn2+, Cu2+, Ba2+, Ca2+, Cd2+, Fe2+, Mg2+, Ni2+ and Pb2+. On the basis of the QM calculations, Hg2+ has a strong electrostatic interaction with the COO– groups of the MCA on the AuNPs surface. This metal ion acts as a linkage agent between the MCA-AuNPs, which facilitates the nanoparticle aggregation, through the elimination of the repulsive interactions. A good agreement between the theoretical results and experimental data indicates the importance of the theoretical methods for understanding the mechanism of ion sensing by the functionalized AuNPs, which is of great interest for designing new sensors based on gold nanoparticles.

Size-dependent elasticity of gold nanoparticle measured by atomic force microscope based nanoindentation

Elasticity is one of the key properties in gold nanoparticles (AuNPs) and plays an essential role in the process design and applications. In this work, we have proposed an Argon plasma based technique to obtain well dispersed and pure AuNPs without surface functional groups. Our investigation on the size-dependent elasticity focused on the AuNPs with the size ranging from 2 nm to 12 nm by using an atomic force microscope based nanoindentation technique under the peakforce quantitative nanomechanical mapping mode. The results show clearly that when the AuNPs are smaller than 6 nm, there is a significant increase in the elasticity as the smallest nanoparticles display a twofold higher elastic modulus of ∼140 GPa compared to bulk gold. Our result provides important experimental evidence that contributes to a better understanding of the size-property relations as well as process design in AuNPs, and it also can be applied to measure the mechanical properties in a wide range of nano-objects.

Platinum monolayers stabilized on dealloyed AuCu core-shell nanoparticles for improved activity and stability on methanol oxidation reaction

Deposition of platinum (Pt) monolayers (PtML) on Au substrate represents a robust strategy to maximally utilize the Pt atoms and meanwhile achieve high catalytic activity towards methanol oxidation reaction for direct methanol fuel cells owing to a substrate-induced tensile strain effect. However, recent studies showed that PtML on Au substrate are far from perfect smooth monoatomic layer, but actually exhibited three-dimensional nanoclusters. Moreover, the PtML suffered from severe structural instability and thus activity degradation during long-term electrocatalysis. To regulate the growth of PtML on Au surface and also to improve its structural stability, we exploit dealloyed AuCu core-shell nanoparticles as a new substrate for depositing PtML. By using high-resolution scanning transmission electron microscopy and energy dispersive X-ray elemental mapping combined with electrochemical characterizations, we reveal that the dealloyed AuCu core-shell nanoparticles can effectively promote the deposition of PtML closer to a smooth monolayer structure, thus leading to a higher utilization efficiency of Pt and higher intrinsic activity towards methanol oxidation compared to those on pure Au nanoparticles. Moreover, the PtML deposited on the AuCu core-shell NPs showed substantially enhanced stability compared to those on pure Au NPs during long-term electrocatalysis over several hours, during which segregation of Cu to the Au/Pt interface was revealed and suggested to play an important role in stabilizing the PtML catalysts.